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Nanoscopic optical rulers beyond the FRET distance limit: Fundamentals and applications
Abstract
In the last few decades, Förster resonance energy transfer (FRET) based spectroscopy rulers have served as a key tool for the understanding of chemical and biochemical processes, even at the single molecule level. Since the FRET process originates from dipole-dipole interactions, the length scale of a FRET ruler is limited to a maximum of 10 nm. Recently, scientists have reported a nanomaterial based long-range optical ruler, where one can overcome the FRET optical ruler distance dependence limit, and which can be very useful for monitoring biological processes that occur across a greater distance than the 10 nm scale. Advancement of nanoscopic long range optical rulers in the last ten years indicate that, in addition to their long-range capability, their brightness, long lifetime, lack of blinking, and chemical stability make nanoparticle based rulers a good choice for long range optical probes. The current review discusses the basic concepts and unique light-focusing properties of plasmonic nanoparticles which are useful in the development of long range one dimensional to three dimensional optical rulers. In addition, to provide the readers with an overview of the exciting opportunities within this field, this review discusses the applications of long range rulers for monitoring biological and chemical processes. At the end, we conclude by speculating on the role of long range optical rulers in future scientific research and discuss possible problems, outlooks and future needs in the use of optical rulers for technological applications.
... Even though the FRET process as such has been studied for many years, modulation of the FRET processes is a relatively new research domain. Beyond the static control of FRET by varying the distance between donors and graphene [28,35,36], electrical control of FRET from individual QDs to graphene by electrical doping of graphene has been reported [15,17,29]. ...
... The molecules were thermally evaporated on either side of the SLG. The thickness of the molecular thin films was selected to be 10 nm as this guarantees a sufficiently strong PL signal while still allowing donor and acceptor molecules to interact [36,46]. The contact electrodes were deposited on the SLG (5 nm Cr and 50 nm Au) using a shadow mask. ...
In artificial structures of molecular or quantum dot emitters in contact with single-layer graphene (SLG) Förster-type resonant energy transfer (FRET) can occur unconditionally due to the gapless band structure of SLG. A significant breakthrough for applications, however, would be the electrical modulation of FRET between arbitrary FRET pairs, using the SLG to control this process and taking advantage of the particular band structure and the monatomic thickness of SLG, far below the typical Förster radius of a few nanometers. For a proof of concept, we have therefore designed a Sandwich device where the SLG was transferred onto holey Si3N4 membranes and organic molecules were deposited on either side of the SLG. The relative photoluminescence (PL) intensities of donor and acceptor molecules changed continuously and reversibly with the external bias voltage, and a variation of about 6% of FRET efficiency has been achieved. We ascribe the origin of the electrical modulation of FRET to important doping-dependent nonlocal optical effects in the near field of SLG in the visible range.
... Fo¨rster resonance energy transfer (FRET) is a non-radiative energy transfer phenomenon. FRET involves distance-dependent interaction (within 20-90 Å) taking place through space between the two fluorophores where a donor in its excited state transfers its energy of excitation to a suitable acceptor molecule that is not accompanied by any photon emission [24][25][26][27][28]. ...
... All the calculated parameters concerning the FRET and NSET phenomena are also tabulated in Table S4. It is pertinent to note that all values of R o and r calculated based on FRET mechanism are within the acceptable range of ~20-90 Å [26][27][28]70,71]. Since there isn't any limit in the donor-acceptor distance (d o or d) calculated using NSET method, so both the FRET as well as NSET mechanisms can be applicable for the current systems. ...
This work demonstrates refolding of unfolded bioconjugated bovine serum albumin [(BSA, 10 μM):gold nanoparticles (AuNPs, 0.0124 μM)] using β-cyclodextrin (β-CD). Protein bioconjugates are first unfolded with 0.2 mM of each of gemini surfactants, 12-4-12,2Br and 12-8-12,2Br- that have hydrophobic spacer groups of different lengths. At this concentration of a gemini surfactant, protein bioconjugates remain in compressed form due to strong hydrophobic interactions imparted by highly hydrophobic microdomain within the core of the gemini micelles formed along the chain of a bioconjugate. The compressed protein bioconjugates get relaxed in presence of a low concentration of β-CD which strips off surfactant molecules from bioconjugate-micelles complexes. Relaxed denatured protein bioconjugates then get refolded once remaining surfactant molecules are stripped off at a higher concentration of β-CD. A step-wise refolding process of bioconjugated protein chains exactly opposite to the unfolding is noted. Binding isotherms are constructed using Förster’s resonance energy transfer (FRET) and nanometal surface energy transfer (NSET) parameters calculated based on energy transfer process occurs between Trp residues and AuNPs. α-helix of protein bioconjugates remains in inverse relationship to β-turns during refolding by β-CD. Refolding is found to be more in presence of 12-8-12,2Br⁻ than 12-4-12,2Br⁻. Secondary/tertiary structural changes of refolded BSA, on being bioconjugated, have been determined through various spectroscopic analysis. An approach towards construing the refolding of denatured AuNPs-bioconjugates as potential materials and impacts of AuNPs on conformations of refolded protein is presented here.
... Despite being an effective and convenient technique, FRET as a nonradiative tool has a limitation regarding the distance and orientation of the transition dipoles of the donor and acceptor [22][23][24]. FRET can successfully measure the separation distance within ~20-90 Å [25][26][27][28]. To resolve this limitation, optical properties of AuNPs have been developed as universal acceptors in the NSET study arising from the molecular donors to the metal NPs [20,29,30]. ...
... All FRET and NSET parameters calculated are also tabulated in Table S2. All values of R o and r displayed by Table S2 lie within the acceptable range of the FRET phenomenon [25][26][27][28]96,97]. On the other hand, there is no such limitation regarding the donor-acceptor distance in the NSET mechanism [20,27,32]. ...
This work demonstrates binding interactions of two cationic gemini surfactants, 12-4-12,2Br⁻ and 12-8-12,2Br⁻ with gold nanoparticles (AuNPs)-conjugated bovine serum albumin (BSA) presenting binding isotherms from specific binding to saturation binding regions of surfactants. The binding isotherm has been successfully constructed using Förster's resonance energy transfer (FRET) and nanometal surface energy transfer (NSET) parameters calculated based on fluorescence quenching of donor, tryptophan (Trp) residue by acceptor, AuNP. Energy transfer efficiency (ET) changes due to alteration in the donor-acceptor distance when surfactants interact with bioconjugates. A solid reverse relationship between α-helix and β-turn contents of BSA-AuNPs-conjugates is noted while interacting with surfactants. 12-8-12,2Br⁻ shows stronger binding interactions with BSA-bioconjugates than 12-4-12,2Br⁻. The effect of bioconjugation on secondary/tertiary structures of BSA in the absence and presence of a surfactant is studied through circular dichroism, fluorescence, and Fourier transform infrared spectroscopic measurements. Motional restrictions imposed by AuNPs on Trp residues of folded and unfolded BSA have been investigated using red edge emission shift (REES) measurements. Finally, the molecular docking results present the modes of interactions of 12-4-12,2Br⁻ and 12-8-12,2Br⁻, and Au-nanoclusters (Au92) with BSA. An approach to describe the binding isotherms of surfactants using AuNPs-bioconjugates as optical-based molecular ruler and possible effects of AuNPs on microenvironment and conformations of the protein is presented.
... In this phenomenon, dipole-dipole interactions between the excited donor molecule (D) and the acceptor molecule (A) staying in the ground state result in a nonradiative exchange of energy between them. The length scale of nanoscopic FRET is restricted to 8 nm, beyond which it is too weak to be used as the energy transfer effi ciency is inversely proportional to the sixth power of the distance between the donor and acceptor molecules [24,25]. Recently, a long-range dipole-surface interaction mechanism based on NSET has been realized, whose range for energy transfer is twice as that for FRET [9]. ...
... Recently, a long-range dipole-surface interaction mechanism based on NSET has been realized, whose range for energy transfer is twice as that for FRET [9]. Here, the rate of energy transfer from the oscillating dipole to the continuum of the electron-hole pair excitations in metal nanoparticles is inversely proportional to the fourth power of the donor-to-acceptor distance [25,26]. In the linear regime, both these techniques are recognized as powerful tools for determining the distance in the donor-acceptor pair within a coupled hybrid [27,28]. ...
We have experimentally realized a morphology-directed nanoscale energy transfer between an emitter, Eosin yellow dye, and three distinct gold nanoshapes, namely, nanospheres, nanopebbles, and nanoflowers. Raman spectroscopy is employed to ensure mutual interaction among the couple hybrids. The results explicitly show that plasmonic structures with sharp edges produce a strong localized electromagnetic field, which substantially suppresses the background fluorescence signals of the analyte. Further, the relationship between the observed quenching of the dye fluorescence and the geometrical factors of the gold nanoshapes is used to comprehend the influence of energy transfers on their enhanced third-order nonlinearity. The experimental findings reveal a relationship between the efficiency of energy transfers and the enhancement of the observed nonlinear optical coefficients. This study may act as the basis for designing active photonic nanocomposites based on their efficient energy transfer interactions.
... In the case of metallic nanoparticles, energy transfer between the donoracceptor pair can be termed as nanoparticle based surface energy transfer (NSET) due to the dipole-surface type energy * Corresponding author: rajiv.manohar@gmail.com transfer [9]. The efficiency of NSET is usually high over FRET. ...
... Here donor is the quantum efficiency of donor entity, the frequency of the donor electronic transition (ω donor ), the Fermi frequency (ω F ), and Fermi wave vector (k F ) of the metallic nanoparticles [9]. Accordingly, the value of d 0 has been calculated using donor = 0.35, ω d = 4.67 × 10 15 s -1 , ω F = 8.4 × 10 15 s -1 , k F = 1.2 × 10 8 cm -1 , and c = 3 × 10 10 cm s -1 . ...
In the recent past, the resonance energy transfer studies using metallic nanoparticles has become a matter of quintessence in modern technology, which considerably extends its applications in probing specific biological and chemical processes. In the present study, metallic-silver nanoparticles of 2–4 nm (diameter) capped with hexanethiol ligand are developed and dispersed in ferroelectric liquid crystal (FLC). The morphology of nanoparticles was characterized using HR-TEM and SEM techniques. Furthermore, a systematic study of energy transfer between the host FLC material (as donors) and metallic-silver nanoparticles (as acceptors) has been explored employing steady state and time resolved fluorescence spectroscopic techniques. The nanoparticle based surface energy transfer (NSET) parameters viz., transfer efficiency, transfer rate, and proximity distance between donor and acceptor, have been determined for NSET couples (FLC material–metallic-silver nanoparticle) composites. It is observed that various NSET parameters and quenching efficiency follow a linear dependence on the concentration of metallic-silver nanoparticles in host FLC material. The nonradiative energy transfer and superquenching effect were analyzed with the help of Stern-Volmer plots. The impact of present study about superquenching effect of the silver nanoparticles can be used for sensing applications that require high degree sensitivity.
... Additional chemical substituents can be introduced into different dyes to modify their electronic properties and tune their absorption and emission properties for FRET-based biosensing. [24,25] Typically, In FRET-based systems, dyes are often connected by non-conjugated spacers, and energy transfer happens across them. In this section, we classified FRET systems based on different fluorophore backbones, with an emphasis on the role of boron dipyrromethene (BODIPY), rhodamine, [26] fluorescein, [27] coumarin [28] and other fluorophores in detecting proteins, small molecules, metal ions and other analytes. ...
Fluorogenic biosensors are essential tools widely used in biomedicine, chemical biology, environmental protection and food safety. Fluorescence resonance energy transfer (FRET) is a crucial technique for developing fluorogenic biosensors that provide mechanistic insight into bioprocesses through time‐spatial bioimaging in living cells and organisms. Although extensive FRET‐based sensors have been developed for detecting or imaging analytes of interest over the past decade, few comprehensive reviews have summarized the recent studies from the fundamental chemical angle about the design and application. In this work, the recent advance in the discovery of FRET biosensors using donor‐acceptor dye combinations is described and they are classified based on different types of analytes, such as mall molecules, proteins, enzymes, nucleic acids and metal ions. This review provides molecular‐level inspiration for the design of FRET‐based biosensors, aiding in their application in biosensing and bioimaging.
... The average separation between particle centers (L) can be calculated using the equation L = N p 1/3 , where N p is the number density of particles. [30] Using the value for d TEM (33 nm) ( Figure S9, Supporting Information), values of L for mixture MGs dispersion studied here (0.07 wt%) is calculated as 130 nm. Hence, this concentration is used to prepare fluorescent and multiresponsive hydrogels with the consideration that the FRET will not occur in this gel. ...
Fluorescent hydrogels have emerged as one of the most promising candidates for developing biomimetic materials and artificial intelligence owing to their unique fluorescence and responsive properties. However, it is still challenging to fabricate hydrogel that exhibits synergistic changes in fluorescence color and shape in response to multistimulus via a simple method. Herein, blue‐ and orange‐emitting fluorescent microgels (MGs) both are designed and synthesized with pH‐, thermal‐, and cationic‐sensitivity via one‐step polymerization, respectively. The two fluorescent MGs are incorporated into transparent doubly crosslinked microgel (DX MG) hydrogels with a preset ratio. The DX MG hydrogels can tune the fluorescent color accompanied by size variation via subjecting to external multistimulus. Thus, DX MG hydrogels can be exploited for multiresponsive fluorescent bilayer actuators. The actuators can undergo complex shape deformation and color changes. Inspired by natural organisms, an artificial morning glory with color and size changes are showcased in response to buffer solutions of different pH values. Besides, an intelligent skin hydrogel, imitating natural calotes versicolor, by assembling four layers of DX MG with different ratios of MGs, is tailored. This work serves as an inspiration for the design and fabrication of novel biomimetic smart materials with synergistic functions.
... The fluorescence of an excited acceptor is stimulated, leading to an increase in its signal. This assay has limitations as the distance between the donor and acceptor must be precisely controlled to obtain a notable FRET effect [9]. FRET also requires a pair of fluorophores; however, the range of the fluorophore with non-overlapped emission spectra is limited [10]. ...
Quenchbody (Q-body) is a unique, reagentless, fluorescent antibody whose fluorescent intensity increases in an antigen-concentration-dependent manner. Q-body-based homogeneous immunoassay is superior to conventional immunoassays as it does not require multiple immobilization, reaction, and washing steps. In fact, simply mixing the Q-body and the sample containing the antigen enables the detection of the target antigen. To date, various Q-bodies have been developed to detect biomarkers of interest, including haptens, peptides, proteins, and cells. This review sought to describe the principle of Q-body-based immunoassay and the use of Q-body for various immunoassays. In particular, the Q-bodies were classified from a structural perspective to provide useful information for designing Q-bodies with an appropriate objective.
... [32][33][34][35][36] The origin of FRET process is found to be dipole-dipole interactions but the transfer of energy between the donor and acceptor is highly reliant on the distance between their centers. [37] FRET has been widely employed in fluorescence applications, as well as in medical diagnosis, biological analysis, and optical imaging. [38][39][40][41] Recently, CD-based FRET systems have been widely used as nanoprobes for various applications as a result of numerous research attempts exploring the potential of CDs. ...
Carbon dots (CDs) emerge as a potential group of photo‐luminescent nano‐materials due to their excellent optical, electrical, and chemical properties, as well as their competence in a wide range of environmental applications. CDs have unique and appealing properties such as excellent stability, low toxicity, water solubility, and derivability. When coupled with CDs, fluorescence resonance energy transfer (FRET) results in the development of highly sensitive ratiometric fluorescence sensor probes with potential applications in bio‐imaging, metal sensing, membrane dynamics, and environmental sensing. In this review, the progress and recent developments in CDs based FRET systems utilized for various environmental applications are conferred. An in‐depth description is provided regarding the numerous donor/acceptor systems which when integrated with CDs generate efficient FRET systems. The review enables researchers to identify and develop specific systems which can be utilized to generate a FRET pair with potential physico–chemical properties that aid the development of the same for various applications.
... , Copyright © 2007 American Chemical Society]The plasmonic ruler equation was established for biological systems interacting with NP and later employed in the plasmonic coupling,156,157 Forster distances in FRET,158 and photothermal effects.155 According to the plasmonic ruler equation, the fractional shift in the dipole resonance can be used to estimate the interparticle distance. ...
... Moreover, gradient overexpression of KIM1 demonstrated gradually enhanced binding between KIM1 and DR5 ( Supplementary Fig. 3b). While FRET assays confirmed the binding between KIM1-CFP and DR5-YFP, it was difficult to probe endogenous KIM1-DR5 interaction by FRET, because the large sizes of primary and secondary antibodies are beyond the detection limit of FRET 20,21 . As future studies, endogenous FRET assays may be performed by engineering cells using CRISPR/Cas9 mediated knock-in system 22 , so that KIM1 and DR5 are labeled endogenously with CFP or YFP, respectively. ...
Acute kidney injury (AKI) exhibits high morbidity and mortality. Kidney injury molecule-1 (KIM1) is dramatically upregulated in renal tubules upon injury, and acts as a biomarker for various renal diseases. However, the exact role and underlying mechanism of KIM1 in the progression of AKI remain elusive. Herein, we report that renal tubular specific knockout of Kim1 attenuates cisplatin- or ischemia/reperfusion-induced AKI in male mice. Mechanistically, transcription factor Yin Yang 1 (YY1), which is downregulated upon AKI, binds to the promoter of KIM1 and represses its expression. Injury-induced KIM1 binds to the ECD domain of death receptor 5 (DR5), which activates DR5 and the following caspase cascade by promoting its multimerization, thus induces renal cell apoptosis and exacerbates AKI. Blocking the KIM1-DR5 interaction with rationally designed peptides exhibit reno-protective effects against AKI. Here, we reveal a YY1-KIM1-DR5 axis in the progression of AKI, which warrants future exploration as therapeutic targets.
... FRET is a special phenomenon of energy transfer between acceptor and donor chromophores. The transfer distance is generally in 1-10 nm range [9][10][11][12][13][14][15][16]. In 1948, Förster proposed the theory of dipole-dipole interactions for the experimental phenomenon of energy transfer. ...
Life science research is advancing rapidly in the 21st century. Many innovative technologies and methodologies are being applied in various fields of the life sciences to reveal how macromolecules interact with each other. The technology of using fluorescent molecules in biomedical research has contributed immensely to progress in this field. Fluorescence-based optical biosensors, which show high specificity, exhibit huge potential for clinical diagnosis and treatment of many of the life-changing diseases. Fluorescence resonance energy transfer (FRET), is a technique that has been widely employed in biosensing ever since its discovery. It is a classic fluorescence technique, and an important biosensing research tool extensively utilized in the fields of toxicology, pharmacology, and biomedicine; many biosensor designs are based on FRET. Radiometric imaging of biological molecules, biomolecular interactions, and cellular processes are extensively performed using FRET biosensors. This review focuses on the selection of FRET donors and acceptors used for biosensing, and presents an overview of different FRET technologies. Furthermore, it highlights the progress in the application for FRET in nucleic acid and protein biosensing, and provides a viewpoint for future developmental trends using FRET technology.
... , Copyright © 2007 American Chemical Society]The plasmonic ruler equation was established for biological systems interacting with NP and later employed in the plasmonic coupling,156,157 Forster distances in FRET,158 and photothermal effects.155 According to the plasmonic ruler equation, the fractional shift in the dipole resonance can be used to estimate the interparticle distance. ...
Nanoplasmonic sensing relies on enhanced electromagnetic fields at the vicinity of nanostructured metal surface to detect molecules at ultra-low concentrations. The EM enhancements are strongly pronounced at junctions between adjacent nanostructures resulting in gap hot-spots. EM enhancements at these hot-spots increase non-linearly as a function of gap distances down to sub-10 regime. Analyte present at these gaps can leverage these EM enhancements, resulting in ultra-high sensitivity in detection. However, such confining gaps affect the ability of large analytes such as biomolecules to enter and thereby leverage EM fields within the gaps. This presents spatial needs to enhance EM fields at odds with those for accommodating biomolecular interactions. This thesis demonstrates the rational design of array configurations that allows the EM hotspots to be better leveraged by the reporter of biomolecular binding event. The thesis uses molecular self-assembly based approach to fabricate reproducible plasmonic nanoarrays on full wafers. Multiple parameters are considered including the dimension, shape, and density of hotspots, surface functionalization, and the choice of substrates, to demonstrate quantitative detection of molecules down to picomolar concentrations.
... Further, a long-range dipole-surface contact mechanism based on NSET has recently been developed, with energy transfer range twice that of FRET ( Figure 6) [19,29]. In metal nanoparticles, the rate of energy transfer from the oscillating dipole to the continuum of electron-hole pair excitations is inversely proportional to the fourth power of the donor to acceptor distance [61,62]. [19]. ...
The unique ability of plasmonic structures to concentrate and manipulate photonic signals in deep sub-wavelength domain provides new efficient pathways to generate, guide, modulate and detect light. Due to collective oscillations exhibited by the conducting electrons of metallic nanoparticles, their local fields can be greatly enhanced at the localized surface plasmon resonance (LSPR). Hence, they offer a versatile platform, where localized surface plasmons can be tuned over a broad range of wavelengths by controlling their shape, size and material properties. It has been realized that plasmonic excitations can strengthen nonlinear optical effects in three ways. First, the coupling between the incident beam of light and surface plasmons results in a strong local confinement of the electromagnetic fields, which in turn enhances the optical response. Second, the sensitivity of plasmonic excitations toward the dielectric properties of the metal and the surrounding medium forms the basis for label-free plasmonic sensors. Finally, the excitation and relaxation dynamics of plasmonic nanostructures responds to a timescale of femtoseconds regime, thus allowing ultrafast processing of the incident optical signals. This chapter aims to discuss all the aforementioned interactions of plasmons and their excitonic hybrids in detail and also represent a glimpse of their experimental realizations.
... This emission can happen when the two molecules are in close proximity usually between 10 and 100 Å via radiative or nonradiative processes [387]. The radiative energy transfer involves the emission of a photon from the donor and then the absorption of that photon by the acceptor [388]. The efficiency of this process is determined by the quantum yield which is the number of emitted photons relative to the number of absorbed photons. ...
Nanoparticles are considered a powerful tool for novel applications ranging from imaging and sensing to therapy. In this thesis, gold nanoparticles functionalised with DNA strands were used for the detection of target oligonucleotides in live cells while upconversion nanoparticles functionalised with DNA strands were used for the detection of target oligonucleotides in a tube. Gold nanoparticles functionalised with synthetic DNA oligonucleotides were used to identify and sort skeletal stem cells upon specific mRNA detection. Human bone marrow stromal cells include a population of skeletal stem cells, with the capacity to differentiate along the osteogenic, adipogenic, and chondrogenic lineages. According to current techniques, the isolation and enrichment of skeletal stem cells from human tissues face challenges when there is no specific skeletal stem cell marker. DNA functionalised AuNPs were able to detect skeletal stem cells based on endocellular mRNA expression and to rapidly sort these cells from human bone marrow. This is a significant approach for tissue engineering as skeletal stem cells can be harnessed to help bone regeneration. The enhancement of the endosomal escape of DNA functionalised gold nanoparticles via the incorporation of a cell-penetrating peptide has been studied in order to maximize the concentration of gold nanoparticles that can detect mRNA and therefore reduce their total amount when incubating with cells. Two different approaches for the functionalisation of gold nanoparticles’ surfaces with peptides are presented. In the first case, gold nanoparticles were functionalised with thiol terminated DNA strands followed by functionalisation with cysteine terminated cell-penetrating peptides. In the second instance, the peptide was conjugated on the 5’ end of the DNA strand. Then, the gold nanoparticles were modified with these conjugate sequences. All the above probes exhibited similar stability towards degradation by endocellular enzymes and similar specificity towards the detection of specific mRNA targets. Finally, the fabrication of an oligonucleotide sensor was developed based on the emissive optical properties of oligonucleotide-coated lanthanide-doped upconversion nanoparticles and the quenching ability of two-dimensional materials; MoS<sub>2</sub>, WS<sub>2</sub> and graphene oxide. In the first system, it was investigated the development of an upconversion nanoparticles sensor that detected polyA sequences and used the twodimensional materials, MoS<sub>2</sub> and WS<sub>2</sub>, as quenchers. In the second system, the fabrication of a DNA sensor for SARS-CoV-2 oligonucleotide detection was demonstrated while in this case, graphene oxide was the quencher. In both cases, monodisperse upconversion nanoparticles were functionalised with single-stranded DNA. In the presence of a complementary oligonucleotide target and the formation of double-stranded DNA, the upconversion nanoparticles could not interact with two-dimensional materials, thus retaining their fluorescence properties. The high sensitivity and specificity of this sensor to detect specific target oligonucleotides were also monitored.
... Both the mechanisms are implemented for the current systems as the R 0 and r values (from FRET) obtained from Table S3 † remain in the admissible range of $20-90Å while the donor-acceptor distance (d 0 or d), calculated using the NSET method, doesn't have any such limiting range. 48,49,84,85 It can be seen from Fig. 4(a) and (b) that E T follows an inverse relationship with r and d for both the surfactant systems and the changes in F/F 0 are in good agreement with the trends of these parameters. With the initial addition of SDS molecules, the protein surfactant complex gets dissociated, and the AuNPs approach near the Trp residues. ...
The present work elucidates binding interactions of sodium dodecyl sulphate (SDS) with the conjugated gold nanoparticles (AuNPs)-bovine serum albumin (BSA), unfolded by each of two gemini surfactants, 1,4-bis(dodecyl-N,N-dimethylammonium bromide)-butane (12-4-12,2Br-) or 1,8-bis(dodecyl-N,N-dimethylammonium bromide)-octane (12-8-12,2Br-). Initially, at a low concentration of SDS there is a relaxation of bioconjugates from their compressed form due to the formation of catanions between SDS and gemini surfactants. On moving towards higher concentrations of SDS, these relaxed unfolded bioconjugates renature by removal of residual bound gemini surfactants. Mixed assemblies of SDS and gemini surfactants formed during refolding of bioconjugates are characterized by DLS and FESEM measurements. A step-by-step process of refolding observed for these denatured protein bioconjugates is exactly the inverse of their unfolding phenomenon. Parameters concerning nanometal surface energy transfer (NSET) and Förster's resonance energy transfer (FRET) phenomenon were employed to develop a binding isotherm. Moreover, there remains an inverse relationship between α-helix and β-turns of bioconjugates during the refolding process. Significantly, in the presence of 12-8-12,2Br-, SDS induces more refolding as compared to that for 12-4-12,2Br-. Bioconjugation shows an effect on the secondary structures of refolded BSA, which has been explored in detail through various studies such as Fourier transform infrared spectroscopy, fluorescence, and circular dichroism (CD). Therefore, this approach vividly describes the refolding of denatured bioconjugates, exploring structural information regarding various catanions formed during the process that would help in understanding distance-dependent optical biomolecular detection methodologies and physicochemical properties.
... The interaction of aptamer/AuNPs conjugate with the fluorescent probe reduced the fluorescence intensity. Although the researchers mistakenly cited the mechanism of this interaction as FRET, while the term surface energy transfer (SET) was often used in the case of energy transfer for metal surfaces (such as AuNPs) (Saini et al. 2007;Ray et al. 2014). In the presence of digoxin and in the saltcontaining medium, the aptamers were separated from the surface of AuNPs and bound to their target. ...
The uncontrolled use of drugs endangers human health and causes drastic economic losses and irreparable consequences. Today, there is a great demand to introduce accurate, potent, real-time, and rapid methodologies for sensitive detection and quantification of drugs. To overcome this challenging difficulty, biosensors have been introduced as valuable tools. Among the diverse kinds of biosensors, aptamer-based biosensors (aptasensors) have evolved as novel candidates for the sensitive evaluation of different groups of drugs, owing to their superior specificity, sensitivity, and selectivity. This chapter encompasses the recent progress in the development of aptasensors to quantitatively monitor various types of drugs. Besides, sensing mechanisms associated with the aptasensors are given that provide ideas to develop the novel aptasensing platforms as the portable test kits for the on-site detection of drugs.
... The interaction of aptamer/AuNPs conjugate with the fluorescent probe reduced the fluorescence intensity. Although the researchers mistakenly cited the mechanism of this interaction as FRET, while the term surface energy transfer (SET) was often used in the case of energy transfer for metal surfaces (such as AuNPs) (Saini et al. 2007;Ray et al. 2014). In the presence of digoxin and in the saltcontaining medium, the aptamers were separated from the surface of AuNPs and bound to their target. ...
Current technics used in food quality assessment require complex equipment and professional personnel, which has financially burdened the food industry. Optical devices are a powerful candidate which can provide simple, cost-effective, and rapid detection approaches with the possibility to be easily manufactured in a large scale to cover the vast need of this industry. This chapter will first present an overview regarding food safety and common analytes. Various optical sensing technics, including colorimetric, fluorescent, chemiluminescent, surface-enhanced Raman scattering (SERS), and surface plasmon resonance (SPR) methods will then be explored with examples of novel sensing platforms developed for food monitoring.
... The interaction of aptamer/AuNPs conjugate with the fluorescent probe reduced the fluorescence intensity. Although the researchers mistakenly cited the mechanism of this interaction as FRET, while the term surface energy transfer (SET) was often used in the case of energy transfer for metal surfaces (such as AuNPs) (Saini et al. 2007;Ray et al. 2014). In the presence of digoxin and in the saltcontaining medium, the aptamers were separated from the surface of AuNPs and bound to their target. ...
The exopolysaccharide botryosphaeran produced by the ascomycetous fungus, Botryosphaeria rhodina MAMB-05, and its chemical-derivative form (carboxymethyl-botryosphaeran) have emerged in the electroanalytical field in recent years as a platform for immobilizing the enzyme laccase on carbon-based electrodes. The bioelectrochemical devices fabricated have presented excellent performance towards the determination of phenolic compounds in food samples, with high sensitivity, selectivity, and long-term storage stability. Other applications have included analysis in the clinical, pharmaceutical, and environmental sectors.
... The interaction of aptamer/AuNPs conjugate with the fluorescent probe reduced the fluorescence intensity. Although the researchers mistakenly cited the mechanism of this interaction as FRET, while the term surface energy transfer (SET) was often used in the case of energy transfer for metal surfaces (such as AuNPs) (Saini et al. 2007;Ray et al. 2014). In the presence of digoxin and in the saltcontaining medium, the aptamers were separated from the surface of AuNPs and bound to their target. ...
Food quality control and analysis have many attributes that are discussed in this chapter. Quality and safety are the major parameters in any food industry, the importance of which is discussed in this chapter. Food analysis involves various steps along with different methods, the selection of which depends on various factors such as composition of food product which are mentioned in this chapter. The brief overview of different analytical techniques including sample preparation techniques, general analysis techniques, determinative and separation techniques, biological techniques, rheological techniques, radiochemical and electrochemical techniques, and their selection methods are also discussed in this chapter.
... As these mechanisms have been reviewed elsewhere, we give only a brief discussion about them. [32][33][34][35][36][37] ICT usually occurs within a molecule, in which an electron is transferred from an electron-rich donor moiety to an electron-deficient acceptor moiety upon photoexcitation. 38 The potentially environment-dependent emission properties allow ICT-based fluorophores to be ideal for the imaging and detection of various biomarkers. ...
The real-time, dynamic optical visualization of lesions and margins ensures not only complete resection of the malignant tissues but also better preservation of the vital organs/tissues during surgical procedures. Most imaging probes with an "always-on" signal encounter high background noise due to their non-specific accumulation in normal tissues. By contrast, activatable molecular probes only "turn on" their signals upon reaction with the targeted biomolecules that are overexpressed in malignant cells, offering high target-to-background ratios with high specificity and sensitivity. This review summarizes the recent progress of activatable molecular probes in surgical imaging and diagnosis. The design principle and mechanism of activatable molecular probes are discussed, followed by specific emphasis on applications ranging from fluorescence-guided surgery to endoscopy and tissue biopsy. Finally, potential challenges and perspectives in the field of activatable molecular probe-enabled surgical imaging are discussed.
... Furthermore, UV and visible emission intensities increased more than 500-fold and 130-fold, respectively, for the nanoparticles without shell protection (Figure 4b). Notably, the transfer efficiency decreased as 1/R 6 [39]. Therefore, the enhancement factor decreased as the distance between the dye and the sensitizer increased. ...
Upconversion nanocrystals that converted near-infrared radiation into emission in the ultraviolet spectral region offer many exciting opportunities for drug release, photocatalysis, photodynamic therapy, and solid-state lasing. However, a key challenge is the development of lanthanide-doped nanocrystals with efficient ultraviolet emission, due to low conversion efficiency. Here, we develop a dye-sensitized, heterogeneous core–multishelled lanthanide nanoparticle for ultraviolet upconversion enhancement. We systematically study the main influencing factors on ultraviolet upconversion emission, including dye concentration, excitation wavelength, and dye-sensitizer distance. Interestingly, our experimental results demonstrate a largely promoted multiphoton upconversion. The underlying mechanism and detailed energy transfer pathway are illustrated. These findings offer insights into future developments of highly ultraviolet-emissive nanohybrids and provide more opportunities for applications in photo-catalysis, biomedicine, and environmental science.
... The best example in this regard is FRET where, upon excitement, a donor chromophore transfers its energy to an acceptor chromophore through non-radiative dipolar coupling. This energy transfer event is governed by one factor of the donor-acceptor distance [10]. Based on distance-dependent properties, activatable fluorescent probes allow the measurement of intracellular events, providing a powerful tool for studying fundamental aspects of cell biology and molecular recognition [11]. ...
Activatable fluorescent probes have been successfully used as molecular tools for biomedical research in the last decades. Fluorescent probes allow the detection of molecular events, providing an extraordinary platform for protein and cellular research. Nevertheless, most of the fluorescent probes reported are susceptible to interferences from endogenous fluorescence (background signal) and limited tissue penetration is expected. These drawbacks prevent the use of fluorescent tracers in the clinical setting. To overcome the limitation of fluorescent probes, we and others have developed activatable magnetic resonance probes. Herein, we report for the first time, an oligonucleotide-based probe with the capability to detect bacteria using magnetic resonance imaging (MRI). The activatable MRI probe consists of a specific oligonucleotide that targets micrococcal nuclease (MN), a nuclease derived from Staphylococcus aureus . The oligonucleotide is flanked by a superparamagnetic iron oxide nanoparticle (SPION) at one end, and by a dendron functionalized with several gadolinium complexes as enhancers, at the other end. Therefore, only upon recognition of the MRI probe by the specific bacteria is the probe activated and the MRI signal can be detected. This approach may be widely applied to detect bacterial infections or other human conditions with the potential to be translated into the clinic as an activatable contrast agent.
... It is well known that fluorescent molecules coming in close contact with noble metal nanoparticles lose their emission properties due to the nanoparticle surface energy transfer (NSET) mechanism. 51,52 In our experiments, the fluorescence signal (505-600 nm with l exc = 495 nm) from FITC labeled ADH was recorded by varying the concentration of the labeled ADH. Then a calibration plot (Fig. 4) was drawn, which correlates the ADH concentration with the fluorescence signal intensity. ...
Characterization of nanoparticle protein corona has gained tremendous importance lately. The parameters which quantitatively establish a specific nanoparticle-protein interaction need to be measured accurately since good quality data is necessary...
... Non-radiative energy transfer-based fluorescent sensors have drawn remarkable research interest to detect toxic chemicals and pathogenic bacteria in food and agricultural product. FRET, a non-radiative distance-dependent energy transfer phenomenon widely applied as a unique, reliable, and sensitive analytical technique to detect various analytes was first proposed by Stryer and Haugland in 1967 as a ''spectroscopic ruler'' , also termed as Förster resonance energy transfer (Ray et al. 2014). FRET is a process in which excited donor molecules transfer energy to the acceptors in the ground state via induced dipole-dipole interactions resulting in the emission spectrum of donner molecules and absorption spectrum of acceptor molecules overlaps (Kalkal et al. 2020). ...
The abuse of pesticides in agricultural land during pre- and post-harvest causes an increase of residue in agricultural products and pollution in the environment, which ultimately affects human health. Hence, it is crucially important to develop an effective detection method to quantify the trace amount of residue in food and water. However, with the rapid development of nanotechnology and considering the exclusive properties of nanomaterials, optical, and their integrated system have gained exclusive interest for accurately sensing of pesticides in food and agricultural samples to ensure food safety thanks to their unique benefit of high sensitivity, low detection limit, good selectivity and so on and making them a trending hotspot. This review focuses on recent progress in the past five years on nanomaterial-based optical, such as colorimetric, fluorescence, surface-enhanced Raman scattering (SERS), and their integrated system for the monitoring of benzimidazole fungicide (including, carbendazim, thiabendazole, and thiophanate-methyl) residue in food and water samples. This review firstly provides a brief introduction to mentioned techniques, detection mechanism, applied nanomaterials, label-free detection, target-specific detection, etc. then their specific application. Finally, challenges and perspectives in the respective field are discussed.
... The increase of plasmon coupling effect induces plasmon peak broadening and signal decrease due to its high NP distancedependent. This distance has been calculated using plasmon hybridization models, demonstrating that distances of 2 to 2.5 times the particle diameter start to induce plasmon coupling [21]. The low NP density, low signal/noisy ratio, and the broadening of the LSPR bands challenge accurate small peak shifts monitoring. ...
Plasmonic nanosensors for label-free detection of DNA require excellent sensing resolution, which is crucial when monitoring short DNA sequences, as these induce tiny peak shifts, compared to large biomolecules. We report a versatile and simple strategy for plasmonic sensor signal enhancement by assembling multiple (four) plasmonic sensors in series. This approach provided a fourfold signal enhancement, increased signal-to-noise ratio, and improved sensitivity for DNA detection. The response of multiple sensors based on AuNSpheres was also compared with AuNRods, the latter showing better sensing resolution. The amplification system based on AuNR was integrated into a microfluidic sequential injection platform and applied to the monitoring of DNA, specifically from environmental invasive species—zebra mussels. DNA from zebra mussels was log concentration-dependent from 1 to 1 × 10⁶ pM, reaching a detection limit of 2.0 pM. In situ tests were also successfully applied to real samples, within less than 45 min, using DNA extracted from zebra mussel meat. The plasmonic nanosensors’ signal can be used as a binary output (yes/no) to assess the presence of those invasive species. Even though these genosensors were applied to the monitoring of DNA in environmental samples, they potentially offer advantage in a wide range of fields, such as disease diagnostics.
Graphical abstract
... The FRET efficiency is inversely proportional to the sixth power of the distance between two dyes, which allows for a very precise and sensitive measurement of the distance. Since R 0 typically has a range of 5 to 6 nm, the smFRET measurement is optimal for measuring distance variations in the range of 2-10 nm, which is the same as the length of dozens base pairs of dsDNA (Ray et al., 2014). Two methods are commonly used to measure the FRET efficiency of fluorophores labeled on a single dsDNA: one is to image tethered samples using total internal reflection (TIR) (Hildebrandt et al., 2015;Kim et al., 2021b); and the other is to measure freely diffusive samples using confocal microscopy (Kapanidis et al., 2004;Kim et al., 2015;Lee et al., 2005). ...
The various DNA-protein interactions associated with the expression of genetic information involve double-stranded DNA (dsDNA) bending. Due to the importance of the formation of the dsDNA bending structure, dsDNA bending properties have long been investigated in the biophysics field. Conventionally, DNA bendability is characterized by innate averaging data from bulk experiments. The advent of single-molecule methods, such as atomic force microscopy, optical and magnetic tweezers, tethered particle motion, and single-molecule fluorescence resonance energy transfer measurement, has provided valuable tools to investigate not only the static structures but also the dynamic properties of bent dsDNA. Here, we reviewed the single-molecule methods that have been used for investigating dsDNA bendability and new findings related to dsDNA bending. Single-molecule approaches are promising tools for revealing the unknown properties of dsDNA related to its bending, particularly in cells.
... While the FRET efficiency is related to the distance between a pair of dyes within a range of 3-10 nm 20 , PIFE tracks increases in fluorescence quantum yields or lifetimes related to the distance between the dye and a surface of a nearby protein in the range of 0-3 nm 19 . ...
Using spectroscopic rulers to track multiple conformations of single biomolecules and their dynamics have revolutionized the understanding of structural dynamics and its contributions to biology. While the FRET-based ruler reports on inter-dye distances in the 3-10 nm range, other spectroscopic techniques, such as protein-induced fluorescence enhancement (PIFE), report on the proximity between a dye and a protein surface in the shorter 0-3 nm range. Regardless of the method of choice, its use in measuring freely-diffusing biomolecules one at a time retrieves histograms of the experimental parameter yielding separate centrally-distributed sub-populations of biomolecules, where each sub-population represents either a single conformation that stayed unchanged within milliseconds, or multiple conformations that interconvert much faster than milliseconds, and hence an averaged-out sub-population. In single-molecule FRET, where the reported parameter in histograms is the inter-dye FRET efficiency, an intrinsically disordered protein, such as the α-Synuclein monomer in buffer, was previously reported as exhibiting a single averaged-out sub-population of multiple conformations interconverting rapidly. While these past findings depend on the 3-10 nm range of the FRET-based ruler, we sought to put this protein to the test using single-molecule PIFE, where we track the fluorescence lifetime of site-specific sCy3-labeled α-Synuclein proteins one at a time. Interestingly, using this shorter range spectroscopic proximity sensor, sCy3-labeled α-Synuclein exhibits several lifetime sub-populations with distinctly different mean lifetimes that interconvert in 10-100 ms. These results show that while α-Synuclein might be disordered globally, it nonetheless attains stable local structures. In summary, in this work we highlight the advantage of using different spectroscopic proximity sensors that track local or global structural changes one biomolecule at a time.
... We used eq 1 for finding the LOD for the distance-dependent NSET assay. 16 ...
The ongoing outbreak of the coronavirus infection has killed more than 2 million people. Herein, we demonstrate that Rhodamine 6G (Rh-6G) dye conjugated DNA aptamer-attached gold nanostar (GNS)-based distance-dependent nanoparticle surface energy transfer (NSET) spectroscopy has the capability of rapid diagnosis of specific SARS-CoV-2 spike recombinant antigen or SARS-CoV-2 spike protein pseudotyped baculovirus within 10 min. Because Rh-6G-attached single-stand DNA aptamer wrapped the GNS, 99% dye fluorescence was quenched because of the NSET process. In the presence of spike antigen or virus, the fluorescence signal persists because of the aptamer-spike protein binding. Specifically, the limit of detection for the NSET assay has been determined to be 130 fg/mL for antigen and 8 particles/mL for virus. Finally, we have demonstrated that DNA aptamer-attached GNSs can stop virus infection by blocking the angiotensin-converting enzyme 2 (ACE2) receptor binding capability and destroying the lipid membrane of the virus.
Thrombin, a proteolytic enzyme, plays an essential role in catalyzing many blood clotting reactions. Thrombin can act as a marker for some blood-related diseases, such as leukemia, thrombosis, Alzheimer's disease and liver disease. Therefore, its diagnosis is of great importance in the fields of biological and medical research. Biosensors containing sandwich-type structures have attracted much consideration owing to their superior features such as reproducible and stable responses with easy improvement in the sensitivity of detection. Sandwich-type platforms can be designed using a pair of receptors that are able to bind to diverse locations of the same target. Herein, we investigate recent advances in the progress and applications of thrombin aptasensors containing a sandwich-type structure, in which two thrombin-binding aptamers (TBAs) identify different parts of the thrombin molecule, leading to the formation of a sandwich structure and ultimately signal detection. We also discuss the pros and cons of these approaches and outline the most logical approach in each section.
Materials are the fundament of the physical world, whereas information and its exchange are the centerpieces of the digital world. Their fruitful synergy offers countless opportunities for realizing desired digital transformation processes in the physical world of materials. Yet, to date, a perfect connection between these worlds is missing. From the perspective, this can be achieved by overcoming the paradigm of considering materials as passive objects and turning them into perceptual, information‐providing matter. This matter is capable of communicating associated digitally stored information, for example, its origin, fate, and material type as well as its intactness on demand. Herein, the concept of realizing perceptual, information‐providing matter by integrating customizable (sub‐)micrometer‐sized communicating supraparticles (CSPs) is presented. They are assembled from individual nanoparticulate and/or (macro)molecular building blocks with spectrally differentiable signals that are either robust or stimuli‐susceptible. Their combination yields functional signal characteristics that provide an identification signature and one or multiple stimuli‐recorder features. This enables CSPs to communicate associated digital information on the tagged material and its encountered stimuli histories upon signal readout anywhere across its life cycle. Ultimately, CSPs link the materials and digital worlds with numerous use cases thereof, in particular fostering the transition into an age of sustainability.
Hypoxanthine concentration is a potential indicator to evaluate the freshness in the early post-mortem of several aquatic products. Based on MnO2 in-situ coated upconversion nanoparticles (UCNPs) and xanthine oxidase (XOD), a novel sensor was conducted for the efficient, sensitive determination of hypoxanthine. In this strategy, upconversion fluorescence quenched by MnO2 would be restored by H2O2 and uric acid (UA), two products from the XOD-catalyzed reactions of hypoxanthine. Through pretreatment with short-time heating and alkylation by N-ethylmaleimide (NEM) to avoid potential interference from reducing substances in the food matrix, this method exhibited satisfactory selectivity. The fluorescence intensity of green emission Igreen was positively proportional to hypoxanthine concentration at a wide range of 0.5-50 mg/L with a detection limit of 0.14 mg/L. Moreover, this convenient method was employed to quantify the hypoxanthine in fish, shrimp, and shellfish samples, showing excellent potential for the application in quality control of aquatic products.
Despite the promising performance of Ru nanoparticles or nanoclusters on nanostructured TiO2 in photocatalytic and photothermal reactions, a mechanistic understanding of the photophysics is limited. The aim of this study is to uncover the nature of light-induced processes in Ru/TiO2 and the role of UV versus visible excitation by time-resolved photoluminescence (PL) spectroscopy. The PL at a 267 nm excitation is predominantly due to TiO2, with a minor contribution of the Ru nanoclusters. Relative to TiO2, the PL of Ru/TiO2 following a 267 nm excitation is significantly blue-shifted, and the bathochromic shift with time is smaller. We show by global analysis of the spectrotemporal PL behavior that for both TiO2 and Ru/TiO2 the bathochromic shift with time is likely caused by the diffusion of electrons from the TiO2 bulk toward the surface. During this directional motion, electrons may recombine (non)radiatively with relatively immobile hole polarons, causing the PL spectrum to red-shift with time following excitation. The blue-shifted PL spectra and smaller bathochromic shift with time for Ru/TiO2 relative to TiO2 indicate surface PL quenching, likely due to charge transfer from the TiO2 surface into the Ru nanoclusters. When deposited on SiO2 and excited at 532 nm, Ru shows a strong emission. The PL of Ru when deposited on TiO2 is completely quenched, demonstrating interfacial charge separation following photoexcitation of the Ru nanoclusters with a close to unity quantum yield. The nature of the charge-transfer phenomena is discussed, and the obtained insights indicate that Ru nanoclusters should be deposited on semiconducting supports to enable highly effective photo(thermal)catalysis.
Due to its primordial function as a drug carrier, human serum albumin (HSA) is extensively studied regarding its binding affinity with developing drugs. Förster resonance energy transfer (FRET) is frequently applied as a spectroscopic molecular ruler to measure the distance between the binding site and the ligand. In this work, we have shown that most of the published results that use the FRET technique to estimate the distance from ligands to the binding sites do not corroborate the crystallography data. By comparing the binding affinity of dansyl-proline with HSA and ovotransferrin, we demonstrated that FRET explains the quenching provoked by the interaction of ligands in albumin. So, why does the distance calculation via FRET not corroborate the crystallography data? We have shown that this inconsistency is related to the fact that a one-to-one relationship between donor and acceptor is not present in most experiments. Hence, the quenching efficiency used for calculating energy transfer depends on distance and binding constant, which is inconsistent with the correct application of FRET as a molecular ruler. We have also shown that the indiscriminate attribution of 2/3 to the relative orientation of transition dipoles of the acceptor and donor (κ2) generates inconsistencies. We proposed corrections based on the experimental equilibrium constant and theoretical orientation of transition dipoles to correct the FRET results.
Nonlinear optical response is a fingerprint of various physicochemical properties of materials related to symmetry, including crystallography, interfacial configuration, and carrier dynamics. However, the intrinsically weak nonlinear optical susceptibility and the diffraction limit of far-field optics restrict probing deep-subwavelength-scale nonlinear optics with measurable signal-to-noise ratio. Here, we propose an alternative approach toward efficient second harmonic generation (SHG) nanoscopy for SHG-active sample (zinc oxide nanowire; ZnO NW) using an SHG-active plasmonic nanotip. Our full-wave simulation suggests that the experimentally observed high near-field SHG contrast is possible when the nonlinear response of ZnO NW is enhanced and/or that of the tip is suppressed. This result suggests possible evidence of quantum mechanical nonlinear energy transfer between the tip and the sample, modifying the nonlinear optical susceptibility. Further, this process probes the nanoscale corrosion of ZnO NW, demonstrating potential use in studying various physicochemical phenomena in nanoscale resolution.
The development of rapid, sensitive, specific and accurate diagnostic tests is essential for improving the treatment outcome of diseases. In the majority of disease diagnosis, nucleic acid-based tests are accepted as a gold standard. In general, these tests provide reliable results, yet they require highly trained personnel and specialized equipmentation. With the introduction of clustered regularly interspaced short palindromic repeats (CRISPR)-Cas systems in diagnostic applications, achieving breakthrough improvements in diagnostic tests is now possible. The specific target sequence recognition ability and trans-cleavage activity of certain Cas proteins enable novel applications of these systems in the development and improvement of diagnostic tests. These improvements and innovations allow for improved sensitivity, specificity and accuracy of point-of-care tests while keeping their costs at affordable levels. In this review, a comprehensive analysis of the common CRISPR-Cas systems used in diagnostic applications and the utilization of these systems in the design of novel biosensors is provided.
Self-luminescence, which eliminates the real-time external optical excitation, can effectively avoid background autofluorescence in photoluminescence, endowing with ultrahigh signal-to-noise ratio and sensitivity in bioassay. Furthermore, in situ generated and emitted photons have been applied to develop excitation-free diagnostics and therapeutic agents against deeply seated diseases. "Enhanced" self-luminescence, referring to the aggregation-induced emission (AIE)-integrated self-luminescence systems, is endowed with not only the above merits but also other superiorities including stronger luminous brightness and longer half-life compared with "traditional" self-luminescence platforms. As an emerging and booming hotspot, the "enhanced" self-luminescence facilitated by the win-win cooperation of the aggregation-induced emission and self-luminescent techniques has become a powerful tool for interdisciplinary research. This tutorial review summarizes the advancements of AIE-assisted self-luminescence including chemiluminescence and afterglow imaging, starting from the discussion on the design and working principles, luminescent mechanisms of self-luminescence fuels, versatile integrated approaches and advantages, and a broad range of representative examples in biosensors and oncotherapy. Finally, the current challenges and perspectives are discussed to further actuate the development of "enhanced" self-luminescence agents for biomedical diagnosis and treatment.
Gold nanorods (AuNRs) have attracted tremendous interest in biomedical fields due to their unique optical properties, tunable surface plasmon, and excellent biocompatibility. Their biomedical applications are mainly influenced by near-infrared (NIR) light, which can guarantee deep penetration into human tissues with minimal loss. However, traditional single AuNRs are unable to carry medicine into the lesion regions. Furthermore, it is difficult for AuNR nanoparticles to be implemented in multimodal imaging-guided synergetic therapy, which has limited the application of AuNRs in the field of theranostics. In recent years, researchers have made great strides in modifying gold nanorods into nanomaterials for the integration of diagnosis and treatment. After modifying different functionalized shells on the outsides of AuNRs, heterostructure AuNRs known as anisotropic gold nanorod (AAuNR) nanoparticles possessed bioimaging and cancer therapy abilities, as well as a variety of other amazing biomedical applications. In addition, AAuNR nanoparticles can combine biomedical imaging and therapy into one system to achieve multimodal bioimaging guided synergetic therapy. In this study, we presented a current review of the latest progress of different types of AAuNRs nanoparticles and their biomedical applications. Furthermore, the challenges and future development trends of AAuNR nanoparticles in the biomedical fields are discussed.
Recently, noble metal nanomaterials have been extensively studied in the fields of biosensing, environmental catalysis, and cancer diagnosis and treatment, due to their excellent electrical conductivity, high surface area, and individual physical and optical properties. Early research on the surface-enhanced Raman scattering (SERS) effect was focused on the cognition of the SERS phenomenon and enhancing its sensitivity for single-molecule detection. With the development of nanomaterials and nanotechnology, the advances and applications based on SERS substrates have been accelerated. Among them, noble metal nanomaterials are mainly used as SERS-active substrates to enhance SERS signals owing to their compelling surface plasmon resonance (SPR) properties. This review provides recent advances, perspectives, and challenges in SERS assays based on engineered noble metal nanomaterials for early cancer diagnosis.
Long range optical rulers measuring distance greater than 10 nm have important applications in monitoring biological processes, nanolithography, and nanometrology. In this work, we show that lateral displacement over 120 nm can be determined by measuring two reflection peaks of the proposed nanostructure. The optical anapole in the nanostructure is excited, resulting from interactions of plasmonic resonance modes of nanoholes perforated in metal films and an array of nanoblocks. Results show that a 120 nm relative displacement between the nanoblocks and nanoholes induces a negative correlated 90% variation of reflection spectrum which can be used for self-referenced measurement. The proposed design could find applications in nanometrology, biosensing, and nanofabrication.
Recently, Förster resonance energy transfer (FRET)-based strategy has been successfully applied to promote the efficiencies of ternary blend organic solar cells (TOSCs). However, the intrinsic mechanism of FRET in the observed enhancement of efficiency has not been deconvolved unambiguously due to the complex photophysics mechanism. In this review, by deeply analyzing recent examples of FRET-incorporated TOSCs, diverse framework structures of FRET pairs were summarized, then the theory, prerequisites and the confirmation methods for FRET were discussed. In particular, the role of FRET theory in the photoconversion process was discussed in detail, including exciton harvesting, exciton diffusion and charge generation. Finally, the existing challenges and future research directions of FRET applications in TOSCs would be proposed.
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In this study, three novel oxy-naphthylchalcone appended cyclotriphosphazene derivatives (3, 4 and 5) were obtained by the nucleophilic substitution reactions of cyclotriphosphazene cores (1, 1a and 1b) with (E)-3-(4-hydroxyphenyl)-1-(naphthalene-2-yl) prop-2-en-1-one (2) in presence of K2CO3/acetone. Novel compounds 3, 4 and 5 were characterized with using NMR (1H and 31P), elemental analysis, mass and FT-IR spectroscopies. In addition, molecular and crystal structures of 2 and 3 were determined by single crystal X-ray crystallography. The photophysical and intramolecular energy transfer properties of novel oxy-naphthylchalcone appended cyclotriphosphazene derivatives (3, 4 and 5) and their precursors (1a and 1b) were examined by steady state-/time resolved fluorescence spectroscopy, UV–Vis absorption spectroscopy and excitation-emission matrix (EEM) analysis. According to obtained results, novel target compounds (4 and 5) demonstrate a highly efficient intramolecular fluorescence resonance energy transfer (FRET) between excited phenol/naphthol groups and oxy-naphthylchalcone group.
By mechanically changing the width of a nanometer gap between two optical antennas, the coupling condition for the antennas can be seamlessly modified. This leads to a shift in the antenna's localized surface plasmon resonance wavelength, and a modification of the intensity in the antenna hotspot, which can reach extraordinarily high values for nanometer gaps. Such systems have in recent years been realized, for example, by using flexible polymers as substrates that are mechanically stretched or bent, or by combining break junctions with plasmonic antennas. Applications can be found, amongst others, in plasmonic strain sensing via color shift sensors, or tunable surface-enhanced Raman spectroscopy platforms. In this article an overview is given over recent work on mechanically tunable gap antennas, with a specific focus on studies at the single-nanostructure level. Different techniques used for mechanical tuning, optical read-out signals that are influenced by the gap width, and potential applications of the resulting structures are presented. Plasmonic break junctions offer a new perspective that allows for added functionalities. The mechanical activation is discussed within the context of single nanoantenna gap tuning by using alternative stimuli.
The optical background such as autofluorescence and light scattering poses a big challenge to quantify nucleic acids with conventional fluorescence-based methods. We report here high-contrast nucleic acid detection with photoswitch-mediated fluorescence resonance energy transfer (FRET), which strongly occurs between the open forms of the photoswitch (a naphthopyran) and the signal fluorophores brought to the surface of the nanoprobes (≲15 nm). The fluorescence change (ΔF) upon UV irradiation is highly sensitive and more robust to quantify the target DNAs than traditional intensity measurements. Therefore, the method works in samples with strong background fluorescence from the unbound fluorophores. The photoswitchable nanoprobes could be easily prepared and interrogated in capillaries for high-throughput measurements. The method was evaluated in both sandwich-like hybridization and DNA label-free detection with a nucleic stain SG. Without DNA amplification and sample pretreatment of blood serum, the photoswitchable nanoprobes provided a limit of detection of 0.5 nM, which is ∼6 to 20 times lower than conventional FRET.
Pluripotency of a DNA tetrahedron (DNATT) has made the iconic framework a compelling keystone in biosensors and biodevices. Herein, distinct from the well-tapped applications in substrate fabrication, we focus on exploring their tracing and signaling potentials. A homologous family of four isostructural DNATT, i.e., DNATTα/β/γ/δ, was engineered to form a sensor circuitry, in which a target-specific monolayer of thiolated DNATTγ pinned down the analyte jointly with the reciprocal DNATTδ into a sandwich complex; the latter further rallied an in situ interdigital relay of biotinylated DNATTα/β into a microsized hyperlink dubbed polyDNATT. Its scale and growth factors were illuminated rudimentarily in transmission electron microscopy and confocal laser scanning microscopy. Using a nonsmall-cell lung cancer-related microRNA (hsa-miR-193a-3p) as the subject, a compound DNA-backboned construct was synthesized, fusing all building blocks together. Its superb tacticity and stereochemical conformality avail the templating of a horseradish peroxidase train, which boosted the paralleled catalytic surge of proton donors, resulting in an attomolar detection limit and a broad calibration range of more than seven orders of magnitude. Such oligomerization bested the conventional hybridization chain reaction laddering at both biomechanical stability and stoichiometric congruency. More significantly, it demonstrates the flexibility of DNA architectures and their multitasking ability in biosensing.
Es wird ein einfaches und sehr empfindliches Verfahren zur quantitativen Messung der Depolarisationsfähigkeit von Lösungen angegeben und seine Handhabung an Beispielen eines darauf aufgebauten Jodmeters erläutert, das einen der Konzentration proportionalen Ausschlag liefert. Es eignet sich u. a. auch besonders für die Verwendung als Coulombmeter für kleine Ladungsmengen. Weiter kann man damit geringe Konzentrationen von Jod oder Natriumthiosulfat mit rein elektrischen Mitteln, d. h. ohne Normallösungen sehr genau bestimmen. Die Meßgrenze liegt bei 1 ccm Lösung unter ¹/1000 γ Jod.
Optical properties of small dielectric spheroids with or without adsorbed molecules are studied theoretically. Expressions for the absorption line shapes, the radiative and nonradiative decay rates, and quantum yields are derived. In the case of a molecule near a spheroid the magnitudes differ dramatically from the corresponding case of a molecule near a plane.
The number of newly engineered nanomaterials is vastly increasing along with their applications. Despite the fact that there is a lot of interest and effort is being put into the development of nano-based biomedical applications, the level of translational clinical output remains limited due to uncertainty in the toxicological profiles of the nanoparticles (NPs). As NPs used in biomedicines are likely to directly interact with cells and biomolecules, it is imperative to rule out any adverse effect before they can be safely applied. The initial screening for nanotoxicity is preferably performed in vitro, but extrapolation to the in vivo outcome remains very challenging. In addition, generated in vitro and in vivo data are often conflicting, which consolidates the in vitro-in vivo gap and impedes the formulation of unambiguous conclusions on NP toxicity. Consequently, more consistent and relevant in vitro and in vivo data need to be acquired in order to bridge this gap. This is in turn in conflict with the efforts to reduce the number of animals used for in vivo toxicity testing. Therefore the need for more reliable in vitro models with a higher predictive power, mimicking the in vivo environment more closely, becomes more prominent. In this review we will discuss the current paradigm and routine methods for nanotoxicity evaluation, and give an overview of adjustments that can be made to the cultivation systems in order to optimise current in vitro models. We will also describe various novel model systems and highlight future prospects.
Here, the authors report the energy transfer from rhodamine 6G dyes to gold nanoparticles. There is a pronounced effect on the photoluminescence and a shortening of the lifetime of the dye when interacting with the Au nanoparticles. The calculated distance (d) between the donor and acceptor varies from 86.06 to 102.47 Å with changing the concentrations of Au and dye. Analysis suggests that the energy transfer from dye to the Au nanoparticles is a surface energy transfer process and follows a 1/d4 distance dependence.
Gold nanorods have been receiving extensive attention owing to their extremely attractive applications in biomedical technologies, plasmon-enhanced spectroscopies, and optical and optoelectronic devices. The growth methods and plasmonic properties of Au nanorods have therefore been intensively studied. In this review, we present a comprehensive overview of the flourishing field of Au nanorods in the past five years. We will focus mainly on the approaches for the growth, shape and size tuning, functionalization, and assembly of Au nanorods, as well as the methods for the preparation of their hybrid structures. The plasmonic properties and the associated applications of Au nanorods will also be discussed in detail.
An on/off SERS aggregation system has been designed to investigate carbohydrate-lectin interactions. Detection of the lectin ConA was achieved at pico molar levels. Discrimination was also demonstrated between two different carbohydrate moieties demonstrating the specific interaction between the carbohydrate and specific protein present.
The collaborative oscillation of conductive electrons in metal nanoparticles results in a surface plasmon resonance that makes them useful for various applications including biolabeling. We investigate the coupling between pairs of elliptical metal particles by simulations and experiments. The results demonstrate that the resonant wavelength peak of two interacting particles is red-shifted from that of a single particle because of near-field coupling. It is also found that the shift decays approximately exponentially with increasing particle spacing and become negligible when the gap between the two particles exceeds about 2.5 times the particle short-axis length.
This chapter focuses on the practical aspects of single-molecule Förster resonance energy transfer (FRET) experiments. Ideal dyes for single-molecule fluorescence studies should possess several characteristics including photostable; bright (high extinction coefficient and quantum yield of emission); stable, showing little intensity fluctuation; excitable and emit in the visible spectrum; relatively small so that they introduce minimum perturbations to the host molecule; and commercially available in a form that can be conjugated to biomolecules. Ideal single-molecule FRET dyes have large Stokes' shifts to minimize the amount of donor emission that bleeds through into the acceptor channel and to reduce the amount of direct excitation of the acceptor by the laser. There are two classes of fluorescence microscopy tools for single-molecule fluorescence studies. The first involves point detection using a single-element detector that is most commonly in the confocal microscope configuration, whereas the second class of tools for single-molecule studies consists of wide-field microscopy with a two-dimensional detector such as a charge-coupled device (CCD) camera. © 2005 American Physiological Society Published by Elsevier Inc. All rights reserved.
Better understanding of core-satellite nanostructures is of great interest to researchers owing to their unusual properties and is key to their promising applications. The well-developed techniques based on protein-nanoparticle interactions were adopted to produce core-satellite nanoassemblies of 10 nm core of Au nanoparticles (AuNPs) covered by Au25@BSA or Au10@histidine nanoclusters (NCs). The photoexcited dynamics in the core-satellite nanoassemblies were studied using steady-state and time-resolved spectroscopic measurements. Fluorescence quenching in AuNP-AuNCs core-satellite nanostructures was observed and confirmed as static quenching. The AuNPs alter neither radiative decay nor nonradiative decay in both nanoclusters. This indicates that the electron/energy transfer within the NP-NCs core-satellite nanoassemblies is absent, in contrast to the results involving other larger NP-NPs core-satellite nanoassemblies.
A metal nanoparticle attached to graphene oxide has the ability to open a new avenue of research with significant opportunities in the biomedical field. In this Letter, we report graphene oxide attached to a popcorn-shaped gold nanoparticle based hybrid SERS probe with ultrasensitive label-free sensing of HIV DNA and bacteria and provide its chemical fingerprint. Our SERS data with the hybrid material shows that it can be used for label-free detection of HIV DNA on the femto-molar level without any labeling. Experimental data with a novel SERS substrate show excellent reproducibility of the SERS signal. The current Letter demonstrates that the label-free SERS detection limit using a hybrid material can be as low as 10 CFU/mL for MRSA bacteria. The possible mechanism for very high sensitivity has been discussed.
The energy transfer between DNA-linked CdSe/ZnS quantum dots (qdots) and gold nanoparticles (AuNPs) is described. The assembly produced qdot–AuNP clusters with satellite-like morphology. Owing to the programmability of the DNA linkage, both assembly as well as disassembly were used as a tool to probe quenching efficiency. Upon assembly, resonance energy transfer between the qdot donor and AuNP acceptor was measured as photoluminescence (PL) quenching. The magnitude of the quenching was approximated upon measurement of PL recovery once the cluster was disassembled by addition of a ssDNA fuel strand, which effectively displaced the qdot-to-AuNP dsDNA linkage. This controllable assembly/disassembly behavior was then used as a morphological tool to separate PL quenching from an inner filter effect originating from the AuNP’s high surface plasmon resonance (SPR) extinction. This corrected quenching value was observed from steady state PL measurements, which were then substantiated by PL decay measurements. Finally, the quenching efficiency was related to cluster spatial properties via use of the nanometal surface resonance energy transfer (NSET) method. The AuNP interface to qdot core distance was estimated at ≈8 nm, which was close to the distances visualized by TEM.
This feature article highlights the recent developments of energy transfer processes of Au-nanoparticle-based assemblies. Many recent studies reveal that the energy transfer from dye to Au nanoparticle is a surface energy transfer process as established from 1/d4 distance dependence. Such distance dependent energy transfer phenomenon serves as spectroscopic ruler for long distance measurement. Recently, energy transfer processes in Au nanoparticle assemblies have been used to understand specific binding site and conformational changes of protein, DNA hybridization, RNA folding/unfolding, metal ion detection, and designing of new optical-based materials using porous materials. Here we highlight various aspects of energy transfer between dye molecule and Au nanoparticle, particularly focusing on the size- and shape-dependent energy transfer, understanding the interactions between biomolecules (protein, DNA, and RNA) and Au nanoparticle and the energy transfer between confined dye and Au nanoparticle. The designing of nanostructures materials with efficient energy transfer between confined dye in porous materials (mesoporous silica, zeolites, and cyclodextrin) and Au nanoparticle for developing new photonic devices has also been highlighted. Interesting findings reveal that Au-nanoparticle-based energy transfer offers an exciting opportunity to overcome many obstacles and this will help to solve the challenging problems for future applications. Finally, a tentative outlook on future developments of this research field is given.
Studying the correlation between the molecular structures of SERS-active analytes and their SERS enhancement factors is important to our fundamental understanding of SERS chemical enhancement. Using a common internal reference method, we quantitatively compared the Raman activities, SERS activities, and SERS enhancement factors for a series of organothiols that differ significantly in their structural characteristics and reported chemical enhancements. We find that while the tested molecules vary tremendously in their normal Raman and SERS activities (by more than 4 orders of magnitude), their SERS enhancement factors are very similar (the largest difference is less than 1 order of magnitude). This result strongly suggests that SERS chemical enhancement factors are not as diverse as initially believed. In addition to shedding critical insight on the SERS phenomena, the common internal reference method developed in this work provides a simple and reliable way for systematic investigation of the correlation between molecular structures and their normal Raman and SERS activities.
We apply the recently developed plasmon hybridization method to nanoparticle dimers, providing a simple and intuitive description of how the energy and excitation cross sections of dimer plasmons depend on nanoparticle separation. We show that the dimer plasmons can be viewed as bonding and antibonding combinations, i.e., hybridization of the individual nanoparticle plasmons. The calculated plasmon energies are compared with results from FDTD simulations.
While single-molecule fluorescence from emitters with high quantum efficiencies such as organic dye molecules can easily be detected by modern apparatus, many less efficient emission processes such as Raman scattering and metal luminescence require dramatic enhancement to exceed the single-particle detection limit. This enhancement can be achieved using resonant optical systems such as plasmonic particles or nanoantennas, the study of which has led to substantial progress in understanding the interaction of quantum emitters with their electromagnetic environment. This review is focused on the advances in measurement techniques and potential applications enabled by a deeper understanding of fundamental optical interaction processes occurring between single quantum systems on the nanoscale. While the affected phenomena are numerous, including molecular fluorescence and also exciton luminescence and Raman scattering, the interaction itself can often be described from a unified point of view. Starting from a single underlying model, this work elucidates the dramatic enhancement potential of plasmonic tips and nanoparticles and also the more deterministic influence of a Fabry-Pérot microresonator. With the extensive knowledge of the radiative behavior of a quantum system, insight can be gained into nonradiative factors as well, such as energy transfer phenomena or spatial and chemical configurations in single molecules.
The application of nanomaterials to detect disease biomarkers is giving rise to ultrasensitive assays, with scientists exploiting the many advantageous physical and chemical properties of nanomaterials. The fundamental basis of such work is to link unique phenomena that arise at the nanoscale to the presence of a specific analyte biomolecule, and to modulate the intensity of such phenomena in a ratiometric fashion, in direct proportion with analyte concentration. Precise engineering of nanomaterial surfaces is of utmost importance here, as the interface between the material and the biological environment is where the key interactions occur. In this tutorial review, we discuss the use of plasmonic nanomaterials in the development of biodiagnostic tools for the detection of a large variety of biomolecular analytes, and how their plasmonic properties give rise to tunable optical characteristics and surface enhanced Raman signals. We put particular focus on studies that have explored the efficacy of the systems using physiological samples in an effort to highlight the clinical potential of such assays.
Surface-enhanced Raman scattering (SERS) hot spots occur when molecules are positioned near regions of strongly enhanced electromagnetic fields on the surface of nano-featured plasmonic substrates. The emission from the molecule is coupled out into the far field by the plasmon modes of the substrate, but due to the diffraction-limit of light, the properties of this coupled molecule-plasmon emitter cannot be resolved using typical far-field optical microscopy techniques. However, by fitting the emission to a model function such as 2-dimensional Gaussian, the relative position of the emitter can be determined with precision better than 5 nm in a process known as super-resolution imaging. This tutorial review describes the basic principles of super-resolution imaging of SERS hot spots using single molecules to probe local electromagnetic field enhancements. New advances using dipole-based fitting functions and spectrally- and spatially-resolved measurements are described, providing new insight into SERS hot spots and the important roles of both the molecule and the substrate in defining their properties.
In 1978 it was discovered, largely through the work of Fleischmann, Van Duyne, Creighton, and their coworkers that molecules adsorbed on specially prepared silver surfaces produce a Raman spectrum that is at times a millionfold more intense than expected. This effect was dubbed surface-enhanced Raman scattering (SERS). Since then the effect has been demonstrated with many molecules and with a number of metals, including Cu, Ag, Au, Li, Na, K, In, Pt, and Rh. In addition, related phenomena such as surface-enhanced second-harmonic generation, four-wave mixing, absorption, and fluorescence have been observed. Although not all fine points of the enhancement mechanism have been clarified, the majority view is that the largest contributor to the intensity amplification results from the electric field enhancement that occurs in the vicinity of small, interacting metal particles that are illuminated with light resonant or near resonant with the localized surface-plasmon frequency of the metal structure. Small in this context is gauged in relation to the wavelength of light. The special preparations required to produce the effect, which include among other techniques electrochemical oxidation-reduction cycling, deposition of metal on very cold substrates, and the generation of metal-island films and colloids, is now understood to be necessary as a means of producing surfaces with appropriate electromagnetic resonances that may couple to electromagnetic fields either by generating rough films (as in the case of the former two examples) or by placing small metal particles in close proximity to one another (as in the case of the latter two). For molecules chemisorbed on SERS-active surface there exists a "chemical enhancement" in addition to the electromagnetic effect. Although difficult to measure accurately, the magnitude of this effect rarely exceeds a factor of 10 and is best thought to arise from the modification of the Raman polarizability tensor of the adsorbate resulting from the formation of a complex between the adsorbate and the metal. Rather than an enhancement mechanism, the chemical effect is more logically to be regarded as a change in the nature and identity of the adsorbate.
We have utilized the discrete dipole approximation to study the localized surface plasmon resonance in infinite, periodic two-dimensional arrays of gold nanospheres with the nanospheres arranged according to the {100} face of an fcc crystal. Specifically, we have performed a systematic study of the sensitivity of both the plasmon resonance wavelength shift and extinction properties considering nanosphere diameters ranging from 20 to 100 nm, and for nanosphere gap distances ranging from 0.5 to 6 times the nanosphere diameter. In doing so, we find that the same universal decay length of the plasmon resonance wavelength shift of about 0.2 units of the nanosphere size that was previously found by Jain et al.(1) for nanoparticle dimers is also operant for two-dimensional arrays. However, we also find that the universality of the plasmon ruler is only valid for arrays with nanospheres smaller than a critical nanosphere diameter of about 70 nm, whereas for larger nanosphere diameters, a decrease in the extinction efficiency as the gap distance decreases and a reduction in the decay constant are observed. Both of these size-dependent optical responses are qualitatively interpreted using a semianalytical coupled dipole approximation that accounts for structural retardation due to the geometric arrangement of the nanospheres, as well as single sphere retardation due to both dynamic depolarization and radiative damping effects. Using the semianalytical theory, we find that the size dependence is primarily due to the effects of dynamic depolarization and structural retardation, which reduces the coupling strength, changes the extinction efficiency trend, and also reduces the decay constant of the plasmon ruler equation for larger diameter nanospheres; similar results were found for infinite, 2D arrays of nanospheres in hexagonal and simple cubic arrangements. Finally, the semianalytical theory is utilized to predict a size dependence of the plasmon ruler for dimers starting at the same critical diameter of 70 nm. However, we find that the size effect is weaker for dimers than for the array case due to the significant reduction in structural retardation for dimers as compared to the array case.
As colloidal semiconductor nanocrystals are developed for a wider range of diverse applications, it becomes more important to gain a deeper understanding of their properties in order to direct synthetic efforts. While most synthetic developments are guided by changes in ensemble properties, certain applications such as those in nano-electronics and nano-photonics rely on properties of nanocrystals at the individual level. For such applications and even for a more detailed understanding of the ensemble behavior, single nanocrystal spectroscopy becomes a vital tool. This review looks at how single nanocrystal spectroscopy has been applied to materials based on modern synthetic techniques and how these studies are elucidating properties that remain hidden at the ensemble level. First, recent theoretical models that are important for understanding many observed phenomena are explored. Then the review highlights new insights into many of the photophysical properties that are of interest in semiconductor nanocrystal materials, such as the ubiquitous spectral instability, magneto-optical identification of the band-edge exciton fine structure, emission from multi-excitons, and the spectroscopic properties of charged nanocrystals that challenge long standing theories on photoluminescence blinking behavior. To date most of the research has been conducted on materials based on cadmium selenide primarily due to its many years of development as a prototypical nanocrystal system. The review ends with a discussion of new materials that would also benefit from a detailed photophysical understanding afforded by single nanocrystal spectroscopy.
Noble metal nanostructures are able to concentrate light into small volumes, which enhances greatly the local electromagnetic (EM) field near the metal nanostructures. The areas with greatly enhanced EM field become "hot spots" for surface-enhanced Raman spectroscopy (SERS), which utilizes the field enhancement properties of metal nanostructures to amplify the usually weak Raman scattering signals. The preparation of metal nanostructures with superior SERS performances is one of the main topics in the SERS field and is important for the applications of SERS in sensing and analysis. In this feature article, we review several different kinds of metal structures for SERS, including coupled metal nanostructures, nanostructure arrays, nano/micro structures with textured surfaces and graphene-mediated SERS substrates. Tip-enhanced Raman spectroscopy (TERS) using the metal tip of the scanning tunneling microscope is also discussed. Besides the intensity enhancement in SERS and TERS, some less studied aspects are highlighted; for example, the remote excitation technique, tuning the nanogap of gold nanorod dimers through strain control on an elastomeric substrate, manipulating Raman emission polarization using asymmetric nanoantennas, and investigating plasmon-enhanced chemical reactions by TERS.
Förster Resonance Energy Transfer (FRET) is the phenomenon of non-radiative transfer of electronic excitations from a donor fluorophore to an acceptor, mediated by electronic dipole-dipole coupling. The transfer rate and, as a consequence, efficiency depend non-linearly on the distance between the donor and the acceptor. FRET efficiency can thus be used as an effective and accurate reporter of distance between two fluorophores and changes thereof. Over the last 50 years or so, FRET has been used as a spectroscopic ruler to measure conformations and conformational changes of biomolecules. More recently, FRET has been combined with microscopy, ultimately allowing measurement of FRET between a single donor and a single acceptor pair. In this review, we will explain the physical foundations of FRET and how FRET can be applied to biomolecules. We will highlight the power of the different FRET approaches by focusing on its application to the motor protein kinesin, which undergoes several conformational changes driven by enzymatic action, that ultimately result in unidirectional motion along microtubule filaments, driving active transport in the cell. Single-molecule and ensemble FRET studies of different aspects of kinesin have provided numerous insights into the complex chemomechanical mechanism of this fascinating protein.
"The possibility of using colloidal silver and gold as condensors for electron storage in artificial photosynthesis has prompted the recent renewed interest in these areas." This statement by Fendler and co-workers in 1983 is even more relevant in today's science and technology. In this tutorial review we summarize research regarding the use of light in the synthesis of metallic nanoparticles. We describe how light of different energies induces a variety of chemical events that culminate in the nucleation and growth of metal nanocrystals. Light can thus be used as a handle to direct metal nanocrystal growth and improve tunability and reproducibility.
The alternating-laser excitation (ALEX) scheme continues to expand the possibilities of fluorescence-based assays to study biological entities and interactions. Especially the combination of ALEX and single-molecule Förster Resonance Energy Transfer (smFRET) has been very successful as ALEX enables the sorting of fluorescently labelled species based on the number and type of fluorophores present. ALEX also provides a convenient way of accessing the correction factors necessary for determining accurate molecular distances. Here, we provide a comprehensive overview of the concept and current applications of ALEX and we explicitly discuss how to obtain fully corrected distance information across the entire FRET range. We also present new ideas for applications of ALEX which will push the limits of smFRET-based experiments in terms of temporal and spatial resolution for the study of complex biological systems.
Since its first demonstration about twenty years ago, single-molecule fluorescence resonance energy transfer (FRET) has undergone remarkable technical advances. In this tutorial review, we will discuss two technical advances that increase the information content of the single-molecule FRET measurements: single-molecule multi-color FRET and single-molecule FRET combined with force or torque. Our expectations for future developments will be briefly discussed at the end.
We present a calculation of the nonradiative damping of a dipole outside a metal surface. The calculation uses a realistic surface potential for the metal conduction electrons in contrast to most earlier studies. A simple experiment is suggested to test the theoretical predictions.
Manufactured nanomaterials with novel physicochemical properties are an important basis for nanosciences and related technologies. Nanotoxicology, aiming to understand the principles of interactions at the nano-bio interface and the relationship between the physicochemical properties of nanomaterials and their toxicological profiles, has become a new frontier in nanoscience. Nearly one decade of nanotoxicology research has shown that the interactions between nanomaterials and proteins, cells, animals, humans and the environment as well as the underlying mechanisms of toxicity for nanomaterials are remarkably complicated, requiring dedicated analytical methodology and tools. Because of their advantages of absolute quantification, high sensitivity, excellent accuracy and precision, low matrix effects and non-destructiveness, nuclear analytical techniques have been playing important roles in the study of nanotoxicology. A systematic summary and comprehensive review of the advanced nuclear analytical and related techniques in nanotoxicology is greatly needed. In this review article, we present a comprehensive overview of nuclear analytical techniques applied to the physicochemical characterization of nanomaterials, structural analysis of bio-nano interactions, visualization of nanomaterials in vitro, quantification of bio-distribution, bio-accumulation, and transformation of nanomaterials in vivo. As important complementary tools, optical imaging technologies are also highlighted. Future directions regarding advanced nuclear analytical approaches for nanotoxicology are also discussed. The rapid development of advanced light source-based techniques will enable new high-throughput screening techniques and provide high sensitivity with low detection limits, which are required for the distribution, imaging, and structural analysis of nanomaterials, and the molecular information of biomarkers for all aspects of nanotoxicology.
That wonderful production of the human mind, the undulatory theory of light, with the phenomena for which it strives to account, seems to me, who am only an experimentalist, to stand midway between what we may conceive to be the coarser mechanical actions of matter, with their explanatory philosophy, and that other branch which includes, or should include, the physical idea of forces acting at a distance; and admitting for the time, the existence of the ether, I have often struggled to perceive how far that medium might account for or mingle in with such actions, generally; and to what extent experimental trials might be devised which, with their results and consequences, might contradict, confirm, enlarge, or modify the idea we form of it, always with the hope that the corrected or instructed idea would approach more and more to the truth of nature, and in the fulness of time coincide with it. The phenomena of light itself are, however, the best and closest tests at present of the undulatory theory; and if that theory is hereafter to extend to and include other actions, the most effectual means of enabling it to do so will be to render its application to its own special phenomena clear and sufficient. At present the most instructed persons are, I suppose, very far from perceiving the full and close coincidence between all the facts of fight and the physical account of them which the theory supplies. If perfect, the theory would be able to give a reason for every physical affection of fight; whilst it does not do so, the affections are in turn fitted to develope the theory, to extend and enlarge it if true, or if in error to correct it or replace it by a better. Hence my plea for the possible utility of experiments and considerations such as those I am about to advance.
The excitation energy of a dye molecule can be transferred specifically from its singlet or its triplet state to an appropriate acceptor held at a precise, adjustable distance of say 100 Å in a monolayer assembly. Dye layers and a thin gold layer were used as energy acceptors.
The Gersten–Nitzan model is applied to study the surface enhanced Raman scattering from a molecule adsorbed on a spherical metallic nanoshell. The nonlocal dielectric response from the nanoshell has been accounted for by using a phenomenological model. For a fixed outer radius of the shell, the enhancement ratio is calculated over a large range of scattering frequency and inner radius of the shell, including the case of a solid metallic particle. The effect due to different core materials is also studied. It is concluded that the nonlocal effects can be significant for very close molecule–shell distances, and for shells with very small sizes and/or thickness, leading to smaller enhancement in general. This can affect the plasmon resonances as well as the optimal shell thickness for the shell acting as a Raman enhancer.
Motivating by recent experiments on surface enhanced Raman scattering (SERS) from colloidal solutions, we present here a simple model to elucidate the effects of extraneous surface charges on the enhanced Raman signal. The model is based on the well-established Gersten-Nitzan model coupled to the modified Mie scattering theory of Bohren and Hunt in the long wavelength approximation. We further introduce corrections from the modified long wavelength approximation to the Gersten-Nitzan model for the improvement of its accuracy. Our results show that the surface charge will generally lead to a blueshift in the resonance frequency and greater enhancements in the SERS spectrum. Possible correlations with the recent experiments are elaborated.
The subdiscipline of chemistry that studies molecular structures in three dimensions is called stereochemistry. One important aspect of stereochemistry is stereoisomers: materials with the same chemical formula but different spatial arrangements of atoms within molecules. The relative positions of atoms have great influence on the properties of chemical substances. Here, in analogy to stereoisomers in chemistry, we propose a new concept in nanophotonics, namely stereometamaterials, which refer to metamaterials with the same constituents but different spatial arrangements. As a model system of stereometamaterials, we theoretically and experimentally study meta-dimers, which consist of a stack of two identical split-ring resonators in each unit cell with various twist angles. The interplay of electric and magnetic interactions plays a crucial role for the optical properties. Specifically, the influence of higher-order electric multipoles becomes clearly evident. The twisting of stereometamaterials offers a way to engineer complex plasmonic nanostructures with a tailored electromagnetic response.
Light-emitting diodes (LEDs) based on colloidal quantum dots (QDs) have attracted considerable attention due to their potential in applications such as color-saturated displays and white light with high color-rendering index. However, cadmium-based QD-LEDs are strictly regulated in industrial applications because of the high toxicity of cadmium. As an alternative, InP-based cadmium-free QDs are recommended owing to their wide emission range that is comparable to that of CdSe, and their environmentally friendly properties when applied to QD-LEDs and white QD-LEDs. This feature article provides an overview of QDs' merits in display and light-emitting applications as well as a discussion of their color tunability, photo-stability, and high luminescence efficiency. We will include optical down-conversion devices using various QDs, electroluminescent devices based on organic and inorganic charge-transporting layers, and printing methods using cadmium based and cadmium free QDs.
We study the validity of the recently proposed universal plasmon ruler in the present work using a combination of numerical techniques based on the finite difference time domain (FDTD) method, and semianalytical theories based on the coupled dipole approximation. By incorporating nonlocal effects for closely spaced two-dimensional gold nanocylinder dimers, we find using both the FDTD and semianalytical approaches that the universal plasmon ruler of Jain et al.(1) is not applicable for gold nanocylinder dimers with diameters smaller than about 20 nm. The nonlocal effects are also found to strongly reduce the electric field enhancements at very small gap distances. Taken together with previous results,(2) we are able to establish the valid size range for the universal plasmon ruler of gold: 20 nm diameter metal nanostructure dimers at the smaller end, and 70 nm diameter metal nanostructure dimers at the larger end.
A theory for surface enhanced Raman scattering (SERS) is developed. Effects due to realistic surface geometry and dielectric properties are included. Three sources of enhanced Raman scattering are noted: the image dipole enhancement effect, the increase of local field (’’lightning rod’’ effect), and the resonant excitation of surface plasmons. The surface is modeled as a hemispheroid protruding from a conducting plane, although other models are considered. The spherical limit is discussed in some detail and molecular orientation effects are considered. Cross sections for Mie, Rayleigh, and Raman scattering are derived.
The decay time of the luminescence of a molecule S in front of a metal mirror depends markedly on its distance from the mirror. This phenomenon is quantitatively explained by considering the radiation field of this dipole, given by Hertz classical equation. This field arrives at the molecule, after being reflected at the mirror, with a retardation of the order of 10−15 sec. The decay time of the luminescence depends on the phase shift produced by this retardation, and thus on the ratio of the distance of the oscillator from the mirror, and the wavelength of the emitted light. By measuring the distance dependence of the decay time of the luminescence this retardation effect can be studied. In quantum‐mechanical terms the phenomenon can be described as being due to a stimulation or inhibition of the emission of the light quantum. In contrast to the known cases of stimulated emission, the stimulating field is the radiation field of the emitter quantum itself. The energy transfer from an excited molecule S to an acceptor A can be treated in a similar manner by considering the phenomenon as a retardation effect. In classical terms the field of S induces A to oscillate, and the induced field of A arriving at S slows down this oscillator. Simple equations are given for the energy transfer from an excited dipole or quadrupole, and for a row of many dipoles, oscillating in phase, to a weakly absorbing acceptor layer. The latter case is considered as a model for a J‐aggregating dye and by comparison with experimental data conclusions concerning the size of a J aggregate are drawn.
The ability to develop new and sensitive methods of biomolecule detection is crucial to the advancement of pre-clinical disease diagnosis and effective patient specific treatment. Surface enhanced Raman scattering (SERS) is an optical spectroscopy amenable to this goal, as it is capable of extremely sensitive biomolecule detection and multiplexed analysis. This perspective highlights where SERS has been successfully used to detect target biomolecules, specifically DNA and proteins, and where in vivo analysis has been successfully utilised. The future of SERS development is discussed and emphasis is placed on the steps required to transport this novel technique from the research laboratory to a clinical setting for medical diagnostics.
Surface properties dictate the behavior of nanomaterials in vitro, in vivo, and in the environment. Such properties include surface charge and hydrophobicity. Also key are more complex supramolecular interactions such as aromatic stacking and hydrogen bonding, and even surface topology from the structural to the atomic level. Surface functionalization of nanoparticles (NPs) provides an effective way to control the interface between nanomaterials and the biological systems they are designed to interact with. In medicine, for instance, proper control of surface properties can maximize therapeutic or imaging efficacy while minimizing unfavorable side effects. Meanwhile, in environmental science, thoughtful choice of particle coating can minimize the impact of manufactured nanomaterials on the environment.
Over the last few years, one of the most important and complex problems facing our society is treating infectious diseases caused by multidrug-resistant bacteria (MDRB), by using current market-existing antibiotics. Driven by this need, we report for the first time the development of the multifunctional popcorn-shaped iron magnetic core-gold plasmonic shell nanotechnology-driven approach for targeted magnetic separation and enrichment, label-free surface-enhanced Raman spectroscopy (SERS) detection, and the selective photothermal destruction of MDR Salmonella DT104. Due to the presence of the "lightning-rod effect", the core-shell popcorn-shaped gold-nanoparticle tips provided a huge field of SERS enhancement. The experimental data show that the M3038 antibody-conjugated nanoparticles can be used for targeted separation and SERS imaging of MDR Salmonella DT104. A targeted photothermal-lysis experiment, by using 670 nm light at 1.5 W cm(-2) for 10 min, results in selective and irreparable cellular-damage to MDR Salmonella. We discuss the possible mechanism and operating principle for the targeted separation, label-free SERS imaging, and photothermal destruction of MDRB by using the popcorn-shaped magnetic/plasmonic nanotechnology.
Fluorescence quenching is a powerful technique used to obtain information about the dynamic changes of proteins in complex macromolecular systems. In this work, graphene is shown to be a very efficient quencher of fluorescence molecules where the quenching effect was one order of magnitude higher than that of gold. The fluorescence intensity was distance-dependent where increasing the distance between the fluorescence molecule and the graphene surface from 4 to 7 nm increased the fluorescence intensity by a factor of 7.5. This type of distance dependence suggests a nonradiative nature in the energy transfer between the graphene and the fluorophore due to the excitation of an exciton.
Chirality in nanoscience may offer new opportunities for applications beyond the traditional fields of chirality, such as the asymmetric catalysts in the molecular world and the chiral propellers in the macroscopic world. In the last two decades, there has been an amazing array of chiral nanostructures reported in the literature. This review aims to explore and categorize the common mechanisms underlying these systems. We start by analyzing the origin of chirality in simple systems such as the helical spring and hair vortex. Then, the chiral nanostructures in the literature were categorized according to their material composition and underlying mechanism. Special attention is paid to highlight systems with original discoveries, exceptional structural characteristics, or unique mechanisms.
We designed a recyclable Hg2+ probe based on Rhodamine B isothiocyanate (RBITC) - poly (ethylene glycol) (PEG)-co-modified gold nanoparticles (AuNPs) with excellent robustness, selectivity and sensitivity. Based on reasonable design, only Hg2+ can displace RBITC from the AuNP surfaces, resulting in a remarkable enhancement of RBITC fluorescence initially quenched by AuNPs. To maintain stability and monodispersity of AuNPs in real samples, thiol-terminated PEG was employed to bind with the remaining active sites of AuNPs. Besides, this displacement assay can be regenerated by adding fresh RBITC into the AuNPs solutions that were already used for detecting Hg2+. Importantly, the detection limit of this assay for Hg2+ (2.3 nM) was lower than the maximum limits guided by the United States Environmental Protection Agency as well as that permitted by the World Health Organization. The efficiency of this probe was demonstrated in monitoring Hg2+ in complex samples such as river water and living cells.
Using chemical synthesis, researchers can produce noble metal nanowires with highly regular, crystalline properties unachievable by alternative, top-down nanofabrication methods. Sitting at the intersection of nanochemistry and nanooptics, noble metal nanowires have generated intense and growing research interest. These nanostructures combine subwavelength transverse dimensions (50–100 nm) and longitudinal dimensions that can reach tens of micrometers or more, which makes them an ideal platform to launch surface plasmon waves by direct illumination of one end of the structure. Because of this property, researchers are using noble metal nanowires as a tool for fundamental studies of subwavelength plasmon-based optics and the properties of surface plasmon guided wave propagation in highly confined geometries below the classical optical diffraction limit. In this Account, we review some of the recent developments in plasmonic nanowire fabrication, nanowire plasmon imaging, and nanowire optical components and devices.
We show how the macrocyclic host, cucurbit[8]uril (CB[8]), creates precise subnanometer junctions between gold nanoparticles while its cavity simultaneously traps small molecules; this enables their reproducible surface-enhanced Raman spectroscopy (SERS) detection. Explicit shifts in the SERS frequencies of CB[8] on complexation with guest molecules provides a direct strategy for absolute quantification of a range of molecules down to 10(-11) M levels. This provides a new analytical paradigm for quantitative SERS of small molecules.
We have developed an absorption spectrum based molecular ruler that measures the distance between two mercapto groups. The conformation of the molecular rulers changes with the distance, which induces an absorption spectrum change. DFT calculation has been carried out to elucidate the relation between the molecular conformation and the absorption spectrum. With this simple method, we can estimate the distance between two mercapto groups on the scale of 0.4-1 nm. This method can also be used to monitor conformation transition, which is demonstrated by a silver ion titration experiment.
This communication reports, for the first time, the design of distance dependent SERS assay for monitoring the photothermal antibacterial activity process.
This Letter deals with the effect of the particle size on the energy transfer from CdSe/ZnS quantum dots to the proximal gold nanoparticles with different sizes. The 3 nm sized gold nanoparticles have negligible localized surface plasmon resonance (LSPR) absorption and quench the fluorescence emission of the quantum dots with a 1/d4 distance-dependence, indicating the nanometal surface energy transfer (NSET) mechanism. The 15 and 80 nm sized gold nanoparticles have strong LSPR absorption bands that overlap with the emission band of the quantum dots. The energy transfer efficiency depends on the 1/d6 separation distance, which is dominated by the dipole–dipole interaction according to Förster resonance energy transfer (FRET). The 80 nm sized gold nanoparticle displays higher quenching efficiency due to the increased spectral overlap of the LSPR band with the emission band of quantum dots.Keywords: energy transfer; surface plasmon resonance; quantum dots; gold nanoparticles; size effect
Modified SERS (surface-enhanced Raman scattering) substrates are based on self-assembled monolayers (SAMs) formed from compounds such as alkanethiols. Chain lengths ranging from ethanethiol to octadecanethiol were used to investigate properties of modified SERS substrates. These properties include determining the magnitude of the SERS electromagnetic enhancement, developing a sensitivity factor for detecting aromatic compounds, and evaluating SERS substrates for performance characteristics such as stability and solvent effects. A SERS electromagnetic enhancement was determined to be 2.1 × 103 for detecting aromatic compounds. The effects of experimental conditions on the SERS detection process were addressed. SERS sensitivity was shown to be highly dependent upon a correlation between the SERS interfacial distance dependence and a hydrophobic effect exhibited by the alkyl chain of the thiol. The distance dependence was more significant than the hydrophobic effect for detecting aromatic compounds. For comparison to the electromagnetic enhancement, a SERS sensitivity factor was determined for detecting benzene in water and in organic solvents. Experimental stability issues, such as solvent and laser exposure, were shown to affect the sensitivity of modified SERS substrates. 1-Propanethiol exhibited the strongest sensitivity and stability under all solvent and experimental conditions.