Surface-enhanced Raman Scattering Research Articles

Trace Detection of Deltamethrin via Au/Cu2O/ZnO SERS Substrates with Multiple Heterojunctions.

Organic pesticide residues accumulate in the human body through dietary consumption, presenting a significant health risk. Therefore, efficient and sensitive detection of these residues is crucial. Surface-enhanced Raman scattering (SERS), as a powerful non-destructive detection technology, has attracted more attention due to its exceptional sensitivity and versatility. This study presents a novel Au/Cu2O/ZnO SERS substrate, synthesized through a multiple-cycle chemical adsorption plus reduction method, which exhibits exceptional sensitivity, stability, and repeatability. The substrate achieves a remarkable limit of detection (LOD) of 10-13 M for Rhodamine 6G (R6G), with an impressive enhancement factor of approximately 3.8 × 1010. Notably, the substrate's efficacy was further demonstrated in the successful detection of deltamethrin with a LOD of 0.01 mg/L. The effects of ZnO, Cu2O, and Au on the SERS performance of the substrate were clarified through a comprehensive analysis of the charge transfer mechanism. Experimental results demonstrate that the multiple heterojunctions within the ternary composite structure significantly facilitate the photo-induced charge transfer, thereby enhancing the SERS activity. This study demonstrates the potential of three-dimensional structures with multiple heterojunctions to significantly improve SERS performance and offers a novel strategy for designing noble metal/semiconductor SERS substrates characterized by dense hotspots and high charge transfer contributions.

Comparison of Raman spectroscopy with mass spectrometry for sequence typing of Acinetobacter baumannii strains: a single-center study.

The rapid and accurate sequence typing (ST) of bacterial pathogens is pivotal in controlling transmission within healthcare settings. Acinetobacter baumannii infection, known for its high transmissibility and drug resistance, presents a major challenge in nosocomial infection control. In this study, surface-enhanced Raman spectroscopy (SERS) was used to differentiate A. baumannii strains with distinct STs based on unique Raman spectral profiles. We then constructed and compared eight machine-learning models on SERS spectra to quickly identify bacterial STs. The results showed that the support vector machine model outperformed matrix-assisted laser desorption/ionization time-of-flight mass spectrometer in determining A. baumannii STs. This approach enables rapid identification of A. baumannii variants with different STs, supporting the early detection and control of nosocomial infections by this multidrug-resistant pathogen.

Recent Developments in SERS Microfluidic Chips: From Fundamentals to Biosensing Applications.

This paper reviews the latest research progress of surface-enhanced Raman spectroscopy (SERS) microfluidic chips in the field of biosensing. Due to its single-molecule sensitivity, selectivity, minimal or no preprocessing, and immediacy, SERS is considered a promising biosensing technology. However, the nondirectional interactions between biological samples and the substrate, as well as fluctuations in the sample environment temperature during signal acquisition, can affect the stability and reproducibility of SERS signals. Integrating SERS spectroscopy with microfluidic chips not only leverages the continuous sample flow, high reaction efficiency, high throughput, and multifunctionality of microfluidic chips to address challenges in biosensing applications but also expands the scope of microfluidic technology by providing a novel on-chip optical detection method. The combination of SERS and microfluidic chips not only enables the complementary advantages of both technologies but also offers a highly promising "combined technology" for the field of biosensing. This paper starts by introducing the enhancement mechanisms of SERS and presents both labeled and label-free SERS strategies. Based on the differences in substrate properties, we broadly categorize SERS microfluidic chips into colloidal nanoparticle-based SERS microfluidic chips and fixed substrate-based SERS microfluidic chips. Finally, we review the latest research progress on SERS microfluidic chips for biosensing biological targets such as nucleic acids, proteins, small biomolecules, and live cells. In the conclusion and outlook section, we summarize the challenges faced by SERS microfluidic chips in biosensing and propose feasible solutions. To better leverage the role of SERS microfluidic chips in biosensing, we also present an outlook on the future development of this combined technology.

AuNPs synthesised in situ from self-assembled peptide hydrogels modulating peptide secondary structure

The disease caused by amyloidosis is thought to be due to the toxicity of the hydrophobic groups exposed by the β-sheet structure among amyloid oligomers. The non-specific binding of nanomaterials to proteins and peptides may be able to modulate the β-sheet structure. In this work, we designed an amphipathic peptide Fmoc-FFCKK-OH based on the amyloid peptide FF sequence in order to evaluate nanomaterials as amyloid aggregation regulators. Au3+ was used to modulate peptide self-assembly to form hydrogels and to form gold nanoparticles (AuNPs) in situ under the reduction of –SH. We simplified the complex process of structural transformation of proteins and peptides by constructing a hydrogel model. The transformation and aggregation behaviour of the secondary structure of peptides on the surface of AuNPs over time was investigated. Circular dichroism (CD) and surface-enhanced Raman scattering (SERS) were used to observe the transition from random coil to β-sheet with some α-helix within Fmoc-FFCKK-OH. This work not only simplifies the complexity of the study but also contributes to the understanding of the role of AuNPs in the regulation of amyloid formation and provides a research basis for AuNPs as amyloid regulators.

Recent Trends in Surface-Enhanced Raman Scattering-Based In Vitro Diagnostics for Translational Biomedical Research.

Surface-enhanced Raman scattering (SERS) spectroscopy has gained prominence in in vitro diagnostics due to its high sensitivity and multiplex detection capabilities. This review highlights recent advances in translational biomedical research using SERS techniques, with a focus on the rapid and accurate diagnosis of intractable diseases such as cancer and infectious diseases such as COVID-19. The review examines SERS-based assays for liquid biopsy biomarkers such as exosomes, circulating tumor cells, and circulating tumor DNAs that have emerged as promising tools in cancer diagnostics and are currently under active investigation in clinical research. Additionally, it explores SERS-based diagnostic techniques developed to overcome the limitations of existing COVID-19 diagnostic methods, including real-time polymerase chain reaction and lateral flow assay immunodiagnostics. Finally, the review addresses the challenges of translating SERS techniques from laboratory research to clinical practice.

Facile Synthesis of Palladium Nanorods: Self-Assembly into Thin 2D Layers for SERS Sensing

This study presents a simple, high-throughput synthesis approach for fabricating palladium (Pd) nanomaterials with anisotropic shapes, specifically Pd nanorods, via a self-assembly process. This method avoids the use of reducing agents, surface functionalization, and stabilizing agents. Palladium–poly(methyl methacrylate) (Pd-PMMA) nanocomposites were successfully synthesized using a vapor-induced phase separation (VIPS) method. The formation of Pd nanorods was controlled by tuning key parameters, such as the Pd precursor concentration, choice of solvents, and spin coating speed. Notably, the resulting nanorods exhibited high reproducibility and ultrasensitivity as a surface-enhanced Raman scattering (SERS) platform, achieving an enhancement factor of approximately 1.8 × 105, despite the relatively weak plasmonic properties of Pd. This work represents a novel, facile strategy for Pd nanorod synthesis, offering new potential for the design of Pd-based nanosensors for chemical sensing applications.

Fabrication of Silicon Surface Microstructures via Vortex Femtosecond Laser Irradiation for Reusable Substrates in SERS Applications.

Surface-enhanced Raman spectroscopy (SERS) is a key technique in analytical chemistry because of its exceptional sensitivity and specificity for detecting a broad spectrum of substances. Herein, a silicon (Si) substrate fabricated using vortex femtosecond laser beams in ambient air is proposed as an innovative, highly sensitive, and reusable platform for advanced SERS applications. The substrate has composite nanostructures adorned with bush-like formations on top of the elongated structures, which is a direct consequence of the orbital angular momentum of the vortex beam. Simulations conducted using COMSOL provide valuable insights into the distribution of hot spots and electromagnetic field across the substrate surface after gold nanoparticles deposition, underscoring the superior SERS detection capabilities of the fabricated substrate using vortex beams as compared to those processed by Gaussian beams. The vortex-fabricated substrate possesses remarkable reusability, stability, and time-resistance. It exhibited outstanding detection performance for malachite green and microcystin-LR, achieving limits of detection values of 3.91 pM and 2.69 pg·mL-1, respectively. Therefore, the Si substrates fabricated using a vortex femtosecond laser beam is an ideal candidate for advancing SERS sensors to new heights.

Requirements for fast multianalyte detection and characterisation via electrochemical-assisted SERS in a reusable and easily manufactured flow cell.

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive analytical technique that captures vibrational spectra of analytes adsorbed to rough coin metal surfaces with remarkable signal intensities. However, its wider application is limited by challenges in substrate range, quantification, and the disposable nature of SERS substrates partly due to irreversible analyte adsorption-commonly referred to as the 'memory effect'. Overcoming these limitations and achieving real-time analysis in flow-through systems remains a key challenge for the advancement of SERS. This study presents a SERS flow cell incorporating an Ag-based SERS substrate and a Pt counter-electrode, enabling the investigation of how electrochemical methods can address existing challenges. Our approach demonstrates that signal intensities can be both enhanced and spectroelectrochemically modified. Additionally, the combination of constant solvent flow and electrochemical potentials enhances the longevity of the SERS substrate, facilitating multianalyte measurements while mitigating the memory effect. Key parameters have been systematically studied, including SERS substrate materials (silver and copper), solvents, buffers, supporting electrolytes, and electrochemical protocols. We achieved consistent and reproducible electrochemical tuning of SERS signals by using halogen-free electrolytes in polar solvents commonly used in techniques like HPLC. The versatility of the system was validated through the analysis of several model compounds and the sequential detection of multiple analytes. We also successfully applied the system to detect and characterise contaminants and pharmaceuticals, highlighting its potential for a wide range of analytical applications.

Highly Sensitive and Interference-Free Detection of Multiple Drug Molecules in Serum Using Dual-Modified SERS Substrates Combined with AI Algorithm Analysis.

Surface-enhanced Raman spectroscopy (SERS) technology has shown broad potential in drug concentration detection, but its application in blood drug monitoring faces significant challenges. The primary difficulty lies in overcoming the interference caused by various biomolecules present in serum, which can severely obscure the SERS signals of target drug molecules. Traditional enhancement substrates are often limited to detecting single drugs and are prone to interference, making the label-free detection of multiple drugs particularly challenging. To address these issues, we developed a novel SERS substrate based on Au@AgNRs, which undergoes a two-step modification to produce Au@AgDBCNRs. This innovative substrate provides exceptional signal amplification, simultaneously allowing the sensitive detection of multiple drug molecules. Moreover, our method eliminates the need for serum deproteinization, enabling the direct detection of drugs in serum while effectively mitigating interference from blood components. The cetyltrimethylammonium bromide coating on Au@AgDBCNRs is an internal standard for drug quantification without additional standards. The platform significantly improves detection accuracy and efficiency by automatically integrating artificial intelligence to recognize and analyze Raman spectral features. This novel SERS platform provides a new idea for therapeutic drug monitoring and is expected to provide rapid, accurate, and cost-effective drug detection in the clinical environment, which has great potential in improving patient care and optimizing drug dosage strategies.

Efficient SERS Substrate HOF@Au in Conjunction with DNAzyme-Mediated DNA Walker as a Signal Amplifier for the Ultrasensitive Detection of Lomefloxacin.

Lomefloxacin (LOM) is an efficacious antibiotic that might lead to liver damage and other adverse reactions if consumed over an extended period. Hence, this study proposed a DNAzyme-mediated DNA walker as a signal amplifier in combination with a substantial quantity of Au nanoparticle (NP)-loaded hydrogen-bonded organic frameworks (HOFs) as a surface-enhanced Raman scattering (SERS) substrate to accomplish the highly sensitive detection of LOM in food. Crucially, due to their high specific surface area and strong adsorption capacity, HOFs act as an ideal substrate for the in situ growth of a large amount of Au NPs, which exhibit a robust and uniform SERS enhancement. Once the target LOM was presented, the DNAzyme was activated to start the DNA walker and produce single DNA in abundance, which further triggered the catalytic hairpin assembly (CHA) cycle. In addition, the multi-interstitial core-shell structure of Au@Ag@4-nitrobenzenethiol (4-NTP)@Au@Hp3 produced more SERS "hot spots" and significantly amplified the local electromagnetic field, with HOF@Au synergistically strengthening the Raman signal of 4-NTP. Using this principle, this sensor achieved the ultrasensitive detection of LOM through the "signal on" strategy, with a detection limit as low as 4.62 × 10-14 mol/L. This strategy explored a meaningful innovative path for the design of a novel SERS biosensor for the sensitive and selective detection of antibiotics in food.

Gold Nanorod Surface-Enhanced Raman Spectroscopy Substrate for l-DOPA Detection: Experimental and Theoretical Approaches.

Experimental efforts aimed at detecting levodopa (l-DOPA) using surface-enhanced Raman scattering (SERS) face a persistent challenge in obtaining a SERS signal with negatively charged nanoparticles. This challenge stems from the repulsion between deprotonated l-DOPA in aqueous solution and the charged surface of the nanoparticles, revealing dependencies on time and concentration to achieve the SERS signal. This study explores the adsorption mechanism of l-DOPA on the surface of gold nanorods (AuNRs) covered with a cetrimonium bromide (CTAB) bilayer as a colloidal solution, subsequently dried onto a solid substrate such as glass, silicon, and Au substrate. Experimental findings are supported by density functional theory theoretical calculations. The comparison between experimental and theoretical results highlights that the SERS profile can be attributed to the adsorption of l-DOPA via the catechol ring, leading to the formation of anionic and dianionic species.

Rapid On-Site and Sensitive Detection of Microplastics Using Zirconium(IV)-Assisted SERS Label.

Microplastics have emerged as significant pollutants in terrestrial and marine ecosystems, with their accumulation posing a threat to human health through biomagnification along the food chain. Developing a rapid, on-site, and sensitive method for detecting microplastics in agri-food and environmental systems is important for assessing and minimizing their potential risks. In this study, we developed a novel surface-enhanced Raman spectroscopy (SERS) technique for the rapid, on-site, and ultrasensitive detection of microplastics. Our innovative technique incorporated Zr4+-assisted SERS label strategies, utilizing rhodamine B as a Raman reporter to improve microplastics analysis. By utilizing Zr4+-assisted SERS label approaches, we can achieve qualitative and ultrasensitive quantification of 10 μm polystyrene microplastics (PSMPs) at concentrations as low as 0.1 ppm with a detection limit of 1 ppb. Furthermore, this approach allows for detecting microplastics in real-world scenarios, with recovery rates exceeding 90% for polystyrene microplastic concentrations ranging from 5 to 30 ppm in tap water systems. When integrated with a portable Raman spectrometer, this innovative approach showcases the rapid, on-site, accurate, and sensitive detection of microplastics and has great potential for analyzing various types of microplastics in agri-food and environmental systems.

Photo-induced multiple charge transfer resonance of Ce-MOF for SERS detection of nucleic acid.

Sensitive and accurate detection of important cancer markers MicroRNAs (miRNAs) is critical to prevent and treat disease. Among many detection techniques, surface-enhanced Raman scattering(SERS) has attracted much attention due to its advantages such as narrow spectral peak, low interference and non-destructive detection. Interestingly, non-noble metal SERS substrates show good prospects due to their outstanding spectral reproducibility and biocompatibility. However, the low SERS sensitivity of non-noble metal substrates also limited their detection performance. Therefore, it is crucial to design a non-noble metal substrate with high SERS sensitivity for nucleic acid detection. In this study, we found that the photo induction (30min) of Ce-MOF has high SERS performance (abbreviated as Ce-MOF30). It is due to that photo-induction can regulate the energy level of the Ce-MOF and break the benzene-C bonds to introduce a defect energy level, which provides additional charge transfer channels. The Ce-MOF30 substrates can achieve an enhancement factor (EF) of 6.71×106 for Methylene blue (MB), about 7-fold higher than pristine Ce-MOF, which is the best Ce-based SERS substrate so far. Finally, a SERS detection platform was fabricated by combining the Mg2+ assisted dual signal amplification for miRNA 141 assay, and the detection limit was 1.72fM. This work proposed a simple photo-induction strategy to enhance SERS performance, which supplied a new detection platform for detection of nucleic acid and further expand the application of non-noble metal substrate in SERS field.

Rapid identification of pathogenic bacteria using data preprocessing and machine learning-augmented label-free surface-enhanced Raman scattering

Despite the advantages of label-free surface-enhanced Raman scattering (SERS) for bacterial detection, the effective implementation of this approach is hindered by several intrinsic limitations, such as the uniformity and spectral similarity of bacterial SERS spectra. In this study, we developed a machine learning (ML)-integrated hydrophobic SERS platform for sensitive bacterial detection and classification. The hydrophobic Si wafer was successfully fabricated through treatment with dimethyldichlorosilane (DMDCS), resulting in a high contact angle (> 100°). To achieve the highest SERS signals for bacteria, the density of gold core–silver shell nanoparticles (Au@AgNPs) was adjusted. Subsequently, the SERS activity of the Au@AgNPs under the coffee-ring effect on normal Si substrates was compared with that under the local concentration effect on hydrophobic Si substrates. Notably, the SERS signal for bacteria detected from the hydrophobic SERS platform, which enabled local enrichment of bacteria and Au@AgNPs, was approximately 33 times higher than that obtained from the normal Si substrates. Moreover, this hydrophobic SERS platform was integrated with ML algorithms to enhance the accuracy of bacterial detection. By applying three data preprocessing techniques, including baseline correction, smoothing, and normalization, we achieved 100 % accuracy in classifying SERS signals for four bacterial species. Our simple and versatile hydrophobic SERS platform, combined with ML models, exhibits immense potential for label-free detection and classification of pathogenic bacteria.

A multifunctional biosensor for selective identification, sensitive detection and efficient photothermal sterilization of Salmonella typhimurium and Staphylococcus aureus.

The foodborne pathogens, e.g., Salmonella typhimurium (S. typ) and Staphylococcus aureus (S. aureus), pose a serious threat to human health. Accurate identification, rapid detection and efficient inactivation are crucial in the early diagnosis and treatment of S. typ and S. aureus. To date, however, the majority of studies have only concentrated on the construction of single-function biological platform for detection or inactivation of S. typ and S. aureus. Therefore, it is imperative to develop a multifunctional surface-enhanced Raman scattering (SERS) biosensor that can effectively sterilize S. typ and S. aureus while simultaneously achieving sensitive detection and selective identification. Herein, we designed and constructed a multifunctional SERS biosensor based on sandwich structure of "capture probe/bacteria/signal probe" in order to simultaneously identify, detect and kill S. typ and S. aureus. Aptamer-modified ZnO/Ag was used as a capture probe to accurately identify and capture the target bacteria in complex environments. Au@Ag-4-MPBA-Aptamer was employed as signal probe to provide the corresponding bacterial SERS "fingerprint" information. The SERS enhancement mechanism of the sandwich-structure ZnO/Ag-Au@Ag SERS substrate was discussed. The sandwich-type SERS biosensor exhibited the strong localized surface plasmon resonance (LSPR) effect and the detection limit for S. typ and S. aureus was as low as 10cfu/mL. Furthermore, the sandwich-type SERS biosensor offered excellent photothermal conversion efficiency (54.32%), enabling photothermal killing of target bacteria when exposed to laser irradiation. A dual enhancement strategy based on a sandwich structure was proposed to maximize the sensitivity of SERS signals using synergistic action of electromagnetic enhancement and chemical enhancement. SERS enhancement factor (EF) was as high as 4.67×105. In addition, the sandwich-type SERS biosensor not only exhibited negligible cytotoxicity, but also was proved to be a promising tool for photothermally inactivate of S. typ and S. aureus in food samples.

Monitoring kinetic processes of drugs and metabolites: Surface-enhanced Raman spectroscopy.

Monitoring the kinetic changes of drugs and metabolites plays a crucial role in fundamental research, preclinical and clinical application. Raman spectroscopy (RS) is regarded as a fingerprinting technique that can reflect molecular structures but limited in applications due to poor sensitivity. Surface-enhanced Raman spectroscopy (SERS) significantly amplifies the detection sensitivity by plasmonic substrates, facilitating the identification and quantification of small molecules in biological samples, such as serum, urine, and living cells. This review will focus on advances in how SERS has been utilized to monitor the dynamic processes of small molecule drugs and metabolites in recent years. We first provide readers with a comprehensive overview of the mechanism and practical considerations of SERS, including enhancement theory, substrate design, sample pretreatment, molecule-substrate interactions and spectral analysis. Then we describe the latest advances in SERS for the detection and analysis of metabolites and drugs in cells, dynamic monitoring of drug in various biological matrices, and metabolic profiling for health assessment in biological fluids. We believe that high-performance SERS substrates, standardized technical regulations, and artificial intelligence spectral analysis will boost sensitive, accurate, reproducible, and universal molecular detection in the future. We hoped this review could inspire researchers working in related fields to better understand and utilize SERS for the analytical detection of drugs and metabolites.

Recent advances in Surface-Enhanced Raman Scattering (SERS) for the diagnosis, treatment, and prognosis of ovarian cancer

Recent advances in Surface-Enhanced Raman Scattering (SERS) for the diagnosis, treatment, and prognosis of ovarian cancer

Practical SERS Substrates by Spray Coating of Silver Solutions for Deep Learning-Assisted Sensitive Antigen Identification

Surface-enhanced Raman spectroscopy (SERS) has long been recognized for its rapid and sensitive detection capabilities; however, challenges persist in practical fabrication of the substrates and interpreting complex data. Herein, we propose a deep learning (DL) assisted SERS approach to enable rapid and sensitive detection of analytes on a practical yet highly effective substrates prepared by direct spray-coating of a nanoparticle-free true solution of a reactive Ag ink and on-site thermal annealing mediated generation of nanostructures. This design ensured homogeneous distribution of Ag nanostructures throughout the entire substrate, significantly increasing the number of hotspots and enhancing the Raman signals, thereby achieving an impressive analytical enhancement factor of ~1010 in a reproducible and consistent manner. The diagnostic utility of this platform was demonstrated by detecting the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein in both buffer and saliva, with detection limits of 74.3pg/mL and 7.43ng/mL, respectively. The DL-assisted SERS not only accurately identified the presence or absence of viral antigen, but also automatically quantified the viral load. This automatic identification achieved an outstanding accuracy of ~99.9%, highlighting the exceptional performance of the proposed platform. This simple, cost-effective, scalable, and ultra-sensitive DL-assisted SERS platform offers significant opportunities for early and precise detection in a range of analytical scenarios.

Multifunctional Surface Enhanced Raman Scattering Substrate Fe 3O4 @AgNPs@MIL-101 for Pretreatment and Rapid Detection of Pesticide Residues on the Surface of Fruit Peels.

A multifunctional surface-enhanced Raman scattering substrate Fe3O4@AgNPs@MIL-101 was prepared. Rapid SERS detection of pesticide residues was realized by direct pre-enrichment and separation on the peel surface. MIL-101 has an ortho-octahedral framework and large pore size, which endowed Fe3O4@AgNPs@MIL-101 with the ability to rapidly adsorb and separate positively charged targets. The introduction of tannic acid realized the insitu growth of AgNPs on the backbone, to modulate the electromagnetic enhancement. Pesticide molecules were adsorbed onto the surface of AgNPs mediated by central S atoms, accompanied by the interaction between pesticide molecules and AgNPs, the corresponding SERS signals of different pesticides were observed. Together with the introduction of magnetic coating Fe3O4, the molecules were enriched in the hotspot and separated to further enhance the SERS performance. Magnet instead of centrifugation was used to simultaneously perform surface extraction and sample separation for a noninvasive, rapid, immediate, and portable assay. The method was accomplished in measurement of thiram and thiabendazole on apple and tangerine epidermis, and the limits of detection (LODs) were 20 ng/cm2 and 4 μg/cm2, respectively. The recovery was reasonable, and it showed that the procedure is valuable for the rapid and nondestructive surface analysis of residual chemicals.

Reduced graphene oxide/gold composite synthesis via laser irradiation for surface enhanced Raman spectroscopy biosensors

Reduced graphene oxide/gold composite synthesis via laser irradiation for surface enhanced Raman spectroscopy biosensors