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Enhancement of the Second Harmonic Response by Adsorbates on Gold Colloids: The Effect of Aggregation
Abstract
The extinction profiles as well as the hyper Rayleigh scattering signal of a highly monodisperse 22 nm diameter gold colloidal sol in the presence of pyridine have been measured. A strong enhancement of the HRS signal is observed in the presence of small amounts of pyridine. The relationship between the extinction spectra, the distribution of aggregated particles, and the second harmonic response has been investigated by evaluating the enhancement factor of the electromagnetic field in the colloids as they slowly aggregate. It is also shown that at larger pyridine concentrations, the hyper Rayleigh scattering signal levels off owing to the formation of large aggregates.
... Since 1980s, in parallel to the theoretical studies, experimental investigations about the SHG of spherical particles have been carried out as well. From the earlier experiments, one can mention the SHG of colloidalsilver microparticles [17,18], even though, at those times, the surface sensitivity of the applied techniques was not confident because of insufficiency in detection related to the aggregation of particles [19] and formation of a charge-transfer complex [20]. Then, using the surface sensitivity of the SHG, more adequate experiments performed to display the molecular absorption on [21][22][23] and transfer between [24] particles, to reveal molecular transport across a liposome bilayer [25][26][27], to determine the electric charge and potential on the particle surface [28,29] and to study the interfacial charge-transfer complex on particles in aqueous suspensions [30]. ...
... In a large number of theoretical and experimental studies regarding to the plasmonics of metallic nanostructures including spherical MNPs, it is proven that the interaction of adjacent elements in a dimer and array of nanostructures can lead to the significant improvement of the SHG via the enhancement of local fields [17][18][19][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. Formation of plasmonic hot spot in the interaction of laser with MNPs inside a dielectric also can lead to the enhancement of SHG which can be used for the monitoring of growth of MNPs and some other dynamic aspects of chemical and biophysical processes [48][49][50][51][52][53][54][55]. ...
In this theoretical study, the problem of Second Harmonic Generation (SHG) in the interaction of laser beam with a Metallic Nanoparticle (MNP) dimer is considered. Using a classical electrodynamics approach, the nonlinear interaction of laser beam fields with Nanoparticles (NPs) is considered taking into account the dipole-dipole interparticle interactions. Analytical formulae are derived for the effect of dipole-dipole interaction on the Second Harmonic (SH) radiation power for two different polarizations of laser beam. It is found that the interaction causes the substantial enhancement of the SH radiation power while for the case when the laser beam field is parallel to the dimer axis, this enhancement is larger. Additionally, the dipole-dipole interaction of NPs leads to the redshift of the peak value with respect to the individual NP radiation. The resonance frequency displacement of the parallel case is more than that of the perpendicular one. The effect of particles size and interparticle separation on the SHG is studied.
... The sensor was constructed based on a phenomenon of salt-induced gold nanoparticles (AuNPs) aggregation [10], which can lead to a change in dielectric constant associated with refractive index of the corresponding solutions [11,12]. Specifically, the sensor was constructed by combining single-stranded DNA (ssDNA) aptamers with unmodified AuNPs. ...
... Once the unmodified AuNPs aggregate, there is a change in the dielectric constant of the surrounding medium [11,12]. According to Maxwell's electromagnetic theory, the refractive index of solution is associated with dielectric constant. ...
... Nanomaterials are more versatile than their bulk counterpart because of their higher specificity and surface activity [1]. Pt, Ag, and Au nanomaterials (NMs) have been widely used in photonics, electronics, and optical devices as catalysts for biosensing and biolabeling agents [2][3][4][5][6][7][8][9]. Despite all the advantages of exploiting this newfound knowledge, environmental concerns have been rising. ...
Nanomaterials, today, are an integral part of our everyday lives, industrial processes and appliances. Biosynthesis, because of its environmental sustainability, is now becoming a hot topic. The biosynthesis of nanomaterials using plant phytochemicals enhances the nanomaterial’s biocompatibility and its compatibility with the environment too. Hence, forthe first time, this study uses Caralluma acutangula (CA) plant extracts to synthesize silver nanoparticles (CA-AgNPs) and characterize them using UV–visible spectroscopy, FTIR, Raman spectroscopy, XRD, TEM, TGA, SEM, EDX, zeta potential, and bandgap analysis. The particle size distributions of CA-AgNPs were observed to fall in the range of 2–6 nm predominantly using TEM images. High crystallinity % was calculated as 86.01 using XRD data. Extracted phytochemicals from CA were characterized and analyzed using GC-MS. The bandgap (Eg) of CA-AgNPs was calculated as 3.01 eV and zeta potential was found to be −16.1 mV. The biosynthesized CA-AgNPs were confirmed for their degradation efficiency of two toxic water pollutant dyes: Congo red, CR (95.24% degradation within 36 min), and methylene blue, MB (96.72% degradation within 32 min), in the presence of NaBH4. Different doses of CA-AgNPs and NaBH4 were checked for their chemical kinetics and rate constant analysis. The chemical kinetics were explored on the basis of integrated rate law model equations and confirmed as pseudo-zero-order reactionsfor CR and MB dyes. The rate constant ‘k’ for CR and MB was calculated as 0.0311 and 0.0431 mol.L−1.min−1, respectively.
... [59] It is known that the absorption maximum (surface plasmon resonance) of gold nanoparticles is around 510 to 530 nm (as opposed to silver at 410 nm), and when aggregated this plasmon band can be shifted to the NIR. [60] Shifting of the plasmon absorption afforded by extended aggregates of Au nanoparticles embedded in the sol-gel makes this substrate well suited for SERS measurements at 785-nm laser excitation. The use of 785-nm diode lasers and very sensitive Si-detectors can be packaged in small lightweight rugged portable and handheld Raman systems that are cost effective, offering a balance of good sensitivity, spectral coverage, and resolution, with minimal fluorescence issues. ...
Surface‐enhanced Raman spectroscopy (SERS) is a rapidly emerging technology that offers a fast, extremely sensitive, and quantitative approach to trace chemical detection. Such a technique incorporated into a portable device is attractive to law enforcement and emergency room personnel for rapid accurate on‐site screening of illicit and abused drugs. Toward this we are developing an analyzer in a hand‐held unit, based on SERS that is integrated with a capillary sensor embedded with activated gold nanoparticles in a porous glass matrix. In this preliminary study we have used this gold sol‐gel capillary to measure aqueous solutions of 14 high‐priority drugs to define sensitivity (lowest measured concentration (LMC) and estimated limit of detection (LOD)), determine concentration dependence and quantification capabilities by constructing calibration curves, examine effects of pH at 3, 7 and 11 on SERS measurements, and perform multicomponent analysis of fentanyl laced drug mixtures and spectral identification on our portable and handheld units. Of particular significance fentanyl was detected with an LMC of 1 ng/mL and estimated LOD at 0.11 ng/mL, while other representative drugs such as cocaine and phenylcyclidine produced LMCs and LODs at 5.0 and 0.77 ng/mL, and 10.0 and 0.62 ng/mL respectively. These sub ng/mL detection limits are comparable or lower than previously reported and confirm that this gold sol‐gel has the potential to meet the sensitivity requirements for saliva analysis. Most importantly, these sensors can be manufactured easily and cheaply, and when integrated with our portable Raman units produce high‐quality spectra and accurate identification within 1.2 sec.
... It is well known that silver and gold spherical nanoparticles used for the purpose of SERS typically have diameters of 10-100 nm. It is also known that the absorption maximum (surface plasmon resonance) of silver nanoparticles is near 410 nm and that of gold is around 510-530 nm, and when aggregated, this plasmon band can be shifted to the NIR [19]. Previous studies reporting on a silver sol and various gold substrates show the formation of metal nanostructures of fractal aggregates [20][21][22]. ...
We used surface-enhanced Raman spectroscopy (SERS) for the rapid and sensitive detection and quantification of caffeine in solution. Such a technique incorporated into a portable device is finding wide applications in trace chemical analysis in various fields, including law enforcement, medicine, environmental monitoring, and food quality control. To realize such applications, we are currently developing portable and handheld trace chemical analyzers based on SERS, which are integrated with a sensor embedded with activated gold nanoparticles in a porous glass matrix. In this study, we used this gold SERS-active substrate to measure aqueous solutions of the drug caffeine as a test chemical to benchmark sensor performance by defining sensitivity (lowest measured concentration (LMC) and estimated limit of detection (LOD)), determining concentration dependence and quantification capabilities by constructing calibration curves; by evaluating the effects of pH values of 3, 7, and 11; and by examining the reproducibility of the SERS measurements. The results demonstrate that the SERS sensor is sensitive, with caffeine detected at an LMC of 50 parts per billion (ppb) with an LOD of 0.63 ppb. The results further show that the sensor is very stable and can be used to make reproducible measurements, even under extremely acidic to basic pH conditions. Vibrational assignments of all observed SERS peaks are made and reported for the first time for caffeine on a gold substrate.
... (14) The variabilities of the size and distribution of GNPs are respectively obtained from the calculated FWHM and by TEM observation. (15,16) Figure 3 shows the FWHM of the GNPs prepared from growth solutions with 300 to 900 μl of added acetone. The addition of 700 μl of acetone gave the maximum FWHM of 61 nm, compared with values of 48 and 50 nm for the addition of 300 and 900 μl of acetone, respectively. ...
... In addition, when an organic solvent is added to the surfactant solution, the organic solvent can usually decompose the polar group of the microcell at the interface of water and hydrocarbon so that the organic solvent will reduce the surface of the ionic micelles. The charge density changes the geometry of the surfactant cell template [17,18]. Therefore, adding organic solvent acetone during the electrolysis process may cause changes in the shape of the microcell template [19][20][21][22]. ...
In this research, our team used a rare electrochemical method to obtain gold nanoparticles (GNPs). The growth solution has been added with nitric acid in order to observe the effect of GNPs. The solution also included cetyltrimethylammonium bromide (CTAB) and acetone. All reactions involved the oxidation of acetone and chain polymerization. Therefore, the GNPs changed to a su pramolecular structure. In addition, our team measured absorption wavelength via ultraviolet/ visible spectrophotometer and found an obviously blue shift. This short absorption wavelength is obviously different from other GNPs.
... [26][27][28][29][30][31][32][33] NPs have small size and very large surface area, which play an important role in their excellent biological activity, as it provides suitable conditions for their interaction with the biological systems, which is not the case with bulkier materials. [34][35][36][37][38][39] Melon seeds are generally discarded as a waste or removed from the fruits and planted, but not used for any other beneficiary aspects. However, melon seeds, especially those of cantaloupe, provide numerous health benefits. ...
Silver oxide nanoparticles (Ag2O NPs) were prepared using cantaloupe (Cucumis melo ) seeds as a fuel by employing a green synthesis method. The prepared Ag2O NPs were investigated using powder X‐ray diffraction (PXRD), UV–visible spectrum, Fourier transform infrared analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy‐dispersive spectroscopy, and photoluminescence studies. PXRD data reveal the establishment of cubic crystal structure of Ag2O NPs. According to SEM and TEM results, the morphology of the prepared NPs was agglomerated and spherical. The photodegradation activity of the prepared Ag2O NPs over methylene blue dye was promising under visible light irradiation. Furthermore, the antimicrobial assay of the synthesized Ag2O NPs was carried out by the disc diffusion method against Gram‐positive and Gram‐negative microbial strains.
Highlights
• This is the first report on the synthesis of silver oxide nanoparticles using a natural reducing agent (cantaloupe seeds extract) for luminescence and dye‐degradation applications.
• Silver oxide nanoparticles were prepared by a combustion‐assisted green method using cantaloupe seeds extract.
• Silver oxide nanoparticles showed promising photocatalytic activity against methylene blue under visible light irradiation.
• From the luminescence study, the silver oxide nanoparticles were observed to be in the visible region which emits yellow light.
• Antibacterial activity (foodborne pathogens) of silver oxide nanoparticles was evaluated.
... From the decades, metal nanoparticles (NPs) are gaining more attention in the field of nanotechnology due to the higher specificity and activity than their bulk counterpart 2 . Metal NPs such as platinum, silver and gold have been broadly used as photonics, electronics, optical device, catalyst, biosensing and bio-labelling agents [3][4][5][6][7][8][9][10] . Among metal NPs, AgNPs have found appropriate claimants as antimicrobial and anticancer agents, wound healing, drug delivery system and waste water treatment [11][12][13][14] . ...
In the present work, we demonstrated the biosynthesis of silver nanoparticles (AgNPs) by highly stable, economic and eco-friendly method using leaf extract of Terminalia arjuna (T. arjuna) and employing as a catalyst for the degradation of methyl orange (MO), methylene blue (MB), congo red (CR) and 4- nitrophenol (4-NP). The biosynthesis of AgNPs was visually validated through the appearance of reddish-brown color and further confirmed by the UV-spectra at 418 nm. The TEM and FE-SEM studies revealed the spherical shape of particles with size ranged between 10–50 nm. Face centered cubic crystalline nature of AgNPs was proved by XRD analysis. The negative value of zeta potential (−21.7) indicated the stability of AgNPs and elemental composition was confirmed by EDS. FT-IR analysis revealed the functional groups present in the plant extract trigger the biosynthesis of AgNPs. The AgNPs exhibited strong degradation of MO (86.68%), MB (93.60%), CR (92.20%) and 4NP (88.80%) by completing the reduction reaction within 20 min. The reaction kinetics followed the pseudo-first-order and displayed k-values (rate constant) 0.166 min−1, 0.138 min−1, 0.182 min−1 and 0.142 min−1 for MO, MB, CR and 4-NP respectively. This study showed an efficient, feasible and reproducible method for the biosynthesis of eco-friendly, cheap and long-time stable AgNPs and their application as potent catalysts against the degradation of hazardous dyes.
... 64 SHG is a coherent signal, but an incoherent signal, hyper-Rayleigh scattering (HRS), was observed from colloids. 65,66 Nappa et al. 67 observed that SHG from small particles was dipolar in nature, but from larger particles, >80 nm, quadrupole scattering was observed. HRS has been observed from nanorods. ...
The historical development of multiphoton microscopy is described, starting with a review of two-photon absorption, and including two- and three-photon fluorescence microscopies, and second- and third-harmonic generation microscopies. The effects of pulse length on signal strength and breakdown are considered. Different contrast mechanisms, including use of nanoparticles, are discussed. Two new promising techniques that can be applied to multiphoton microscopy are described.
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... whereas in the case of cysteine around 520 nm it is possible to see an increase in the absorbance that clearly indicates slight but not negligible aggregation phenomena, at this wavelength the spectra obtained by increasing the concentration of homocysteine do not show any variation. Starting from the Mie-Gans model, different authors (Galletto et al 1999;Rouillat et al 2001) consider the aggregates of gold nanoparticles as objects of elongated shape (ellipsoids) and show that a spherical-shaped metallic cluster has a unique SPR peaked at about 520 nm, while a prolate ellipsoid gives two characteristic extinction signals, one at the same frequency of the spherical particles and the other redshifted. The same trend has also been reported for silver nanoparticles (Contino et al 2015) that in the presence of aggregates, besides the characteristic SPR peak at about 400 nm, show another peak redshifted. ...
Fluorescent-labelled nanoparticles conjugate the SPR of nanomaterials as well as the fluorescence properties of the capping dye. In this work, we report a study on the synthesis of fluorescent l-tyrosine (l-Tyr) and fluorescein (Fluo)-capped silver nanoparticles (AgNPs) carried out by a fine-tuning of the analytical concentration of the reagents. The AgNPs have been characterized by TEM, UV–Vis, ATR–FTIR, and photoluminescence (PL) spectroscopy and DLS. The adsorption of cysteine and homocysteine on the surface of the nanoparticles has been studied to evaluate their overall evolution in solution and their possible interactions with more complex systems, such as proteins. Opposed to homocysteine, cysteine induces aggregation either of tyrosine- and fluorescein-capped nanoparticles, which are therefore promising systems for the discrimination of biothiols. Furthermore, tyrosine-capped AgNPs, in spite of the better coordinating characteristics of this amino acid with respect to fluorescein, show aggregation abilities with cysteine greater than the fluorescein-capped ones that are unexpectedly more stable and thus less prone to aggregation phenomena.
... Numerous approaches used to date include a reduction in chemical, photochemical and solutions reaction in thermal decomposition and reverse micelles of Ag compounds, electrochemical, biosynthesis, radiation-assisted and recently, biosynthesis using living-plant systems. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] The present work reports the synthesis of Ag NPs via green route using Ixora coccinea as fuel. The prepared Ag NPs were characterized using powder X-ray diffraction (PXRD), UV-Visible spectrum (UV-Vis), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of the Ag NPs ( Figure 1). ...
Silver nanoparticles (Ag NPs) was synthesized by green synthesis method using
Ixora coccinea leaves extract as fuel. The structure and morphology of the product
were characterized by Powder X-ray Diffraction, UV–Visible spectroscopy, Scanning
Electron Microscopy and Transmission Electron Microscopy. The nanoparticles (NPs)
were subjected to photocatalytic and antimicrobial studies. PXRD pattern demonstrates
that the formed product belongs to the cubic crystal system. SEM images show that the
particles are agglomerated to form spherical like structure and the average crystallite
sizes were found to be 20nm. The prepared Ag NPs exhibit excellent photocatalytic
activity for the photodegradation of methylene blue (MB) indicating that the Ag NPs
are potential photocatalytic semiconductor materials. Ag NPs exhibit significant
bactericidal activity against gram-positive (Pseudomonas aeruginosa, Escherichia coli
and Klebsiella aerogenes) and gram-negative (Staphylococcus aureus) bacteria using
the disc diffusion method. The study successfully demonstrates the synthesis of Ag
NPs by simple eco-friendly route employing Ixora coccinea as a fuel that exhibits
superior Photodegradative and antibacterial activities.
... NPs in colloidal solutions. The formation of gold particle assembly leads to an increase in dielectric constant of the surrounding medium, hence shifting the plasmon peak to a lower energy [35].The Au1 shows very good stability for few weeks and Au2 and Au3 show stability for a week at room temperature, but they are stable for a longer period when kept at 4 • C. ...
The unique electronic and chemical property of colloidal gold nanoparticles in aqueous solution is being extensively studied for the development of new generation nanoscale devices. In this work, gold colloids of different colour, morphology and size were synthesized using leaf extract of guava (Psidium guajava) under ambient conditions. The role of leaf extract of Psidium guajava as a reducing, stabilising and aggregation inducing agent was explored in this
study. Two different coloured gold colloids, red and black, were formed with increasing the leaf extract concentration. The red coloured colloids are monodisperse whereas black colloids
showed aggregate structures in TEM analysis. Black coloured gold aggregates show broadband absorption due to interparticle plasmonic coupling. In addition to this, the near field enhancement contributed by these colloidal aggregates generates high energy electrons and
promote intra-band transition. These properties are responsible for the improved optical and photocatalytic behaviour shown by the black gold colloids compared to monodispersed red gold colloids. Bio-inspired gold aggregates by this fast and green approach is suitable for various sensing and optoelectronic applications. The synthesis strategy, characterization and photocatalytic application of nanoscale gold particles self-assembled into an aggregate structure has been discussed in this work.
Keywords: Black gold; Induced aggregation; Nanostructures; Self-assembly
... [23,24] Pyridine also induces aggregation and has been shown to increase the HRS intensity by up to 10fold. [25,26] All previous reported data was collected for a single excitation wavelength or a limited wavelength range near the corresponding linear plasmon band. [21,[27][28][29] Using a spectrally resolved method (see Figure 1a), we report the spectral information of HRS over a much broader excitation wavelength range. ...
Gold nanoparticles (AuNPs) are regarded as promising building blocks in functional nanomaterials for sensing, drug delivery and catalysis. One remarkable property of these particles is the localized surface plasmon resonance (LSPR), which gives rise to augmented optical properties through local field enhancement. LSPR also influences the nonlinear optical properties of metal NPs (MNPs) making them potentially interesting candidates for fast, high resolution nonlinear optical imaging. In this work we characterize and discuss the wavelength dependence of the hyper‐Rayleigh scattering (HRS) behavior of spherical gold nanoparticles (GNP) and gold nanorods (GNR) in solution, from 850 nm up to 1300 nm, covering the near‐infrared (NIR) window relevant for deep tissue imaging. The high‐resolution spectral data allows discriminating between HRS and two photon photoluminescence contributions. Upon particle aggregation, we measured very large enhancements (ca. 10⁴) of the HRS intensity in the NIR, which is explained by considering aggregation‐induced plasmon coupling effects and local field enhancement. These results indicate that purposely designed coupled nanostructures could prove advantageous for nonlinear optical imaging and biosensing applications.
... However, at higher concentrations, the extinction band at around 500 nm gradually decreased indicating the decrease of the assembly density. Meanwhile, the relative intensity of extinction band at around 700 nm became higher, which reflected the aggregation of the nanorods 51 . As a result, the SERS substrate fabricated with 4 mM NaCl was used for subsequent DNA analysis. ...
Accurate and sensitive identification of DNA mutations in tumor cells is critical to the diagnosis, prognosis and personalized therapy of cancer. Conventional polymerase chain reaction (PCR)-based methods are limited by the complicated amplification process. Herein, an amplification-free surface enhanced Raman spectroscopy (SERS) approach which directly detects point mutations in cancer cells has been proposed. A highly sensitive and uniform SERS substrate was fabricated using gold@silver core-shell nanorods, achieving an enhancement factor of 1.85×106. By combining the SERS-active nanosubstrate with molecular beacon probes, the limit of detection reached down to 50 fM. To enable parallel analysis and automated operation, the SERS sensor was integrated into a microfluidic chip. This novel chip-based assay was able to differentiate between mutated and wild-type KRAS genes among a variety of other nucleic acids from cancer cells in 40 min. Owing to the simple operation and fast analysis, the SERS-based DNA assay chip could potentially provide insights into clinical cancer theranostics in an easy and inexpensive manner at the point of care.
... The resonant increase in the nonlinear signal in the presence of a second-harmonic plasmon resonance was investigated, for example, for gold nanoparticles placed in a liquid [14], at a liquid-air interface [15], and in matrices of aluminum oxide [16] and quartz [17]. It was shown that SHG is an efficient method for monitoring the aggregation of nanoparticles with a sensitivity that is many times higher than that of the method based on the measurement of the extinction spectrum of a colloidal solution [14,18]. Moreover, nonlinear light scattering can be used to determine the size and hyperpolarizability of metal particles of different sizes [19,20]. ...
A one-dimensional combined plasmonic–photonic system tailored for the enhancement of nonlinear optical effects is proposed and implemented. In this structure, a layer of silver plasmonic nanoparticles is placed in the cavity region of a photonic-crystal microcavity made of porous silicon. A multifold increase in an optical second harmonic generation signal in comparison to the structure without plasmonic nanoparticles is demonstrated.
... The properties of NPs were strongly depended on the size, shape and surface nature (Xu et al., 2013;Jose et al., 2016;Vidya et al., 2016). Synthesized NPs have extensive properties in catalysis (Muthu et al., 2017), optical device (Galletto et al., 1999), electrochemical analysis (Welch et al., 2006), electronic (Daniel et al., 2004), photonics (Maier et al., 2001), information storage (Sun et al., 2000), biosensing (Han et al., 2001;West et al., 2003), biolabeling (Nicewarner-pena et al., 2001), and biomedical materials (Mirkin et al., 1996). Among the various noble metals AgNPs have been widely studied due to broad application in the fields of physics, chemistry, materials science, optoelectronics, renewable energies, environmental remediation, biomedical, high antimicrobial and catalytical nature (Ahmed et al., 2015;Lopez-Esparza et al., 2016;Ruiz-Baltazar et al., 2017;Saha et al., 2017). ...
In the present study, microwave assisted biogenic synthesis of silver nanoparticles (Ag NPs) was carried out by using aqueous leaf extract of Lepidagathis cristata (L. cristata) which can act itself as a reducing and capping agent. This method was very precious due to their economic and eco-friendly benefits. The microwave assisted biogenic synthesized Ag NPs were characterized and analyzed by various instruments such as ultraviolet-visible spectroscopy (UV-vis), fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDS). The UV-vis absorption spectrum peak at 430 nm, corresponds to the characteristic peak of Ag NPs. The functional biomolecules present in the L. cristata were identified by FT-IR spectroscopy, the XRD analysis explored that the synthesized Ag NPs have high crystallinity, face-centered cubic structure, and spherical shape. Ag NPs properties like size and stability (Zeta potential) of the NPs were calculated by Nano Particle Size Analyzer (NPSA). Further, we evaluated the antibacterial activity of the Ag NPs. The microwave assisted biogenic synthesized Ag NPs to show an excellent antibacterial activity against bacteria's like Escherichia coli, Pseudomonas aeruginosa (Gram -Ve bacteria), Streptococcus pneumonia (gram +Ve bacteria) and the zone of inhibition range was determined.
... Example of such effect is surface-enhanced Raman scattering with significant enhancement effect [2]. The presence of metallic particles influences strongly linear and non-linear optical (NLO) properties [3,4], in particular fluorescence [5] of hybrid systems. ...
The unique linear and non-linear optical (NLO) properties of small noble metal nanoclusters in hybrid systems formed with peptides will be overviewed. Focus is on two aspects based on theoretical concepts. First, enhancement of absorption of biomolecules by small silver clusters in non-scalable regime in which each atom counts will be illustrated on example of peptides involving aminoacids. Second, concept for design of new NLO-phores based on ligated noble metal nanoclusters in which ligands (peptides) have dual role stabilizing metal clusters and inducing non-linearity. Both complementary directions have attractive potential for medical application. The small silver clusters with their unique optical properties and simple linking to peptides should allow optical labelling of functional intracellular proteins opening perspective for development of new sensors. Understanding of leading factors giving rise to large non-linear properties of peptide ligated small silver nanoclusters allows to propose novel ligand-core NLO-phores for bioimaging as well as for other applications.
... The second plasmon resonance band of gold appeared as a shoulder and then as maximum near λ = 600 nm. This long wavelength mode is the excitation of plasmon resonance along the linear chains of nanoparticles (chain mode) [24] that is intrinsic for gold aggregates with different cross-linking agents [25,26]. In our case, it was due to the growth of aggregates of Au NPs caused by DAE binding (Fig. 3a). ...
The photochromic properties of furan-based diarylethenes and their interaction with citrate-capped gold nanoparticles were investigated by ultraviolet/visible absorption spectroscopy and transmission electron microscopy. We identified the optimal concentration of diarylethenes in water-ethanol mixture required for stability of colloidal systems. Nanoparticles coupled with diarylethene derivatives exhibit a new surface plasmon resonance band coming from their aggregation. We analyzed the effects of functional side-chain groups on aggregation process. These results can be considered as a basis for further designing of novel hybrid nanomaterials and optoelectronic elements.
Electronic supplementary material
The online version of this article (doi:10.1186/s11671-017-2044-6) contains supplementary material, which is available to authorized users.
... Use of plants in synthesis of nanoparticles is quite novel leading to truly green chemistry which provide advancement over chemical and physical method as it is cost effective and environment friendly easily scaled up for large scale synthesis and in this method there is no need to use high pressure, energy, temperature and toxic chemicals. Now days we are using bacteria, fungi for the synthesis of nanoparticles [12][13][14][15][16][17][18] but use of leaf extract [19][20] reduce the cost as well as we do not require any special culture preparation and isolation techniques. There have been many reports on the synthesis of silver nanoparticles by using leaf extracts. ...
The biosynthesis of metal nanoparticles is an expanding research area due to
the potential applications for the ecofriendly development of novel
technologies. Generally, nanoparticles are prepared by a variety of chemical
methods which are not environmentally friendly. A green synthesis of silver
nanoparticle was carried out using Myrica esculenta leaf extract. On treatment
of aqueous solutions of 1mM silver nitrate (AgNO3) with leaf extract, silver
nanoparticles could be rapidly synthesised within 6 hours. These nanoparticles
were characterized with UV-Vis spectroscopy, X-ray diffractometer (XRD)
and transmission electron microscope (TEM).TEM analysis revealed that the
silver nanoparticles were polydisperse and of different morphologies ranging
from 45 to 80 nm in size. X-ray diffraction (XRD) results reveal that these
nanostructures exhibit a face-centered cubic crystal structure.
... The observed peak was slightly wider and red-shifted respect to that obtained for the aqueous dispersion of Au@PVP NPs. As reported by Liao et al for gold NPs of similar size [35], and as expected from the Mie theory [41], the presence of linear aggregates of gold NPs should produce the appearance of a second, red-shifted absorption band, associated to the longitudinal mode of the electronic plasma oscillation along the long axis of the gold NPs chains. This second mode could be responsible for the widening and red shift of the absorption band observed in the case of gold nanocomposites (figure 4(a)). ...
Green laser irradiation successfully activated self-healing processes in epoxy-acid networks modified with low amounts of gold nanoparticles (NPs). A bio-based polymer matrix, obtained by crosslinking epoxidized soybean oil (ESO) with an aqueous citric acid (CA) solution, was self-healed through molecular rearrangements produced by transesterification reactions of â-hydroxyester groups generated in the polymerization reaction. The temperature increase required for the triggering of these thermally activated reactions was attained by green light irradiation of the damaged area. Compression force needed to assure a good contact between crack faces was achieved by volume dilatation generated by the same temperature rise. Gold NPs dispersed in the polymer efficiently generated heat in the presence of electromagnetic radiation under plasmon resonance, acting as nanometric heating sources and allowing remote activation of the self-healing in the crosslinked polymer.
... For gold and silver spherical nanoparticles, the nonlinear response from dimers reported in [8,9] was several orders of magnitude greater than from monomers. In colloidal solutions of metal nanoparticles, second harmonic generation and two-photon luminescence strongly depend not only on nanoparticle size, material and type of solvent but also on the degree of particle aggregation [10][11][12][13][14][15]. Cluster formation of nanoparticles is usually accompanied by significant enhancement of the twophoton luminescence signal [10,11]. ...
Second harmonic generation and two-photon luminescence from colloidal gold nanoparticles in the 980–1300 nm wavelength range of exciting femtosecond radiation were investigated experimentally. The measured polarization and spectral characteristics of the second harmonic and two-photon luminescence demonstrate that the observed nonlinear optical signal is determined by the dimers constituting several percent of the total nanoparticle number.
... A new band from 500 to 800 nm appears, shifting to longer wavelength. This is because aggregated NPs appear, as described by Mie theory 32 . When the isopropanol to water ratio was over 7:1, the Ag NPs were completely aggregated to the bottom of solution. ...
Silica-coated SERS tags have been attracting greater attention in recent years. However, the reported methods to synthesize these tags are tedious, and often subjected to the limited signal intensity. Here, we report a facile and general method to prepare the silica-coated Ag SERS tags with the enhanced signal intensity by no introducing the primers. This approach mainly depends on the colloidal stability of the Ag NPs in alcohol solution. By decreasing the concentration of salt in Ag NP solution, the citrate-stabilized Ag NPs can be well dispersed in alcohol solution. Based on this, the Ag SERS tags can be directly coated with thickness-controlled and homogeneous silica shells. This approach is highly reproducible for silica shell growth and signal intensity, not depending on the properties of Raman molecules, proved by 7 kinds of the Raman molecules. Moreover, this kind of SERS tags coated with silica hold the stronger SERS signals than the traditional method due to no interference from the priming molecules.
... For gold and silver spherical nanoparticles, the nonlinear response from dimers reported in Ref. [8,9] was several orders of magnitude greater than from monomers. In colloidal solutions of metal nanoparticles second harmonic generation and two-photon luminescence strongly depend not only on nanoparticle size, material and type of solvent but also on the degree of particle aggregation [10][11][12][13][14][15]. Cluster formation of nanoparticles is usually accompanied by significant enhancement of the two-photon luminescence signal [10,11]. ...
Second harmonic generation and two-photon luminescence from colloidal gold nanoparticles in the 980-1300 nm wavelength range of exciting femtosecond radiation were investigated experimentally. The measured polarization and spectral characteristics of the second harmonic and two-photon luminescence demonstrate that the observed nonlinear optical signal is determined by the dimers constituting several percent of the total nanoparticle number.
... One of the typical applications of AuNPs in current research is the colorimetric detection of metal ions in the environment as well as in physiological systems because they possess excellent optical properties, such as high extinction coefficients and distance-dependent plasmonic absorption [9,10]. However, the challenge moving forward is to prevent aggregation of the nanoparticles in high-ionic-strength solutions because aggregation restricts the broad and practical application of AuNPs in the detection of ionic species [11,12]. ...
New Schiff base-coated gold nanoparticles (AuNPs) of type AuNP@L (where L: thiolated Schiff base ligand) have been synthesized and characterized using various spectroscopic techniques. The AuNPs and AuNP@L were imaged by transmission electron microscopy (TEM) and were confirmed to be well-dispersed, uniformly distributed, spherical nanoparticles with an average diameter of 8–10 nm. Their potential applications for chemosensing were investigated in UV-Vis and fluorescence spectroscopic
studies.TheAuNP@Lexhibited selectivity for Fe3+ in an ethanol/water mixture (ratio 9 : 1 v/v).Theabsorption and emission spectral
studies revealed a 1 : 1 binding mode for Fe3+, with binding constants of 8.5 × 10
5 and 2.9 × 10
5M−1, respectively.
... Due to their unique properties, metal nanoparticles are widely used in catalysis, 1,2 chemical sensing and biosensing, 3,4 photonics, 5 electronics, 6,7 optics, 8 DNA sequencing, 9 surface-enhanced Raman spectroscopy, 10,11 and pharmaceuticals. 12,13 The preferred route for their preparation has been, and still is, the reduction of metal salts in solutions. ...
An environmentally friendly route to prepare stable concentrated aqueous dispersions of silver nanoparticles is described. It was found that Arabic gum, a well known stabilizing agent, can also rapidly and completely reduce Ag 2O to metallic silver in alkaline solutions (pH > 12.0) and elevated temperature (65 °C). The average size of the silver nanoparticles could be tailored from 10 to 30 nm by varying the experimental conditions. By hydrolyzing either enzymatically or chemically the polysaccharide, it was possible to isolate dispersed silver nanoparticles suitable for both biological and printable electronics applications. For the latter purpose, concentrated dispersions of silver particles were prepared and used for depositing thin uniform layers, which could be sintered into conductive films at low temperatures.
Ligand decoration of noble metallic nanoparticles is often needed for some applications, such as biochemical sensing, catalysis and nanotechnology, and the understanding of its process is of great importance. The second harmonic scattering (SHS) technique with advantages of surface-sensitivity and label-free detection, provides intrinsic information for such a research. In this work, the second harmonic(SH) scattering patterns of two types of ligands (cetyltrimethylammonium chloride and L-cysteine) capped gold nanoparticles (GNPs) with the same radii are measured. Both the intensities and shapes of the SH scattering patterns are changed after the ligand exchange process. In order to explain the pattern changes, the analytic expressions of SH scattering are derived theoretically for a relatively large nanoparticle based on Dadap’s multipolar theory. Considering the derived relationship between the multipole (up to octopole) contributions and the power of the nanosphere radius, the effective size effect is introduced to express the SH scattering signal change for different ligand decorations and well explain the experimental results. This theory provides a new perspective of the SH scattering response to different capping ligands and offers a possible quantitative method to analyze interface physical chemistry for ligands on the surface of nanoparticles.
The objective of this study was to eliminate organic pollutants from the fluid stage employing silver nanocatalyst relationship with NaBH4 using Morinda citrifolia leaf extract. Silver nanoparticles were effectively evolved utilizing the pyto-reduction method. The inferred nanocatalyst was preliminary confirmed by UV–Visible, FT IR, EDX, SEM/TEM-HR TEM, and DLS spectroscopic investigations. The size and morphology of the silver nanoparticles were ascertained to be 28 nm with spherical shape morphological characteristics through SEM/TEM microscopic examination. As a potential outcome, silver catalyst has such an elevated catalytic performance, when it comes to decomposing organic dyes include alizarin red, pararosaniline, eosin blue, methyl violet, and Congo red. Among the organic pollutants eliminated employing by silver nanocatalyst, the degradation of Congo red was found to be the most efficacious 100% in about 5 min respectively.
Different nanoscale tungsten oxides with phenomenal photocatalytic properties were orchestrated through a super-fast arrangement ignition amalgamation strategy . The outcomes showed that the WO3 and W18O49 could be orchestrated with various fills (glycine, urea, urea and citrus extract) and the powders introduced mesoporous structures with various morphologies, for example, nanoparticles, nanorods and nanoneedles. Itemized response components of different frameworks were distinguished, and the particular jobs of various powers were examined . Also, the integrated powders showed fantastic photocatalytic proficiency, debasing natural mixtures in 50 min under UV-obvious light illumination. The work recommends that arrangement ignition combination can be utilized as another procedure to plan nanosized stoichiometric and oxygen-opportunity rich nonstoichiometric oxides with brilliant properties .
Hybrid nanoparticles composed of an efficient nonlinear optical core and a gold shell can enhance and tune the nonlinear optical emission thanks to the plasmonic effect. However the influence of an incomplete gold shell, i.e., isolated gold nano-islands, is still not well studied. Here LiNbO3 (LN) core nanoparticles of 45 nm were coated with various densities of gold nano-seeds (AuSeeds). As both LN and AuSeeds bear negative surface charge, a positively-charged polymer was first coated onto LN. The number of polymer chains per LN was evaluated at 1210 by XPS and confirmed by fluorescence titration. Then, the surface coverage percentage of AuSeeds onto LN was estimated to a maximum of 30% using ICP-AES. The addition of AuSeeds was also accompanied with surface charge reversal, the negative charge increasing with the higher amount of AuSeeds. Finally, the first hyperpolarizability decreased with the increase of AuSeeds density while depolarization values for Au-seeded LN were close to the one of bare LN, showing a predominance of the second harmonic volumic contribution.
In this study, silver nanoparticle (AgNP) synthesis was carried out using Onosma sericeum Willd. aqueous extract for the first time, with a simple, economical, and green method without the need for any other organic solvent or external reducing or stabilizing agent. A variety of AgNPs, all of different particle sizes, were synthesized by controlling the silver ion concentration, extract volume, temperature, and pH. It was determined that the optimum conditions for AgNP synthesis were 1 mM AgNO3, pH 8, 25 °C, 20 g/200 mL extract, silver nitrate, and extract ratio 5:1 (v/v). The AgNPs were defined using UV-Vis spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The particle size distribution and zeta potential measurements of the AgNPs were measured using the dynamic light scattering (DLS) technique. It was determined that the AgNPs with a particle size of less than 10 nm showed a higher catalytic effect in the reduction of 2-nitrobenzenamine. It was also found that these nanoparticles had a cytotoxic effect on the MCF-7 breast cancer cell line depending on dosage and time. The resulting IC50 values were between 76.63 µg/mL and 169.77 µg/mL. Furthermore, the biosynthesized AgNPs showed effective antibacterial activity against the Acinetobacter baumannii bacteria. The results of the study showed that synthesized AgNPs can have a promising role in biomedical and nanobiotechnology applications.
The preparation of gold nanoparticles through reduction of chloroauric acid by trisodium citrate, also known as the Turkevich synthesis, was analysed both ex situ and in situ. In situ experiments consist of dynamically tracking second and third harmonic light scattering and multiphoton luminescence. By complementing in situ data with ex situ quenching experiments, which enabled further UV-vis-NIR Spectroscopy, TEM and DLS characterization, we obtained new insight in the mechanistic process of gold nanoparticle growth. Our results reveal that the growth proceeds through a metastable state of aggregation and offer additional evidence for a sharp transition from metallic molecular cluster to plasmonic nanoparticle behaviour in the initial stage of the process. While multiphoton luminescence can be used as a marker for this transition, second and third harmonic scattering reveal surface and bulk information such as size, shape and the presence of aggregates.
As a convenience and robust point-of-care diagnostics technique for biomarkers, surface-enhanced Raman scattering (SERS)-based lateral flow immunoassay (LFIA) has attracted attentive attentions. In traditional paper-based LFIA, its hydrophilic surface with the so-called coffee-ring effect will inhibit the sensitivity and quantitative ability, which made the results less satisfying. Here, an attractive hydrophilic-hydrophobic polymer strip with Raman internal standard (IS) was developed by magnetron sputtering hydrophilic Ag nanoparticles (NPs) onto the specific area of the hydrophobic polydimethylsiloxane (PDMS). The target analytes can be enriched on the test and control lines formed by the hydrophilic Ag regions, which significantly improved the adaptability of SERS-based LFIA strip in the ultra-sensitive and quantitative monitoring of trace Ferritin (FER). Typically, assisted by raspberry-like Au NPs as immunoprobes, such hydrophilic-hydrophobic LFIA strip could achieve a limit of detection for FER as low as 0.41 pg/mL. Moreover, calibrated linear relationship with R² values of 0.992 in the analysis was successfully demonstrated by rationally using the Raman signals of PDMS as a reference. Such an improved LFIA platform may give another promising technique for the trustworthy monitoring and treatment of cancer.
Quantitative immunoassay of specific tumor markers in clinical serum is critical for early monitoring and treatment of cancer. Herein, a surface-enhanced Raman scattering (SERS)-active immunostructure, consisting of [email protected]@Ag core-shell nanoparticles as immunoprobes and Au nanowires (NWs)/polydimethylsiloxane (PDMS) film as immunosubstrate, was proposed for the quantitative determination of prostate-specific antigen (PSA) and alphafetoprotein (AFP). In this method, the ultrasensitive detection of the two tumor markers could be achieved in parallel on the curved flexible Au NWs/PDMS substrate. And, a recyclable detection with limit of detections (LODs) of 0.49 pg/mL for PSA and 0.72 pg/mL for AFP could be realized, attributing to the excellent photocatalytic property and magnetic separation of [email protected]@Ag core-shell NPs. Moreover, improved linear relationships with R2 values of 0.986 and 0.996 in the detection were perfectly obtained by utilizing the intrinsic SERS peak of PDMS as internal standard (IS). In addition, the trace two antigens of PSA and AFP in serum samples of cancer patients have been monitored using the developed immunoassay protocol, which shows superiority than chemiluminescent immunoassay (CLIA). Such novel quantitative and recyclable SERS-based immunoassay would provide an alternative reliable method for the early accurate diagnosis of cancer.
Patterned Ag thin films were obtained through laser irradiation at ambient conditions. We investigated the effects of laser scanning rate for the structure and optical properties of patterned Ag films. XPS results show that the volume fractions of Ag and Ag2O are dependent on the laser scanning rate. The localized surface plasmon resonance was observed in the as-irradiated samples and increased with the acceleration of the scanning rate. Moreover, with the variations of laser scanning rates and excitation energy, these samples exhibit tunable self-defocusing nonlinearity caused by charge transfer and the enhanced electromagnetic field at the interface between Ag and Ag2O.
Gold nanoparticles (AuNPs) are an obvious choice for rapid advance in nanotechnology due to their amenability of synthesis, functionalization and less toxicity. Functionalization of AuNP surface with 4-amino-3,5-dimercapto-1,2,4-triazole (ADMT) ligand as ADMT-AuNPs was investigated with the aim to probe the suitability of innovative product to develop new antibacterial and anticancer strategies. Various characterization studies like UV-spectra, Zeta size, Zeta potential, XRD, SEM, TEM and FTIR results of AuNPs and ADMT-AuNPs have been performed to study the structural and electronic properties. The studies revealed that the functionalized nanoparticles are highly crystalline in nature with the sizes ranging between 20-22 and 50-55 nm for AuNPs and ADMT-AuNPs, respectively with FCC structures. The characterization data reveals that the synthesized nanoparticles are stable and presence of strong interactions between the metallic surface and the organic ligand. Further, ADMT-AuNPs showed good antibacterial activity against Gram-positive and Gram-negative bacteria. MTT assay exhibited the cell viability with an IC50 value of 45.32 % v/v for ADMT-AuNPs against breast adenocarcinoma (MCF-7) cell lines. Molecular characterization i.e., in silico docking analysis helped in identifying and organizing the structural similarity/diversity at the molecular level. The in silico study indicated that the structure S1a has good glide score and glide energy for H-bonding among the possible conformations against bacterial and breast cancer protein. Molecular docking studies confirmed the introduction of conformational changes that are essential to surpass the potential energy barriers of ADMT-AuNPs for biocompatibility and proved that they hold a promising future in the medical field.
To synthesize noble metal nanomaterials in controlled sizes and dimensions, various approaches and mechanisms have been developed. The successful utilization of noble metal nanoparticles (NMNPs) relies on the availability of synthetic methods generating nanoparticles with the desired characteristics, namely high solubility in water, adequate morphology, and surface functionalities. Control over the shape and size of the nanoparticles is usually achieved through the careful selection of the experimental conditions, namely reducing agents, type and concentration of precursors, reaction time, temperature, UV light, (co)solvent, and capping agents. Depending on the reduction potentials of the metal precursor and the reducing-agent systems, reduction can occur at room temperature or at elevated temperatures. In general, citrate plays a role as a stabilizing agent with preparations of gold nanoparticles requiring relatively high temperatures due to its weak reducing strength. The use of amine–borane complexes is essential for the syntheses of monodisperse metallic nanoparticles. Upon the addition of strong reductants, such as NaBH4, metal cations are reduced rapidly, resulting in an immediate color change of the reaction mixture. Rationally designed molecular building blocks allow for the precise control of particle size and morphology of the supramolecular aggregate, and various defined structures, including spherical micelles, rodlike micelles, or vesicles. Molecules which control the overall crystal growth are known as “capping agents,” the term frequently used for specific adsorption of surface-active molecules on selective crystal planes of a particular geometry. Additives such as surfactants, polymers, foreign ions, ligands, and impurities present in the reaction medium have been observed to play important roles in controlling the morphology of particles produced. Surfactants, ligands, or polymers were commonly added as stabilizers to impart stability to nanoparticles against aggregation, since colloidal particles tend to aggregate to decrease the overall surface area and energy. In a typical liquid-phase synthesis, the nanoparticle formation process undergoes three distinct stages as follows: (1) reduction and generation of active nuclei; (2) formation of seed particles upon collision of active nuclei; and (3) formation of larger nanoparticles via a growth process, which may be Ostwald ripening or aggregation. The nanoparticle growth is generally categorized by two processes: diffusion-controlled Ostwald-ripening and aggregation/coalescence. Nowadays, a molecule which can act both as a reducing and capping agent is preferred so that the reaction takes place in one step and there is no need for an external reducing agent. Multifunctional amines and nitrogen-containing polymers have also been tested for the synthesis of nanoparticles. Poly(ethylene oxide)-poly(propylene oxide)-based block copolymers are well known as dispersion stabilizers and templates for the synthesis of mesoporous materials and nanoparticles. Coordination chemistry offers simplicity, stable bonding, and ligand-metal specificity, enabling ligand-bearing components to be assembled into supramolecular structures using appropriate metal ions. This approach is particularly compatible with surface chemistry, as binding of metal ions activates the surface toward ligand binding, and vice versa. Some stabilizing agents can also be used as a reducing agent. Ionic liquids (ILs) are a viable option as stabilizing agents because of their ionic character and can be easily made task-specific as phase-transfer catalysts due to their tunable nature. Ligand exchange reactions have proven a particularly powerful approach to incorporate functionality in the ligand shell of thiol-stabilized nanoparticles and are widely used to produce organic- and water-soluble nanoparticles with various core sizes and functional groups. NMNPs can be intercalated into the gallery regions of montmorillonite and formed hybrid framework. Models of particle (crystal) development consider two basic steps: nucleation and growth. The creation of a new phase from a metastable state is nucleation. Seed-mediated growth method has been demonstrated to be a powerful synthetic route to generate a range of different types of metal nanoparticles. This method separates the nucleation and growth stage of nanoparticle syntheses by introducing presynthesized small seed particles into a growth solution typically containing a metal precursor, reducing agent, surfactants, and some additives. Dissolution of silver nanoparticles, for example, occurs through oxidation of metallic Ag and release of Ag⁺ into solution (or dissolution rate is accelerated). Release of Ag⁺ is determined by intrinsic physicochemical properties of silver nanoparticles and by those of the solution. Parameters that either enhance or suppress silver nanoparticle dissolution are ionic strength, pH, dissolved oxygen concentration, temperature, dissolved complexing ligands (organic matter, sulfur, chlorine), silver surface coating, shape, and size. The surfactants find their way to various environmental segments and thus pose serious health hazards. Several different polymer-based anticancer agents have been approved for clinical use, for passive tumor targeting. Prominent examples of macromolecular drug carrier systems evaluated in patients are poly(ethylene glycol), poly(l-glutamic acid), poly[N-(2-hydroxypropyl)methacrylamide], and their copolymers. Copolymers based on N-(2-hydroxypropyl)methacrylamide (i.e., HPMA) were used to improve the tumor-directed delivery of doxorubicin.
Highly dispersed anisotropic Ag nanostructures were synthesized within the channels of 3-aminopropyltrimethoxysilane (APTMS)-modified mesoporous SBA-15 for catalyzing the reduction of p-dinitrobenzene, p-nitrophenol, and p-nitroacetophenone, respectively. A green templating process without involving any reducing agent, by varying the amount (1–10 wt.%) of Ag loading followed by calcination at 350 °C under H2 led to change in the morphology of Ag nanoparticles from nanospheres (~7–8 nm) to nanorods (aspect ratio ~12–30 nm) without any deformation in mesoporous sieves. In comparison to white bare SBA-15, gray-colored samples were formed with Ag impregnation exhibiting absorption bands at 484 and 840 nm indicating the formation of anisotropic Ag nanostructures within mesoporous matrix. TEM and FE-SEM micrographs confirmed the presence of evenly dispersed Ag nanostructures within as well as on the surface of mesoporous matrix. AFM studies indicated a small decrease in the average roughness of SBA-15 from 20.59 to 19.21 nm for 4 wt.% Ag/m-SBA-15, illustrating the encapsulation of majority of Ag nanoparticles in the siliceous matrix and presence of small amount of Ag nanoparticles on the mesoporous support. Moreover, due to plugging of mesopores with Ag, a significant decrease in surface area from 680 m²/g of SBA-15 to 385 m²/g was observed. The Ag-impregnated SBA-15 catalyst displayed superior catalytic activity than did bare SBA-15 with 4 wt.% Ag-loaded catalyst exhibiting optimum activity for selective reduction of p-nitrophenol to p-aminophenol (100 %), p-nitroacetophenone to p-aminoacetophenone (100 %), and p-dinitrobenzene to p-nitroaniline (87 %), with a small amount of p-phenylenediamine formation.
In the graphite oxide (GO) suspension purification process, some metallic impurities in GO cannot be separated. The residual metallic impurities dominate graphite oxide properties and have a negative influence on applications. Therefore, the removal of metallic impurities from graphite oxide has been brought into focus now. Single factor experiments and orthogonal experiments are used to get the optimal purification condition. The results show that purification agent, temperature, stirring intensity and contact time affect the purification degree, and the purification agent is the most important element for the purification efficiency. The optimal purification condition is 10% hydrochloric acid (H10), 20 °C, 0 rpm and 60 min. Besides, the theoretical stage is calculated by the mass conservation equation and distribution balance equation and the minimum stage is 3 under the optimal purification condition.
An innovative method for stabilization of gold nanoparticles (GNPs) in the aqueous solution using natural plant extract from Aloe vera is presented in this work. A detailed spectroscopic analysis of the GNPs after the interaction of Aloe vera gel in different molar ratios (1:50 and 1:150) and pH values (5.3 and 7.4) reveals the excellent capping property and stabilizing nature of gel. Morphological feature as well as surface protection of GNP surfaces was confirmed by Field Emission Scanning Electron Microscopic (FE-SEM) analysis and Fourier Transform Infra -Red (FTIR) Spectroscopy respectively. It was found that higher ratios of GNPs and Gel lead to more stabilization of nanoparticles. Flocculation parameter was found to be less with increasing ratios at both the pH values indicating the stability of nanoparticles.
Silver nanoparticles (Ag NPs) synthesized from silver nitrate solutions using the esterase-containing latex of the E. Tirucalli plant widely found in a large region in Karnataka, India. Plant-mediated synthesis of nanoparticles is a green chemistry approach that intercom-nects nanotechnology and plant biotechnology. The effect of extract concentration, contact time, and temperature on the reaction rate and the shape of the Ag nanoparticles was investigated. The nanoparticles have been characterized by powder X-ray diffraction, UV-visible spectroscopy, photoluminescence spectroscopy and morphology by scanning electron microscope, transmission electron microscopy, as a function of the ratio of silver ions to reducing agent molecules. Powder X-ray diffraction patterns show that the crystal structure obtained is face-centered cubic (fcc). The morphology of the silver nanoparticle was uniform with well-distributed elliptical particles with a range from 15 to 25nm. Ag NPs exhibit significant antibacterial activity against Bacillus cereus using the agar well diffusion method.
Iridium-doped SiO2 nanoparticles have been synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. The size of the particles and the thickness of the coating can be controlled by manipulating the relative rates of the hydrolysis and condensation reaction of TEOS within the micro-emulsion. The average size of synthesized Ir-doped SiO2 nanoparticles were in the size range of 12-20 nm and the Ir particles 2-5 nm. The effects of synthesis parameters, such as the molar ratio of water to TEOS, and the molar ratio of water to surfactant, are discussed.
Development of biologically inspired experimental processes for the synthesis of nanoparticles might be important in biomedical applications. Solanum torvum extract when challenged with chloroauric acid leads to formation of gold nanoparticles. The formations of gold nanoparticles were studied by UV-vis spectra and their size of gold nanoparticles in the colloidal solutions was investigated by HRTEM, the average size of gold nanoparticles nanoparticles was found to be 8.4 nm. The rapid reduction of AuCl4 -ions highlights the possibility of green pathways to produce technologically important nanomaterials.
Methods for the preparation of nano-sized metal particles are considered. Theoretical approaches to the analysis of electron behaviour in systems with quantum-size effects are outlined. The results of experimental investigations of the thermodynamic and optical characteristics of small metal particles and thin films are presented. The data of experiments on the electron dynamics in single nanoparticles and nanoparticle ensembles are described. The self-organisation of nanoparticles into supported ordered structures in considered.
The potentiality of different phenolic compounds, belonging to both hydroxycinamic (caffeic, sinapinic and ferulic acids) and hydroxybenzoic (protocatechuic, syringic and vanillic acids) families to generate different gold nanoparticles (AuNPs) has been investigated. The synthesized AuNPs were characterized by transmission electron microscopy (TEM) andUV-Vis absorption spectroscopy. The influence of different experimental parameters, such as pH, ionic strength, buffer concentration, temperature and presence or absence of a stabilizer agent in AuNP synthesis has been studied. In all cases, the addition of a stabilizer has influence in both the amount of AuNP synthesized and in their size. On the other hand, different UV-vis spectra were obtained depending on the phenolic acid used as reducing agent, which was attributed to the different reducing power and stabilization capacity of the different phenolic acids. Finally, the prepared AuNPs showed good catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol by an excess of NaBH4.
In this work, the nonlinear optical response of assembled metallic nanoparticles at interfaces was studied using Second Harmonic Generation. First, the nanoparticles were characterised using incoherent second harmonic generation, a technique also called Hyper Rayleigh Scattering. Thioalkane-capped silver and gold nanoparticles, both nanospheres and nanorods, were investigated and the role of this capping layer on the quadratic hyperpolarisability of these particles was underlined. The particles were then deposited at the air/liquid interface in a Langmuir trough to investigate the role of the interparticles interactions in large assemblies. Both the linear and the nonlinear optical response of these metallic films formed at the surface of the trough provided evidence of a strong coupling between adjacent particles upon compression leading to a phase transition of the film once the interparticle distance is less than a critical value. These studies were complemented with experiments performed at the liquid/liquid interface and at the glassy carbon/electrolyte interface to examine in greater details the role of roughness at the nanoscale on the enhancement of the SHG response
During the last decade, surface plasmon resonance (SPR) has become widely used to characterize a biological surface and to characterize binding events in the fields of chemistry and biochemistry. Research in this field has been favoured by the tremendous growth in nanofabrication methods among which soft lithographies are alternatively emerging. The purpose of this thesis work was to develop soft UV nanoimprint lithography, an emerging flexible technology allowing patterning on large area of subwavelength photonic nanostructures. The main advantages offered by soft UV nanoimprint lithography concern the simple patterning procedure and the low cost of the experimental setup (see state-of-art presented in chapter 1). Chapters 2 and 3 present the fabrication of master stamps, the study of nanoimprinting parameters coupled with the optimization of the etching process in order to get metallic nanostructures with limited pattern defects. The physical mechanisms of the transmission phenomenon exalted by surface plasmons were studied based on arrays of imprinted gold nanoholes (chapter 4). Extraordinary light transmission has been experimentally demonstrated. The geometrical effects on the position transmission peak were systematically analyzed. Proof-of-concept measurements performed in simple fluidic device indicate a response to small changes in refractive index in the surface vicinity. Finally, chapter 5 proposes a novel design for the optical sensor which is based on "nanocavities" exhibiting coupled localized plasmons. This LSPR sensor offers an improvement of one order of magnitude of the Figure of Merit compared to classical LSPR sensors. The resonance properties of these innovative nanocavities have been studied from numerical simulations and discussed based on their geometrical dependence. Since this system has demonstrated higher sensitivity for detection of biomolecules, it is thus fully adapted to study immunochemical binding interactions.
SERS of pyridine adsorbed on electrodispersed platinum electrodes is reported. Electrodispersed platinum surfaces are obtained by electroreducing hydrous platinum oxide layers. The intensity of the Raman scattering for adsorbed pyridine is enhanced by at least one order of magnitude, after normalizing with respect to the area increase. The estimated Raman enhancement factor is lower than that reported for roughened silver electrodes but it is still sufficiently large to allow Raman scattering from adsorbates on platinum to be detectable. Surface changes (ageing) of the metal surface can be also followed by SERS.
SERS for pyridine adsorbed on a Rh electrode is presented. SERS-active Rh electrodes were electrochemically obtained in 1 M KHOH after the growing of a thick layer of rhodium oxide. Raman spectra for adsorbed pyridine are potential dependent. Results are compared with those for pyridine adsorbed on Rh-covered SERS-active silver electrodes.
Second-harmonic generation is shown to be sensitive enough to detect
molecular monolayers adsorbed on a silver surface. Adsorption of AgCl
and pyridine on silver during and after an electrolytic cycle can be
easily observed.
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.
The optical constants n and k were obtained for the noble metals (copper, silver, and gold) from reflection and transmission measurements on vacuum-evaporated thin films at room temperature, in the spectral range 0.5-6.5 eV. The film-thickness range was 185-500 Å. Three optical measurements were inverted to obtain the film thickness d as well as n and k. The estimated error in d was ± 2 Å, and that in n, k was less than 0.02 over most of the spectral range. The results in the film-thickness range 250-500 Å were independent of thickness, and were unchanged after vacuum annealing or aging in air. The free-electron optical effective masses and relaxation times derived from the results in the near infrared agree satisfactorily with previous values. The interband contribution to the imaginary part of the dielectric constant was obtained by subtracting the free-electron contribution. Some recent theoretical calculations are compared with the results for copper and gold. In addition, some other recent experiments are critically compared with our results.
The incoherent second-order nonlinear light scattering in a macroscopically isotropic molecular liquid has emerged as a simple and widely applicable technique for the experimental determination of the first hyperpolarizability of nonlinear optical molecules in solution. The technique has become widely known as hyper-Rayleigh scattering. Until recently, electric-field-induced second-harmonic generation was the only solution technique to determine molecular hyperpolarizabilities. Apart from being more complex a technique, the applied field also limits its applicability to neutral and dipolar solutions. In this paper, we present the specific advantages of the new hyper-Rayleigh scattering technique and exemplify its wider scope with results from three different kinds of molecular materials: octopoles, biological chromophores, and quantum colloids.
Intense Raman scattering by pyridine molecules adsorbed on silver or gold aqueous sol particles of dimensions comparable to the wavelength is reported. The degree of intensity enhancement is strongly dependent on the excitation wavelength, with a sharp resonance Raman maximum for excitation at the wavelength of the Mie extinction maximum of the metal particles, and for the silver sols the Raman maximum is shown to follow the extinction maximum to longer wavelengths with increase in particle size. A new resonance Raman phenomenon is thus proposed which is the Raman component of resonant Mie scattering, and in which the polarizability of the metal particles is modulated by the vibrations of the adsorbed molecules. These observations confirm that surface plasma oscillations are involved in the intense Raman scattering already reported for molecules adsorbed at roughened silver surfaces. The metal dielectric function requirements for resonant Mie scattering enable the optimum excitation wavelength for plasma resonance-enhanced Raman studies at the surface of other metals to be estimated.
Au 100~x Ag x layer of silver atoms. Since both electromagnetic and chemical theories predict that the Raman enhancement depends strongly on the morphology of colloidal particles, we have used two methods to approach the particle size and shape distributions of these mixed colloids. The —rst one compares the pro—les of the experimental and calculated extinction bands of surface plasmon resonances. The second one deals with low frequency Raman spectra from particle mechanical vibrations (acoustic modes). Using a recent model that we have developed to simulate the band pro—les of these spectra, we can obtain the size and shape of the resonant particles underlying the SERS eÜect. These distributions, deduced from both foregoing methods, are compared with those obtained by transmission electronic microscopy (TEM) and allow us to suggest that several scales of particle sizes lead to the SERS eÜect. This latter result is related to the fractal nature of partially aggregated colloids displaying scale invariance. We have also analyzed the physicochemical properties of the two probes (pyridine and acridine) when they are adsorbed onto these mixed colloids. The results show that the acridine species bound to the surface depends strongly on the addition of a very small amount of silver at the gold surface. These mixed colloids allow SERS spectra of acridine to be obtained when the laser excitation takes place in the green (514.5 nm) while in pure gold colloids, acridine does not display any SERS spectrum at this excitation wavelength.
The recent emergence of advanced technological applications for colloidal gold suspensions and related particle assemblies and interfaces has created a demand for new chemical and physical techniques with which to characterize them. For macroscopic samples/interfaces, coherent second harmonic generation (SHG) has proven itself a useful characterization tool due, at least in part, to metal-based plasmon enhancement. In an effort to defeat or bypass the size restrictions inherent to SHG, we have utilized a related incoherent methodology, hyper-Rayleigh scattering (HRS), to interrogate aqueous colloidal suspensions of 13 nm diameter gold particles. The nanoscale particles have proven to be remarkably efficient scatterers; when evaluated in terms of the first hyperpolarizability (β), HRS signals from the gold particles substantially surpass those observable from the best available molecular chromophores. Moreover, the present experiments indicate that β is highly sensitive to colloid aggregation and imply that HRS is an effective tool for the characterization of symmetry-reducing perturbations of nanoscale interfaces.
Irradiation of a pulsed Nd:YAG laser at 532 nm to gold particles of less than 50 nm in aqueous solution was found to cause the shape change and size reduction of the particles. Typically, the nonspherical gold particles between 20 and 50 nm in diameter disappeared, whereas the number of gold particles of spherical shape less than 10 nm increased. The size reduction ceased after 5 min irradiation. The maximum diameter in the size distribution decreased to ca. 10 nm when the laser fluence was increased up to nearly 800 mJ cm-2. The temperature of the gold particles was estimated from the absorbed laser energy by the particles and was found to rise as high as the boiling point of gold; these results were supported by the measurements of the blackbody radiation from the particles. The shape change and size reduction are considered to occur through melting and vaporization of the gold particles. The high temperature, which causes melting and vaporization, is a result of the strong absorption of the laser energy by the particles and the low heat transfer to the surrounding water.
Ag-coated Au colloidal particles have been prepared by reduction of Ag+ in the presence of preformed Au colloids. The composition of the Au100-xAgx particles was varied from x = 0 to 80. SERS spectra of pyridine, p-nitroso-N,N‘-dimethylaniline (p-NDMA), and trans-1,2-bis(4-pyridyl)ethylene (BPE) have been obtained with these colloids. At monolayer Ag coverages (x < 10), the optical spectra of Ag-coated Au particles are indistinguishable from uncoated Au particles. However, the SERS behavior of aggregated colloids with 647.1 nm excitation is extremely dependent upon the Ag:Au ratio. Very small amounts of Ag (x ≤ 5) lead to an increase in SERS intensity, but further increases lead to complete loss of signal. For p-NDMA and pyridine, these data can be explained by Ag inhibition of adsorbate-induced aggregation. The initial increase in SERS intensity results from production of smaller aggregates that exhibit a surface plasmon band in better alignment with the excitation wavelength; higher ratios of Ag eliminate aggregation and all SERS enhancement. For BPE, the same Ag-induced loss of SERS is observed, even though each of the Au100-xAgx colloidal solutions is clearly aggregated by BPE adsorption. This finding suggests that submonolayers of Ag modulate specific chemical interactions between the Au and BPE that are responsible for SERS.
The excitation profile of the 1014 cm−1 Raman band of pyridine adsorbed on colloidal gold particles, and the extinction and elastic scattering spectra of the colloids, are measured as the colloids slowly aggregate in the presence of pyridine. Transmission electron microscopy shows that the aggregates formed are predominantly strings of particles rather than compact clusters, and the dipolar plasma modes of the aggregates are therefore split into longitudinal and transverse components. It is shown that only for excitation under the longitudinal resonance extinction band is there a large Raman intensity enhancement. The Raman excitation profile maximum corresponding to excitation under this resonance moves progressively to longer wavelengths, increasing substantially in height, as the aggregation proceeds. Thus aggregation is most advantageous for the realization of large Raman signals from these colloids, the Raman intensity at a given excitation wavelength increasing approximately as the square of the absorbance at that wavelength as the aggregation proceeds. These observations are discussed in relation to the electromagnetic field enhancement contribution to the surface Raman effect, with which they are in general agreement, and the large increase in ¦ϵ¦2 for gold and silver with increase in wavelength is shown to be a significant factor in accounting for some of these effects of aggregation.
Raman spectroscopy has been employed for the first time to study the role of adsorption at electrodes. It has been possible to distinguish two types of pyridine adsorption at a silver electrode. The variation in intensity and frequency of some of the bands with potential in the region of the point of zero charge has given further evidence as to the structure of the electrical double layer; it is shown that the interaction of adsorbed pyridine and water must be taken into account.
After a preliminary survey with the electron microscope of various preparations of colloidal gold, a study was made of the process of nucleation and growth in gold colloids. It was shown that nucleating agents may be identified with reducing agents which form a mixed polymer with chlorauric ion before the reduction to the nucleus takes place. It was also shown that the law of growth is exponential. The average size, the deviation from the average size and the character of the particle size distribution curve are determined by the amount of gold, the nucleation process and the law of growth.
Hyper Rayleigh scattering in solution is used for the determination of the first order hyperpolarizability b(colloid) of gold colloids in the size range 5–22 nm; these hyperpolarizabilities are found to range from 0.60 × 10–25 esu for 5 nm diameter colloids to up to 16.6 × 10–25 esu for 22 nm diameter colloids at the second harmonic wavelength of 532 nm; the strong size dependence of the hyperpolarisabilities reported here suggests that hyper Rayleigh scattering experiments can efficiently be used to calibrate the particle diameter of colloidal suspensions.
The second order nonlinear response from 4 nm diam gold clusters embedded in an alumina matrix deposited on a pure silica substrate has been recorded as a function of the wavelength of the fundamental incident beam. The spectrum exhibits a narrow resonance band peaked at 520 nm as a result of the coupling of the second harmonic field with the surface plasmon of the particles. The nonlinear second harmonic response of gold clusters is found to be blueshifted compared to the bulk, due to the finite size effects on the cluster optical properties, as already observed with the linear response. Furthermore, this nonlinear response appears to be well described with a simple free electron model where the valence electrons only participate through the screening of the ionic cores, owing to the weakness of the interband transition contribution.
Colloidal gold nanoparticles in toluene solution, synthesised using a two-phase liquid/liquid system, display second harmonic generation, wavelength analysis of which indicates the narrow frequency band of the gold surface plasmon for nanoparticles present at the air/toluene interface.
The self-assembly of monodisperse gold and silver colloid particles into monolayers on polymer-coated substrates yields macroscopic
surfaces that are highly active for surface-enhanced Raman scattering (SERS). Particles are bound to the substrate through
multiple bonds between the colloidal metal and functional groups on the polymer such as cyanide (CN), amine (NH2), and thiol (SH). Surface evolution, which can be followed in real time by ultraviolet-visible spectroscopy and SERS, can
be controlled to yield high reproducibility on both the nanometer and the centimeter scales. On conducting substrates, colloid
monolayers are electrochemically addressable and behave like a collection of closely spaced microelectrodes. These favorable
properties and the ease of monolayer construction suggest a widespread use for metal colloid-based substrates.