Surface-enhanced Raman Scattering Substrates Research Articles

Novel Ratiometric Surface-Enhanced Raman Scattering (SERS) Biosensor for Ultrasensitive Quantitative Monitoring of Human Carboxylesterase-1 in Hepatocellular Carcinoma Cells Using Ag-Au Nanoflowers as SERS Substrate.

In this study, we developed ratiometric surface-enhanced Raman scattering (SERS) biosensors using Ag-Au alloy nanoflowers as SERS substrates, molecules having amide bonds and alkyne groups (Tag A) as Raman reporters, and sodium thiocyanate as an internal standard molecule (Tag B) for the sensitive detection of human carboxylesterase-1 (hCE1) in HepG-2 cells. The correlation between HepG-2 cell damage and hCE1 activity levels was investigated. Both Tag A's alkyne group and Tag B's cyanide group produced characteristic SERS signals in the Raman-silent region (I2000cm-1 and I2115cm-1, respectively). The hydrolysis of the amide bond in Tag A via hCE1 and the shedding of the alkyne group led to a reduction in the SERS signal intensity observed at I2000cm-1. Conversely, the SERS signal intensity of Tag B at I2115cm-1 exhibited a consistent pattern. As the activity level of hCE1 and the ratiometric peak intensity (I2000cm-1/I2115cm-1) correlated negatively, hCE1 could be quantitatively detected within the range of 10-2 to 2 × 102 ng·mL-1, with a detection limit of 7.3 pg·mL-1. The ratiometric SERS probe strategy, in which a ratio response is employed, permits sensitive and reproducible SERS detection by facilitating intrinsic calibration to rectify signal fluctuations resulting from temporal and spatial variations in the detection conditions. Concurrently, the implementation of Raman-silent region reporter molecules mitigates the interference from endogenous biomolecules in SERS measurements and offers a novel approach for achieving highly sensitive and interference-free detection of intracellular hCE1.

Construction and Application of Au NRs/4-MBA/PAM Ratiometric Surface-Enhanced Raman Scattering Substrate for Fish Veterinary Drug Residue Detection

Surface-enhanced Raman scattering (SERS) is widely used for trace detection of substances, and the key to this technology lies in the preparation of the substrate material. In this study, a composite SERS material of Au NRs/4-MBA/PAM was constructed and characterized to better immobilize the reference molecule 4-mercaptobenzoic acid (4-MBA). Electron transmission microscopy results demonstrated that the PAM film helps Au NRs to pack closely, enhancing the stability of the material structure and reducing the interference of external environmental factors on the response of 4-MBA, thus improving the accuracy of quantitative determination. Comparative experimental results with the Au NRs/4-MBA substrate showed that the relative standard deviations (RSDs) of the detection results for MG on different batches of Au NRs/4-MBA/PAM were less than 8.0%, and the RSDs of different points on the same material were less than 10.0%, indicating that the Au NRs/4-MBA/PAM has higher uniformity, better reproducibility, and higher sensitivity in detecting malachite green (MG). Applying this material in the recovery determination of fish extract showed that the recovery rates of MG were between 75.60% and 83.24%. Therefore, the Au NRs/4-MBA/PAM substrate can accurately detect and quantify veterinary drug residue in complex matrices such as food tissue.

Phase-Engineered Transition Metal Dichalcogenides for Highly Efficient Surface-Enhanced Raman Scattering.

Phase engineering of two-dimensional (2D) transition metal dichalcogenides (TMDs) is an attractive avenue to construct new surface-enhanced Raman scattering (SERS) substrates. Herein, 2D WS2 and MoS2 monolayers with high-purity distorted octahedral phase (1T') are prepared for highly sensitive SERS detection of analytes (e.g., rhodamine 6G, rhodamine B and crystal violet). 1T'-WS2 and 1T'-MoS2 monolayers show the detection limits of 8.28 × 10-12 and 8.57 × 10-11 M for rhodamine 6G, with the enhancement factors of 4.6 × 108 and 3.9 × 107, respectively, which are comparable to noble-metal substrates, outperforming semiconducting 2H-W(Mo)S2 monolayers and most of the reported non-noble-metal substrates. First-principles density functional theory calculations show that their Raman enhancement effect is mainly ascribed to highly efficient interfacial charge transfer between the 1T'-W(Mo)S2 monolayers and analytes. Our study reveals that 2D TMDs with semimetallic 1T' phase are promising as next-generation SERS substrates.

Optical SERS sensor with dandelion flower-like Ag/ZnFe2O4 nanotubes on the Si pyramids for detecting trace dyes

It is difficult for metal-modified semiconductor nanotubes to obtain surface-enhanced Raman scattering (SERS) substrates through long-range ordered 3D assembly, which adversely affects both Raman signal enhancement and Raman signal uniformity. Here, ZnFe2O4 nanotubes with Ag nanoparticles modified on the inner and outer walls are induced to grow on the surface of the ordered Si pyramid by ZnO nanonedles as sacrificial templates. In this way, the composite nanotubes (Ag/ZnFe2O4) are assembled into dandelion flower-like 3D aggregates with a periodic arrangement of hexagonal close packing. This 3D ordered SERS substrate based on Ag/ZnFe2O4 nanotubes has excellent anti-reflective performance and carrier separation ability, which is conducive to the enhancement of Raman signal. When the SERS substrate is used as a sensor, it can achieve the single molecule (10-13M) detection level of Rhodamine 6G, the enhancement factor (EF) is 3.14 × 109, and the linear fit (R2) of quantitative analysis is as high as 0.998 from 10-13 to 10-4M. Meanwhile, the long-range ordered arrays on the SERS substrate can ensure the signal uniformity of sensor, which relative standard deviation (RSD) is as low as 3.37%. In addition, the photocatalytic self-cleaning capability of SERS substrate ensures that the sensor can be reused. Finally, the mechanism of the photogenerated carrier migration of Ag/ZnFe2O4 and its contribution to Raman signal enhancement were analyzed.

Dendritic copper nanostructures for ultrasensitive detection of rhodamine 6G and Congo red

Surface-Enhanced Raman Scattering (SERS) is a fast-responding and non-destructive ultra-sensitive detection technique that can replace traditional chromatographic and spectroscopic analysis techniques. In this experiment, dendritic copper nanostructures were prepared by the solid-state ionics method and the vacuum hot evaporation process with an applied current of I=9μA. Using them as a SERS substrate, Raman detection was performed on the dye molecules Rhodamine 6G (R6G) and Congo Red (CR) to determine SERS enhancement performance. It is found that the growth of the prepared copper nanostructures has a top-end dominant phenomenon. The fractal dimension of the copper nanostructure was calculated using fractal theory, and it was revealed to be 1.560. Scanning electron microscopy (SEM) results showed that a large number of 60-80 nm regularly arranged copper nanoparticles were attached to the surface of the dendritic copper nanostructure. This is beneficial to increase the surface roughness of the substrate and improve the detection level of dye molecules. Subsequently, copper nanostructures can sensitively detect R6G and CR solutions as low as 1×10-13 mol/L and 1×10-7 mol/L, reaching single-molecule levels. The Raman mapping experiment showed that the mean relative standard deviation (RSD) values of R6G and CR were 12.3% and 12.9%, indicating high uniformity and reproducibility of the structure. This structure effectively achieves the fusion of uniformity, repeatability, and sensitivity, and shows broad application prospects in food detection.

Mechanically Flexible, Large-Area Fabrication of Three-Dimensional Dendritic Au Films for Reproducible Surface-Enhanced Raman Scattering Detection of Nanoplastics.

The escalating crisis of nanoplastic pollution in water and food products demands the development of novel methodologies for detection and recycling. Despite various techniques available, surface-enhanced Raman scattering (SERS) is emerging as a highly efficient technique for the trace detection of micro/nanoplastics. However, the development of highly reproducible and stable, flexible SERS substrates that can be used for sensitive detection in environmental medium remains a challenge. Here, we report a fabrication of large-area, three-dimensional (3D), and highly flexible SERS substrate based on porous dendritic Au films onto a flexible indium tin oxide (ITO) substrate via facile, thermal evaporation of Au over the vacuum-compatible deep eutectic solvent (DES)-coated glass substrate and subsequent direct transfer process. The as-fabricated 3D dendritic Au/ITO flexible substrates can be used for ultrasensitive SERS detection of crystal violet (CV) as probe analyte molecules with the limit of detection (LOD) as low as 6.4 × 10-15 M, with good signal reproducibility (RSD of 11.3%). In addition, the substrate showed excellent sensitivity in detecting nanoplastics such as poly(ethylene terephthalate) (200 nm) and polystyrene (100 nm) with LODs reaching up to 0.051 and 8.2 μg/mL, respectively. This work provides a facile approach for the preparation of highly flexible plasmonic substrates, showing great potential for the SERS detection of a variety of environmental pollutants.

Homogeneous Mo1−xRexS2 monolayer and lateral 1T’@2H heterostructures for significantly enhanced and highly reproducible SERS responses and mechanistic insights

As a promising surface-enhanced Raman scattering (SERS) substrate, two-dimensional (2D) nanomaterials ensure the uniformity and reproducibility of the SERS response. However, their extremely flat surfaces are not beneficial for high-capacity binding of analytes and significant enhancement of Raman signals. In this contribution, monolayer Mo0.27Re0.73S2 alloys with distorted lattice and modulated optoelectronic structure are facilely fabricated by space-confined chemical vapor deposition (CVD), exhibiting a significantly enhanced SERS performance with an enhancement factor of 2.0 × 1011. As demonstrated, the continuous increment of Re ratio results in a phase transition from 2H to 1T’ for homogeneous Mo1−xRexS2 monolayers. As a result, the 1T’-phase Mo0.27Re0.73S2 alloys achieve a sensitive detection of down to 10−15 M for Rhodamine 6G while the value on MoS2 or ReS2 is only 10−9 M. Additionally, the alloy-based SERS substrate demonstrates excellent SERS detection reproducibility, long-term stability, and universality. Referring to the space-confined CVD, a dynamics-controlled process is further employed for the in-situ fabrication of 1T’@2H Mo1−xRexS2 heterostructures, providing a new approach and insight for facilely building varied phases-based lateral heterostructures by the control of composition ratio. Overall, this work demonstrates the enormous potential of alloy engineering in improving the SERS performance of TMDs and the convenient fabrication of out-of-phase TMD alloys.

Unveiling multimodal hot carrier excitation in plasmonic bimetallic Au@Ag nanostars for photochemistry and SERS sensing

AbstractPlasmonic nanostructures stand at the forefront of nanophotonics research, particularly in sensing and energy conversion applications. Their unique ability to confine light energy at the nanoscale makes them indispensable for a wide array of technological advancements. The study of these structures often makes use of different materials and, even more extensively, explores new shapes and configurations to extend our common repertoire of useful nanophotonics tools. Exploring the creation of bimetallic plasmonic nanostructures combines these two dimensions determining the space of possible plasmonic resonators and opens the possibility of tailoring systems with behavior unavailable to single-metal plasmonic structures. In this paper, we delve into the exploration of bimetallic systems employing plasmonic nanostars. These structures have demonstrated remarkable capabilities for surface-enhanced Raman scattering (SERS) spectroscopy and photochemistry, due to the strong plasmonic response of their peaks, whose disposition following a spherical symmetry makes them largely polarization- and orientation-insensitive. Herein, we report the colloidal synthesis of two different water-stable Au@Ag nanostars, explore their performance as photocatalysts and SERS substrates, and provide an in-depth account of their non-trivial physical response.

Reusable SERS Platform of Femtosecond Laser Processed Substrate for Detection of Malachite Green

This study presents the development of highly efficient Surface-Enhanced Raman Scattering (SERS) substrates through femtosecond (fs) laser processing of crystalline silicon (Si), resulting in mountain-like microstructures. These microstructures, when decorated with gold nanoparticles (Au NPs), exhibit remarkable SERS performance due to the creation of concentrated hotspots. The enhanced Raman signals originate from the excitation of localized surface plasmon resonance (LSPR) of the Au NPs and the multi-scale rough morphology of the Si substrates. Finite-element method simulations confirm the electromagnetic field enhancement in narrow gaps, supporting the experimental observations. The fabricated substrates show high uniformity, oxidation resistance, long-term stability, and exceptional reproducibility, making them ideal for molecular detection, especially in food safety applications. A remarkable enhancement factor (EF) of 1010 is attained in the detection of Malachite Green (MG), boasting a limit of detection (LoD) as low as 10−14 M. This underscores the immense potential of this technique for achieving highly sensitive and dependable SERS-based sensing capabilities.

Plasmonic chitosan cross-linked dialdehyde chitosan aerogels as 3D surface-enhanced Raman scattering substrates for sensitive and reliable detection

Surface Enhanced Raman Scattering (SERS) has the advantages of non-destructive detection and high sensitivity, however, low hotspots utilisation and inhomogeneous distribution limit its application. In response to the problem of underutilization of hotspots in most SERS substrates, a crosslinking of chitosan with dialdehyde chitosan aerogels loaded with Ag NPs (CDSA) as SERS substrates with chitosan (CS) as the main body and dialdehyde chitosan (DACS) as the reducing and cross-linking agent were prepared. Unlike other 3D structures such as hydrogels, CDSA can capture probe molecules in a much shorter period of time and enhance SERS signals by collapse. The SERS performance of CDSA was evaluated by rhodamine 6 G (R6G) and methylene blue (MB), indicating that the CDSA substrate has good stability (90 days), repeatability (RSD=4.15 %) and reproducibility (RSD=4.86 %). The enhancement factors (EFs) was 1.3×108 for R6G and 9.2×107 for MB. Both gas sample and liquid sample were detected to evaluate the performances of CDSA in practical application. 4-Aminothiophenol (4-ATP) was utilized to test the efficacy of CDSA on gas-phase to-be-tested substances and the limit of detection (LOD) was 0.59 mg/L. The tests performed on sildenafil (SD) in real samples showed recoveries ranging from 97.5 % to 103.4 % with a LOD of 0.055 mg/L. It was indicated that the CDSA substrate could serves as a satisfactory SERS sensor for sensitive and rapid detection for both gas phase and liquid samples.

Plasmonic Nanocubes with a Controllable "Crescent Arc" Facet: Tunable Hotspot Engineering for Highly Reliable and Sensitive SERS Detection.

The fine control of the nanogap and morphology of metal nanoparticles (NPs) has always been an obstacle, hindering the development and application of surface-enhanced Raman scattering (SERS) quantitative detection. Here, Au/4-mercaptobenzoic acid@Ag@Au-Ag bimetal core-shell nanocubes (NCs) with a "crescent arc" facet (C-Au/4MBA@Ag NCs) as a highly reliable and sensitive surface-enhanced Raman scattering SERS substrate is proposed for the first time. The bifunctional internal standard (IS) molecules (4MBA) govern the morphology of metal shells to maintain cubic configuration and provide calibration for SERS signals' flotation. In parallel, the controllable curvature of the C-Au/4MBA@Ag NCs is directly modulated by adjusting the relative rates of the galvanic replacement and co-reduction reaction, which generates a controllable interparticle nanogap to offer large depositing spaces for analytes and improve authoritative SERS signals' enhancement. The proposed C-Au/4MBA@Ag NCs exhibit an enhancement factor of up to 4.8 × 1010 and contribute to the ultralow RSD (7.9%). These C-Au/4MBA@Ag NCs also enable the detection of hazardous pesticide residues such as methamidophos and thiram in herbal plants with a complex matrix, with an average detection accuracy of up to 96%. In summary, this study achieves a fine control strategy of the "crescent arc" surface for improving SERS performance and explores the practical application potential for accurate and sensitive Raman detection of hazardous substances.

Development and Biomedical Application of Non-Noble Metal Nanomaterials in SERS.

Surface-enhanced Raman scattering (SERS) is vital in many fields because of its high sensitivity, fast response, and fingerprint effect. The surface-enhanced Raman mechanisms are generally electromagnetic enhancement (EM), which is mainly based on noble metals (Au, Ag, etc.), and chemical enhancement (CM). With more and more studies on CM mechanism in recent years, non-noble metal nanomaterial SERS substrates gradually became widely researched and applied due to their superior economy, stability, selectivity, and biocompatibility compared to noble metal. In addition, non-noble metal substrates also provide an ideal new platform for SERS technology to probe the mechanism of biomolecules. In this paper, we review the applications of non-noble metal nanomaterials in SERS detection for biomedical engineering in recent years. Firstly, we introduce the development of some more common non-noble metal SERS substrates and discuss their properties and enhancement mechanisms. Subsequently, we focus on the progress of the application of SERS detection of non-noble metal nanomaterials, such as analysis of biomarkers and the detection of some contaminants. Finally, we look forward to the future research process of non-noble metal substrate nanomaterials for biomedicine, which may draw more attention to the biosensor applications of non-noble metal nanomaterial-based SERS substrates.

Two- and Three-Dimensional Ag-Au Nanoalloying: Heterogeneous Building Blocks Enhancing Near-Field Focusing.

In this study, we report a strategy for fabricating binary surface-enhanced Raman scattering (SERS) substrates composed of plasmonic Pt@Ag and Pt@Au truncated-octahedral (TOh) dual-rim nanoframes (DNFs) functioning as a "nanoalloy." Pt TOh frameworks act as a scaffold to develop nanoarchitectures with surface decoration using plasmonically active materials (i.e., Au or Ag), resulting in identical sizes and shapes for the two distinct plasmonic elements, facilitating the fabrication of a "nanoalloy" blend of two shape-complex building blocks. The structural complexity from the dual-rim on (111) facets, combined with the mirror charge effect (i.e., enhanced polarization between Ag and Au) at the interface of heterogeneous components, significantly amplifies SERS activity. We carefully investigated near-field focusing of binary SERS substrates through single-particle and bulk SERS measurements corroborated by finite element method (FEM) calculations. Crucially, we developed free-standing superpowders (SPs) in which each heterogeneous building block formed micron-sized supercrystals with adjustable component ratios. These plasmonic SPs were applied to contaminated areas for analyte detection, demonstrating their potential for practical SERS applications.

Introduction and Development of Surface-Enhanced Raman Scattering (SERS) Substrates: A Review.

Since its discovery, the phenomenon of Surface Enhanced Raman Scattering (SERS) has gradually become an important tool for analyzing the composition and structure of substances. As a trace technique that can efficiently and nondestructively detect single molecules, the application of SERS has expanded from environmental and materials science to biomedical fields. In the past decade or so, the explosive development of nanotechnology and nanomaterials has further boosted the research of SERS technology, as nanomaterial-based SERS substrates have shown good signal enhancement properties. So far, it is widely recognized that the morphology, size, composition, and stacking mode of nanomaterials have a very great influence on the strength of the substrate SERS effect. Herein, an overview of methods for the preparation of surface-enhanced Raman scattering (SERS) substrates is provided. Specifically, this review describes a variety of common SERS substrate preparation methods and explores the potential and promise of these methods for applications in chemical analysis and biomedical fields. By detailing the influence of different nanomaterials (e.g., metallic nanoparticles, nanowires, and nanostars) and their structural features on the SERS effect, this article aims to provide a comprehensive understanding of SERS substrate preparation techniques.

Perfluorodecanethiol-Functionalized Silver Nanoparticles on Polyester Films as High-Performance Surface-Enhanced Raman Spectroscopy Substrates.

The insufficient capabilities of current surface-enhanced Raman scattering (SERS) substrates in enriching dilute analytes from complex media severely restrict detection sensitivity, hampering practical applications. To meet this demand, in this study, a novel super hydrophobic membrane that can be directly prepared on a large scale based on the silver nanoparticles (AgNPs) functioning with perfluorodecanethiol (PFDT) is fabricated and evaluated as an SERS substrate. Firstly, polyester (PET) films modified with sodium chloride were proven to be capable of loading AgNPs, and the sizes of AgNPs were investigated. In addition, the PFDT concentration and reaction time for functionalizing the surface of AgNPs have been optimized. The relationship between the hydrophobic properties of the film and its SERS performance was then studied. The PET@Ag-PFDT film demonstrates two orders of magnitude superior SERS performance than the unmodified PET@Ag substrate, with a detection limit of folic acid approaching 5 × 10-10 M.

Structural-modulated substrate of MXene for surface-enhanced Raman scattering sensing.

The distinctive structure of MXene offers exceptional electron transport properties, abundant surface chemistry, and robust mechanical attributes, thereby bestowing it with remarkable advantages and promising prospects in the realm of surface-enhanced Raman scattering (SERS). This review comprehensively outlines the evolution, synthesis methodologies, and characterization techniques employed for MXene-based SERS substrates. It delves into the intricacies of its SERS enhancement mechanism, substrate variants, and performance metrics, alongside showcasing its diverse applications spanning molecular detection, biosensing, and environmental monitoring. Furthermore, it endeavors to pinpoint the research bottlenecks and chart the future research trajectories for MXene-based SERS substrates.

Synergistic enhancement of chemical and electromagnetic effects in a Ti3C2Tx/AgNPs two-dimensional SERS substrate for ultra-sensitive detection

BackgroundIt is well established that surface-enhanced Raman scattering (SERS) is one of the most commonly used spectral analysis techniques in real-world applications, including chemical and biological sensing, analytical detection, and even forensics. It offers high sensitivity, high resistance to solvents, photobleaching, and limited spectrum bands. In general, SERS is caused by two mechanisms, the electromagnetic enhancement mechanism (EM) and the chemical enhancement mechanism (CM), although the exact mechanism is not yet known. For increased sensitivity, a SERS substrate based on EM coupled with CM is essential. ResultsUsing electrostatic self-assembly, we fabricated many homogeneous hot spots for the substrate by evenly mixing positive charge Ag nanoparticles (AgNPs) with negative charge Ti3C2Tx. In addition, there is a clearly enhanced effect due to the high affinity between the tested molecule and Ti3C2Tx, which facilitates molecule-to-molecule charge transfer. After successfully preparing the Ti3C2Tx/AgNPs substrate, the R6G dye molecule was used to investigate its SERS activity. According to the results, the substrate can reach an enhancement factor of 3.8 × 108. Furthermore, it has been demonstrated that the coupling effect between EM and CM is the main reason for the excellent performance of the Ti3C2Tx/AgNPs composite substrate. Based upon the results of detecting the two biomarkers, adenosine triphosphate and folic acid, the detection limits were determined to be 4.27 × 10−9 M and 7.26 × 10−13 M, respectively. Significance and noveltyTwo-dimensional metal carbide Ti3C2Tx material can be used to obtain CM in surface Raman scattering. It has been demonstrated that the combination of CM and EM with nano-precious metals can produce an extremely sensitive SERS substrate that is dependable and stable. Additionally, the Ti3C2Tx/AgNPs study offers a novel perspective for the advancement of the SERS coupling mechanism in addition to providing direction for realistic detection.

Fabrication of Surface-Enhanced Raman Scattering (SERS) Substrates in Analytical Science by Natural-inspired Materials: A Review

Surface-Enhanced Raman Scattering (SERS) spectroscopy, as a novel rapid detection technology, offers molecular fingerprinting capabilities that achieve trace-level detection. The key to optimizing SERS sensitivity and reliability lies in the precise control of the nanostructures of SERS substrates. Nature, through billions of years of evolution, has served as a masterful creator, developing organisms with remarkable abilities based on micro/nanostructures, such as the superhydrophobicity of lotus leaves and the strong adhesive forces of gecko feet. This review categorizes the recent developments in SERS substrates inspired by natural materials into three main types: plant-based, animal-based, and virus-based. Each category is explored in detail, describing how their unique nanoarchitectures inspire the development of highly sensitive SERS substrates, along with their fabrication methods and applications in analytical science. Additionally, the review identifies current challenges, such as the uniformity and scalability of naturally inspired SERS substrates and suggests future directions, including the integration of hybrid biomimetic structures and advanced manufacturing techniques. By fostering a deeper understanding of these nature-inspired materials, we aim to enhance the practical application of SERS in analytical science in the future.

Preparation and Application of Two-Dimensional Ta4C3 MXene/Gold Nanostar Composite SERS Substrates for Thiram Detection.

Surface-enhanced Raman scattering (SERS) is a novel spectroscopic technique that enables the identification of analytes through analysis of their unique chemical signatures. Its high sensitivity, specificity, and rapid response make it a valuable tool in a range of fields, including biological detection, food safety, and environmental monitoring. However, traditional SERS nanoparticle substrates are susceptible to instability and agglomeration. In this study, Ta4C3 MXene/gold nanostar (AuNSs) hybrids were prepared as SERS substrates. By optimizing the experimental conditions of AuNSs, the optimal preparation method for the Ta4C3 MXene/AuNSs composite structure was identified. The addition of MXene to the Ta4C3 MXene/AuNSs hybrid substrates was found to enhance the sensitivity of the composite for Raman detection, as evaluated using 4-aminothiophenol (PATP) as a Raman molecule. This improvement in sensitivity is attributed to the enhanced electromagnetic properties of the hybrid substrates, which facilitate more efficient charge transfer and enhance the Raman scattering process. The limit of detection (LOD) of Ta4C3 MXene/AuNSs is 10-9 M for PATP and 10-7 M for thiram solutions. In addition, good reproducibility and spatial uniformity were obtained for the Raman signals of Ta4C3 MXene/AuNSs. Furthermore, Ta4C3 MXene/AuNSs were combined with filter paper to create paper-based SERS substrates that could be used for detection. By directly wiping the apple peel and subsequently detecting the thiram residues using Ta4C3 MXene/AuNSs, the level of detection of thiram residues on the peel surface was down to 7.8 ng/cm2.

Laser-induced the enhancement of Raman scattering performance in WO3-x/Ag composite films

Non-stoichiometric tungsten oxide (WO3-x) has controllable defects, high charge density, and good synergy with other materials to exhibit good surface-enhanced Raman scattering (SERS) properties. Its heterojunction structure provides an opportunity to develop high-quality and low-cost SERS substrates. This study obtained WO3-x/Ag composite thin films were obtained by Nd: YAG fiber pulsed laser modification at ambient conditions. The effects of interactions between heterojunctions and laser modification on the samples’ morphology, composition, and optical properties were investigated. The absorption peaks exhibited a red shift by varying the laser scan speeds, and the SERS properties of the sample were evaluated by methylene blue (MB) dye. The results show that the laser-modified WO3-x/Ag films have good stability as SERS substrates. The characteristic peaks of MB can still be detected after 90 days in the air. The WO3-x/Ag films also have good homogeneity and a low detection limit, with a limit of detection (LOD) as low as 10−7 M, and an enhancement factor as high as 1.34 × 104. The simulated results by the finite difference in time domain (FDTD) showed substantial agreement with those of the experimental ones.