Designing surface-enhanced Raman scattering (SERS) platforms beyond hotspot engineering: emerging opportunities in analyte manipulations and hybrid materials

Instantaneous trace detection of nitro-explosives and mixtures with nanotextured silicon decorated with Ag-Au alloy nanoparticles using the SERS technique

The development of recyclable surface enhanced Raman scattering (SERS) based sensors has been in huge demand for trace level explosives detection. A simple, hybrid Silicon (Si) nanotextured target-based SERS platform is fabricated through patterning micro square arrays (MSA) on Si using femtosecond (fs) laser ablation technique at different fluences. Using the hybrid target Si MSA substrate loaded/decorated with Ag-Au alloy NPs (obtained using femtosecond ablation in liquids) we demonstrate the trace level detection of organic nitro-explosives [picric acid (PA), 2,4-dinitrotoluene (DNT), and 1, 3, 5-trinitroperhydro-1, 3, 5-triazine (RDX)] and their mixtures. The microstructures/nanostructures of MSA fabricated at an input fluence of 9.55 J/cm², and decorated with Ag-Au alloy NPs, exhibited exceptional SERS enhancement factors (EFs) up to ∼10¹⁰ for MB, ∼10⁶ for PA, and ∼10⁴ for RDX with the detection limits obtained being ∼5 pM, ∼36 nM, and ∼400 nM for MB, PA and RDX respectively. Furthermore, we demonstrate these SERS substrates possess good reproducibility (RSD values < 15%) and a superior performance compared to a commercial Ag substrate (SERSitive, Poland). Three binary mixtures, i.e. MB-PA, MB-DNT, PA-DNT at different concentrations, were also investigated using the same SERS substrate to test the efficacy. Further, the SERS spectra of dyes, explosives, and complex mixtures were utilized for discrimination/classification using principal component analysis.

Fabrication of Hybrid Silver Microstructures from Vermiculite Templates as SERS Substrates

There is great interest in developing complex, 3D plasmonic materials with unusual structural properties. This can be achieved via template-assisted approaches exploiting scaffold elements to engineer unique plasmonic substrates, which would be otherwise impossible to synthesize. Herein, we present a novel, simple, and low-cost template-assisted method for producing interconnected 3-D silver microstructures by utilizing vermiculite, a well-known silicate, as both in-situ reductant and template for silver growth. The silicate network of the vermiculite can be easily removed by dissolution with hydrofluoric acid, which, simultaneously, leads to the formation of a magnesium fluoride skeleton supporting a plasmonically active silver film. Optical, morphological, and chemical properties of the materials were extensively investigated, revealing, for example, that hybrid silver microstructures can be exploited as valuable SERS substrates over a broad spectral range of excitation wavelengths.

Multiplex Surface-Enhanced Raman Scattering Identification and Quantification of Urine Metabolites in Patient Samples within 30 min

Successful translation of laboratory-based surface-enhanced Raman scattering (SERS) platforms to clinical applications requires multiplex and ultratrace detection of small biomarker molecules from a complex biofluid. However, these biomarker molecules generally exhibit low Raman scattering cross sections and do not possess specific affinity to plasmonic nanoparticle surfaces, significantly increasing the challenge of detecting them at low concentrations. Herein, we demonstrate a "confine-and-capture" approach for multiplex detection of two families of urine metabolites correlated with miscarriage risks, 5β-pregnane-3α,20α-diol-3α-glucuronide and tetrahydrocortisone. To enhance SERS signals by 10¹²-fold, we use specific nanoscale surface chemistry for targeted metabolite capture from a complex urine matrix prior to confining them on a superhydrophobic SERS platform. We then apply chemometrics, including principal component analysis and partial least-squares regression, to convert molecular fingerprint information into quantifiable readouts. The whole screening procedure requires only 30 min, including urine pretreatment, sample drying on the SERS platform, SERS measurements, and chemometric analyses. These readouts correlate well with the pregnancy outcomes in a case-control study of 40 patients presenting threatened miscarriage symptoms.

Paper-Based SERS Sensing Platform Based on 3D Silver Dendrites and Molecularly Imprinted Identifier Sandwich Hybrid for Neonicotinoid Quantification

Real-time monitoring of neonicotinoid pesticide residues is of great significance for food security and sustainable development of the ecological environment. Herein, a paper-based surface-enhanced Raman scattering (SERS) amplified approach was proposed by virtue of multilayered plasmonic coupling amplification. The unique plasmonic SERS multilayer was constructed using three-dimensional (3D) silver dendrite (SD)/electropolymerized molecular identifier (EMI)/silver nanoparticle (AgNP) sandwich hybrids with multiple hotspots and a strong electromagnetic field in nanogaps. Dendritelike 3D silver materials with remarkably high accessible surface areas and the lightning rod effect constituted the first-order enhancement of paper-based sensors. Molecular identifiers coated upon an SD layer as the interlayer were used for target capture and enrichment. Subsequently, AgNPs featuring rough surface and local plasma resonance decorated as the top layer formed the secondary enhancement of the amplification strategy. As the most brilliant part, dendritelike 3D silver coupled with AgNPs has established double Ag layers to accomplish a multistage enhancement of SERS signals based on the superposition of their electromagnetic fields. Owning to the distinctive design of the multiple coupling amplification strategy, the fabricated SERS paper chips demonstrated impressive specificity and ultrahigh sensitivity in the detection of imidacloprid (IMI), with a detection limit as low as 0.02811 ng mL^-1. More importantly, the multiple SERS enhancement paper chip holds great potential for automated screening of a variety of contaminants.

Inverse design of nanoparticles for enhanced Raman scattering

We show that topology optimization (TO) of metallic resonators can lead to ∼10² × improvement in surface-enhanced Raman scattering (SERS) efficiency compared to traditional resonant structures such as bowtie antennas. TO inverse design leads to surprising structures very different from conventional designs, which simultaneously optimize focusing of the incident wave and emission from the Raman dipole. We consider isolated metallic particles as well as more complicated configurations such as periodic surfaces or resonators coupled to dielectric waveguides, and the benefits of TO are even greater in the latter case. Our results are motivated by recent rigorous upper bounds to Raman scattering enhancement, and shed light on the extent to which these bounds are achievable.

Ultrasensitive SERS-Based Plasmonic Sensor with Analyte Enrichment System Produced by Direct Laser Writing

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.

Suppression of coffee-ring effect via periodic oscillation of substrate for ultra-sensitive enrichment towards surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) has attracted extensive interest due to excellent molecule recognition and sensitive concentration detection. Nevertheless, the coffee ring effect (CR) during the analyte evaporation always causes an uneven distribution of the assembled hot-spots, and hence the unreliable SERS signal is produced. In this study, for the first time, we present a suppressed coffee ring (SCR) system via a combination of a magnetically functionalized membrane and reciprocating magnetic field to dynamically suppress the CR for highly reliable and ultra-sensitive SERS detection. The enrichment mechanism of the nanoparticles and the analyte molecules within the sessile droplet based on the proposed system was studied. We experimentally observed that the driving frequency could well affect the final pattern, and typically a higher driving frequency facilitated a smaller coverage area with better enrichment performance. With the use of R6G molecule and (100 nm) gold nanoparticles, we examined the uniformity and SERS of the assembled 'hot-spots' in the SCR system. The results indicate that the uniformity can be greatly improved via SCR in comparison of ring stain, with the RSD of a Raman signal as low as 7.1% even at a low concentration of 10^-12 mol L^-1. Such system also enables the further enhancement in the SERS signal, with the detection limit down to 10^-16 mol L^-1, the enhancement factor magnitude up to 10¹³, and the linear relationship between the SERS intensity and the analyte concentrations within the range of 10^-6-10^-12 and 10^-12-10^-16 mol L^-1, respectively. The applicability of the SCR-based SERS detection for diverse analytes was also proved with a similar but further enhanced signal of MB and 4-ATP. We believe that the excellent SCR-based SERS performance via the proposed system has great potentials for ultra-sensitive detection and/or precise quantitative analysis in various research fields and applications.

Surface-enhanced Raman scattering-based detection of hazardous chemicals in various phases and matrices with plasmonic nanostructures

Surface-enhanced Raman scattering (SERS)-based sensors utilize the electromagnetic-field enhancement of plasmonic substrates with the chemical specificity of vibrational Raman spectroscopy to identify trace amounts of a wide variety of different target analytes while being minimally affected by photobleaching. However, despite many advantageous features of this method, SERS sensors, particularly for detecting hazardous chemicals, suffer from several limitations such as requirement of gigantic signal enhancement that is often poorly controllable, subtle change and degradation of the SERS substrate, consecutive fluctuation of the signal, the lack of reliable receptors for capturing targets of interest and the absence of general principles for detecting various chemicals in different phases and matrices. To overcome these limitations and for SERS sensors to find practical use, one must (1) acknowledge the characteristics of the matrices of target systems, (2) finely engineer and tune the receptors of the SERS sensor to properly extract the target analyte from the phase, and (3) implement additional mechanistic modifications to enhance the plasmonic signal. This minireview underlines the difficulties associated with different phases and a wide range of target analytes, and introduces the practical measures undertaken to overcome the respective difficulties in SERS-based detection of hazardous chemicals.

Complexes Formed by Hydrophobic Interaction between Ag-Nanospheres and Adsorbents for the Detection of Methyl Salicylate VOC

Surface-enhanced Raman spectroscopy (SERS) has been widely investigated in many applications. However, only little work has been done on using SERS for the detection of volatile organic compounds (VOCs), primarily due to the challenges associated with fabricating SERS substrates with sufficient hotspots for signal enhancement and with the surface interfacially compatible for the VOCs. This study investigated the phase transfer of Ag-nanospheres (AgNSs) from the aqueous phase to the non-aqueous phase by electrostatic interaction induced by cationic surfactants, and the feasibility of the transferred AgNSs as SERS substrates for the determination of methyl salicylate VOC. Results indicated that one of three cationic surfactants, tetraoctylammonium bromide (TOAB) dissolved in organic solvent showed successful phase transfer of the AgNSs confirmed by several characterization analyses. The complex formed by hydrophobic interaction between the transferred AgNSs and Tenax-TA adsorbent polymer was able to be utilized as a SERS substrate, and the volatile of methyl salicylate could be easily determined from SERS measurements at 4 h static volatile collection. Therefore, the proposed new techniques can be effectively employed to areas where many VOCs relevant to food and agriculture need to be analyzed.

Label-Free MicroRNA Optical Biosensors

MicroRNAs (miRNAs) play crucial roles in regulating gene expression. Many studies show that miRNAs have been linked to almost all kinds of disease. In addition, miRNAs are well preserved in a variety of specimens, thereby making them ideal biomarkers for biosensing applications when compared to traditional protein biomarkers. Conventional biosensors for miRNA require fluorescent labeling, which is complicated, time-consuming, laborious, costly, and exhibits low sensitivity. The detection of miRNA remains a big challenge due to their intrinsic properties such as small sizes, low abundance, and high sequence similarity. A label-free biosensor can simplify the assay and enable the direct detection of miRNA. The optical approach for a label-free miRNA sensor is very promising and many assays have demonstrated ultra-sensitivity (aM) with a fast response time. Here, we review the most relevant label-free microRNA optical biosensors and the nanomaterials used to enhance the performance of the optical biosensors.

Graphene Oxide-Assisted and DNA-Modulated SERS of AuCu Alloy for the Fabrication of Apurinic/Apyrimidinic Endonuclease 1 Biosensor

Fabrication of high-performance surface-enhanced Raman scattering (SERS) biosensors relies on the coordination of SERS substrates and sensing strategies. Herein, a SERS active AuCu alloy with a starfish-like structure is prepared using a surfactant-free method. By covering the anisotropic AuCu alloy with graphene oxide (GO), enhanced SERS activity is obtained owing to graphene-enhanced Raman scattering and assembly of Raman reporters. Besides, stability of SERS is promoted based on the protection of GO to the AuCu alloy. Meanwhile, it is found that SERS activity of AuCu/GO can be regulated by DNA. The regulation is sequence and length dual-dependent, and short polyT reveals the strongest ability of enhancing the SERS activity. Relying on this phenomenon, a SERS biosensor is designed to quantify apurinic/apyrimidinic endonuclease 1 (APE1). Because of the APE1-induced cycling amplification, the biosensor is able to detect APE1 sensitively and selectively. In addition, APE1 in human serum is analyzed by the SERS biosensor and enzyme-linked immunosorbent assay (ELISA). The data from the SERS method are superior to that from ELISA, indicating great potential of this biosensor in clinical applications.

Manipulating "Hot Spots" from Nanometer to Angstrom: Toward Understanding Integrated Contributions of Molecule Number and Gap Size for Ultrasensitive Surface-Enhanced Raman Scattering Detection

Narrower gaps between metal nanoparticles (so-called "hot spots") in surface-enhanced Raman scattering (SERS) substrates contribute to stronger electromagnetic (EM) enhancement; however, the accompanying steric effect hinders analyte molecules entering hot spots to access the benefit. To comprehensively understand integrated contributions of the gap size and molecule number accommodated in hot spots and then optimize design of SERS substrates, the thermal shrinking method was employed to manipulate hot spots and the "hottest zone" was defined to evaluate the integrated contributions to SERS intensity of the two factors. In the conventional shrink-adsorption mode, the contributions of the molecule number and gap size are competitive when the gap width is comparable with the target molecule size, which leads to oscillating behavior of SERS intensity versus gap size, and it is analyte molecule size dependent. This result suggests that engineering hot spots should be target molecule directed to achieve ultrasensitive detection. In the proposed adsorption-shrink mode, the contributions of the molecule number and gap size are synergistic, which makes the detection ability of the adsorption-shrink mode attains a single-molecule (SM) level. Excellent performance of the adsorption-shrink SERS strategy benefits detection of trace level pollutants in complex environments. Detection ranges for contaminants with different metal affinity, such as thiram, malachite green (MG), and formaldehyde, are as low as parts per billion, even down to parts per trillion.

Tracking Airborne Molecules from Afar: Three-Dimensional Metal-Organic Framework-Surface-Enhanced Raman Scattering Platform for Stand-Off and Real-Time Atmospheric Monitoring

Stand-off Raman spectroscopy combines the advantages of both Raman spectroscopy and remote detection to retrieve molecular vibrational fingerprints of chemicals at inaccessible sites. However, it is currently restricted to the detection of pure solids and liquids and not widely applicable for dispersed molecules in air. Herein, we realize real-time stand-off SERS spectroscopy for remote and multiplex detection of atmospheric airborne species by integrating a long-range optic system with a 3D analyte-sorbing metal-organic framework (MOF)-integrated SERS platform. Formed via the self-assembly of Ag@MOF core-shell nanoparticles, our 3D plasmonic architecture exhibits micrometer thick SERS hotspot to allow active sorption and rapid detection of aerosols, gas, and volatile organic compounds down to parts-per-billion levels, notably at a distance up to 10 m apart. The platform is highly sensitive to changes in atmospheric content, as demonstrated in the temporal monitoring of gaseous CO₂ in several cycles. Importantly, we demonstrate the remote and multiplex quantification of polycyclic aromatic hydrocarbon mixtures in real time under outdoor daylight. By overcoming core challenges in current remote Raman spectroscopy, our strategy creates an opportunity in the long-distance and sensitive monitoring of air/gaseous environment at the molecular level, which is especially important in environmental conservation, disaster prevention, and homeland defense.

Sandwiching analytes with structurally diverse plasmonic nanoparticles on paper substrates for surface enhanced Raman spectroscopy

This report describes the systematic combination of structurally diverse plasmonic metal nanoparticles (AgNPs, AuNPs, Ag core-Au shell NPs, and anisotropic AuNPs) on flexible paper-based materials to induce signal-enhancing environments for surface enhanced Raman spectroscopy (SERS) applications. The anisotropic AuNP-modified paper exhibits the highest SERS response due to the surface area and the nature of the broad surface plasmon resonance (SPR) neighboring the Raman excitation wavelength. The subsequent addition of a second layer with these four NPs (e.g., sandwich arrangement) leads to the notable increase of the SERS signals by inducing a high probability of electromagnetic field environments associated with the interparticle SPR coupling and hot spots. After examining sixteen total combinations, the highest SERS response is obtained from the second layer with AgNPs on the anisotropic AuNP paper substrate, which allows for a higher calibration sensitivity and wider dynamic range than those of typical AuNP-AuNP arrangement. The variation of the SERS signals is also found to be below 20% based on multiple measurements (both intra-sample and inter-sample). Furthermore, the degree of SERS signal reductions for the sandwiched analytes is notably slow, indicating their increased long-term stability. The optimized combination is then employed in the detection of let-7f microRNA to demonstrate their practicability as SERS substrates. Precisely introducing interparticle coupling and hot spots with readily available plasmonic NPs still allows for the design of inexpensive and practical signal enhancing substrates that are capable of increasing the calibration sensitivity, extending the dynamic range, and lowering the detection limit of various organic and biological molecules.

Designing dendronic-Raman markers for sensitive detection using surface-enhanced Raman spectroscopy

Surface-Enhanced Raman Spectroscopy (SERS) is well-established as a tool for bio-diagnostics but is often limited by analyte sensitivity and the need for specialized substrates. Signal enhancement can be achieved by attaching multiple Raman markers to a single analyte. Dendronic frameworks with multiple Raman markers attached to the periphery offer an opportunity to examine this idea. In this article, dendrons with thiophenol groups on their periphery were synthesized and tested as a SERS analyte. For this study, simple gold nanoparticles (∼60 nm) were used as a substrate. A 102 fold enhancement in detection was observed upon going from a mono-thiophenol (MT) to a tetra-thiophenol (TT). Dendronic Raman markers increased the probability of SERS occurrence at lower concentrations when compared to a single Raman active molecule. This strategy extends the applicability of SERS, as these analyte molecules can be just mixed or drop-casted on any kind of SERS substrate.

Three-Dimensional Surface-Enhanced Raman Scattering Platforms: Large-Scale Plasmonic Hotspots for New Applications in Sensing, Microreaction, and Data Storage

Surface-enhanced Raman scattering (SERS) is a molecular-specific spectroscopic technique that provides up to 10¹⁰-fold enhancement of signature Raman fingerprints using nanometer-scale 0D to 2D platforms. Over the past decades, 3D SERS platforms with additional plasmonic materials in the z-axis have been fabricated at sub-micrometer to centimeter scale, achieving higher hotspot density in all x, y, and z spatial directions and higher tolerance to laser misalignment. Moreover, the flexibility to construct platforms in arbitrary sizes and 3D shapes creates attractive applications besides traditional SERS sensing. In this Account, we introduce our library of substrate-based and substrate-less 3D plasmonic platforms, with an emphasis on their non-sensing applications as microlaboratories and data storage labels. We aim to provide a scientific synopsis on these high-potential yet currently overlooked applications of SERS and ignite new scientific discoveries and technology development in 3D SERS platforms to tackle real-world issues. One highlight of our substrate-based SERS platforms is multilayered platforms built from micrometer-thick assemblies of plasmonic particles, which can achieve up to 10¹¹ enhancement factor. As an alternative, constructing 3D hotspots on non-plasmonic supports significantly reduces waste of plasmonic materials while allowing high flexibility in structural design. We then introduce our emerging substrate-less plasmonic capsules including liquid marbles and colloidosomes, which we further incorporate the latter within an aerosol to form centimeter-scale SERS-active plasmonic cloud, the world's largest 3D SERS platform to date. We then discuss the various emerging applications arising only from these 3D platforms, in the fields of sensing, microreactions, and data storage. An important novel sensing application is the stand-off detection of airborne analytes that are several meters away, made feasible with aerosolized plasmonic clouds. We also describe plasmonic capsules as excellent miniature lab-in-droplets that can simultaneously provide in situ monitoring at the molecular level during reaction, owing to their ultrasensitive 3D plasmonic shells. We highlight the emergence of 3D SERS-based data storage platforms with 10-100-fold higher storage density than 2D platforms, featuring a new approach in the development of level 3 security (L3S) anti-counterfeiting labels. Ultimately, we recognize that 3D SERS research can only be developed further when its sensing capabilities are concurrently strengthened. With this vision, we foresee the creation of highly applicable 3D SERS platforms that excel in both sensing and non-sensing areas, providing modern solutions in the ongoing Fourth Industrial Revolution.

Ag Nanorods-Based Surface-Enhanced Raman Scattering: Synthesis, Quantitative Analysis Strategies, and Applications

Surface-Enhanced Raman Scattering (SERS) is a powerful technology that provides abundant chemical fingerprint information with advantages of high sensitivity and time-saving. Advancements in SERS substrates fabrication allow Ag nanorods (AgNRs) possess superior sensitivity, high uniformity, and excellent reproducibility. To further promote AgNRs as a promising SERS substrate candidate to a broader application scope, oxides are integrated with AgNRs by virtue of their unique properties which endow the AgNRs-oxide hybrid with high stability and recyclability. Aside from SERS substrates fabrication, significant developments in quantitative analysis strategies offer enormous approaches to minimize influences resulted from variations of measuring conditions and to provide the reasonable data analysis. In this review, we discuss various fabrication approaches for AgNRs and AgNRs-oxide hybrids to achieve efficient SERS platforms. Then, we introduce three types of strategies which are commonly employed in chemical quantitative analysis to reach a reliable result. Further, we highlight SERS applications including food safety, environment safety, biosensing, and vapor sensing, demonstrating the potential of SERS as a powerful and promising technique. Finally, we conclude with the current challenges and future prospects toward efficient SERS manipulations for broader real-world applications.

Photochemical preparation of gold nanoparticle decorated cyclodextrin vesicles with tailored plasmonic properties

We report a photochemical strategy for the preparation of plasmonic vesicles by the in situ formation of gold nanoparticles at the surface of cyclodextrin host vesicle templates decorated with photoactive guest polymers. Upon irradiation with UV light, these carefully designed polymer shells undergo a Norrish type I reaction to generate reducing radicals for the in situ reduction of gold salts and simultaneously provide a stabilizing matrix allowing for a dense decoration with discrete gold seeds. In a highly controlled growth procedure the gold particle size can be adjusted between 3 and 28 nm resulting in an increasing interparticle plasmonic coupling as revealed by a pronounced redshift of the surface plasmon resonance (SPR) band and an enhanced absorption at wavelengths above 600 nm. This unique combination of cyclodextrin vesicles capable of specifically recognizing guest molecules with a plasmonic particle shell displaying multiple interparticle gaps acting as electromagnetic hotspots shows great potential for surface-enhanced Raman scattering (SERS) applications.

In Situ Surface-Enhanced Raman Spectroscopy of Cellular Components: Theory and Experimental Results

In the last decade, surface-enhanced Raman spectroscopy (SERS) met increasing interest in the detection of chemical and biological agents due to its rapid performance and ultra-sensitive features. Being SERS a combination of Raman spectroscopy and nanotechnology, it includes the advantages of Raman spectroscopy, providing rapid spectra collection, small sample sizes, characteristic spectral fingerprints for specific analytes. In addition, SERS overcomes low sensitivity or fluorescence interference that represents two major drawbacks of traditional Raman spectroscopy. Nanoscale roughened metal surfaces tremendously enhance the weak Raman signal due to electromagnetic field enhancement generated by localized surface plasmon resonances. In this paper, we detected label-free SERS signals for arbitrarily configurations of dimers, trimers, etc., composed of gold nanoshells (AuNSs) and applied to the mapping of osteosarcoma intracellular components. The experimental results combined to a theoretical model computation of SERS signal of specific AuNSs configurations, based on open cavity plasmonics, give the possibility to quantify SERS enhancement for overcoming spectral fluctuations. The results show that the Raman signal is locally enhanced inside the cell by AuNSs uptake and correspondent geometrical configuration generating dimers are able to enhance locally electromagnetic fields. The SERS signals inside such regions permit the unequivocal identification of cancer-specific biochemical components such as hydroxyapatite, phenylalanine, and protein denaturation due to disulfide bonds breaking between cysteine links or proline.

A Review on Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) has become a powerful tool in chemical, material and life sciences, owing to its intrinsic features (i.e., fingerprint recognition capabilities and high sensitivity) and to the technological advancements that have lowered the cost of the instruments and improved their sensitivity and user-friendliness. We provide an overview of the most significant aspects of SERS. First, the phenomena at the basis of the SERS amplification are described. Then, the measurement of the enhancement and the key factors that determine it (the materials, the hot spots, and the analyte-surface distance) are discussed. A section is dedicated to the analysis of the relevant factors for the choice of the excitation wavelength in a SERS experiment. Several types of substrates and fabrication methods are illustrated, along with some examples of the coupling of SERS with separation and capturing techniques. Finally, a representative selection of applications in the biomedical field, with direct and indirect protocols, is provided. We intentionally avoided using a highly technical language and, whenever possible, intuitive explanations of the involved phenomena are provided, in order to make this review suitable to scientists with different degrees of specialization in this field.

Silver-based surface enhanced Raman spectroscopy devices for detection of organophosphorus pesticides traces

The detection of traces of substances by surface-sensitive techniques such as surface enhanced Raman spectroscopy (SERS) explores the interaction of adsorbed molecules on plasmonic surfaces to improve the limit of detection of analytes. This article is an overview about recent development in SERS substrates applied in the detection of organophosphorus pesticides on plasmonic surfaces (arrays of metal nanoparticles). The morphology, roughness, chemical functionalization degree, and aggregation level of plasmonic centers are some of the critical parameters to be controlled in the optimization of SERS signal from specific analytes.

A long-period and high-stability three-dimensional surface-enhanced Raman scattering hotspot matrix

A simple and effective method to construct a long-period and high-stability 3D hotspot matrix with the assistance of glycerol.