Enhanced Raman Scattering Research Articles

Quantitative Study of Plasmonic Gold Nanostar Geometry Toward Optimal SERS Detection

Complex shapes of gold nanostars (GNS) have been the major obstacle to the comprehensive understanding of the rich plasmonic phenomena of GNS. We conducted extensive, systematic numerical study of far-field and near-field spectral responses of GNS for varying geometrical parameters (e.g., number of spikes, spike tip angle, and spike-to-core ratio) to elucidate the relationship between the optical property and the geometry of GNS. We found that symmetric configurations of GNS spikes generated both dipole and quadrupole localized surface plasmon (LSP) modes, their hybridization resulted in the final near-field intensity at the spike tips, and there existed a specific GNS geometry that optimized the hybridization and thus the E-field intensity for any given wavelength. From these results, we further identified the shapes of GNS that generated the strongest Surface Enhanced Raman Scattering (SERS) enhancement factors in the visible and NIR spectral range. Hence, our results provide guiding principles in determining the optimal geometry of GNS for SERS applications with any choice of excitation wavelength.

One-pot and rapid detection of SARS-CoV-2 viral particles in environment using SERS aptasensor based on a locking amplifier

With the frequent detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in dwellings and wastewater, the risk of transmission of environmental contaminants is of great concern. Fast, simple and sensitive sensors are essential for timely detecting infection and controlling transmission through environment fomites. Herein, we developed a Surface Enhanced Raman Scattering (SERS) aptasensor, which can realize ultrasensitive and rapid assay of SARS-CoV-2 viral particles. In this strategy, we designed a novel locking amplifier which is activated only in the presence of virus by aptamer recognition. The reaction process was carried out though one-pot method at 37 °C, which can save time and resources. In addition, magnetic beads used in reaction system can simplify operation, as well as provide ideas for developing biosensing robots via magnetic field. This SERS aptasensor can detect SARS-CoV-2 virus with a LOD of 260 TU/µL within 40 min in the linear range of 625–10,000 TU/µL. Therefore, this convenience, speediness, sensitivity, and selectivity of detection has great prospects in analyzing SARS-CoV-2 viral particles or other viruses in environment as well as monitoring of environmental virus sources.

Tunable photochemical deposition of silver nanostructures on layered ferroelectric CuInP2S6

Two-dimensional layered ferroelectric materials, such as CuInP2S6 (CIPS), are promising candidates for novel and high-performance photocatalysts, owing to their ultrathin layer thickness, strong interlayer coupling, and intrinsic spontaneous polarization, while how to control the photocatalytic activity in layered CIPS remains unexplored. In this work, we report for the first time, the photocatalytic activity of ferroelectric CIPS for the chemical deposition of silver nanostructures (AgNSs). The results show that the shape and spatial distribution of AgNSs on CIPS are tunable by controlling layer thickness, environmental temperature, and light wavelength. The ferroelectric polarization in CIPS plays a critical role in tunable AgNS photodeposition, as evidenced by layer thickness and temperature dependence experiments. We further reveal that AgNS photodeposition process starts from active site creation, selective nanoparticle nucleation/aggregation, to continuous film formation. Moreover, AgNS/CIPS heterostructures prepared by photodeposition exhibit excellent resistance switching behavior and good surface enhancement Raman Scattering activity. Our findings provide new insight into the photocatalytic activity of layered ferroelectrics and offer a new material platform for advanced functional device applications in smart memristors and enhanced chemical sensors.

(Invited) Multiplexed Label-Free Biosensing Using 2D-Heterostructures: Materials Stability and Signal Uniformity

Two-dimensional materials (2DM) has been already applied for bio- and chemical sensing[1],[2]. Even individual 2D materials often outperform bulk analogues, showing strong response and being compatible with flexible technologies, thus opening horizons for wearable and Point-of-Care applications[3]. Most recently, emergent need to achieve better, more precise and sensitive drug detection in medicine and health care has been addressed by developing new types of biosensors[4]. Extending properties of individual 2DMs by constructing their van der Waals heterostructures, either lateral or vertical, offers new response and/or transduction mechanisms and further improvement of device performance. Such heterostructures have potential for label-free biosensing and could be designed and/or integrated together to generate several signals in response to a single analyte. Such a capability enables a multimodal detection, which exceeds single-mode biosensing through its higher throughput, as well as by better ability to differentiate the analyte from background signals in a complex media, and potentially allows multiplexing (responding by several channels to a group of substances in parallel).Despite significant efforts were invested into discovery of newer and better 2D materials with biosensing capabilities, there is only limited knowledge of factors that could limit its performance. Indeed, atomically thin 2D materials have an ultimate surface-to-volume ratio which helps sensing, but may result in surface non-uniformities at the nanometer scale such as: atomic impurities, adsorbates, single atom and lattice defects, wrinkles and ruptures – to name just a few. Such defects may modulate their sensing properties. Here, a new multidimensional optical imaging technique will be presented which is capable to detect lattice mismatch and work function difference in the heterostructure material. Those result in strain and charge transfer and vary optical response at the nanometer scale, hard to detect and study by normal characterization tools.We present a vertical heterostructure comprised of monolayer graphene and single layer flakes of MoS2. An optical label-free detection of doxorubicin, a common cancer drug, is reported via three independent optical detection channels (photoluminescence shift, Raman shift and Graphene Enhanced Raman Scattering). Non-uniform broadening of components of multimodal signal correlates with the statistical distribution of local optical properties of the 2DM heterostructure. It will be shown how mapping of distribution for doping and strain (taken with sub-diffractional resolution) allows one to understand the role of those for modulation of electronic properties of 2D material.Acknowledgement: partial support is acknowledged from NSF CHE-2032582, CHE-2032601, DMR-1539916 and DMR-2011839 grants. [1] Oh, S.-H.; et.al, Nature Communications 2021, 12, 3824. [2] Bolotsky, A.; et.al, ACS Nano 2019, 13, 9781. [3] Pang, Y.; et.al, Small 2020, 16, 1901124. [4] Moradi, R; Small (2021). doi: 10.1002/smll.202104847

Quartz Tube Enhanced Raman Scattering Spectroscopy

Raman spectroscopy is widely used in many fields with the advantages of simultaneous species detection and molecular fingerprint characteristics, but the low detection sensitivity limits its further development, especially for highly scattering or turbid mediums. In this consideration, a new method called quartz tube enhanced Raman scattering spectroscopy was proposed for the first time in this paper. A quartz tube was inserted into the powder sample to improve the coupling of light into the medium and increase the interaction volume of the laser with the sample (“volume-excitation”), multiple scattering of the light within the turbid medium resulted in an increased Raman signal. In this paper, the effect of different sizes of quartz tubes on the sensitivity enhancement was studied. The results show that the enhancement factor of the signal intensity was nearly 5.37 (the Raman signal of HCO3−) compared to traditional Raman spectroscopy technology. Furthermore, the method was successfully applied to improve the Raman signal intensity of the mixed sample (1:5, m (PO43−):m (HCO3−)) and detect the baking soda powder buried under a 6 mm thick layer of potassium dihydrogen phosphate powder. The results show that the technology will open a new way for the quantitative analysis and detection of powder samples.

Surface enhanced Raman scattering (SERS)-active bacterial detection by Layer-by-Layer (LbL) assembly all-nanoparticle microcapsules

Polymeric microcapsules composed by the Layer-by-Layer (LbL) approach have been used for various applications including drug delivery into cells and in vivo, conducting enzyme catalyzed reactions, performing sensoric functions. Typically, LbL-assembled microcapsules have been formulated via alternating deposition of positively and negatively charged polyelectrolytes onto sacrificial templates or so-called cores. In this work, we extend the LbL assembly to produce microcapsules solely based on nanoparticles instead of polymers. We have identified that 5 layers of nanoparticles is the minimum number of layers for a stable assembly of capsules on calcium carbonate templates. Subsequently, these capsules comprised of nanoparticles were applied as Surface Enhanced Raman Scattering (SERS) platform, where the nanoparticle-based shell of capsules is shown to enable SERS of both solutes and macromolecular structures such as bacterial cells.

Effect of Yield Silver Nanoparticles in Enhancing Raman Signal of SERS Substrate Fabricated on Whatman Filter Paper

On Whatman Filter Paper, Surface Enhanced Raman Scattering (SERS) Substrate was created from colloidal silver nanoparticles by drop casting in varied volume colloidal nanoparticles of 3 ml and 6 ml. Using Raman Spectroscopy, SERS substrates were investigated for their ability to enhance 500 ppm of Deltamethrin pesticides Raman Signal. The number of colloidal nanoparticles is related to the volume of colloidal nanoparticles, indicating that high yields nanoparticle synthesis. The results demonstrate that fabricating SERS substrates in 6 ml increased Raman signal more than fabricating nanoparticles in 3 ml.

Raman Scattering Enhancement by silver Nanostructures Prepared by Electrical Exploding Wire Technique

This project aims to fabricate nanostructures (AgNPS) using the electrical exploding wire (EEW) technique using Rhodamine 6G dye as the probe molecule, investigate the effect of AgNPS on the absorption spectra and surface-enhanced Raman scattering (SERS) activities, and advance using porous silicon as an active substrate for surface-enhanced Raman scattering (SERS). X-Ray diffraction (XRD) was used to investigate the structural properties of the nanostructures (AgNPs). Field emission scanning electron microscopy (FE-SEM) was used to investigate surface morphology. A double beam UV-Vis Spectrophotometer was used to analyze the mixed R6G laser dye(of concentration 1x M) absorption spectra with the nanostructures AgNPS (of concentration 24x M). A sunshine Raman microscope device (the objective lens used was (50x)). was used to analyze R6G combined with nanostructures Raman spectra. All samples have shown SERS activity that increased with increasing the hot spots. The SERS enhancement factor for R6G dye(of 1x10-6 M concentration) when mixed with (AgNPS) nanostructures has reached to(2.48 x 106) and the lowest detection limit reached to (1 x 10-14 M) at the wave number (1652 cm-1) using excited laser source (λexc. = 532nm)

Symmetry Breaking in Gold Nanocylinder Grating: Influence on Plasmonic Properties and on Surface Enhanced Raman Scattering Performances

Symmetry Breaking in Gold Nanocylinder Grating: Influence on Plasmonic Properties and on Surface Enhanced Raman Scattering Performances

A Mini Review on Surface-Enhanced Raman Scattering based Nanoclusters for Sensing and Imaging Applications

Background: The invention of enhanced Raman scattering by adsorbing molecules on nanostructured metal surfaces is a milestone in the development of spectroscopic and analytical techniques. Important experimental and theoretical efforts were geared towards understanding the Surface Enhanced Raman Scattering effect (SERS) and evaluating its significance in a wide range of fields in different types of ultrasensitive sensing applications. Methods: Metal nanoclusters have been widely studied due to their unique structure and individual properties, which place them among single metal atoms and larger nanoparticles. In general, the nanoparticles with a size less than 2 nm is defined as nanoclusters (NCs) and they possess distinct optical properties. In addition, the excited electrons from absorption bands results in the emission of positive luminescence associated to the quantum size effect in which separate energy levels are produced. Results: It is demonstrated that fluorescent based SERS investigations of metal nanoparticles have showed more photostability, high compatibility, and good water solubility, has resulted in high sensitivity, better imaging and sensing experience in the biomedical applications. Conclusion: In the present review, we report recent trends in the synthesis of metal nanoclusters and their applications in biosensing and bio-imaging applications due some benefits including cost-effectiveness, easy synthesis routes and less consumption of sample volumes. Outcomes of this study confirms that SERS based fluorescent nanoclusters could be one of thrust research areas in biochemistry and biomedical engineering.

Rapid Detection of Metal Ions in the Aqueous Medium by Colorimetry and Surface Enhanced Raman Scattering Using Vanillic Acid-Coated Silver Nanoparticles

Rapid and inexpensive detection of heavy metal pollution is highly required these days in order to combat pollution. Noble metal nanoparticles coated by organic molecules having surface plasmon resonance have recently played key role in conceptualizing and fabricating sensing devices for the detection of heavy metals. The present study uses the utility of vanillic acid coated silver nanoparticles (V-AgNPs) synthesized by chemical reduction for the colorimetric and surface-enhanced Raman scattering detection of heavy metal ions in aqueous solution. The synthesized V-AgNPs are of approximately 5–15 nm in size. The addition of synthesized V-AgNPs colloidal solution to control and metal ion laced water samples turns the solution color grayish black except for Cr(III) ions. The addition of V-AgNPs colloidal solution to the water samples containing Cr(III) ions turns the solution transparent. Furthermore, the addition of V-AgNPs to water samples containing Cr(III) ions and Mo(VI) creates unique Raman spectral signatures with high intensities that were used for the identification of these metal ions in aqueous solution. The addition of V-AgNPs to metal ions causes aggregation of the nanoparticles which results in change in color and Raman scattering signals. The obtained color patterns and Raman spectral signatures show the potential of V-AgNPs for low cost, timeless, affordable, convenient, sensitive, selective, and rapid detection of heavy metal ions in aqueous media.

Low-Cost Surface Enhanced Raman Scattering for Bio-Probes

Raman Spectroscopy is a well-known method for identifying molecules by their spectroscopic “fingerprint”. In Surface Enhanced Raman Scattering (SERS), the presence of nanometallic surfaces in contact with the molecules enormously enhances the spectroscopic signal. Raman enhancing surfaces are often fabricated lithographically or chemically, but the throughput is low and the equipment is expensive. In this work a SERS layer was formed by the self-assembly of silver nanospheres from a hexane suspension onto an imprinted thermoplastic sheet (PET). In addition, the SERS layer was transferred and securely bonded to other surfaces. This is an important attribute for probes into solid specimen. Raman spectra were obtained with Rhodamine 6G (R6G) solution concentrations ranging from 1 mm to 1 nm. The methods described here produced robust and sensitive SERS surfaces with inexpensive equipment, readily available materials, and with no chemical or lithographic steps. These may be critical concerns to laboratories faced with diminishing funding resources.

The Role of Surface Enhanced Raman Scattering for Therapeutic Drug Monitoring of Antimicrobial Agents

The rapid quantification of antimicrobial agents is important for therapeutic drug monitoring (TDM), enabling personalized dosing schemes in critically ill patients. Highly sophisticated TDM technology is becoming available, but its implementation in hospitals is still limited. Among the various proposed techniques, surface-enhanced Raman scattering (SERS) stands out as one of the more interesting due to its extremely high sensitivity, rapidity, and fingerprinting capabilities. Here, we present a comprehensive review of various SERS-based novel approaches applied for direct and indirect detection and quantification of antibiotic, antifungal, and antituberculosis drugs in different matrices, particularly focusing on the challenges for successful exploitation of this technique in the development of assays for point-of-care tests.

Fabrication of Silver Nanostructures in the Form of Particles, Dendrites and Flowers on Silicon for Use in SERS Substrates

Surface Enhanced Raman Scattering (SERS) is a technique that is increasingly being used to detect trace amounts of various types of molecules, especially organic and biological molecules. The SERS effect is available mainly due to the SERS substrate - a noble metal surface that is rough at the nano level or a set of noble metal nanoparticles in a certain arrangement. Such a SERS substrate acts as an analyte Raman signal amplifier and can provide amplification up to millions of times and even more. The amplification coefficient of the SERS substrate is determined mainly by the number of ‘hot spots’ it contains as well as the ‘hotness’ of these spots. In turn, a ‘hot spot’ is a certain space around the tips or a nanogap between particles, where the local electromagnetic field is intensely enhanced, while the ‘hotness’ is determined by the sharpness of the tips (the sharper the hotter) and tightness of the gaps (the narrower the hotter). This report presents an overview of the research results of fabricating a type of SERS substrate with a high enhancement factor, which is the SERS substrate made from silver nanostructures coated on the silicon surface. With the aim of increasing the number of ‘hot spots’ and their quality, as well as ensuring uniformity and reproducibility of the SERS substrate, silver nanostructures have been fabricated in various forms, such as nanoparticles, nanodendrites and nanoflowers. In addition, the report also mentions the use of the above silver nanostructures as SERS substrates to detect trace amounts of some pesticides and other toxic agents such as paraquat, pyridaben, thiram, cyanide...

Graphene Oxide/Silver Nanoparticles Platforms for the Detection and Discrimination of Native and Fibrillar Lysozyme: A Combined QCM and SERS Approach.

We propose a sensing platform based on graphene oxide/silver nanoparticles arrays (GO/AgNPs) for the detection and discrimination of the native and toxic fibrillar forms of an amyloid-prone protein, lysozyme, by means of a combination of Quartz Crystal Microbalance (QCM) and Surface Enhanced Raman Scattering (SERS) measurements. The GO/AgNPs layer system was obtained by Langmuir-Blodgett assembly of the silver nanoparticles followed by controlled adsorption of GO sheets on the AgNPs array. The adsorption of native and fibrillar lysozyme was followed by means of QCM, the measurements provided the kinetics and the mechanism of adsorption as a function of protein concentration as well as the mass and thickness of the adsorbed protein on both nanoplatforms. The morphology of the protein layer was characterized by Confocal Laser Scanning Microscopy experiments on Thioflavine T-stained samples. SERS experiments performed on arrays of bare AgNPs and of GO coated AgNP after native, or fibrillar, lysozyme adsorption allowed for the discrimination of the native form and toxic fibrillar structure of lysozyme. Results from combined QCM/SERS studies indicate a general construction paradigm for an efficient sensing platform with high selectivity and low detection limit for native and amyloid lysozyme.

Turing Structured Au/Graphene Oxide‐Polyethylene Glycol Thin Film for Surface Enhanced Raman Scattering Detection of Trace Dye

AbstractSurface‐enhanced Raman scattering (SERS) has been hailed as one of the most powerful approaches in detecting compounds with trace amount. However, difficulties with the SERS substrate, including its instability, technological dependence, and the lack of hotspots, often obstruct its practical use. To address these issues, herein, unique Turing structured gold‐coated graphene oxide‐polyethylene glycol (GO‐PEG) SERS substrate is designed, which presents a highly stable and pre/posttreatment‐free substrate with enhanced hotspots to detect a hazardous azo dye (methyl orange, MO) in trace amount (10−5 m). An exciting enhancement factor (EF) of 2.4 × 107 is obtained from GO‐PEG substrate compared with the conventional planar SERS substrate, owing to the increased hotspots and fluorescence quenching of MO molecules. Turing patterns remain structurally intact, even after 10 days of preparation, showing the dependability of the SERS substrate. Furthermore, the enhanced SERS signals are obtained at a high laser power of 12 mW, which also shows the stability of prepared substrate at harsh operating conditions. This study has the potential to radically change the way. SERS substrates are utilized in trace detection and accelerate the development of new pattern‐based SERS platforms for trace‐level material detection.

Graphene as a Surface Enhancement Raman Scattering (SERS) Substrate

The discovery of surface-enhanced Raman spectroscopy (SERS) presents an opportunity for the development of ultrasensitive biosensors. SERS allows for fingerprint detection of biomolecules at low concentrations and can perform single-molecule detection. The most used SERS substrates are Plasmonic metal nanostructures such as Au and Ag mainly because of their superior electrical conductivity. The Plasmonic metal nanoparticles enhance the Raman signal of the target biomolecules through the electromagnetic field mechanism. Despite the successful use of metal nanostructures, alternative materials have been sought which can exhibit similar or better properties than their metal counterparts. Materials such as graphene which has excellent electrical properties and high surface area are good candidates for SERS applications. Graphene is a 2D nanomaterial consisting of sp2 hybridized carbon atoms. The use of graphene in SERS is termed graphene-enhanced Raman spectroscopy (GERS) and is reported to use a charge transfer mechanism. Both graphene and metal nanostructures can be used together as SERS substrate and the synergistic effect of their mechanism can improve the enhancement factor and the sensitivity of the biosensor, however, the use of graphene as a SERS substrate is still at an early stage. GERS can be applied in disease diagnosis, detection of food additives, and biological species biosensors. The use of GERS in biosensors such as glucose biosensors presents an opportunity for ultrasensitive biosensors which can greatly improve the lives of individuals living with diabetes. In this review insights will be given on how to successfully circumvent the challenges associated with small Raman cross-section of glucose detection for use in medical application.

Plasmonic Rare-Earth Nanosheets as Surface Enhanced Raman Scattering Substrates with High Sensitivity and Stability for Multicomponent Analysis.

Looking for high-performance substrates is an important goal of current surface enhanced Raman scattering (SERS) research. Herein, ultrathin multilayer rhenium (Re) nanosheets as a rare-earth metal substrate are found to have extraordinary SERS performance. These Re nanosheets are prepared through a convenient low-temperature molten salt strategy, and their total thickness is ∼5 nm, including 3-4 layers of ultrathin nanosheets with a thickness of only ∼1 nm. The viscosity of molten salt plays a key role in the formation of these ultrathin layered nanosheets. These nanosheets exhibit a strong and well-defined localized surface plasmon resonance (SPR) effect in the visible light region. The plasmonic Re nanosheets show excellent SERS performance with high sensitivity, chemical stability, and signal repeatability. The lowest detection limit for toxic compounds is 10-12 mol, and the corresponding Raman enhancement factor is 9.1 × 108. A composite enhancement mechanism caused by localized-SPR and charge transport has played an important role in the rare-earth-SERS. High-throughput multiassay analysis is performed on the flexible membrane assembled from the Re nanosheets, which highlights that our system is capable of rapid separation and identification of the samples containing various analytes.

Power Spectral Density Analysis for Optimizing SERS Structures.

The problem of optimizing the topography of metal structures allowing Surface Enhanced Raman Scattering (SERS) sensing is considered. We developed a model, which randomly distributes hemispheroidal particles over a given area of the glass substrate and estimates SERS capabilities of the obtained structures. We applied Power Spectral Density (PSD) analysis to modeled structures and to atomic force microscope images widely used in SERS metal island films and metal dendrites. The comparison of measured and calculated SERS signals from differing characteristics structures with the results of PSD analysis of these structures has shown that this approach allows simple identification and choosing a structure topography, which is capable of providing the maximal enhancement of Raman signal within a given set of structures of the same type placed on the substrate.

Enhanced Raman Scattering of Silver/Foam Nickel Composite Structure Based on Ultraviolet Induction

Enhanced Raman Scattering of Silver/Foam Nickel Composite Structure Based on Ultraviolet Induction