Surface-enhanced Raman Scattering Research Articles

Broadband surface enhanced infrared absorption with multiple Fano resonance by metallic oblique-wire-bundle metamaterial absorbers

Higher sensitivity with specific recognition of a sensor could ease the burden of sample purification or labelling procedure for specific testing and detection and there appear two methods including surface enhanced infrared absorption (SEIRA) and surface enhanced Raman scattering (SERS), promising better sensitivity and specificity, simultaneously, via detection of molecular footprints. Furthermore, researchers employ Fano resonance to further boost the detection limit of SEIRA by coupling between two absorption bands from molecules and metamaterials. Still, the current metamaterial absorbers are almost narrow band and require a specific design, only suitable for limited chemicals. Thus, in this work, we would like to design a broadband oblique-wire-bundle (OWB) metamaterial absorber (MA) which could interact with multiple functional groups’ absorption from a sample, thus easing the burden of custom-made resonators. In experiments, indeed, our designed OWB MA developed four Fano resonance responses with three PMMAs’ functional groups and one function group from carbon dioxide. The counterpart planar MA also performed SEIRA yet without occurrence of Fano resonance as a comparison. We believe this proposed OWB MA could facilitate the development of rapid detection in the field of food safety and chemical detection.

Precise Methylation Detection of Tumor Suppressor Gene Promoters by Magnetic Enrichment and Nano Silver Adduct-Promoted Surface-Enhanced Raman Scattering.

Noninvasive liquid biopsies can be used for early tumor diagnosis by identifying the methylation level of the tumor suppressor genes (TSGs)-a reliable index for cancer evaluation. However, identifying trace circulating genes from specimens remains challenging. This work introduces a novel method that combines magnetic isolation and surface-enhanced Raman scattering (SERS) to concentrate and detect the methylated TSG promotors. A superparamagnetic iron oxide nanoparticle modified with streptavidin is prepared as a universal magnetic bead. Biotin-terminated probe single-strand DNA (ssDNA) is immobilized on the magnetic beads through biotin-streptavidin bioconjugation. Artificial target ssDNA fragments with various methylation levels are applied as a promoter gene model. Concentrated double-strand DNA (dsDNA) is produced by a hybridizing probe and target ssDNA on magnetic nanobeads, as well as an additional magnetic isolation process. The well-prepared DNA adduct, which consists of 3nm cisplatin-modified Ag nanoclusters, can specifically bind with guanine-cytosine base pairs of dsDNA. Ag-nanoparticle-induced localized SERS amplified signals of 5-methylcytosine (5-mC) from the dsDNA in Raman spectra, enabling accurate methylation level measurement in mixtures of 0-1µm methylated DNA, with a detection limit of 0.05µm. This method shows promise for enabling the methylation level evaluation of various TSGs and promoters in early cancer liquid biopsies.

In Situ SERS Monitoring of Schiff Base Reactions via Nanoparticles on a Mirror Platform

Schiff base reactions are widely used in pharmacy, catalysis, and volatile aldehyde detection. However, common biomarker sensing methods struggle to monitor this reaction process precisely due to their sensitivity, their time-consuming nature, and complex substrates. Here, we introduce the Nanoparticle-on-Mirror structure for in situ monitoring this reaction process through the application of a Au nanoparticle-p-Aminothiophenol-Au thin-film platform by surface-enhanced Raman scattering (SERS). Owing to the exposure of -NH2 groups and the local ultra-strong electromagnetic field in the nanocavity, the Schiff base reactions process can be rapidly monitored within two minutes. Meanwhile, the monitoring platform can detect benzaldehyde molecules as low as 10−6 M, showing excellent SERS performance. Notably, the Au-nanoparticle-p-Aminothiophenol-Au thin-film platform exhibited anti-interference and specificity, being able to identify BA in the presence of interference. The use of the Au-nanoparticle-p-Aminothiophenol-Au thin-film platform provides a sensing method for Schiff base reactions with accuracy and simplicity of operation, achieving a balanced approach for low-cost and high-performance real-time monitoring, which is expected to be applied in various catalytic reaction process monitoring and catalyst design processes.

SERS-Based Microfluidic Bioscreening Platform for Selective Detection of β-Amyloid Peptides.

This study reports development of a microfluidic device for highly sensitive and selective detection of a β-amyloid peptide (Aβ1-42) in simulated cerebrospinal fluid, using surface-enhanced Raman spectroscopy (SERS). The device ensemble comprises a purine ligand (Pu) and its interaction with silver nanoparticles (AgNPs) to generate SERS hotspots. The low surface energy of the synthesized Pu ligand and high surface energy of AgNPs are utilized for the functionalization and formation of a Pu-AgNP SERS substrate. We have integrated a novel polydimethylsiloxane (PDMS) microfluidic device with Pu-AgNPs using a combination of photo- and soft lithography fabrication, sealed by thermal cross-linking with another layer of PDMS, to produce an effective screening platform for Aβ1-42. The SERS spectrum from the microfluidic device affords almost noise-free measurements, with excellent limit-of-detection values.

Streamlined Flow Synthesis of Plasmonic Nanoparticles and SERS Detection of Uremic Toxins with Trace-Level Liquid Volumes in a Microchamber.

Rapid detection of uremic toxins is crucial due to their severe health risks, including oxidative stress, inflammation, neurotoxicity, cardiovascular complications, and progression of chronic kidney disease. Surface-enhanced Raman spectroscopy (SERS) may provide sensitive, fast, and clinical-grade real-time monitoring of these toxins, enabling effective management with timely dialysis treatments. This study introduces a 3D-printed microchamber that integrates the fabrication of plasmonic metal nanoparticles for the in-flow detection of biological toxins and pharmaceutical drugs using SERS, making it ideal for on-site diagnostics in clinical settings. The microchamber supports quantitative and highly reproducible detection with liquid volumes under 100 μL, which is crucial for trace-level biomarker detection and minimizing cross-contamination. It employs a tunable solvent exchange method for the in situ synthesis of silver nanoparticles (AgNPs) on flexible PDMS or rigid Si wafer substrates, avoiding costly nanofabrication techniques. Ultralow detection limits were achieved for two model compounds and three pharmaceutical drugs: 10-11 M for rhodamine 6G, 10-7 M for adenine, and 10-6 M for the pharmaceutical drugs. A total of 13 biological toxins, including three neurotransmitters, one neuromodulator, five amino acids, two polyamines, and two urea cycle metabolites, were detected with quantitative limits ranging from 10-3 to 10-6 M, all below permissible levels and aligning with physiological conditions. SERS detection within microchambers facilitates rapid on-site analysis, proving ideal for personalized health monitoring, point-of-care diagnostics, and environmental pollution assessment.

Exploring the role of graphene-metal hybrid nanomaterials as Raman signal enhancers in early stage cancer detection

Molecular diagnosis plays a significant role in detection of biomolecules linked to early stage cancer since it offers greater sensitivity and reliability for identification of biomarker level changes as the disease progresses. The application of vibrational spectroscopy in biomarker detection is defined by the fingerprint spectrum of a molecule originating from single-molecule vibrations. This characteristic makes surface enhanced Raman spectroscopy (SERS) a promising tool for identification of biomarkers. The performance of the SERS technique largely depends on the material being used as the SERS substrate. Graphene, with its large surface area and abundance of aromatic regions, is considered advantageous as SERS substrate. Combining graphene with metal nanomaterials considerably increases SERS signal intensity, thereby enhancing detection sensitivity. Therefore, this review emphasizes the significance of selecting graphene-metal nanohybrids as suitable SERS substrates for signal amplification. The detail understanding of the mechanism of graphene-metal hybrid in SERS based detection of early stage cancer is also presented. Furthermore, several examples demonstrated the application of graphene-metal hybrid nanomaterials in detecting biomarkers and cancer cell differentiation using SERS imaging.

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.

High performance SERS boosting by Fabry- Pérot cavities of silica-gold-silicon multilayers

Surface-enhanced Raman scattering (SERS), an advanced technique for molecular spectroscopy, relies heavily on the preparation of SERS active materials that can significantly enhance the Raman scattering signals for highly sensitive detection of trace molecules. Traditionally, SERS measurements are performed on silicon or silica substrates, the SERS performance is determined by the structure of SERS materials. Here, we show that the SERS signal can be amplified and modulated using Fabry-Pérot (F-P) cavities made of silica-silicon (SiO2-Si) or silica-gold-silicon (SiO2-Au-Si) multilayers as substrates. Periodic SERS signal variations as SiO2 thickness increases are observed, exhibiting optimal enhancement with the SiO2 thickness of 250 nm due to the optical interference in the cavity. Although the signal enhancement by optical interference is weaker than that by plasmonic resonance, additional signal amplification is essential for highly sensitive SERS materials. Moreover, we applied this strategy to detect thiram in bean sprout extracts, demonstrating that the detection sensitivity is two orders of magnitude higher than that using Si substrates. The utilization of the pseudo-internal standard intensity calibration method facilitates the quantitative analysis of thiram concentrations. Our results provide a promising approach for further amplification of SERS signals with great potential for practical applications.

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.

Ecofriendly magnetic nanocomposite (Fe3O4/SiO2/Ag) fabrication for sustainable dye wastewater management: catalysis and SERS for a cleaner approach.

Our study focuses on sustainable dye wastewater management through catalysis, scrutinized by surface-enhanced Raman spectroscopy (SERS) using an ecofriendly magnetic nanocomposite (Fe3O4/SiO2/Ag (FSA)). To our knowledge, the use of green synthesis for fabricating nanocomposites from a single source, namely Nerium oleander leaves, has not been extensively explored. This poses a distinctive and challenging approach, differentiating it from conventional chemical methods. Analytical investigations confirm the nanocomposite morphology, featuring Fe3O4 cubic cores with SiO2 spheres and silver nanoparticles (AgNPs) decoration. Efficient catalysis rapidly degrades unary and binary dye systems (MB, RhB, and MB + RhB), with high efficiency in short durations (MB: 96% in 10min, RhB: 94% in 2min, MB + RhB: 96% MB and 91% RhB in 9min) and with elevated "k" values. SERS monitors water quality, revealing complete degradation and quenching of dye fingerprints with fabricated nanocomposite FSA. The nanocomposite exhibits reusability over four cycles by easy recovery of catalyst with external magnet. The nanocomposite achieved 89.7% degradation efficiency in real-time household wastewater treatment. The proposed research aligns with UN SDGs 6 and 15 and this approach holds promise for advancing industrial waste management.

Microcavity Array-Based Digital SERS Chip for Rapid and Accurate Label-free Quantitative Detection of Live Bacteria.

In this study, we developed a novel digital surface-enhanced Raman spectroscopy (SERS) chip that integrates an inverted pyramid microcavity array, a microchannel cover plate, and a multilayer gold nanoparticle (AuNP) SERS substrate. This innovative design exploits the synergistic effects of the microcavity array and the microchannel to enable rapid and large-scale digital discretization of bacterial suspensions. The concentration effect of the picoliter cavities, combined with the superior Raman enhancement effect of the multilayer AuNP SERS substrate, allows for the precise identification of live bacteria within the microcavities through in situ and label-free SERS testing after a short incubation period. By counting the resulting positive or negative signals, the concentration of the target analyte can be directly determined via Poisson statistics. Experimental results demonstrate that this method enables the accurate quantification of Escherichia coli (E. coli) BL21 within a 4-h incubation period. Compared with traditional analog SERS detection methods, our proposed digital SERS detection strategy reduces the impact of signal intensity fluctuations, thereby significantly improving detection efficiency and accuracy. We believe that this digital SERS chip has great application prospects in the fields of bacterial detection, antibiotic resistance analysis, and cellular dynamics monitoring.

Phase Transformation on Two-Dimensional MoTe2 Films for Surface-Enhanced Raman Spectroscopy.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have recently become attractive candidate substrates for surface-enhanced Raman spectroscopy (SERS) owing to their atomically flat surfaces and adjustable electronic properties. Herein, large-scale 2D 1T'- and 2H-MoTe2 films were prepared using a chemical vapor deposition method. We found that phase structure plays an important role in the enhancement of the SERS performances of MoTe2 films. 1T'-MoTe2 films showed a strong SERS effect with a detection limit of 1 × 10-9 M for the R6G molecule, which is one order of magnitude lower than that of 2H-MoTe2 films. We demonstrated that the SERS sensitivity of MoTe2 films is derived from the efficient photoinduced charge transfer process between MoTe2 and adsorbed molecules. Moreover, a prohibited fish drug could be detected by using 1T'-MoTe2 films as SERS substrates. Our study paves the way to the development and application of high-performance SERS substrates based on TMD phase engineering.

Theoretical study of surface-enhanced Raman spectroscopy of dimethyl methylphosphonate

In this study, the surface-enhanced Raman spectroscopy spectra of dimethyl methyl phosphonate, which serves as a surrogate for the chemical warfare agent sarin, were modeled using density functional theory calculations. In addition, the fundamental mechanisms underlying the enhancement of surface-enhanced Raman spectroscopy are investigated. A comprehensive examination was conducted of the adsorption behavior and Surface-Enhanced Raman Spectroscopy enhancement effects resulting from the interaction between dimethyl methylphosphonate and silver clusters. Moreover, a comparison was made between the findings of the present study and the results of previous experiments in order to ascertain the optimal positions for the adsorption of silver clusters on dimethyl methylphosphonate molecules. In this article, the kinetics of the interaction between dimethyl methylphosphonate and silver clusters were theoretically explored through six different adsorption configurations. It was found that the configuration involving the dimethyl methylphosphonate structure and silver clusters containing three silver atoms exhibited the highest stability. By integrating Raman spectroscopic data with our theoretical insights, the vibrational modes, Raman spectra, and surface-enhanced Raman spectra of dimethyl methylphosphonate molecules were systematically correlated using Gaussian 09 and GaussView 5.0.8 software for detailed image-based analysis.

Enhanced SERS signal in the hybrid substrate through electronic modulation of CVD grown single-layer graphene

The ever-growing demand for sensitive and reliable detection of hazardous material in the food chain and trace detection of chemical entities in a variety field attracted advanced Surface Enhanced Raman Spectroscopy (SERS) active material such as graphene-based hybrid SERS. The graphene‑silver nanostructures (AgNS) based hybrid SERS substrates are explored to understand the critical role of pristine graphene grown by chemical vapor deposition (CVD) on SERS signal and its possible mechanism. A lithography-free fabrication process has been developed for growth of uniform array of AgNS with varying both particle sizes and inter-particle gaps. The optimal AgNS with feature size ~40 nm and inter-particle spacing of ~13 nm demonstrated the maximum SERS enhancement with Rhodamine 6G (R6G). The single-layer graphene (SLG) grown by CVD with the aid of controlling the reaction geometry with growth under a free molecular regime leads to the highest quality graphene with I2D/IG ratio of ~3.58 and ID/IG ratio of 0.1539. The flow regime-controlled CVD-grown SLG integrated with AgNS and its SERS enhancement mechanism is explored for trace detection of R6G. The graphene with its ability to modulate the electronic structure and tune it relative to the highest occupied molecular orbital-lowest occupied molecular orbital (HOMO-LUMO) levels of R6G molecules resulted in improved SERS signal by about an order for graphene-AgNS hybrid structure as compared to bare AgNS. The obtained findings paved the way for the futuristic and reliable hybrid SERS substrate for trace-level detection of a wide range of chemical entities.

DLC based substrate enabling single molecule detection by Surface Enhanced Raman Spectroscopy (SERS)

This work shows a new and surprising application of Diamond-Like Carbon as Surface Enhanced Raman Spectroscopy (SERS) substrate. It was investigated with the well-known Rhodamine 6G (R6G) as SERS test molecule and extended the detection limit to the astonishing attomolar level, which means single molecule detection. The SERS substrate started by depositing excellent quality Diamond-Like Carbon (DLC) on aluminum, followed by laser modification of the DLC in a delimited area that defines the SERS substrate. The laser action gives electrical conductivity between the scratched surface and the aluminum. Silver was electrodeposited on this delimited area. The high Enhancement Factor was around 5 × 1012 at an R6G concentration of 7 × 10−18 M, observed only at few (and difficult to hit upon) points since the surface density was smaller than 2 R6G molecules/mm2. At each of the larger concentrations tested (7 × 10−15, 7 × 10−12, 7 × 10−9 and 7 × 10−6 M), the Raman intensities were in the same order of magnitude along the whole substrate, indicating a pretty homogeneous sensitivity. The repeatability among 5 samples tested at 7 × 10−12 M showed a standard deviation of only 18 %. The nano porous structure of the silver deposits, shown by Field Emission Gun Scanning Electron Microscopy (FEG-SEM) appears to be like many other studies with electroplated silver. However, the Raman spectra backgrounds show that amorphous carbon is interacting with the silver nanoparticles. A probable explanation for the superior EF is the synergistic contributions of plasmon enhancement from silver and chemical enhancement from amorphous carbon nanostructure.

Recyclable NiO/g-C3N4/ag hybrid substrates for sensitive SERS detection and photo-degradation of residual pesticides in beverages

In this research, we fabricated an innovative NiO/CN/Ag composite through the straightforward electrostatic assembly of Ag nanoparticles and g-C3N4 sheets onto NiO nanoflowers. This composite enables both surface enhanced Raman spectroscopy (SERS) detection and photo-degradation of pesticides. The results reveal NiO/CN/Ag can quantitatively detect thiram (TRM) and diquat dibromide (DQDB) in water, with a limit of detection (LOD) of 10−9 M, and also exhibit outstanding photo-degradation efficiency, exceeding 95 % for TRM and DQDB within 90 min under simulated sunlight. Significantly, after the organic reagent (citric acid) on NiO/CN/Ag was completely removed through simulated solar irradiation, the signal-to-noise ratios of SERS spectra on NiO/CN/Ag were enhanced, achieving LODs of 10−8 M for TRM and DQDB in different fruit juices and dried flower teas. Additionally, the composite demonstrate impressive recyclability, maintaining robust SERS signals and high degradation rates even after five cycles of “detection-degradation” processes.

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.

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.

A multilevel cooperative attention network of precise quantitative analysis for predicting ractopamine concentration via adaptive weighted feature selection and multichannel feature fusion

Surface enhanced Raman spectroscopy (SERS) holds great potential due to its rapid detection and high sensitivity. However, issues such as signal noise, fluctuations, and spectral shifts can negatively impact its performance in detecting ractopamine in pork. Hierarchical Gradient Aware Spectral Network (HGASNet) was proposed to address these issues. The key innovations are the Spectral Gradient Weighted Attention (SGWA) and Multi-Channel Peak Attention Mechanism (MCPAM) modules within HGASNet. The SGWA module dynamically adjusts feature weights, enhancing sensitivity to critical Raman spectral shifts. Meanwhile, MCPAM leverages multi-channel attention to better capture long range dependencies and fuse global and local information. Additionally, HGASNet's hierarchical structure incrementally extracts and integrates features at various levels, enabling the model to focus on global features in the higher layers while preserving fine-grained local details in the lower layers. Experimental results show HGASNet outperforming existing approaches, achieving R2 of 0.9972, RMSRE of 0.0413, RMSLE of 0.0548, sMAPE of 6.47 %, and MAPE of 6.72 %.