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Quantitative Surface-Enhanced Raman Scattering Ultradetection of Atomic Inorganic Ions: The Case of Chloride
Abstract
Surface-enhanced Raman scattering (SERS) spectroscopy can be used for the determination and quantification of biologically representative atomic ions. In this work, the detection and quantification of chloride is demonstrated by monitoring the vibrational changes occurring at a specific interface (a Cl-sensitive dye) supported on a silver-coated silica microbead. The engineered particles play a key role in the detection, as they offer a stable substrate to support the dye, with a dense collection of SERS hot spots. These results open a new avenue toward the generation of microsensors for fast ultradetection and quantification of relevant ions inside living organisms such as cells. Additionally, the use of discrete particles rather than rough films, or other conventional SERS supports, will also enable a safe remote interrogation of highly toxic sources in environmental problems or biological fluids.
... This material provides a dense collection of electromagnetic hot spots upon illumination with visible light. 9 Subsequently, the plasmonic beads were coated with MOF providing a plasmonic material with properties that are the same as, or even better than, common nanostars coated with MOFs, but in the visible. Finally, to probe the efficiency of this composite for ultratrace analysis of ions, and exploiting the affinity of MOFs for nonpolar organic molecules, a selective dye for copper, bathocuproine, 32 was adsorbed in the composite material. ...
... Such colloidally stable 3D collections of closely spaced NPs onto the PS core yield highly intense SERS signals. 9,10 The resulting PS@Ag beads ( Figure 1b and Figure S2) were then redispersed into a cetyltrimethylammonium bromide (CTAB) aqueous solution below the critical micelle concentration (CMC) before the direct growth of the outer ZIF-8 shell. Here, CTAB molecules have two important effects. ...
Herein, we designed and synthesized a hybrid material comprising polystyrene submicrobeads coated with silver nanospheres. This material provides a dense collection of electromagnetic hot spots upon illumination with visible light. The subsequent coating with a metal-framework and the adsorption of bathocuproine on it yield an optical sensor for SERS that can specifically detect Cu(II) in a variety of aqueous samples at the ultratrace level. Detection limits with this method are superior to those of induced coupled plasma or atomic absorption and comparable with those obtained with induced coupled plasma coupled with a mass detector.
... Moreover, it remains challenge to detect molecules with weak or no affinity to noble metal nanomaterials, such as some organic molecules and volatile organic compounds, hindering the widespread application of SERS technology [14][15][16]. In order to capture analyte molecules to the "hot spot" region of plasmonic nanostructures, many strategies have proposed, including utilizing chemical interactions to confine molecules to the SERS-active region [17,18], physical analyte concentrating method and introducing secondary sorbent materials [14,19,20]. Among them, integrating plasmonic nanoparticles with porous sorbent materials to construct hybrid platform is a well-studied and effective approach. ...
The presence of hazardous substance in river water poses a severe threat to both the ecological environment and human health. Therefore, designing and preparing highly sensitive SERS platform for monitoring the hazardous substance is of great significance. Herein, the Ag nanoflowers (NFs)@ZIF-8 core-shell nanocomposite was synthesized and utilized as SERS substrate. Using crystal violet as model molecule, this substrate achieved a detection limit of 10−10 M and superior uniformity with relative standard deviation of less than 15%, and the enhancement factor (EF) for crystal violet was calculated about 4.37×106. Besides, the SERS signal only showed a slight attenuation after 3 months storage. As a demonstration, the SERS platform achieved sensitive detection of two hazardous substances thiram and methylene blue with detection limits of 10−7 M and 10−8 M. And the recoveries of SERS detection for thiram and methylene blue in river water were between 70%-182%. The electromagnetic enhancement provided by Ag NFs and the enriching effect of ZIF-8 shell collectively contribute to the excellent performance of the Ag NFs@ZIF-8 SERS platform. This work delivers a promising strategy for constructing hybrid SERS platform for highly sensitive detection.
... [108,109] By taking benefit of this argument, inorganic ion detection can be accomplished indirectly by monitoring the SERS spectral changes of a molecular probe (Raman reporter) during its interface with a particular inorganic ion. [110,111] With the fast development of surface modification technology, the sensing mechanism is no longer limited to the identification effect between an inorganic ion and Raman reporter; other effects of an inorganic ion with a separate recognition unit or a SERS-active substrate can also be used for the design of a SERS-based sensor for inorganic ion detection. [109] SERS [112] is a spectral-rich approach for probing vibrational modes of individual bonds. ...
Heavy metals ions as metallic pollutants are a growing global issue due to their adverse effects on the aquatic ecosystem, and human health. Unfortunately, conventional detection methods such as atomic absorption spectrometry exhibit a relatively low limit of detection and hold numerous disadvantages , and therefore, the development of an efficient method for in-situ and real-time detection of heavy metal residues is of great importance. The aptamer-based sensors offer distinct advantages over antibodies and emerged as a robust sensing platform against various heavy metals due to their high sensitivity, ease of production, simple operations, excellent specificity, better stability, low immunogenicity, and cost-effectiveness. The nucleic acid aptamers in conjugation with nanomaterials can bind to the metal ions with good specificity/selectivity and can be used for on-site monitoring of metal ion residues. This review aimed to provide background information about nanomaterials-based aptasensor, recent advancements in aptamer conjunction on nanoma-terials surface, the role of nanomaterials in improving signal transduction, recent progress of nano-materials-based aptasening procedures (from 2010 to 2022), and future perspectives toward the practical applications of nanomaterials-based aptasensors against hazardous metal ions for food safety and environmental monitoring.
... The relative peak area percentages of α-FeOOH, α-Fe 2 O 3 , γ-FeOOH and Fe 3 O 4 at different HPs were used to represent their relative content ( Figure 12) [32]. The relative content of α-Fe 2 O 3 varies greatly from 0.1 to 5 MPa but remained unchanged at higher HP. ...
The effect of hydrostatic pressure (HP) on the corrosion behaviour of X80 steel is investigated to assist the development of deep-sea oil and gas resources. The results show that the corrosion current increases as HP increases whereas the charge transfer resistance follows the opposite trend. The corrosion products are composed of γ-FeOOH, α-Fe2O3 and α-FeOOH at atmospheric pressure, while Fe3O4 is only formed at a high HP. Additionally, the inner layer of the corrosion products contains more Fe3O4 compared with the surface corrosion layer. HP accelerates the corrosion rate of X80 steel due to its effect on the chemical and physical properties of the corrosion products, including the promoted reduction of γ-FeOOH and the formation of wider and deeper cracks on the corrosion product layer.
... One strategy to impart an atomic ion with a SERS signal consists in having it interact with a Raman-active chelator which will see its own SERS spectrum modified upon recognition of the analyte 31 . Zn 2+ , Hg 2+ , Co 2+ , Cu 2+ and Cl − have been quantified in this way using conventional metal cation and anion ligands [32][33][34][35] . However, these studies exploited schemes that were not suitable for large measurement campaigns because of the high manufacturing cost of the SERS-active plasmonic nanomaterials or the time-consuming procedures for sample preparation. ...
Surface Enhanced Raman Scattering (SERS) has been widely praised for its extreme sensitivity but has not so far been put to use in routine analytical applications, with the accessible scale of measurements a limiting factor. We report here on a frugal implementation of SERS dedicated to the quantitative detection of Zn²⁺ in water, Zn being an element that can serve as an indicator of contamination by heavy metals in aquatic bodies. The method consists in randomly aggregating simple silver colloids in the analyte solution in the presence of a complexometric indicator of Zn²⁺, recording the SERS spectrum with a portable Raman spectrometer and analysing the data using multivariate calibration models. The frugality of the sensing procedure enables us to acquire a dataset much larger than conventionally done in the field of SERS, which in turn allows for an in-depth statistical analysis of the analytical performances that matter to end-users. In pure water, the proposed sensor is sensitive and accurate in the 160–2230 nM range, with a trueness of 96% and a precision of 4%. Although its limit of detection is one order of magnitude higher than those of golden standard techniques for quantifying metals, its sensitivity range matches Zn levels that are relevant to the health of aquatic bodies. Moreover, its frugality positions it as an interesting alternative to monitor water quality. Critically, the combination of the simple procedure for sample preparation, abundant SERS material and affordable portable instrument paves the way for a realistic deployment to the water site, with each Zn reading three to five times cheaper than through conventional techniques. It could therefore complement current monitoring methods in a bid to solve the pressing needs for large scale water quality data.
... First of all, specific chemical interactions between analyte molecules and nanoantennas can be used to guide analyte towards EM "hot spots". Within this approach, one utilizes either chemical modification of the analyte molecules (to enlarge their intrinsically weak Raman cross-section) [12] or intermediate molecules with good affinity to SERS-active nanostructure (to capture selectively the analyte via specific chemical bonds) [13,14]. However, such chemistry-based enrichment strategies are analyte-specific and cannot be considered as a universal tool. ...
We report an easy-to-implement device for surface-enhanced Raman scattering (SERS)-based detection of various analytes dissolved in water droplets at trace concentrations. The device combines an analyte-enrichment system and SERS-active sensor site, both produced via inexpensive and high-performance direct femtosecond (fs)-laser printing. Fabricated on a surface of water-repellent polytetrafluoroethylene substrate as an arrangement of micropillars, the analyte-enrichment system supports evaporating water droplet in the Cassie–Baxter superhydrophobic state, thus ensuring delivery of the dissolved analyte molecules towards the hydrophilic SERS-active site. The efficient pre-concentration of the analyte onto the sensor site based on densely arranged spiky plasmonic nanotextures results in its subsequent label-free identification by means of SERS spectroscopy. Using the proposed device, we demonstrate reliable SERS-based fingerprinting of various analytes, including common organic dyes and medical drugs at ppb concentrations. The proposed device is believed to find applications in various areas, including label-free environmental monitoring, medical diagnostics, and forensics.
... First of all, specific chemical interactions between analyte molecules and nanoantennas can be used to guide analyte towards EM "hot spots". Within this approach, one utilizes either chemical modification of the analyte molecules (to enlarge their intrinsically weak Raman cross-section) [12] or intermediate molecules with good affinity to SERS-active nanostructure (to capture selectively the analyte via specific chemical bonds) [13,14]. However, such chemistry-based enrichment strategies are analyte-specific and cannot be considered as a universal tool. ...
We report an easy-to-implement device for SERS-based detection of various analytes dissolved in water droplets at trace concentrations. The device combines an analyte-enrichment system and SERS-active sensor site, both produced via inexpensive and high-performance direct fs-laser printing. Fabricated on a surface of water-repellent polytetrafluoroethylene substrate as an arrangement of micropillars, the analyte-enrichment system supports evaporating water droplet in the Cassie-Baxter superhydrophobic state, thus ensuring delivery of the dissolved analyte molecules towards the hydrophilic SERS-active site. The efficient pre-concentration of the analyte onto the sensor site based on densely-arranged spiky plasmonic nanotextures results in its subsequent label-free identification by means of SERS spectroscopy. Using the proposed device, we demonstrate reliable SERS-based fingerprinting of various analytes, including common organic dyes and medical drugs at ppb concentrations. The proposed device is believed to find applications in various areas, including label-free environmental monitoring, medical diagnostics, and forensics.
... SERS spectral variations with temperature during PTT process: (A) Time-dependent SERS spectra recorded from a single cell during PPT-induced cell death with annotation of different vibrational peaks together with the corresponding dark-field images [42]; (B) Temperature-dependent SERS spectra of ICG conjugated gold nanostars SERS tags. The linear plots of the intensity ratio of the bands in the SERS spectra are baseline corrected and normalized to the same scale of 667 cm −1 and 729 cm −1 versus the temperature and temperature change [43].SERS is a powerful spectroscopic tool for the detection of ions and SERS-based sensors have been developed accordingly[44][45][46][47]. Zinc is an essential trace element and plays important biological and physiological roles in human physiology and the Zn (II) ion concentration can be used as a biomarker for early diagnosis of some diseases. ...
Surface-enhanced Raman scattering (SERS) has become a mature spectroscopic technique with the fast development in the past four decades, and its detection applications in the fields of chemistry, materials science, biochemistry and life sciences are rapidly expanding. In particular, advances in the design and construction of SERS-based biosensors have delivered tremendous development in the biological and biomedical sensing applications. Electromagnetic enhancement contributes dominantly to SERS enhancement, and the hotspot structures are crucial to sensitive and reproducible detection performance. SERS-based biosensors can be produced by direct and indirect techniques according to the sensing needs. In this mini-review, the enhancing mechanism and SERS structures are briefly described and the various common fabrication techniques are discussed. Recent state-of-the-art applications of SERS-based biosensors such as detection of ex vivo biofluids and biomolecules such as proteins, DNAs and microRNAs, as well as monitoring of cellular properties including pH, temperature and ion concentrations, are reviewed.
... A strategy is to monitor the SERS vibrational pattern changes that undergoes a spe- cially designed ligand in response to the ion presence. Ion sensitive SERS nanosensors have been reported in many cases as H + (pH) sensing based on the ioniza- tion/deionization of the carboxylic group of 4- mercaptobenzoic acid (MBA) [42], halide sensing as in the case of Cl - [43] upon interaction with a Cl-sensitive molecular probe that has a high SERS cross-section, Hg 2+ [44] based on its coordination with human te- lomeric G-quadruplex DNA, Cd 2+ [45] using Raman- encoded NPs, alkaline and alkaline earth metal cations by electrostatic interactions [46]. ...
... Analysis of these anions using SERS has also be reported. Although most of these methods are applied in environmental measurement [65][66][67], a large potential of SERS as a powerful tool has shown in the study of plant and animal stress tolerance. Moreover, Tran's group exploited a self-designed Raman spectroscopy system aimed to get high signal-to-noise ratio, which may be worth learning by researchers [66]. ...
A wide variety of biotic and abiotic stresses continually attack plants and animals, which adversely affect their growth, development, reproduction, and yield realization. To survive under stress conditions, highly sophisticated and efficient tolerance mechanisms have been evolved to adapt to stresses, which consist of the variation of effector molecules playing vital roles in physiological regulation. The development of a sensitive, facile, and rapid analytical methods for stress factors and effector molecules detection is significant for gaining deeper insight into the tolerance mechanisms. As a nondestructive analysis technique, surface-enhanced Raman spectroscopy (SERS) has unique advantages regarding its biosensing applications. It not only provides specific fingerprint spectra of the target molecules, conformation, and structure, but also has universal capacity for simultaneous detection and imaging of targets owing to the narrow width of the Raman vibrational bands. Herein, recent progress on biotic and abiotic stresses, tolerance mechanisms and effector molecules is summarized. Moreover, the development and promising future trends of SERS detection for stress-related substances combined with nanomaterials as substrates and SERS tags are discussed. This comprehensive and critical review might shed light on a new perspective for SERS applications.
... Functionalization of polystyrene (PS) beads: Surface functionalization of PS beads (Ikerlat Polymers, 500 nm) was achieved with poly (allylamine hydrochloride) (PAH, Mw = 17,500). [22] PAH was dissolved in 0.5 M NaCl (pH 5.0) with a polymer concentration of 1 mg mL À1 . Then, the positively charged PAH solution (25 mL) was added to the PS beads (12.5 mg) and stirred at room temperature for 30 min. ...
Fast and versatile optical SERS methods represent a major advance in chemical analysis of environmental samples such as water. To date, however, these ultrasensitive methods are hindered by two key drawbacks: (i) colloidal stability; and, (ii) chemical diversity, both arising from the compositional complexity of natural samples. Here, we present an engineered material that, due to its unique microporous structure, imparts colloidal stability and provides selectivity while confining a densely populated film of gold nanoparticles optimized for the generation of large electromagnetic fields. The material is tested against natural water for the ultraquantification of dichlorodiphenyl‐trichloroethane (DDT), a ubiquitous environmental pollutant.
... In the first category, the analyte usually induces a significant structural change of the probe. Alvarez-Puebla and coworkers (151) reported amino-MQAE-modified SERS microbeads that were capable of delivering a picomolar LOD of chloride. This group further detected FtsZ protein from E. coli using ZipA protein-functionalized NPs (152). ...
Owing to its extreme sensitivity and easy execution, surface-enhanced Raman spectroscopy (SERS) now finds application for a wide variety of problems requiring sensitive and targeted analyte detection. This widespread application has prompted a proliferation of different SERS-based sensors, suggesting the need for a framework to classify existing methods and guide the development of new techniques. After a brief discussion of the general SERS modalities, we classify SERS-based sensors according the origin of the signal. Three major categories emerge from this analysis: surface-affinity strategy, SERS-tag strategy, and probe-mediated strategy. For each case, we describe the mechanism of action, give selected examples, and point out general misconceptions to aid the construction of new devices.Wehope this review serves as a useful tutorial guide and helps readers to better classify and design practical and effective SERS-based sensors. Expected final online publication date for the Annual Review of Analytical Chemistry Volume 11 is June 12, 2018. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... A strategy is to monitor the SERS vibrational pattern changes that undergoes a spe-cially designed ligand in response to the ion presence. Ion sensitive SERS nanosensors have been reported in many cases as H + (pH) sensing based on the ionization/deionization of the carboxylic group of 4mercaptobenzoic acid (MBA) [42], halide sensing as in the case of Cl - [43] upon interaction with a Cl-sensitive molecular probe that has a high SERS cross-section, Hg 2+ [44] based on its coordination with human telomeric G-quadruplex DNA, Cd 2+ [45] using Ramanencoded NPs, alkaline and alkaline earth metal cations by electrostatic interactions [46]. ...
In this review, we introduce the reader the analytical technique, surface-enhanced Raman scattering motivated by the great potential we believe this technique have in biomedicine. We present the advantages and limitations of this technique relevant for bioanalysis in vitro and in vivo and how this technique goes beyond the state of the art of traditional analytical, labelling and healthcare diagnosis technologies.
... Molecular recognition probe-modified surface-enhanced Raman scattering (SERS) platforms can realize the selective detection of organic molecules, 14,15 biomolecules, 16−18 small inorganic molecules, 19 and ions. 19,20 Additionally, SERS has a strong ability to resist the interference from other substances in the sample matrix. 21 −29 On the other hand, SERS can provide the fingerprint spectrum of the pesticide analyte. ...
Dithiocarbamate (DTC) pesticides are widely used for fruits, vegetables and mature crops to control fungal diseases. Their residues in food could pose a threat to human health. Therefore surface-enhanced Raman scattering (SERS) based sensor is developed to detect DTC pesticides because SERS can provide the characteristic spectrum of pesticides and avoid the use of a molecular recognition probe in the sensor. To achieve high sensitivity, good anti-interference ability and robustness of the SERS sensor, a silver nanocube-reduced graphene oxide (AgNC-rGO) sponge is devised. In the AgNC-rGO sponge, the rGO sheets form a porous scaffold that physically holds the AgNCs, which create narrow gaps between the neighboring AgNCs, leading to the formation of “hot spots” for SERS signal amplification. When DTC pesticides coexist with aromatic pesticides in a sample matrix, the AgNC-rGO sponge can selectively detect DTC pesticides due to the preferential adsorption of DTC pesticides on the Ag surface and aromatic pesticides on the rGO surface, respectively, which can effectively eliminate the interference of the SERS signals of aromatic pesticides, and facilitate the qualitative and quantitative analysis of DTC pesticides. The AgNC-rGO sponge shows a great potential as a SERS substrate for selective detection of DTC pesticides.
... Some other studies used core-satellite nanostructures for enhancing Raman reporter molecules that were placed at the hot spots but not for determining the concentrations of molecules 30,31,33,34,[48][49][50] . Many of the core-satellite nanostructures used for SERS detection of molecules were based on detection schemes that utilized either DNA aptamers and Raman reporter molecules 28,29,36,37,[51][52][53] or certain kinds of chemical interactions [54][55][56] , but the availability of suitable aptamers and chemical reactions could limit the use of the nanostructures for the detection of other molecules. Some of the SERS substrates formed with core-satellite nanostructures did not have many SERS hot spots in the z-direction, and the density of the nanostructures in the xy-plane was not maximized 14,27,57 . ...
We demonstrate three-dimensional surface-enhanced Raman spectroscopy (SERS) substrates formed by accumulating plasmonic nanostructures that are synthesized using a DNA-assisted assembly method. We densely immobilize Au nanoparticles (AuNPs) on polymer beads to form core-satellite nanostructures for detecting molecules by SERS. The experimental parameters affecting the AuNP immobilization, including salt concentration and the number ratio of the AuNPs to the polymer beads, are tested to achieve a high density of the immobilized AuNPs. To create electromagnetic hot spots for sensitive SERS sensing, we add a Ag shell to the AuNPs to reduce the interparticle distance further, and we carefully adjust the thickness of the shell to optimize the SERS effects. In addition, to obtain sensitive and reproducible SERS results, instead of using the core-satellite nanostructures dispersed in solution directly, we prepare SERS substrates consisting of closely packed nanostructures by drying nanostructure-containing droplets on hydrophobic surfaces. The densely distributed small and well-controlled nanogaps on the accumulated nanostructures function as three-dimensional SERS hot spots. Our results show that the SERS spectra obtained using the substrates are much stronger and more reproducible than that obtained using the nanostructures dispersed in solution. Sensitive detection of melamine and sodium thiocyanate (NaSCN) are achieved using the SERS substrates.
... The principal goals of constructing these composite materials include the formation of stable hot spots, the increase in size of the plasmonic platform up to the micrometer scale in order to make easier their integration into sensing devices; and the development of analyte-trapping capability to concentrate the target molecule. Materials selected as support for plasmonic particles include inorganic oxides, mainly silica [9] or iron oxides [10], and polymers such as polystyrene [11]. As a matrix, the preferred materials are usually polymers including agarose [12,13], polyacrylic acid [14], polyallylamine [14], polyurethane [15], poly(N-isopropyl acrylamide-acrylic acid-2-hydroxyethyl acrylate) [16] or polystyrene [15], using techniques such as microfluidic flow focusing [12], or suspension [17] and living polymerization [18]. ...
... Our group has been largely involved in the investigations aimed at the rational design of novel SERS substrates, with long-term stability and large enhancement efficiency [15][16][17][18]. Among others, we have designed and produced discrete particles consisting of an inorganic micrometric or submicrometric core homogenously coated with plasmonic nanoparticles which possesses several important positive features of simple metal colloids (simple fabrication methods and normally available in all spectroscopy laboratories; facile surface-functionalization, high SERS activity in their aggregated forms etc) while introducing dramatic improvements in terms of stability, signal reproducibility and experimental flexibility [19][20][21]. These hybrid materials act as robust microscopic carriers of large ensembles of interparticle hotspots concentrated in their external shell. ...
Rapid advances in nanofabrication techniques of reproducibly manufacturing plasmonic substrates with well-defined nanometric scale features and very large electromagnetic enhancements paved the way for the final translation of the analytical potential of surface-enhanced Raman scattering (SERS) to real applications. A vast number of different SERS substrates have been reported in the literature. Among others, discrete particles consisting of an inorganic micrometric or sub-micrometric core homogeneously coated with plasmonic nanoparticles stand out for their ease of fabrication, excellent SERS enhancing properties, long-term optical stability and remarkable experimental flexibility (manipulation, storage etc). In this article, we performed a systematic experimental study of the correlation between the size of quasi-spherical gold and silver nanoparticle and the final optical property of their corresponding assembles onto micrometric polystyrene (PS) beads. The size and composition of nanoparticles play a key role in tuning the SERS efficiency of the hybrid material at a given excitation wavelength. This study provides valuable information for the selection and optimization of the appropriate PS@NPs substrates for the desired applications.
The integration of Au and Ag into nanoalloys has emerged as an intriguing strategy to further tailor and boost the plasmonic properties of optical substrates. Conventional approaches for fabricating these materials via chemical reductions of metal salts in solution suffer from some limitations, such as the possibility of retaining the original morphology of the monometallic substrate. Spontaneous nanowelding at room temperature has emerged as an alternative route to tailor Au/Ag nanomaterials. Herein, we perform a thorough study on the cold-welding process of silver nanoparticles onto gold substrates to gain a better understanding of the role of different variables in enabling the formation of well-defined bimetallic structures that retain the original gold substrate morphology. To this end, we systematically varied the size of silver nanoparticles, dimensions and geometries of gold substrates, solvent polarity and structural nature of the polymeric coating. A wide range of optical and microscopy techniques have been used to provide a complementary and detailed description of the nanowelding process. We believe this extensive study will provide valuable insights into the optimal design and engineering of bimetallic plasmonic Ag/Au structures for application in nanodevices.
Circulating tumor cells (CTCs) can be the seeds of tumor metastasis and are closely linked to cancer-related death. Fast and effective detection of CTCs is important for the early diagnosis of cancer and the evaluation of micrometastasis. However, the extreme rarity and heterogeneity of CTCs in peripheral blood make sensitive detection of CTCs a big challenge. In this paper, a TiO2-based surface-enhanced Raman scattering (SERS) bioprobe is reported for the first time with outstanding ultrasensitive specificity, excellent stability of the signal, and good biocompatibility for the detection of CTCs. The TiO2 NPs were encoded with alizarin red (AR) and functionalized with reduced bovine serum protein (rBSA) and folic acid (FA). The limit of detection (LOD) for 4-mercaptobenzoic acid (4-MBA) and AR molecules adsorbed on the TiO2 SERS substrate is 5 × 10-7 M. The designed TiO2-based SERS bioprobe can be effectively utilized in detecting four diverse types of cancer cells in rabbit blood, which shows good sensitivity of the SERS detection technology. Finally, precise targeting of CTCs based on the SERS bioprobe with the function of fluorescence imaging is also confirmed by the fluorescence colouration test. This work offers a novel strategy for CTC detection and the development of non-noble metal semiconductor-based SERS platforms for tumor diagnosis.
As a novel tagging material, surface enhanced Raman scattering (SERS) nanotags have attracted extensive attention and have been widely used in biological imaging or bio-analysis. Among them, the main reason is that the SERS effect can produce 10⁶–10¹⁴ times of signal enhancement, which has even reached the required sensitivity of single molecule detection; second, the Raman scattering process is very short, which effectively avoids the phenomena of photobleaching, energy transfer, and signal quenching in the excited state, so the SERS nanotags have good optical stability; third, the Raman shift is not affected by the excited laser wavelength, so the use of near-infrared light source can effectively avoid the interference of spontaneous fluorescence of biological endogenous substances, which is conducive to the nondestructive and high contrast imaging research of biological samples; finally, the band of SERS spectrum is sharp (the bandwidth is generally less than 2 nm), theoretically, 10–100 kinds of characteristic Raman bands can be distinguished at the same time, so it is very suitable for multichannel detection and multicolor imaging. In addition, when noble metal nanoparticles (NPs) such as gold or silver NPs enter cells, they can enhance the intrinsic Raman signals of biomacromolecules in cells. Therefore SERS nanotags can not only be used for label imaging, but also for label-free detection of endogenous substances in cells. Compared with fluorescent labeling technology, SERS imaging can directly reflect the distribution of various molecules in cells, which provides a broader application prospect for SERS nanotags in biomedical field. This chapter mainly introduces the design and synthesis of SERS nanotags from the perspectives of material composition, spatial configuration, signal output, and function integration. Of course, it is easy to elaborate, and also briefly introduces their applications. In this chapter, we focus on a class of SERS nanotags located in the silent region of the spectrum. They have obvious advantages in complex biological systems, which is a remarkable progress in the field of SERS nanotags in recent years.
Herein, we present a method to obtain particles composed of a segregated alloy of silver coated with gold. These particles are achieved through the controlled Ostwald ripening of small gold nanoparticles (NPs) onto the surfaces of larger silver particles. The prepared segregated nanoalloyed colloids benefit from the advantages of gold and silver with none of their drawbacks. These platforms provide optical efficiencies which are superior to those of silver with the chemical resistance and biocompatibility of gold.
Conventional substrates for surface‐enhanced Raman spectroscopy (SERS) present some limitations. Plasmonic colloids are unstable in complex real samples and do not present hot spots. Conversely, engineered thin films are expensive and allow the study of a limited volume of sample. Hybrid platforms based in the adsorption of colloids on optically inert nano or microscaled materials put together the advantages of both classical methods for analysis. As the particles are densely packed, their assemblies present the same optical activities as the thin films, and because the inert template is usually colloidally stable, the assemblies behave as colloidal particles. This review focus on the different strategies proposed, up to date, to produce homogeneous nanoparticles (NPs) assemblies supported on colloidal templates for different applications.
Inorganic ions determination has been receiving increased attention due to its strong environmental and biomedical impact. Surface‐enhanced Raman scattering (SERS) spectroscopy has been considered to be a promising alternative method for inorganic ions analysis. Initially, the detection of inorganic ions is indirectly achieved by monitoring the SERS spectral alteration of a molecular probe (Raman reporter) upon its interaction with a specific inorganic ion. Recent years, based on incorporation of a functional molecule, an aptamer, and a nanocatalyst into a sensing system, numerous new methods have been proposed for the construction of sensitive SERS‐based inorganic ion sensors. Herein, this review is devoted to the recent advances in SERS‐based sensors for the determination of inorganic ions and specially focuses on the sensing mechanism and sensing methods. In addition, the current challenges and future research opportunities in utilizing SERS‐based methods for inorganic ions sensing are briefly featured. This review is devoted to the recent advances in SERS‐based sensors for the determination of inorganic ions and specially focuses on the sensing mechanism and sensing methods. In addition, the current challenges and future research opportunities in utilizing SERS‐based methods for inorganic ions sensing are briefly featured.
The discovery in 1974 of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is considered a landmark in the history of spectroscopic and analytical techniques. Much experimental and theoretical effort has been spent toward understanding the surface enhanced Raman scattering (SERS) effect, and demonstrating its potential toward various types of ultrasensitive sensing applications in a wide variety of fields. Forty five years later, SERS has blossomed as an extremely rich area of research and technology, but additional efforts are still needed before it can be routinely used as a commercial product. In this Review, prominent authors from all over the world joined efforts to summarize the current state-of-the-art in understanding and using SERS, as well as to propose what can be expected in the near future, in terms of research, applications, and technological development.
Surface-enhanced Raman scattering (SERS) is a molecule-specific spectroscopic technique with diverse applications in (bio)chemistry, clinical diagnosis and toxin sensing. While hotspot engineering has expedited SERS development, it is still challenging to detect molecules with no specific affinity to plasmonic surfaces. With the aim of improving detection performances, we venture beyond hotspot engineering in this tutorial review and focus on emerging material design strategies to capture and confine analytes near SERS-active surfaces as well as various promising hybrid SERS platforms. We outline five major approaches to enhance SERS performance: (1) enlarging Raman scattering cross-sections of non-resonant molecules via chemical coupling reactions; (2) targeted chemical capturing of analytes through surface-grafted agents to localize them on plasmonic surfaces; (3) physically confining liquid analytes on non-wetting SERS-active surfaces and (4) confining gaseous analytes using porous materials over SERS hotspots; (5) synergizing conventional metal-based SERS platforms with functional materials such as graphene, semiconducting materials, and piezoelectric polymers. These approaches can be integrated with engineered hotspots as a multifaceted strategy to further boost SERS sensitivities that are unachievable using hotspot engineering alone. Finally, we highlight current challenges in this research area and suggest new research directions towards efficient SERS designs critical for real-world applications.
Biofluid analysis by surface-enhanced Raman scattering (SERS) is usually hindered by nonspecific interferences. It is challenging to drive targeted molecules towards sensitive areas with specific capture and quantitative recognition in complex biofluids. Herein, a highly specific and quantitative SERS analyzer for small molecule dopamine (DA) in serum is demonstrated on a portable Raman device by virtue of a transducer of mercaptophenylboronic acid (MPBA) and a site-directed decoration of plasmonic Ag dendrites on superhydrophobic surface. Theoretical simulations of molecular vibrations and charge distributions demonstrate the predomination of Raman surface selection rules in molecular reorientation upon the binding of DA. This recognition event is translated into ratiometric changes in spectral profile which evidences excellent capability on SERS quantitation. The rules can well distinguish DA from its common interferents including fructose, glucose, sucrose and ascorbic acid which all generate weak but completely opposite spectral changes. Moreover, benefitting from wettability difference, the target DA in diluted serum can be specifically enriched on transducer-capped Ag surface, and the adsorption of other interferences is resisted by superhydrophobic features. It paves the new way for labelling a single SERS tag to simultaneously realize identification and quantification of small molecules in complex biological media.
Driven by the growing demand for healthcare and point-of-care test applications, next-generation diagnostic tools of diseases require sensing platforms that enable rapid, quantitative readout of analytes with excellent specificity and sensitivity. Although label-free detection permits simplicity, flexibility and high specificity, it has usually poor throughput, limited sensitivity and requires professional instrumentation. Label-based detection using optical labels overcomes many of these drawbacks and has been demonstrated to be an effective alternative for improved sensing performances. The current research focus has been directed towards innovating high-performance optical labels for ultrasensitive biosensing and disease diagnostics in place of conventional optical labels. Surface-enhanced Raman scattering (SERS) labels have proven to be excellent labels for biosensing because of their merits in many aspects, such as flexibility, less interference from biological matrices, high photostability, easy multiplex encoding, etc. These fantastic features make SERS labels particularly suitable for ultrasensitive detection of disease biomarkers in body fluids and targeted imaging of diseased cells and tissues, respectively. In this Review, we introduce the design and deployment of SERS labels for ultrasensitive detection, and summarize recent research progress in the development of SERS label-based sensing platforms and their applications in disease biomarker detection, targeted cellular imaging and spectroscopic detection of tumor lesions. First, we will discuss the design principles and comprehensive considerations of SERS labels, and the on-demand integration of functionalities. Next, we introduce the design of SERS sensing platforms on basis of SERS labels for ultrasensitive and selective detection of diverse pathology-related biomarkers, including proteins, nucleic acids, small molecules and inorganic ions. In addition, through the rational incorporation of targeting ligands on SERS labels, novel SERS probes are created for targeting near-infrared (NIR) imaging and spectroscopic detection of tumor, taking advantages of large NIR light penetration depth, high brightness, stability, etc. Our and other research efforts have demonstrated the promising potential of SERS label-based sensing platforms for detection of diverse circulating biomarkers for non-invasive disease diagnostics and deep-tissue spectroscopic detection of tumor. It is believed that this review will motivate further exploration of clinical applications of SERS labels in near future.
The detection of hepatocellular carcinoma (HCC) circulating tumor cells (CTCs) from a blood sample can be a very powerful noninvasive approach for the early detection and therapy of liver cancer. However, the extremely rare cells in blood containing billions of other cells make the capture and identification of CTCs with sufficient sensitivity and specificity a real challenge. Here, a magnetically assisted surface-enhanced Raman scattering (SERS) biosensor for HCC CTCs detection is reported for the first time. The biosensor consists of two basic elements including an anti-ASGPR antibody-Fe3O4@Ag MNPs and an anti-GPC3 antibody-Au@Ag@DTNB NRs. According to the dual-selectivity of the anti-ASGPR and anti-GPC3 antibodies and the dual-enhancement SERS signal of the MNPs silver shell and the Au@Ag NRs SERS tags, a limit of detection of 1 cell/mL for HCC CTC in human peripheral blood samples with a linear relationship from 1 to 100 cells/ mL can be obtained. The system showed good performance in real serum which suggested they would be a promising tool for HCC clinical diagnosis.
This feature article focuses on the use of colloid chemistry to engineer metallic nanostructures toward application in surface enhanced Raman scattering (SERS) sensing, in particular for 'real-life' applications, where the analyte may be present in complex mixtures. We present a broad summary of the field, including recent advances that have been developed during the past 10 years. Real-life applications require a rational design and we aimed at identifying the key elements involved in it. The discussion is centered around colloidal plasmonic nanoparticles and therefore we start from the library of morphologies that have been reported in the literature. To complete the picture, colloidal self-assembly, surface chemistry and the combination with materials science techniques are highlighted. Considering the progress in the field, SERS may ultimately realize its full potential as an ultrasensitive tool for routine analytical applications.
In this work, we propose a new sensitive, selective and portable surface enhanced Raman spectroscopy (SERS) methodology for the rapid on site detection of Pb(II) pollution in water. The new method utilises aminobenzo-18-crown-6 (AB18C6) as a selective recognition molecule to form a spontaneous complex with Pb(II) ions. The formed AB18C6-Pb(II) complex was rapidly immobilised onto a nanostructured gold substrate via Au-N bond formation and reproducibly screened by SERS using a handheld Raman device. For the SERS measurements, a substrate was fabricated by electrochemical deposition of gold nanostructures onto a flat gold disc, creating multiple hotspots for ultrasensitive SERS measurements. The limit of quantification (LOQ) for Pb(II) ions by the SERS method was 2.20. pM. The limit of detection (LOD) was 0.69. pM which is five orders of magnitude lower than the maximum Pb(II) level of 72. nM allowed by the US Environmental Protection Agency. The high sensitivity of the SERS substrate is attributed to the coupling between the Surface Plasmon Polariton (SPP) of its gold surface, the localised Surface Plasmon Resonance (SPR) of the gold nanostructures and the Raman radiation from the immobilised AB18C6-Pb(II) complex. The new SERS detection method was successfully applied for the selective and rapid screening of Pb(II) ion contamination in water proving its practical application for environmental analysis.
Changes in protein expression levels and protein structure may indicate genomic mutations and may be relate to some diseases. Therefore, the precise quantification and characterization of proteins can be used for the disease diagnosis. Compared with several other alternative methods, surface-enhanced Raman scattering (SERS) spectroscopy is regarded as an excellent choice for the quantification and structural characterization of proteins. Herein, we review the main advance of using plasmonic nanostructures as SERS sensing platform for this purpose. Three design approaches, including direct SERS, indirect SERS, and SERS-encoded nanoparticles are discussed in the direction of developing new precise approaches of quantification and characterization of proteins. While this review is focused on proteins, in order to highlight concepts of SERS-based sensors also detection of other biomolecules will be discussed.
A highly sensitive and recyclable surface-enhanced Raman scattering (SERS) chip sensor is designed for the determination of silver ions. It is based on the specific reversible binding between silver ions and glucose oxidase (GOD). The sensing chip is made by layer-by-layer assembling GOD on a metal nanoparticle-assembled, SERS-active chip with a positive charged polyelectrolyte as a linker. Iso-alloxazine, a chromophore in flavin adenine dinucleotide (FAD) in GOD, coordinates with silver ions, which causes significant variation in SERS spectra of GOD. The reaction shows high sensitivity and selectivity for silver ions with the detection limit of 1.0×10⁻¹⁰ M. Most significantly, the bonded Ag(Ｉ) in GOD can be reduced to Ag(0) by sodium borohydride and the GOD structure can be recovered then. Thus, the chip sensor is recyclable. Merits of using GOD as a novel SERS probe toward Ag⁺ are embodied in not only a simplified sensor structure based on its dual role of Ag⁺ accepter and SERS signal reporter, but also a nontoxic label to biological systems, indicating that it is promising for tracing Ag⁺in vivo.
Errors in intravenous (IV) drug therapies can cause human harm and even death. There are limited label-free methods that can sensitively monitor the identity and quantity of the drug being administered. Normal Raman spectroscopy (NRS) provides a modestly sensitive, label-free and completely non-invasive means of IV drug sensing. In the case that the analyte cannot be detected within its clinical range with Raman, a label-free surface-enhanced Raman spectroscopy (SERS) approach can be implemented to detect the analyte of interest. In this work, we demonstrate two individual cases where we use NRS and electrochemical SERS (EC-SERS) to detect IV therapy analytes within their clinically relevant ranges. We implement NRS to detect gentamicin, a commonly IV-administered antibiotic and EC-SERS to detect dobutamine, a drug commonly administered after heart surgery. In particular, dobutamine detection with EC-SERS was found to have a limit of detection 4 orders of magnitude below its clinical range, highlighting the excellent sensitivity of SERS. We also demonstrate the use of handheld Raman instrumentation for NRS and EC-SERS, showing that Raman is a highly sensitive technique that is readily applicable in a clinical setting.
Using the polyoxometalate (PW) as a photoreduction agent, the uniform PW/reduced graphene oxide (RGO)/Ag film was fabricated via electrostatic self-assembly followed by UV reduction. Importantly, the film can be used as a surface enhanced Raman scattering probe for the selective detection of trace formaldehyde. Compared with those of the PW/RGO film and the PW/Ag film, the PW/RGO/Ag film displays the higher sensitivity, and the detection limit for formaldehyde can reach about 10⁻⁸ molL⁻¹.
In this work, free-standing nanowires with high transparency are fabricated from Polyimide (PI), adopting a lithography-free and micromachining-compatible process, which involves only PI spin-coating and Ar-plasma bombardment. By sputtering a thin layer of noble metal on the nanowires, surface-enhanced Raman scattering (SERS) devices can be obtained. Since the fabrication process is independent of substrate materials, nanowires are able to be generated on glass substrates, thus transparent SERS devices are achieved. In the devices, penetration of laser from the back side to detect molecules on the top surfaces is allowed. With such devices, a new route for practical detection of various analytes is opened, consequently, application fields of the SERS devices can be broadened.
As one of the most toxic heavy metals, hexavalent chromium (Cr(VI)) has long been a concern due to its threats to human health and the environment. In this work, we develop a sensitive surface-enhanced Raman scattering (SERS) sensor for highly specific detection of Cr(VI) using hollow sea urchin-like TiO2@Ag nanoparticles (NPs). The TiO2@Ag NPs are functionalized with glutathione (GSH) and used as substrates with 2-mercaptopyridine (2-MPy) as a Raman reporter for a recyclable SERS-active sensor, enabling ultrasensitive detection of Cr(VI). Excellent SERS signals of 2-MPy reporters are detected when GSH complexation with Cr(VI) causes aggregation of the TiO2@Ag NPs. The developed sensor exhibits good linearity in the range from 10 nM to 2 μM for Cr(VI) with a detection limit of ca. 1.45 nM. It features excellent selectivity to Cr(VI) over other interfering metal ions, and good application for quantitative analysis of Cr(VI) in water samples. Moreover, the proposed SERS sensor can be fully regenerated when exposed to UV light as a result of the self-cleaning ability of the substrates. In contrast to the traditional SERS detection, the present work shed new light on the design and synthesis of hierarchically self-assembled 3D substrate for SERS, catalysis and biosensor development.
Silver nanoparticles (AgNPs) were deposited onto the monodispersed carboxylic polystyrene (CPS) spheres by an improved in situ reduction method. The size and coverage density of the AgNPs on the surface of CPS spheres could be easily tailored by tuning the concentrations of carboxylic functional groups and silver precursor. The morphologies and structures of the resulting CPS/Ag hybrid particles were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-Vis-NIR spectrometer and X-ray photoelectron spectroscopy (XPS), etc. The surface enhanced Raman scattering (SERS) performances of the resulting uniform CPS/Ag hybrid particles were investigated using 4-aminobenzenethiol (4-ABT) as the probe molecule. The optimized CPS/Ag hybrid particles show high enhancement factor (EF) of 2.71×107, low limit of detection (LOD) of 10−10 m and good reproducibility with relative standard deviation (RSD) of 9.64 %. The good SERS improvement properties demonstrate these hybrid particles could be employed as simple and effective substrates in the SERS spectroscopy.
This study proposes a facile method for synthesis of Au-coated magnetic nanoparticles (AuMNPs) core/shell nanocomposites with nanoscale rough surfaces. MnFe2O4 nanoparticles (NPs) were first modified with a uniform polyethyleneimine layer (2 nm) through self-assembly under sonication. The negatively charged Au seeds were then adsorbed on the surface of the MnFe2O4 NPs through electrostatic interaction for Au shell formation. Our newly developed sonochemically assisted hydroxylamine seeding growth method was used to grow the adsorbed gold seeds into large Au nanoparticles (AuNPs) to form a nanoscale rough Au shell. Au-coated magnetic nanoparticles (AuMNPs) were obtained from the intermediate product (Au seeds decorated magnetic core) under sonication within 5 min. The AuMNPs were highly uniform in size and shape and exhibited satisfactory surface-enhanced Raman scattering (SERS) activity and strong magnetic responsivity. PATP was used as a probe molecule to evaluate the SERS performance of the synthesized AuMNPs with a detection limit of 10(-9) M. The synthesized AuMNPs were conjugated with Staphylococcus aureus (S. aureus) antibody for bacteria capture and separation. The synthesized plasmonic AuNR-DTNB NPs, whose LSPR wavelength was adjusted to the given laser excitation wavelength (785 nm), were conjugated with S. aureus antibody to form a SERS tag for specific recognition and report of the target bacteria. S. aureus was indirectly detected through SERS based on sandwich-structured immunoassay, with a detection limit of 10 cells/mL. Moreover, the SERS intensity at Raman peak of 1331 cm(-1) exhibited a linear relationship to the logarithm of bacteria concentrations ranging from 10 cells/mL to 10(5) cells/mL.
An Ag@MSiO2@Ag three core-shell architecture was synthesized by a facial hydrothermal method. The features of the sample were characterized by SEM, TEM, and AFM images, EDS analyses and absorption spectra. This novel nanostructure exhibited excellent SERS properties due to the formation of hot spots around the inner and outer Ag NPs, which was identified by theoretical calculations. A detection limit of the analyte molecule was obtained as low as 10-11 M by using this SERS nanostructure. Moreover, the homogeneity of SERS signals from the three core-shell nanostructure was exploited by Raman mapping. Our studies show that the unique Ag@MSiO2@Ag three core-shell nanostructure has significant potential to realize SERS substrate with both sensitivity and stability, which are important in SERS-based immunoassay.
An indicator-mediated surface-enhanced Raman scattering (SERS) sensor platform with highly uniform SERS sensitivity was fabricated by modifying the 4-Mercaptopyridine (4-MPY) molecules as indicator onto the surface of the Ag nanoparticles which were anchored onto the silicon wafer. The present SERS sensor platform realized quantitative detection of Zn2+.
The unconscious use of metallic nanoparticles (NPs) has been documented since Roman times. Gold NPs have been detected in the golden cover of metallic objects of the pre-Columbian era. By the middle of the nineteenth century, science had begun to focus on understanding the origins of these different colors. Michael Faraday, in 1857, produced the first colloidal gold suspensions by reducing an aqueous gold chloride solution with phosphorus. The relevant effects originating from the nm-size of NPs are reviewed for the case of gold and silver in this chapter. Top-down synthesis of metallic NPs starts from the bulk material and uses physical microfabrication methods such as laser ablation to obtain NPs dispersions. In a bottom-up synthesis the starting point is a chemical precursor. The chapter concludes with a discussion on the applications of gold and silver nanoparticles.
As a promising analytical technique in recent years, surface-enhanced Raman spectroscopy (SERS) has received extensive attention due to its low limit of detection, high sensitivity and high specificity. Despite its tremendous potential, SERS was not widely applied in quantitative analysis of chemical and biological samples in the past years. However, the explosive development of nanotechnology and nano-fabrication has assisted the development of SERS as a quantitative analysis tool. As the enhancement of Raman scattering strongly depends on nanoscale surface morphology of the enhancing surface and can be easily influenced by other factors in an experiment, it is still a challenge to obtain reliable results comparable to those obtained from state-of-the-art analysis methods. The fabrication of three kinds of enhancing media including traditional solid substrates, colloidal nanoparticles and plasmonic nanostructures based on nano-fabrication and their respective advantages and drawbacks for quantitative SERS detection are summerized in this review. Furthermore, how to improve the sensitivity and reliability is investigated in aspects of molecular orientation, excitation wavelength, internal standard and data analysis. Meanwhile, several successful cases of quantitative SERS detection are presented. Finally, applications and prospects of its future researches are proposed.
A magnetically assisted surface-enhanced Raman scattering (SERS) biosensor for single-cell detection of S. aureus based on aptamer recognition is reported for the first time. The biosensor consists of two basic elements including a SERS-substrate (Ag-coated magnetic nanoparticles, AgMNPs) and a novel SERS tag (AuNR-DTNB@Ag-DTNB core-shell plasmonic NPs or DTNB-labeled inside-and-outside plasmonic NPs, DioPNPs). Uniform, monodisperse, and superparamagnetic AgMNPs with favorable SERS activity and magnetic responsiveness are synthesized by using polymer polyethylenimine. AgMNPs use magnetic enrichment instead of repeated centrifugation to prevent sample sedimentation. DioPNPs are designed and synthesized as a novel SERS tag. The Raman signal of DioPNPs is 10 times stronger than that of the commonly used SERS tag AuNR-DTNB because of the double-layer DTNB and the LSPR position adjustment to match the given laser excitation wavelength. Consequently, a strong SERS enhancement is achieved. Under the optimized aptamer density and linker length, capture aptamer-modified AgMNPs can achieve favorable bacteria arrest (up to 75%). With the conventional Raman spectroscopy, the limit of detection (LOD) is 10 cells/mL for S. aureus detection, and a good linear relationship is also observed between the SERS intensity at Raman peak 1331 cm-1 and the logarithm of bacteria concentrations ranging from 101 to 105 cells/mL. Besides, with the help of the newly-developed SERS mapping technique, the single-cell detection of S. aureus is easily achieved.
We fabricated Au:Ag nanocap arrays by co-sputtering Au and Ag onto two-dimensional polystyrene (PS) colloidal sphere templates in a magnetron sputtering system for the surface-enhanced Raman scattering (SERS) substrate. In contrast to the bilayer Au/Ag, the co-sputtering Au:Ag bimetal array formed the protrusion network of Ag and Au nanoparticles, which contributed to Raman enhancement in the waxberry-like structure. The metal protrusions formed waxberry-like shell in which the PS beads were encapsulated. At the same time, the Au:Ag bimetal arrays exhibit 4-fold more enhancement in the SERS signal intensity of Rhodamine 6G at the 1649cm(-1) than Au/Ag bilayer array, which is ascribed to the plasmon coupling between the nanoparticles of Au and Ag on the sample. When the PS colloidal particle templates were etched by O2-plasma before sputtering process, the nanogaps affected the surface plasmon resonance (SPR), and the optimal gaps between adjacent Au:Ag nanocaps generated even stronger SERS enhancements. This SERS substrate of Au:Ag showed high sensitivity and reproducibility. The EF of Au:Ag nanocap array substrate onto which Rhodamine 6G (R6G) were adsorbed was evaluated as 6.72×10(10).
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Here, we report an efficient and facile method for constructing plasmonic gold nanostructures with controlled morphology on a Si wafer and its use as a surface enhanced Raman scattering (SERS) reporting system for specific detection of HClO. To achieve this substrate, the core gold nanoparticles (AuNPs, ~100 nm) with a monolayer of 4-mercaptoimidazole (MI) ligands were covalently linked to a thiol-derived Si wafer (MI-AuNPs@SH-Si). Taking advantage of the intermolecular NH•••N hydrogen bond (HB) provided by the neighboring imidazole moiety, multiple satellite AuNPs (~12 nm) decorated with both MI and a Raman reporter are assembled around the core MI-AuNPs at pH 6.0. The uniform morphology of the AuNP-based nanostructures on the Si wafer offer a high density of hot spots with good SERS performance for detecting HClO. The fast oxidation of the imidazole moieties by HClO causes HB destruction and therefore separation of the satellite AuNPs from the core AuNPs, which gives rise to SERS signal damping of the chip that is employed for HClO analysis. This simple and cost-effective method is highly selective for HClO over common interferences and several reactive oxygen spe-cies, and enabled rapid analysis at concentrations as low as 1.2 μmol L-1. The present approach is applied to analyze water and human serum samples with satisfactory results.
The surface-enhanced Raman scattering (SERS) spectra for phthalimide (PIMH) vacuum evaporated, cast onto silver island films, and from colloidal silver are clearly identified with the formation of a phthalimide-silver complex (chemisorption). The phthalimide-silver complex (PIMAg) has been obtained from the PIMH potassium salt and AgNO 3. The Raman scattering spectrum of the isolated complex is in agreement with the SERS spectra of the silver surface complex. The experiments were carried out using three laser lines at 514.5, 633, and 780 nm. The photochemical decomposition of the surface complex is detected with all laser lines. The spectral interpretation is aided using Hartree-Fock and local density functional theory (S-VWN) calculations, carried out to compute simulated SERS spectra using the molecular complex PIMAg and the PIMH. The calculated surface complex (SERS) Raman spectrum using S-VWN was found to be in good agreement with the observed spectrum. The observed Raman spectrum for the surface complex may contain the Raman-active modes allowed in the total irreducible representation of the complex symmetry point group. However, the number of observed vibrations can be reduced due to further constraints introduced by molecular and field orientations at the surface (surface selection rules or propensity rules).
Surface-enhanced Raman scattering (SERS) spectroscopy can be used for the label-free determination and quantification of relevant small biometabolites that are hard to identify by conventional immunological methods, in the absence of labelling. In this work, detection is based on monitoring the vibrational changes occurring at a specific biointerface (a monoclonal antibody, mAb) supported on silver-coated carbon nanotubes (CNT@Ag). Engineered CNT@Ag play a key role, as they offer a stable substrate to support the biointerface, with a high density of hot spots. Proof of concept is demonstrated through the analysis and quantification of the main cocaine metabolite benzoylecgonine. These results open a new avenue toward the generation of portable sensors for fast ultradetection and quantification of relevant metabolites. The use of discrete particles (CNT@Ag@mAb) rather than rough films, or other conventional SERS supports, will also enable a safe remote interrogation of highly toxic sources in environmental problems or in biological fluids.
The ability to control the size, shape, and material of a surface has reinvigorated the field of surface-enhanced Raman spectroscopy (SERS). Because excitation of the localized surface plasmon resonance of a nanostructured surface or nanoparticle lies at the heart of SERS, the ability to reliably control the surface characteristics has taken SERS from an interesting surface phenomenon to a rapidly developing analytical tool. This article first explains many fundamental features of SERS and then describes the use of nanosphere lithography for the fabrication of highly reproducible and robust SERS substrates. In particular, we review metal film over nanosphere surfaces as excellent candidates for several experiments that were once impossible with more primitive SERS substrates (e.g., metal island films). The article also describes progress in applying SERS to the detection of chemical warfare agents and several biological molecules.
This critical review gives a short overview of the widespread use of gold nanoparticles in biology. We have identified four classes of applications in which gold nanoparticles have been used so far: labelling, delivering, heating, and sensing. For each of these applications the underlying mechanisms and concepts, the specific features of the gold nanoparticles needed for this application, as well as several examples are described (142 references).
We demonstrate spatially resolved probing and imaging of pH in live cells by mobile and biocompatible nanosensors using surface-enhanced Raman scattering (SERS) of 4-mercaptobenzoic acid (pMBA) on gold nanoaggregates. Moreover, we also show that this concept of pH nanosensors can be extended to two-photon excitation by using surface-enhanced hyper-Raman scattering (SEHRS). In addition to the advantages of two-photon excitation, the SEHRS sensor enables measurements over a wide pH range without the use of multiple probes.
When light interacts with matter, it can scatter in-elastically from vibrational quantum states. During that process, photons may lose energy to, or gain it from, vibrational excitations. A change in the photon energy must produce a concomitant shift in the frequency of the scattered light (see box 1). The phenomenon, called the Raman effect, was experimentally discovered in 1928 by C. V. Raman and K. S. Krishnan in India and, independently, by Leonid Mandelstam and Grigory Landsberg in the former Soviet Union.
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Core–shell and multishell bimetallic AuAg nanoparticles have been synthesized by successive reduction of metal salts with ascorbic acid on pre-made seeds in the presence of a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The coverage of the seeds is extremely uniform, although in some cases deviations from a spherical shape are observed with the formation of nanorods or nanoprisms. The evolution of the optical properties as further metal layers are deposited is very dramatic and can be modelled using Mie theory for multilayer spheres. However, preliminary results using high-resolution STEM-XEDS elemental mapping suggest that the actual distribution of the two metals within the multilayer spheres may involve (partial) alloying of the metals.
The behaviour of a simple type of ion-selective electrode for halogens and silver has been studied. The electrode consists of a plastic body filled with carbon paste, the surface of which can be easily renewed. The paste composition is based on carbon-nujol (5:1, w/v) or carbon-paraffin wax (3:1,w/w) containing a prepared mixture of silver halide-silver sulphide (1–30%). The electrodes have low ohmic resistance and show a rapid Nernstian response (within 2–5 mV) for halide and silver ions down to 5·10-5 M chloride, 1·10-5 M bromide and 5·10-7 M iodide with the respective electrodes. Ions forming very stable complexes with halide or silver and those having strong oxidizing or reducing action interfere.
In this work, we have devised and fabricated a magnetic + optical, bifunctional colloidal system that combines flexible handling and efficient SERS analytical capabilities. This system comprises silica-coated magnetic gamma-Fe(2)O(3) (maghemite) cores, coated with a dense monolayer of gold nanorods presenting long-term optical stability and a high density of hot spots per area unit. The magnetic functionality allows for the use of a small number of capsules that can be later concentrated under a magnetic field for SERS analysis thereby increasing the detection limits.
Multilayer films of organic compounds on solid surfaces have been studied for more than 60 years because they allow fabrication
of multicomposite molecular assemblies of tailored architecture. However, both the Langmuir-Blodgett technique and chemisorption
from solution can be used only with certain classes of molecules. An alternative approach—fabrication of multilayers by consecutive
adsorption of polyanions and polycations—is far more general and has been extended to other materials such as proteins or
colloids. Because polymers are typically flexible molecules, the resulting superlattice architectures are somewhat fuzzy structures,
but the absence of crystallinity in these films is expected to be beneficial for many potential applications.
Visible and near-infrared optical excitations are common currency in the biological world, and consequently, they are routinely used to investigate microscopic phenomena taking place in living organisms and their environment. However, the wavelength of light within that energy region is above hundreds of nanometers, thus averting the possibility of direct nanometer-scale resolution. We show in this Perspective that narrow gaps between metals and sharp tips in colloidal gold particles constitute excellent “light confiners” that permit solving this problem, and in particular, they lead to record levels of surface-enhanced Raman scattering. Our results are framed in the context of a historical quest toward achieving optical focusing in the near field, and we offer a tutorial explanation of why evanescent waves such as plasmons are needed for deep-subwavelength focusing. These results provide the required elements of intuition to understand light concentration at the nanometer scale and to design optimized systems for application in ultrasensitive optical analyses and nonlinear photonics.
The surface-enhanced Raman scattering (SERS) spectra for phthalimide (PIMH) vacuum evaporated, cast onto silver island films, and from colloidal silver are clearly identified with the formation of a phthalimide−silver complex (chemisorption). The phthalimide−silver complex (PIMAg) has been obtained from the PIMH potassium salt and AgNO3. The Raman scattering spectrum of the isolated complex is in agreement with the SERS spectra of the silver surface complex. The experiments were carried out using three laser lines at 514.5, 633, and 780 nm. The photochemical decomposition of the surface complex is detected with all laser lines. The spectral interpretation is aided using Hartree−Fock and local density functional theory (S-VWN) calculations, carried out to compute simulated SERS spectra using the molecular complex PIMAg and the PIMH. The calculated surface complex (SERS) Raman spectrum using S-VWN was found to be in good agreement with the observed spectrum. The observed Raman spectrum for the surface complex may contain the Raman-active modes allowed in the total irreducible representation of the complex symmetry point group. However, the number of observed vibrations can be reduced due to further constraints introduced by molecular and field orientations at the surface (surface selection rules or propensity rules).
The "surface selection rules", i.e., the modification of the band intensities of a spectrum due to the proximity of the carrier to a surface, which are pertinent to surface-enhanced Raman are considered for the case of a molecule adsorbed on a metal sphere as a model. One concludes that there are three types of bands in the spectrum classed according to the Raman polarizability components which contribute strongly to them. Each type is characterized by its own SER excitation spectrum. It is also shown that in the spectral region between the bulk and surface plasma resonance frequencies of the sphere the electric field component parallel to the surface of the illuminated colloid particle may exceed the normal component. Calculations illustrating these points are presented as are experimental results obtained from the SER spectrum of phthalazine adsorbed on aqueous silver sol. The ratio of the intensities of a1 modes and b2 modes are shown to fit the ratio calculated on the basis of the electromagnetic model, provided one modifies the latter suitably to shift the surface plasma frequency to the red in order to take into account the effect colloid aggregation.
Several negatively charged dyes were investigated for their possible adsorption on the surface of silver and gold colloidal particles. Those dyes that were found to adsorb on the particles were then checked for surface enhancement of Raman scattering. Highly efficient surface-enhanced Raman scattering (SERS) was observed from a carbocyanine dye in both sols. Excitation-dependence studies as well as adsorption studies confirm the SERS nature of the Raman spectra obtained. The dye is probably aggregated on adsorption and is probably attached through the naphthalene side moiety to the surface. Less efficient SERS was also observed for copper phthalocyanine.
Raman spectra of noble-metal phenylthiolates and the corresponding surface-enhanced Raman (SER) spectra of the surface species on copper, silver, and gold are reported. Periodic trends were found in both the bulk Raman spectra of the phenylthiolates and the SER spectra. Intensities of the Raman spectra approach that of liquid thiophenol as the metal changes from copper to silver to gold. The SER spectra were used to obtain orientations of the thiophenol species at the noble-metal surfaces. Orientations were determined through the electric field enhancement of vibrations normal to the metal surface. The model developed in this paper allows one to determine both the azimuthal and axial angles of C2v molecules at surfaces. This is possible by performing the SERS measurement in media of differing indexes of refraction. For silver and gold we found the axial angle THETA = 85 and 76-degrees, respectively. The azimuthal angle PHI was found to vary from 32 to 0-degrees from silver to gold. The SER spectra of copper were too weak for accurate angle determinations with a surrounding media other than air. However, the SER spectrum observed on copper in air does indicate a near-perpendicular orientation.
In the last century the production and application of halides assumed an ever greater importance. In the fields of medicine, dentistry, plastics, pesticides, food, photography etc many new halogen containing compounds have come into everyday use. In an analogous manner many techniques for the detection and determination of halogen compounds and ions have been developed with scientific journals reporting ever more sensitive methods.
The 19th century saw the discovery of what is now thought of as a classical method for halide determination, namely the quenching of fluorescence. However, little analytically was done until over 100 years after its discovery, when the first halide sensors based on the quenching of fluorescence started to emerge. Due to the typical complexity of fluorescence quenching kinetics of optical halide sensors and their lack of selectivity, they have found little if any place commercially, despite their sensitivity, where other techniques such as ion-selective electrodes, x-ray fluorescence spectroscopy and colorimetry have dominated the analytical market.
In this review article the author summarizes the relevant theory and work to date for halide sensing using fluorescence quenching methods and outlines the future potential that fluorescence quenching based optical sensors have to offer in halide determination.
A series of 15 anion-selective membranes, based on quaternary ammonium compounds of different constitution and on a variety of plasticizers in different compositions of the solvent polymeric membranes, lead throughout to the selectivity sequence$$ClO_4 - > SCN - > I - > NO_3 - > Br - > Cl - > HCO_3 - \sim OAc - \sim SO_4 ^2 - \sim HPO_4 ^2 - .$$. A detailed analysis demonstrates that the selectivity pattern of such systems may be drastically modified only ifa)
a mobile, positively charged site with a sufficiently strong and specific interaction with anions is chosen and/or
b)
an electrically neutral anion-selective membrane component is used.
Herein we developed a rapid and simple method which used surface-enhanced Raman spectroscopy (SERS) coupled with antibody-modified silver dendrites to detect ovalbumin (OVA), the egg white protein, introduced into whole milk. OVA was first captured out of milk by use of antibody-modified silver dendrites and then directly measured on the silver dendrites by Raman spectroscopy. Results show that this method is capable of detecting OVA at 0.1 μg/mL in phosphate buffered saline (PBS) and 5 μg/mL in milk within 30 min based on the principal component analysis. This method has the potential for wide use in areas such as allergenic protein detection and bioterrorism agent detection in complex matrixes.
Metal ion carboxylato complexes possess ion-specific carboxylate Raman bands. Using this attribute we follow the chromatographic separation of a microliter aliquot of an initially equimolar solution of Pb(2+) and Hg(2+) using the surface-enhanced Raman spectroscopy spectra of their carboxylato complexes as unique identifiers. A glass capillary whose interior is lined with a dense layer of gold nanoparticles treated with 4-mercaptobenzoic acid simultaneously acts as a separation medium and an efficient SERS reporter of the step-by-step separation process. The observed adsorption-desorption equilibrium along the capillary is shown to conform with theory. Although Hg(2+) complexes with COO(-) much more strongly than Pb(2+), it is the Pb(2+) that survives the separation process as the sole surface species. We show that this is because so much mercury is taken out of solution during early separation steps that the surface equilibrium is ultimately driven toward adsorbed Pb(2+).
Colloidal nanoparticles are often stabilized by high surface charges. These create an electrical potential that may strongly affect the concentration of dissolved ions, which presents a formidable problem for the use of nanoparticles in ion-sensing applications. This effect is investigated systematically with organic fluorophore-gold nanoparticle hybrids, which have a chloride-sensitive fluorophore attached at varying distances from their surface. The distance-dependent fluorescence response is quantitatively assessed using fluorescence spectroscopy.
Raman signals from molecules adsorbed on a noble metal surface are enhanced by many orders of magnitude due to the plasmon resonances of the substrate. Additionally, the enhanced spectra are modified compared to the spectra of neat molecules; many vibrational frequencies are shifted, and relative intensities undergo significant changes upon attachment to the metal. With the goal of devising an effective scheme for separating the electromagnetic and chemical effects, we explore the origin of the Raman spectra modification of benzenethiol adsorbed on nanostructured gold surfaces. The spectral modifications are attributed to the frequency dependence of the electromagnetic enhancement and to the effect of chemical binding. The latter contribution can be reproduced computationally using molecule−metal cluster models. We present evidence that the effect of chemical binding is mostly due to changes in the electronic structure of the molecule rather than to the fixed orientation of molecules relative to the substrate.
A bifunctional adenosine-sensitive double-stranded DNA aptamer was used to create and control a surface-enhanced Raman spectroscopy (SERS) hot spot between a bulk Au surface and a gold nanoparticle (Au NP) attached to the aptamer via a biotin-avidin linkage. The Au NP was decorated with 4-aminobenzenethiol (4-ABT), a Raman reporter molecule. In the presence of adenosine, the target molecule, the SERS spectrum of 4-ABT increased in intensity by (concentration-dependent) factors as large as ∼4; in situ, atomic force microscopy imaging showed the mean height of the Au NP-bearing aptamer to decrease by ∼5 nm consistent with the observed SERS intensity change. Because the aptamer's geometrical change is induced by one or two molecules, while the resulting SERS intensity changes involve many reporter molecules residing in the modified hot spot, the aptamer amplifies the SERS effect.
One promising, but currently underexplored, area for the future of drinking water pathogen monitoring stems from the development of nanomaterial-enabled detection strategies. The nanoscience literature contains numerous reports of nanoenabled biosensors; however, to date only a small percentage have focused on the detection of whole cells, in general, and waterborne pathogens, in particular. There are significant opportunities for the use of nanoenabled biosensors for environmental monitoring, and this review is intended to both illustrate the state of this field and to spur additional research in this area.
Gold nanoparticles coated with a thin layer of an oxide allow molecules adsorbed on surfaces as diverse as those of platinum, yeast cells or citrus fruits to be characterized routinely in the laboratory. Surface-enhanced Raman scattering (SERS) spectroscopy is a powerful analytical technique able to detect substances down to single molecule level. Its applications are limited, however, because to realize a substantial Raman signal requires metal substrates that either have roughened surfaces or take the form of nanoparticles. An innovative approach is now demonstrated, where the substance under investigation, on a generic substrate, is covered by a layer of 'smart dust' consisting of gold nanoparticles coated by an ultrathin insulating shell of silica or alumina. The nanoparticles provide Raman signal amplification, and the coating keeps them separate from each other and from the probed substance. The new technique, termed SHINERS (shell-isolated nanoparticle-enhanced Raman spectroscopy), is demonstrated by probing pesticide residues on the surfaces of yeast cells and citrus fruits. It could be useful in materials science and the life sciences, as well as for the inspection of food safety, drugs, explosives and environmental pollutants.
Small Ag clusters incorporating both the pH-sensitive Raman probe molecule 4-mercaptobenzoic acid and a fluorescent dye are used to determine the local pH from the spatially mapped surface-enhanced Raman spectra correlated with the fluorescence, allowing simultaneous single-particle tracking and local pH sensing.
Surface-enhanced Raman scattering (SERS) spectroscopy is one of the most powerful analytical techniques for identification of molecular species, with the potential to reach single-molecule detection under ambient conditions. This Concept article presents a brief introduction and discussion of both recent advances and limitations of SERS in the context of diagnosis and biodetection, ranging from direct sensing to the use of encoded nanoparticles, in particular focusing on ultradetection of relevant bioanalytes, rapid diagnosis of diseases, marking of organelles within individual cells, and non-invasive tagging of anomalous tissues in living animals.
The surface-enhanced Raman scattering (SERS) activity of nanoporous gold (NPG) can be boosted by controlled surface passivation. The SERS activities of unfunctionalized NPG were first optimized by etching substrates with NaI/I(2) (triiodide) and using 2-mercaptopyridine (2-MP) as the probing analyte. Gains in analyte sensitivity were then achieved by passivating the superficial regions of the NPG substrates with dimethyldithiocarbamate (Me(2)DTC) while leaving the more recessed "hot spots" available for SERS detection. Partial surface passivation with DTCs increased the substrate sensitivity to chemisorptive analytes such as 2-MP by an order of magnitude, whereas surface saturation lowered the sensitivity by an order of magnitude. The partially passivated NPG films can also be functionalized with supramolecular receptors for chemoselective SERS. Installation of a DTC-anchored terpyridine enabled the detection of divalent metal ions at trace levels, as determined by the complexation-induced shift of a characteristic Raman peak of the metal ion receptor.
This Account provides an overview of the methods that are currently being used to study the electromagnetics of silver and gold nanoparticles, with an emphasis on the determination of extinction and surface-enhanced Raman scattering (SERS) spectra. These methods have proven to be immensely useful in recent years for interpreting a wide range of nanoscience experiments and providing the capability to describe optical properties of particles up to several hundred nanometers in dimension, including arbitrary particle structures and complex dielectric environments (adsorbed layers of molecules, nearby metal films, and other particles). While some of the methods date back to Mie’s celebrated work a century ago, others are still at the forefront of algorithm development in computational electromagnetics.
The relationship between surface-enhanced resonance Raman scattering (SERRS) intensity and the rate of deposition during silver-island film preparation was examined, using zinc tetraphenylporphine (ZnTPP) as the adsorbate. The effect of the deposition rate on the optical properties of the films at specific wavelengths was also analyzed. The data show that the film extinction (the term extinction is used rather than absorption because the spectra have not been corrected for reflection or scattering losses) increases exponentially at 514 and 458 nm as the deposition rate is decreased. SERRS intensities also increase exponentially at these two excitation wavelengths with a decrease in the deposition rate. The optical density is linearly related to the SERRS intensity, and maximal enhancement is observed for films with the greatest extinction at these excitation wavelengths. In contrast, neither the extinction at 406 nm nor the SERRS scattering intensities resulting from excitation at this wavelength differ substantially. The surface-enhanced Raman scattering (SERS) intensity and the electronic spectra of 4,4'-bipyridine (BP) adsorbed onto silver films as a function deposition rate were also examined. The behavior of the nonresonantly enhanced BP is comparable to that of the resonantly enhanced ZnTPP samples. The effects of the surface morphology, as determined from transmission electron micrographs of the films at various deposition rates, on the corresponding electronic spectra and SERS/SERRS spectra are described.
A constrained, iterative Fourier deconvolution method is employed to enhance the resolution of Raman spectra of biological molecules for quantitative assessment of macromolecular secondary structures and hydrogen isotope exchange kinetics. In an application to the Pf1 filamentous bacterial virus, it is shown that the Raman amide I band contains no component other than that due to alpha-helix, indicating the virtual 100% helicity of coat proteins in the native virion. Comparative analysis of the amide I band of six filamentous phages (fd, If1, IKe, Pf1, Xf, and Pf3), all at the same experimental conditions, indicates that the subunit helix-percentage ranges from a high of 100% in Pf1 to a low of 71% in Xf. Deconvolution of amide I of Pf3 at elevated temperatures, for which an alpha-to-beta transition was previously reported (Thomas, G. J., Jr., and L. A. Day, 1981, Proc. Natl. Acad. Sci. USA., 78:2962-2966), allows quantitative evaluation of the contributions of both alpha-helix and beta-strand conformations to the structure of the thermally perturbed viral coat protein. Weak Raman lines of viral DNA bases and coat protein side chains, which are poorly resolved instrumentally, are also distinguished for all viruses by the deconvolution procedure. Application to the carbon-8 hydrogen isotope exchange reaction of a purine constituent of transfer RNA permits accurate determination of the exchange rate constant, which is in agreement with calculations based upon curve-fitting methods.
The chloride-sensitive fluorescent indicator MQAE (N-(6-methoxyquinolyl) acetoacetyl ester) has been used for determination of the intracellular free chloride concentration in rat brain synaptoneurosomes. Loading of the synaptoneurosomes with MQAE occurs by transmembrane diffusion. Calibration of the intracellular MQAE was done by determining the correlation between fluorescence intensity and intrasynaptoneurosomal Cl- concentration in the presence of the Cl-/OH- exchanger tributyltin and the K+/H+ exchanger nigericin, starting from zero Cl- concentration. The total quenchable signal of MQAE was determined by adding KSCN in the presence of the K+ ionophore valinomycin. The correlation between the reciprocal of the fluorescence intensity and the chloride concentration was linear at least up to 50 mM Cl-. The fluorescence of freshly prepared synaptoneurosomes was then measured and the obtained value was plotted into the calibration curve and the corresponding Cl- was read. The mean intrasynaptoneurosomal chloride concentration was 14 +/- 4 mM. We also quantitatively estimated the Cl- flux after addition of the barbiturate, pentobarbitone that opens GABAA receptor-Cl(-)-channels, to the synaptoneurosomes. An addition of 1 mM pentobarbitone corresponded to an approx. 0.59 mM change in the intrasynaptoneurosomal free chloride concentration. The results show that the chloride-sensitive fluorescent indicator MQAE is a useful tool when determining intracellular chloride activity, and in quantitative determination of chloride fluxes in living cells and subcellular preparations.
Urinary electrolytes are invaluable in the differential diagnosis and treatment of certain acid-base diseases. We have evaluated the accuracy and precision of three different automated chemistry analyzers and a chloridometer (Corning 925 Chloridometer, Hitachi 717 and 917 and Vitros 950) for chloride, sodium and potassium using standard solutions. Data indicate that the ISE modules on the Hitachi 717 and 917 analyzers measure sodium and potassium accurately and precisely throughout the studied concentration range. The Vitros 950 system had the poorest precision and accuracy performance at the low levels of sodium and potassium. The chloride ion-selective membranes on the Hitachi analyzers seriously overestimate the chloride concentration at all levels. The manual dilution method on the Vitros 950 analyzer for chloride measurements showed good precision and accuracy only at the higher chloride levels. For chloride determination the chloridometer displayed the best accuracy with good precision. We recommend that laboratories use chloridometers for the measurement of urinary chloride, and that the CAP include low chloride samples in their proficiency testing program for urine chloride.
An overview is given of the preparation, formation, structure, and applications of self-assembled monolayers (SAMs) formed from alkanethiols (and derivatives of alkanethiols) on gold, silver, copper, palladium, platinum, mercury, and alloys of these metals. Emphasis is on advances made in this area over the past five years (1999-2004). First, the structure and mechanism of formation of SAMs formed by adsorption of n-alkanethiols on metals are described. Following this, the applications of SAMs where they act as nanostructures themselves, enable other nanosystems, interact with biological nanostructures, and form patterns on surfaces with critical dimensions below 100 nm are outlined. Furthermore, an attempt is made to outline what is not understood about these SAMs and which of their properties are not yet controlled. Finally, some of the important opportunities that still remain for future progress in research involving SAMs are sketched.
Bromate, a well known by-product of the ozonation of drinking water, has been included among the substances which have to be monitored in the drinking water according to the last EC Directive 251/98 on potable water with a regulated limit of 10 microg l(-1). The need of performing routine analysis at this limit is a driving force for the developing of new simple and sensitive methods of detection, which should be also able to overcome the effect of matrix composition. This work explored the use of mass spectrometry detection with electrospray ionisation hyphenated to a reagent free ion chromatograph with hydroxide gradient elution for the determination of bromate in drinking water. The use of a high capacity hydroxide selective column operated in gradient mode allowed to avoid the interference by carbonate peak, which moved to longer retention times. The effect of increasing chloride concentrations from 0 to 250 mg l(-1), which is the guideline limit for drinking water in Directive 251/98/EC, was to decrease absolute mass spectrometric response and chromatographic efficiency and, on the consequence, to increase the effective detection limits. The effect of the chloride concentration on the detection of bromate is discussed.
We show that an Au nanoshell with a pH-sensitive molecular adsorbate functions as a standalone, all-optical nanoscale pH meter that monitors its local environment through the pH-dependent surface-enhanced Raman scattering (SERS) spectra of the adsorbate molecules. Moreover, we also show how the performance of such a functional nanodevice can be assessed quantitatively. The complex spectral output is reduced to a simple device characteristic by application of a locally linear manifold approximation algorithm. The average accuracy of the nano-"meter" was found to be +/-0.10 pH units across its operating range.
We present a new density functional called M06-HF. The new functional has full Hartree-Fock exchange, and therefore it eliminates self-exchange interactions at long range. This leads to good performance in TDDFT calculations of both Rydberg and charge-transfer states. In addition, the functional satisfies the uniform electron gas limit, and it is better than the popular B3LYP functional, on average, for ground-electronic-state energetics.
Humic acid (HA) solutions provide an unexpected medium for direct fabrication of gold nanoparticles (HA-AuNP) and a clear window for surface-enhanced Raman scattering (SERS) with many potential applications in the ultrasensitive chemical analysis of environmental pollutants. It is demonstrated that the HA-AuNP fabrication can be easily achieved in a wide range of pH (2 to 12). The background SERS spectra of HA is relatively weak in absolute intensity, allowing the detection of the enhanced Raman signal from trace amount of contaminants. An in-situ approach is illustrated where the HA-AuNP fabrication is carried out with a HA solution containing the target pollutant. The technique may allow for the direct detection of organic pollutants present in the humic fraction of soil.
Romo-Herrera for carrying out the XPS and SEM measurements, respectively. This work was funded by the Spanish Ministerio de Ciencia e Innovaci on
- Acknowledgment
- C We
- Serra
- Cacti
- Universidade
- J M Vigo
Acknowledgment. We thank C. Serra (CACTI, Universidade de Vigo) and J. M. Romo-Herrera for carrying out the XPS and SEM measurements, respectively. This work was funded by the Spanish Ministerio de Ciencia e Innovaci on (MAT2010-15374 and MAT2008-05755) the Xunta de Galicia (10 PXIB314218PR, 09TMT011314PR and 08TMT008314PR), the German Research Foundation (DFG, Grant PA794/11-1) and by the European Commission (Grant Nanognostics).
- J Zhao
- A O Pinchuk
- J M Mcmahon
- S Li
- L K Ausman
- A L Atkinson
- G Schatz
Zhao, J.; Pinchuk, A. O.; McMahon, J. M.; Li, S.; Ausman, L. K.;
Atkinson, A. L.; Schatz, G. C. Methods for Describing the
Electromagnetic Properties of Silver and Gold Nanoparticles. Acc. Chem. Res. 2008, 41, 1710–1720.
- R A Sperling
- P Rivera-Gil
- F Zhang
- M Zanella
- W J Parak
Sperling, R. A.; Rivera-Gil, P.; Zhang, F.; Zanella, M.; Parak,
W. J. Biological Applications of Gold Nanoparticles. Chem.
Soc. Rev. 2008, 37, 1896-1908.
Gaussian 09, revision A
- B Mennucci
- G A Petersson
Mennucci, B.; Petersson, G. A. et al. Gaussian 09, revision
A.02,; Gaussian, Inc.: Wallingford, CT, 2009.
- H F Lodish
Lodish, H. F. Mol. Cell. Biol.; Scientific American Books:
New York, 1999.
Atomic Absorption, Atomic Emission, and Flame Emission Spectrometry
- K W Jackson
- T M Mahmood
Jackson, K. W.; Mahmood, T. M. Atomic Absorption, Atomic
Emission, and Flame Emission Spectrometry. Anal. Chem.
1994, 66, 252R-279R.
- Y Zhao
- J N Newton
- J Liu
- A Wei
- Sers Dithiocarbamate-Coated
- Substrates
Zhao, Y.; Newton, J. N.; Liu, J.; Wei, A. Dithiocarbamate-Coated SERS Substrates: Sensitivity Gain by Partial Surface
Passivation. Langmuir 2009, 25, 13833-13839.
- H F Lodish
Lodish, H. F. Mol. Cell. Biol.; Scientific American Books:
New York, 1999.