Surface-enhanced Raman spectroscopy: benefits, trade-offs and future developments

Label-free surface-enhanced Raman scattering quantitative analysis of dual electromagnetically enhanced flexible core-shell nanoparticles containing internal standards

We designed and synthesized a flexible Au@PB@Ag NPs-CFs surface-enhanced Raman scattering (SERS) substrate with self-calibration functionality. Compared to traditional core-shell structured substrates with internal standards, our proposed substrate, which fully encapsulates a Prussian Blue (PB) layer, exhibits dual electromagnetic enhancement effects on both the PB self-calibration signal and the pesticide signal due to the localized surface plasmon resonance within the silver shell cavity. The results show that after signal calibration, the relative standard deviation decreased from 30.34 % to 11.24 %. The water-dispersible Au@0.8 PB@Ag NPs loaded on chitosan demonstrated extremely high sensitivity for the detection of alcohol-soluble pesticides thiram and thiabendazole, with detection limits as low as 0.015 μM and 0.098 μM, respectively. Additionally, due to the substrate's flexibility and excellent uniformity, it effectively addresses the "coffee ring" effect and enables quantitative detection through direct swabbing, with spiked recovery rates ranging from 81 % to 116.6 %.

High-uniformity, low-cost, ultra-dense arrays of Au-capped plastic nanopillars fabricated via nanoimprint lithography as reliable SERS substrates

Nanoimprint lithography (NIL) is gradually becoming a powerful tool for the fabrication of periodic nanostructures. This method can offer a more cost-effective solution for large-scale manufacturing compared to methods that only rely on deep ultraviolet (DUV) immersion, since the product of DUV immersion can be utilized as a Si mold to fabricate a reusable plastic stamp mold. In this work, arrays of plastic nanopillars coated with nanostructured gold film exhibiting ultra density prepared through NIL and Au sputtering are successfully developed. The obtained plastic nanopillar substrate is templated from Si nanopillar substrate with a pitch of 90 nm. As a result, the plastic nanopillar features a similar pitch size. Besides, benzenedithiol (BDT) was used as the standard analyte to evaluate the uniformity of the substrates as well as the SERS enhancement effect. Eventually, it is demonstrated that the substrate constituted of Au-capped plastic nanopillar shows a low coefficient of variation (CV) at 5.46 % along with a strong SERS enhancement effect. These performances match with the Si based SERS substrate manufactured via DUV immersion reported in our previous work.

Nano biosensor unlocks tumor derived immune signals for the early detection of ovarian cancer

Ovarian cancer is a critical health issue for women nowadays. Its impact is significant because of its high mortality rate (324,603 worldwide), late-stage diagnosis and poor survival rate. Lack of screening tests, vague symptoms, misdiagnosis, and age factor makes it even more difficult to detect. Neutrophils, a subset of immune cells, undergo tumor-specific changes as ovarian cancer progresses inside ovarian tumour microenvironment. Therefore, monitoring the time-specific activity of neutrophils in circulation has the potential to aid in the diagnosis of ovarian cancer. Most ovarian tumor-specific antigens are unknown, making it difficult to identify neutrophils associated with ovarian tumor. We present ovarian tumor-associated circulating neutrophil cell profiling as a stand-alone cancer diagnostic method using a liquid biopsy. Using a SERS-functionalized nano probe, the metabolic profiles of neutrophils from ovarian tumor interaction are detected. We demonstrate that neutrophils associated with cancer stem cells have a distinct metabolic profile and are useful in the diagnosis of early ovarian cancer. Using 5 μL of peripheral blood and an artificial neural network, the characteristics of neutrophil profiles in patient blood could distinguish cancer cohort from non-cancer (healthy) with a 90 % sensitivity and 100 % specificity. Our results demonstrate the viability of using circulating neutrophils for non-invasive cancer diagnostics.

SERS-ATB: A comprehensive database server for antibiotic SERS spectral visualization and deep-learning identification

The rapid and accurate identification of antibiotics in environmental samples is critical for addressing the growing concern of antibiotic pollution, particularly in water sources. Antibiotic contamination poses a significant risk to ecosystems and human health by contributing to the spread of antibiotic resistance. Surface-enhanced Raman spectroscopy (SERS), known for its high sensitivity and specificity, is a powerful tool for antibiotic identification. However, its broader application is constrained by the lack of a large-scale antibiotic spectral database crucial for environmental and clinical use. To address this need, we systematically collected 12,800 SERS spectra for 200 environmentally relevant antibiotics and developed an open-access, web-based database at http://sers.test.bniu.net/. We compared six machine learning algorithms with a convolutional neural network (CNN) model, which achieved the highest accuracy at 98.94%, making it the preferred database model. For external validation, CNN demonstrated an accuracy of 82.8%, underscoring its reliability and practicality for real-world applications. The SERS database and CNN prediction model represent a novel resource for environmental monitoring, offering significant advantages in terms of accessibility, speed, and scalability. This study establishes the large-scale, public SERS spectral databases for antibiotics, facilitating the integration of SERS into environmental programs, with the potential to improve antibiotic detection, pollution management, and resistance mitigation.

Detection of Cancer Biomarkers: Review of Methods and Applications Reported from Analytical Perspective

One in five deaths in developed countries is related to cancer. The cancer prevalence is likely to grow with aging population. The affordable and accurate early diagnostics of cancer based on detection of cancer biomarkers at low concentration during its early stages is one of the most efficient way to decrease mortality and human suffering from cancer. The data from 201 analytical papers are tabulated in 9 tables, illustrated in 8 figures and used for comparative analysis of methods applied for cancer biomarker detection, including polymerase chain reaction, Loop-mediated isothermal amplification (LAMP), mass spectrometry, enzyme-linked immunosorbent assay, electroanalytical methods, immunoassays, surface enhanced Raman scattering, Fourier Transform Infrared and others in terms of above-mentioned performance parameters. Median and/or average limit of detection (LOD) are calculated and compared between different analytical methods. We also described and compared LOD of the methods used for detection of three frequently detected cancer biomarkers: carcinoembryonic antigen, prostate-specific antigen and alpha-fetoprotein. Among those methods of detection, the reported electrochemical sensors often demonstrate relatively high sensitivity/low LOD while they often have a moderate instrumental cost and fast time to results. The review tabulates, compares and discusses analytical papers, which report LOD of cancer biomarkers and comprehensive quantitative comparison of various analytical methods is made. The discussion of those techniques applied for cancer biomarker detection included brief summary of pro and cons for each of those methods.

Surface-enhanced Raman spectroscopy based on 2,3-naphthalenedicarboxaldehyde derivative reagent for highly sensitive detection of cysteine and homocysteine

The study presents a simple, efficient, and sensitive methodology which combines condensation reaction with surface-enhanced Raman spectroscopy (SERS) to detect cysteine (Cys) and homocysteine (Hcy). Experimental conditions which include reaction temperature, time, and buffer pH can be used to influence the derivatization reaction of 2,3-dinaphthaldehyde (NDA) with Cys and Hcy. Quantitative analysis was conducted on the characteristic peaks of the products of Cys (1377 cm-1) and Hcy (665 cm-1) after reacting with NDA. The intensity of characteristic Raman peaks is linearly related to the concentrations of Cys and Hcy (10-12-10-4 mol/L), with a correlation coefficient R2 greater than 0.99. This method combines SERS and derivatization reaction, has significant application potential for detecting Cys and Hcy in biological media because to its excellent sensitivity and simplified use.

Collapse-enhanced SERS effect of self-crosslinked plasmonic starch aerogels for sensitive detection of food contaminants

A flexible 3D plasmonic starch aerogel substrate was fabricated for susceptible detection of thiabendazole (TBZ) and doxycycline hydrochloride (DH). Based on the unique structure features of starch, an aerogel with high porosity and a large specific surface area was formed without any extra cross-linking agents. Silver nanoparticles (Ag NPs) uniformly distribute throughout starch aerogel and generate dense hot spots while aerogel structure collapses, which leads to significant SERS enhancement. The as-prepared aerogel substrate exhibits good SERS activity with a low detection limit of 1 × 10-10 M for rhodamine 6G and 1 μg/L for 4-Aminothiophenol (4-ATP). In practical application for real sample, the TBZ residue on the surface of citrus was successfully detected by wipe sampling, with a good recovery rate of 96.2 %-98.8 % and a low limit of detection (LOD) of 0.031 mg/L range from 0.1 to 100 mg/L. The substrate also exhibited excellent performance in detecting DH in chicken, with recovery rates ranging from 96.9 % to 98.1 %. The LOD was 0.066 mg/L, and the detection range spanned from 0.1 to 100 mg/L. Results demonstrate that the prepared aerogel is an ideal material as a SERS substrate due to its unique properties such as strong adsorption capacity, dense hot spot, and ease of use. Therefore, the developed SERS platform-based flexible 3D plasmonic aerogel substrate paves a new avenue for highly sensitive SERS detection in the field of food safety.

Large-Area Ultrathin Covalent-Organic Framework Membranes for Surface-Enhanced Raman Scattering: Optimal Performance Through Thickness Control

Exploration and construction of novel π-conjugated organic semiconductors with low cost, small background interference, and excellent performance as surface-enhanced Raman scattering (SERS) substrates is one of the current focuses for the development of SERS technology. Based on precise control over synthesis conditions, a series of large-area tetraphenylporphyrin-based 2D covalent-organic framework membranes (2D-porphyrin-COFs) with high uniformity and precisely controllable thickness are constructed as SERS substrates. The delicate balance among the intensity of the substrate interference, the degree of π-conjugation extension, and the proportion of the edge-on channels within the total exposed region results in the optimal SERS performance of ultrathin multilayer 2D-porphyrin-COFs with the thickness between 5.0 to 9.0 nm toward MB, including the enhancement factor on the order of 105 and the experimental limit of detection down to 10-8 M, which are comparable to classic plasmonic metal substrates. This work highlights the powerful application potential of COFs in the SERS field and unveils thickness control as an effective strategy to facilitate the exploration of high-performance organic SERS substrates.

Energy-level rich nanorings hybridizing Ag, Au and AgCl as high-performance SERS substrate for numerous molecules

The current surface-enhanced Raman scattering (SERS) substrates typically feature a single energy level, posing challenges in coordinating electromagnetic enhancement (EM) and chemical enhancement (CM), thereby limiting the sensitive detection of numerous crucial target molecules. In this study, novel aggregated nanorings (a-NRs) hybridizing Ag, Au and AgCl are constructed as SERS substrates. On one hand, the obtained a-NRs exhibit robust localized surface plasmon resonance absorption, whose wavelength can be tuned to match three commonly used laser wavelengths (532, 633 and 785 nm) to gain strong EM effect. On the other hand, these materials possess the Fermi levels of Au nanoparticles and Au/Ag alloy, in addition to the valence band and conduction band of AgCl. The abundant energy levels of the obtained a-NRs facilitate increased charge transfer opportunities for molecules, leading to a strong CM effect. Therefore, the obtained a-NRs show ultra-high SERS sensitivity towards numerous molecules. Moreover, the unique chemical composition makes the obtained a-NRs have good long-term stability in terms of SERS activity. Besides providing high-performance SERS substrates, the valuable experience for coordinating EM and CM to construct highly active SERS substrate demonstrated in this work are expected to significantly advance the application of SERS.

Innovative applications of SERS in precision medicine: In situ and real-time live imaging

Surface-enhanced Raman scattering (SERS), a molecular spectroscopic technique with high sensitivity and specificity, has demonstrated groundbreaking potential in precision medicine in recent years. This review systematically summarizes recent advancements in SERS technology for in situ and real-time live imaging, focusing on its core value in early tumor diagnosis, intraoperative navigation, drug delivery monitoring, and dynamic pathological analysis. By optimizing nanoscale probe design-including targeted functionalization, enhanced biocompatibility, and integration with imaging systems-SERS overcomes the sensitivity and spatiotemporal resolution limitations of traditional imaging techniques, enabling precise capture and dynamic tracking of molecular events in live biological environments. The article further analyzes challenges in clinical translation, such as signal stability in complex biological environments, multimodal imaging coordination, and standardized data processing methods. Future directions for personalized therapy and intelligent integrated diagnostics are also discussed.

Recent advances in semiconductor nanostructure-based surface-enhanced Raman scattering sensors

Surface-enhanced Raman scattering (SERS) has become a transformative analytical tool, attracting growing interest for its wide-ranging applications. The development of SERS-active materials is now a central research area, spurring innovation in various types of SERS substrates. While noble metal-based substrates remain extensively studied, semiconductor-based, non-metal substrates are garnering attention due to their unique advantages: excellent chemical stability, high carrier mobility, biocompatibility, and precise fabrication control. However, their generally weaker enhancement effects limit their utility, underscoring the need for strategies to boost their SERS activity. Understanding the complex enhancement mechanisms in semiconductor-based SERS substrates is critical for designing next-generation materials with metal-like enhancement factors (EFs). The interplay of charge transfer, localized surface plasmon resonance, and photonic effects makes the enhancement process inherently challenging to unravel. Therefore, the search for new materials with exciting optoelectronic properties, as well as more innovative solutions to increase their SERS sensitivity, continues to grow. In this review, we explore the latest advancements in semiconductor-based SERS substrates, dissecting the complex enhancement mechanisms and various modification strategies aimed at achieving metal-like high EFs. We present a comprehensive analysis of the methods used to improve the SERS performance of semiconductor substrates and conclude with potential future directions for advancing this dynamic field.

Highly sensitive and reproducible SERS substrate based on ordered multi-tipped Au nanostar arrays for the detection of myocardial infarction biomarker cardiac troponin I

Acute myocardial infarction (AMI) is a severe cardiovascular disease, for which early diagnosis is critical for reducing mortality and improving patient outcomes. Cardiac troponin I (cTnI) is widely recognized as the "gold standard" biomarker for AMI due to its high specificity and sensitivity. The concentration of cTnI correlates directly with different stages of AMI. Therefore, the accurate detection of cTnI concentration is of paramount importance. However, the low concentration of cTnI in biological fluids requires ultrasensitive detection methods. In this study, we developed a sandwiched surface enhanced Raman scattering (SERS)-based biosensor composed of SERS-immune substrate, target antigen, and SERS nanotags and realized sensitive and accurate detection of cTnI. The SERS-immune substrate features an ordered, multi-tipped monolayer of Au nanostars fabricated using a three-phase interfacial self-assembly method and 4-(2-hydroxyerhyl)piperazine-1-erhanesulfonic acid (HEPES) buffer modification. Compared to Au nanosphere SERS substrates, the Au nanostar SERS substrates exhibited about a 3-fold increase in Raman enhancement and demonstrated good uniformity and batch stability. This novel SERS detection platform, leveraging dual plasmonic enhancement from both the SERS-immune substrate and SERS nanotags, achieves detection of cTnI with a limit of detection (LOD) as low as 9.09 pg mL-1 and a relative standard deviation (RSD) as low as 11.24%. Thus, the Au nanostar SERS substrates developed in this study demonstrate significant potential for rapid and accurate detection of cTnI.

Deep Learning-Powered Colloidal Digital SERS for Precise Monitoring of Cell Culture Media

Maintaining consistent quality in biomanufacturing is essential for producing high-quality complex biologics. Yet, current process analytical technologies (PAT) often fall short in achieving rapid and accurate monitoring of small-molecule critical process parameters and critical quality attributes. Surface-enhanced Raman spectroscopy (SERS) holds great promise but faces challenges like intensity fluctuations, compromising reproducibility. Herein, we propose a deep learning-powered colloidal digital SERS platform. This innovation converts SERS spectra into binary "ON/OFF" signals based on defined intensity thresholds, which allows single-molecule event visualization and reduces false positives. Through integration with deep learning, this platform enables detection of a broad range of analytes, unlimited by the lack of characteristic SERS peaks. Furthermore, we demonstrate its accuracy and reproducibility for studying AMBIC 1.1 mammalian cell culture media. These results highlight its rapidity, accuracy, and precision, paving the way for widespread adoption and scale-up as a novel PAT tool in biomanufacturing and diagnostics.

Electrochemical UV-SERS of adenine on cobalt electrode

The combination of surface-enhanced Raman spectroscopy in the ultraviolet spectral region (UV-SERS) with resonance Raman scattering enhancement, referred to as UV-SERRS, enables ultrasensitive and reliable detection of biomolecules because of the strong electronic transition of many biologically important compounds in UV region. Adenine solution studies by UV-Raman spectroscopy revealed pre-resonant enhancement of various modes by 2-16 times at 325 nm excitation wavelength. Adsorption and structural properties of adenine on a cobalt electrode were probed by UV-SERS. The nanostructured cobalt electrode was prepared via electrodeposition from diluted aqueous CoSO4 solutions under negative electrode potentials. Using 325 nm excitation, potential-dependent UV-SERS spectra of adenine adsorbed on the Co electrode were obtained. Based on analysis of isotopic H2O/D2O substitution, concentration- and potential-dependent spectra, the bonding and structure of adsorbed molecule were revealed. Adenine primarily adsorbs in its N9H form, interacting with cobalt through the N7 atom of the imidazole ring and the amino group, with its ring plane nearly perpendicular to the surface. These findings highlight adenine's potential as a model for studying nucleobase-metal interactions, which is crucial for applications in biosensing, molecular electronics, and surface passivation. The study underscores cobalt's viability as a cost-effective, stable and magneto-plasmonic UV-SERS substrate, opening new avenues for the development of advanced analytical techniques.

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.

Tris(2,2'-bipyridine)ruthenium(II)-silver nanoparticle electrostatic nanoaggregates (AgNPs@[Ru(bpy)3]2+ ENAs) as novel SERS nanotags for rapid, sensitive and selective immunosensing

Tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)3]2+), as a versatile molecule, has been widely applied in various fields, such as photocatalysis, electrochemiluminescence and fluorescence probes, solar cell and LED due to its excellent optical and electrical properties, good water solubility, high chemical stability. In this work, we prepared electrostatic nanoaggregates from [Ru(bpy)3]2+ and silver nanoparticles (AgNPs@[Ru(bpy)3]2+ ENAs) as a new type of SERS nanotags. Each [Ru(bpy)3]2+ ion carries two positive charges with strong affinity to negative surfaces, which enables a strong electrostatic interaction between [Ru(bpy)3]2+ and negatively charged silver nanoparticles (AgNPs) and fast (within 10 min) formation of AgNPs@[Ru(bpy)3]2+ ENAs. The prepared AgNPs@[Ru(bpy)3]2+ ENAs had a very strong and stable SERS activity due to abundant bipyridine molecules in [Ru(bpy)3]2+ and the location of many [Ru(bpy)3]2+ SERS reporters at the electromagnetic "hot spots" (i.e. the junction of two adjacent AgNPs), and thus could act as novel and excellent SERS nanotags. Further conjugated with antibodies, AgNPs@[Ru(bpy)3]2+ nanotags were used to develop new SERS-based immunochromatography test strips (SERS-ICTSs), showing excellent sensing performances. The AgNPs@[Ru(bpy)3]2+ ENAs based SERS-ICTSs not only inherit the merit of fast and visualize quantitative analysis from traditional ICTSs, but also realize much more sensitive biosensing (with detection limit of 25 pg/mL HCG) using the SERS technology.

Proteomics-on-a-Chip - Microfluidics meets proteomics

Proteomics provides an understanding of biological systems by enabling the detailed study of protein expression profiles, which is crucial for early disease diagnosis. Microfluidic-based proteomics enhances this field by integrating complex proteome analysis into compact and efficient systems. This review focuses on developing microfluidic chip structures for proteomics, covering on-chip sample pretreatment, protein extraction, purification, and identification in recent years. Furthermore, our work aims to inspire researchers to select proper methodologies in designing novel, efficient assays for proteomics applications by analyzing trends and innovations in this field.

Surface-Enhanced Raman Spectroscopy for Biomedical Applications: Recent Advances and Future Challenges

The year 2024 marks the 50th anniversary of the discovery of surface-enhanced Raman spectroscopy (SERS). Over recent years, SERS has experienced rapid development and became a critical tool in biomedicine with its unparalleled sensitivity and molecular specificity. This review summarizes the advancements and challenges in SERS substrates, nanotags, instrumentation, and spectral analysis for biomedical applications. We highlight the key developments in colloidal and solid SERS substrates, with an emphasis on surface chemistry, hotspot design, and 3D hydrogel plasmonic architectures. Additionally, we introduce recent innovations in SERS nanotags, including those with interior gaps, orthogonal Raman reporters, and near-infrared-II-responsive properties, along with biomimetic coatings. Emerging technologies such as optical tweezers, plasmonic nanopores, and wearable sensors have expanded SERS capabilities for single-cell and single-molecule analysis. Advances in spectral analysis, including signal digitalization, denoising, and deep learning algorithms, have improved the quantification of complex biological data. Finally, this review discusses SERS biomedical applications in nucleic acid detection, protein characterization, metabolite analysis, single-cell monitoring, and in vivo deep Raman spectroscopy, emphasizing its potential for liquid biopsy, metabolic phenotyping, and extracellular vesicle diagnostics. The review concludes with a perspective on clinical translation of SERS, addressing commercialization potentials and the challenges in deep tissue in vivo sensing and imaging.

Recent advances in the design of SERS substrates and sensing systems for (bio)sensing applications: Systems from single cell to single molecule detection

The Raman effect originates from spontaneous inelastic scattering of photons by matter. These photons provide a characteristic fingerprint of this matter, and are extensively utilized for chemical and biological sensing. The inherently lower generation of these Raman scattered photons, do not hold potential for their direct use in sensing applications. Surface enhanced Raman spectroscopy (SERS) overcomes the low sensitivity associated with Raman spectroscopy and assists the sensing of diverse analytes, including ions, small molecules, inorganics, organics, radionucleotides, and cells. Plasmonic nanoparticles exhibit localized surface plasmon resonance (LSPR) and when they are closely spaced, they create hotspots where the electromagnetic field is significantly enhanced. This amplifies the Raman signal and may offer up to a 10 14-fold SERS signal enhancement. The development of SERS active substrates requires further consideration and optimization of several critical features such as surface periodicity, hotspot density, mitigation of sample or surface autofluorescence, tuning of surface hydrophilicities, use of specific (bio) recognition elements with suitable linkers and bioconjugation chemistries, and use of appropriate optics to obtain relevant sensing outcomes in terms of sensitivity, cross-sensitivity, limit of detection, signal-to-noise ratio (SNR), stability, shelf-life, and disposability. This article comprehensively reviews the recent advancements on the use of disposable materials such as commercial grades of paper, textiles, glasses, polymers, and some specific substrates such as blue-ray digital versatile discs (DVDs) for use as SERS-active substrates for point-of-use (POU) sensing applications. The advancements in these technologies have been reviewed and critiqued for analyte detection in resource-limited settings, highlighting the prospects of applications ranging from single-molecule to single-cell detection. We conclude by highlighting the prospects and possible avenues for developing viable field deployable sensors holding immense potential in environmental monitoring, food safety and biomedical diagnostics.

Surface-enhanced Raman spectroscopy as effective tool for detection of sialic acid as cancer biomarker

Sialic acid, a negatively charged nine-carbon monosaccharide, is mainly located at the terminal end of glycan chains on glycoproteins and glycolipids of cell surface and most secreted proteins. Elevated levels of sialylated glycans have been known as a hallmark in numerous cancers. As a result, sialic acid acts as a useful and accessible cancer biomarker for early cancer detection and monitoring the disease development during cancer treatment which is crucial in elevating the survival rate. The detection of sialic acid has been done by many tools including surface-enhanced Raman spectroscopy (SERS) which gained incredible attention due to its high selectivity and sensitivity. However, currently, comprehensive reviews of sialic acid detection and imaging as a cancer biomarker using SERS are still lacking. Here, we present the significant breakthroughs in SERS-based detection of sialic acid levels on cells, tissues, and body fluids due to the presence of cancer, different cancer metastasis stages, and in response to the external stimuli. This review covers the SERS substrate and novel SERS strategies, using lectin, boronic acid, metabolic glycan labelling and label-free methods, for sialic acid detection as cancer biomarker. The remaining challenges to detect sialic acid and prospect of future development of SERS for other carbohydrate-based cancer biomarker, for instance fucose, are also discussed.

Efficient Simulation of Surface-Enhanced Raman Scattering with a Simplified Damped Response Theory

Theoretical studies on enhancement mechanisms of surface-enhanced Raman scattering (SERS) are usually carried out with full quantum mechanical methods to capture the specific interactions between molecules and substrates. However, due to the computational costs of methods like time-dependent density functional theory (TDDFT), simplified model systems are commonly adopted. In the framework of TDDFT, the damped response theory is usually invoked to give a unified description of both on- and off-resonance Raman spectra based on the calculation of polarizability derivatives. However, the computational costs of full TDDFT allow for modeling SERS spectra only using small metal clusters. In this work, we demonstrate the implementation of an efficient method that simplifies the damped response calculations for the simulation of both on- and off-resonance SERS spectra. This simplified damped response method is named as TBAOResponse. We first compare the absorption spectra of a regular small system calculated with TBAOResponse and full TDDFT to benchmark the new method. Then, we demonstrate the efficiency and accuracy of the new method by comparing the on- and off-resonance SERS spectra calculated with different methods. Compared to full TDDFT, while significant improvement of efficiency is achieved, the simplified damped response maintains good accuracy for SERS calculation. We further showcase the efficiency of TBAOResponse by calculating the SERS spectra for a system that is computationally demanding with full TDDFT. This new method is promising for modeling SERS systems when a full quantum mechanical description of both the substrate and the molecule is necessary.

Unlocking the Potential of Gallic Acid-Based Metal Phenolic Networks for Innovative Adsorbent Design

Metal phenolic networks (MPNs) have attracted significant attention due to their environmentally benign nature, broad compatibility, and universal adhesive properties, making them highly effective for modifying adsorbent surfaces. These supramolecular complexes are formed through the coordination of metal ions with natural phenolic ligands, resulting in stable structures while retaining the active adsorption sites of the ligands, thereby enhancing the adsorption performance of unmodified substrates. Among various MPNs, metal ion gallic acid (GA) networks are particularly well-known for their exceptional stability, biological activity, and superior adsorption ability. This review offers a comprehensive examination of GA-based MPN adsorbents, focusing on their formation chemistry, characterization techniques, and applications. The coordination chemistry underlying the stability of GA-metal complexes is analyzed through equilibrium studies, which are critical for understanding the robustness of MPNs. The main analytical methods for assessing metal ligand interactions are discussed, along with additional characterization techniques for evaluating adsorbent properties. This review also explores various synthesis and performance enhancement strategies for GA-based MPN adsorbents, including stand-alone MPNs, MPN-mediated mesoporous materials, MPN-MOF composites, and MPN-coated substrates. By consolidating current advancements in MPN-based adsorbents and offering fundamental insights into their chemistry and characterization, this review serves as a valuable resource for researchers seeking to develop stable, functional metal-organic materials. It aims to drive innovation in sustainable and efficient adsorbent technologies for diverse environmental and industrial applications.

Antibody screening-assisted multichannel nanoplasmonic sensing chip based on SERS for viral screening and variants identification

The Omicron variants of SARS-CoV-2 have been spreading globally and have never disappeared from our sight, indicating that their coexistence with humans has become a fact, and monitoring its evolution and spread remains a current task. Although polymerase chain reaction (PCR) is the most commonly used virus detection method, it requires labor-intensive and time-consuming procedures in a laboratory setting. Herein, a multichannel nanoplasmonic sensing chip based on surface enhanced Raman spectroscopy (SERS) was developed for detecting N and S proteins, as well as IgG and IgM, related to SARS-CoV-2 Omicron variants. Through a self-screening process, specific antibodies for on-site and rapid identification of important variants of concern (VoCs) were obtained, and their binding was confirmed by protein structure analysis. The use of these S protein specific antibodies can accurately identify Omicron VoCs (BA. 5, BF.7，XBB.1.5) with the detection limit (LoD) of 0.16 pg/mL. Then, the proposed SERS array chip was integrated with a hand-held Raman spectrometer to successfully detect the Omicron subvariants in real saliva samples within only 20 min, greatly reducing the detection time of PCR. This sensing technology will provide a powerful and rapid point-of-care testing (POCT) method for virus diagnosis, subtype identification, and post-infection antibody level monitoring.

Ag@CDS SERS substrate coupled with lineshape correction algorithm and BP neural network to detect thiram in beverages

Surface enhanced Raman scattering (SERS) has been proved an effective analytical technique due to its high sensitivity, however, how to identify and extract useful information from raw SERS spectra is still a problem that needs to be resolved. In this work, a composite SERS substrate was prepared by encapsulating Ag nanoparticles within dialdehyde starch (Ag@CDS) to obtain dense "hot spot", and then a novel spectral preprocessing algorithm namely lineshape correction algorithm (LCA) was developed to separate the characteristic peaks of analytes from the original SERS spectra. Based on Ag@CDS and LCA, thiram residues in different beverages were quantitatively detected using back propagation (BP) neural network regression model. It was found that LCA provided an easy-to-use method for improving prediction ability of BP model. The Rp2 of BP model was improved from 0.2384, 0.3647 and 0.5581 to 0.9327, 0.9127 and 0.9251 for the quantitative detection of thiram residue in apple juice, grape juice and milk, respectively, while LCA was used for SERS spectra preprocessing. The optimal model can accurately detect thiram residue with a low limit of detection at 1.0 × 10-7 M, which is far below the maximum residue limit of thiram (2.9 × 10-5 M) regulated by the US Environmental Protection Agency. This study demonstrated that the proposed LCA can be used as a simple and valid spectra-preprocessing method in SERS quantitative detection.

Bilirubin: Photophysical and photochemical properties, phototherapy, analytical methods of measurement. A short review

Bilirubin, a yellow bile pigment, plays an important role in the body, being a potent antioxidant and having anti-inflammatory, immunomodulatory, cytoprotective, and neuroprotective functions. This makes bilirubin promising as a therapeutic and diagnostic agent in biomedicine. However, excess bilirubin is toxic and should be removed from the body. Bilirubin exhibits photochemical activity, which has been the subject of numerous studies up to now. Such studies are relevant because the bilirubin photochemistry provides the basis for bilirubin removing in phototherapy of neonatal jaundice (neonatal hyperbilirubinemia) and for some therapeutic applications. Furthermore, it can model several elementary processes of molecular photonics. In particular, the bilirubin molecule is capable of ultrafast Z-E photoisomerization and contains two almost identical dipyrromethenone chromophores capable of exciton coupling. The present review considers the data on the photophysical and photochemical properties of bilirubin and ultrafast routes of its phototransformations, as well as its photochemical reactions in phototherapy of neonatal hyperbilirubinemia and the ways to decrease the possible adverse effects of the phototherapy. The main analytical methods of bilirubin measurement in biological systems are also viewed.

Innovative quantum dots-based SERS for ultrasensitive reporting of contaminants in food: Fundamental concepts and practical implementations

Food contamination poses serious health risks, compelling the discovery of new methods to guarantee regulatory compliance and build consumer conviction. Surface Enhanced Raman Spectroscopy (SERS) has come into sight as a sophisticated approach for the ultrasensitive discovery of toxins in food and water, proposing non-destructive, quick, and precise analysis. Instantaneously, quantum dots (QDs) are astonishing nanomaterials, characterized by distinctive attributes such as quantum confinement and optical photostability. This article extends a decisive outline of SERS technology, pointing out its amalgamation with QDs and discussing numerous augmentation approaches i.e., chemical enhancement, electromagnetic enhancement, Van Hove singularities, the Brus equation, Förster resonance energy transfer, band gap energy, and quantum yield. The amalgamation of SERS with QDs commands an important promise in international food security and conservational sustainability. Nevertheless, QDs provide several compensations, they also aspect a few concerns, counting probable toxicity, stability problems, and predisposition to interference. To tackle these items, further research is required to synthesize safer, more stable QD materials and to refine protocols for practical real-world applications. While some reviews on SERS have been published recently, to our knowledge, the current review is the first one dedicated to QDs-assisted SERS in food safety.

Chemically Enhanced Raman Scattering Enabled by Organic Semiconductor Molecules with Deep Lowest Unoccupied Molecular Orbitals

Organic semiconductor materials (OSMs) have emerged as innovative platforms for surface-enhanced Raman scattering (SERS). For now, SERS activity has been established in only a few materials like thiophene-based derivatives, and the potential of the broader OSM library is largely untapped. Systematic exploration of energy level alignment between analytes and the OSM substrates is highly desirable for further material screening and optimization. We introduce a strategy utilizing OSMs with the deep lowest unoccupied molecular orbital (LUMO) levels, exemplified by TCNQ and HATCN, as novel SERS active platforms realizing efficient detection of multiple organic dyes otherwise undetectable under low-energy incident laser irradiation at 785 nm. Our study showcases selective SERS enhancement for analytes with diverse highest occupied molecular orbital levels, highlighting the pivotal role of LUMO levels in both SERS activity and molecular sensitivity. This work elucidates the molecular structure-SERS activity correlation, facilitating the development of novel SERS substrates via the strategy of LUMO level tuning.

Fabrication of Ag based Surface Enhanced Raman Scattering substrates with periodic mask arrays by electron beam deposition

BACKGROUND

Surface-enhanced Raman scattering (SERS) has attracted much attention as a powerful detection and analysis tool with high sensitivity and fast detection speed. The intensity of the SERS signal mainly depended on the highly enhanced electromagnetic field of nanostructure near the substrate. However, the fabrication of high-quality SERS nanostructured substrates is usually complicated, makes many methods unsuitable for large-scale production of SERS substrates. A new strategic preparation method is needed, which is simple and inexpensive in the preparation process, can achieve large-scale mass production, and also ensures the good performance of the SERS substrate.

RESULTS

For the first time, we propose constructing a silver (Ag) surface-enhanced Raman scattering (SERS) substrate with different angular quadrilateral periodic arrays by combining a mask plate and vapor deposition. The mask plate can precisely control the period and angle of the nano-arrays, and thus regulate the intensity of the local "hot spots". The analytical results show that the tetragonal periodic Ag SERS substrate with a 15° angle of the mask plate exhibits a significant enhancement effect in the detection of Rhodamine 6G (R6G), Rhodamine B (RhB), and Methyl Orange (MO) probe molecules, and the limit of detection (LOD) of this substrate is low as 10-11 mol/L for all the three solutions. The enhancement factors (EFs) are 6.5 × 106, 4.2 × 105, and 2.6 × 105, respectively. The accuracy of the experimental results was further verified through a finite-difference time-domain (FDTD) simulation.

SIGNIFICANCE AND NOVELTY

In this paper, we propose that the SERS substrate was fabricated using the new strategy with a lower detection limit for multiple dye molecules simultaneously. The results show that the SERS substrate prepared in this study has great potential for applications in high-performance SERS sensors. Additionally, this new preparation method may also be applicable to other metal materials, offering broad research prospects.

ZIP-8/Ag-based size-selective SERS nanoplatform for ultrasensitive urea detection in milk samples: effects of analyte molecular dimensions on adsorption capacity and sensing performance

Being well-known as an excellent sorbent, metal-organic frameworks (MOFs) have been employed to intergrate with noble metal nanoparticles to fabricate active substrates for surface-enhance Raman spectroscopy (SERS) sensing applications. In this work, we employed three organic molecules with different molecular dimensions, including urea, methylene blue (MB) and Congo red (CR) for investigating SERS performance of a ZIP-8/Ag heterostructure. While every dimension of urea is smaller than the pore size of ZIP-8, MB and CR has one dimension larger than that of the pore size. The results show that only urea experienced large SERS enhancements on ZIP-8/Ag sensing platform. In contrast, MB and CR exhibited lower SERS intensity on ZIP-8/Ag than on pure Ag nanoparticle substrates. Adsorption capacities of those analyte were then calculated to confirm that urea could be adsorbed into ZIP-8/Ag at the best rate. The size-dependent mechanism of analyte adsorption and improving SERS signal was then confirmed using two other organic compounds: 4-nitrophenol (4-NP) and chloramphenicol (CAP). Thanks to the size-selective adsorption, small molecules such as urea and 4-NP can be effectively detected in the presence of large interfering molecules, which is useful for developing advanced SERS applications. The ZIP-8/Ag-based SERS sensor could detect urea at impressive concentrations as low as 1.48 × 10-10 M in standard solutions and 10-8 M in milk.

Advances and applications of dynamic surface-enhanced Raman spectroscopy (SERS) for single molecule studies

Dynamic surface-enhanced Raman spectroscopy (SERS) is nowadays one of the most interesting applications of SERS, in particular for single molecule studies. In fact, it enables the study of real-time processes at the molecular level. This review summarizes the latest developments in dynamic SERS techniques and their applications, focusing on new instrumentation, data analysis methods, temporal resolution and sensitivity improvements, and novel substrates. We highlight the progress and applications of single-molecule dynamic SERS in monitoring chemical reactions, catalysis, biomolecular interactions, conformational dynamics, and real-time sensing and detection. We aim to provide a comprehensive review on its advancements, applications as well as its current challenges and development frontiers.

A Review on Perception of Binding Kinetics in Affinity Biosensors: Challenges and Opportunities

There are challenges associated with design and development of affinity biosensors due to the complicated multiphysics nature of the system. Understanding the binding interaction between target molecules and immobilized receptors and its kinetics is a crucial step to develop robust and reliable biosensor technologies. Evaluation of binding kinetics in biosensors becomes more important and challenging for clinical samples with a complex matrix. Despite drastic advancements in biosensor technologies, having a practical perception of the binding kinetics has remained a critical bottleneck due to limited fundamental understanding. This Review aims to provide a comprehensive discussion on concepts and advances developed so far for the perception of binding kinetics in affinity biosensors. Here, modeling approaches and measurement techniques are presented to characterize the binding interactions in biosensor technologies, while the effect of fouling and secondary factors in the binding interactions will be discussed in the concept of kinetics. This Review will investigate the existing research gaps and potential opportunities in the perception of binding kinetics and challenges to develop robust and reliable biosensors.

Precision Fabrication and Optimization of Nanostructures for Exosome Detection via Surface-Enhanced Raman Spectroscopy

Exosome detection is crucial for biomedical research and clinical diagnostics due to their unique characteristics. Surface-enhanced Raman spectroscopy (SERS) based on nanostructure substrates with local field enhancement capability is a promising detection approach. However, the random distribution of nanostructures leads to uneven "hotspots" distribution, which limits their application in SERS detection. Here, we systematically investigated the impact of experimental parameters on nanostructure morphology and analyzed their formation mechanism, achieving controllable nanocone fabrication. Subsequent experiments confirmed the reliability and effectiveness of the fabricated nanocone in exosome SERS detection. This work not only realized flexible control of nanostructures but also expanded their application prospects in the field of exosome analysis.

A novel controllable nanocyclic plasma coupled array in SERS trace detection of multi-component pollutants

The development and design of a novel, uniform and highly active local electromagnetic field enhanced structure is crucial for expanding Surface-enhanced Raman Scattering (SERS) applications. In this study, we developed Ag ring-coupled nanoarrays (Ag RCNAs) with controllable nanogaps using a substrate rotary evaporation coating technique with self-assembled polystyrene (PS) microspheres as templates. This straightforward and cost-effective method efficiently prepares plasma-coupled nanoarrays. Ag RCNAs demonstrated high sensitivity in detecting organic dyes, our prepared Ag RCNAs showed high sensitivity (with the limit of detection of 10-8 M), high signal reproducibility (with the relative standard deviation of 6.73 %). Furthermore, Ag RCNAs showed remarkable sensitivity to a broad spectrum of dyes in river water, indicating the large-area uniform and highly active circular-ring-shaped nanogaps can realize highly sensitive detection of various pollutants. This approach offers advantages in electromagnetic field enhancement, tunable nanogaps, uniformity, reproducibility, and recyclability, making it promising for applications in environmental monitoring, bioassays, food safety, and medical diagnostics.

Deep Learning-Powered Colloidal Digital SERS for Precise Monitoring of Cell Culture Media

Maintaining consistent quality in biopharmaceutical manufacturing is essential for producing high-quality complex biologics. Yet, current process analytical technologies (PAT) struggle to achieve rapid and highly accurate monitoring of small molecule critical process parameters and critical quality attributes. While Raman spectroscopy holds great promise as a highly sensitive and specific bioanalytical tool for PAT applications, its conventional implementation, surface-enhanced Raman spectroscopy (SERS), is constrained by considerable temporal and spatial intensity fluctuations, limiting the achievable reproducibility and reliability. Herein, we introduce a deep learning-powered colloidal digital SERS platform to address these limitations. Rather than addressing the intensity fluctuations, the approach leverages their very stochastic nature, arising from highly dynamic analyte-nanoparticle interactions. By converting the temporally fluctuating SERS intensities into digital binary "ON/OFF" signals using a predefined intensity threshold by analyzing the characteristic SERS peak, this approach enables digital visualization of single-molecule events and significantly reduces false positives and background interferences. By further integrating colloidal digital SERS with deep learning, the applicability of this platform is significantly expanded and enables detection of a broad range of analytes, unlimited by the lack of characteristic SERS peaks for certain analytes. We further implement this approach for studying AMBIC 1.1, a chemically-defined, serum-free complete media for mammalian cell culture. The obtained highly accurate and reproducible results demonstrate the unique capabilities of this platform for rapid and precise cell culture media monitoring, paving the way for its widespread adoption and scaling up as a new PAT tool in biopharmaceutical manufacturing and biomedical diagnostics.

Surface-enhanced Raman spectroscopy: a half-century historical perspective

Surface-enhanced Raman spectroscopy (SERS) has evolved significantly over fifty years into a powerful analytical technique. This review aims to achieve five main goals. (1) Providing a comprehensive history of SERS's discovery, its experimental and theoretical foundations, its connections to advances in nanoscience and plasmonics, and highlighting collective contributions of key pioneers. (2) Classifying four pivotal phases from the view of innovative methodologies in the fifty-year progression: initial development (mid-1970s to mid-1980s), downturn (mid-1980s to mid-1990s), nano-driven transformation (mid-1990s to mid-2010s), and recent boom (mid-2010s onwards). (3) Illuminating the entire journey and framework of SERS and its family members such as tip-enhanced Raman spectroscopy (TERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) and highlighting the trajectory. (4) Emphasizing the importance of innovative methods to overcome developmental bottlenecks, thereby expanding the material, morphology, and molecule generalities to leverage SERS as a versatile technique for broad applications. (5) Extracting the invaluable spirit of groundbreaking discovery and perseverant innovations from the pioneers and trailblazers. These key inspirations include proactively embracing and leveraging emerging scientific technologies, fostering interdisciplinary cooperation to transform the impossible into reality, and persistently searching to break bottlenecks even during low-tide periods, as luck is what happens when preparation meets opportunity.

Optical Bionanosensors for Sepsis Diagnostics

Sepsis is a global health challenge, characterized by a dysregulated immune response, leading to organ dysfunction and death. Despite advances in medical care, sepsis continues to claim a significant toll on human lives, with mortality rates from 10-25% for sepsis and 30-50% for septic shock, making it a leading cause of death worldwide. Current diagnostic methods rely on clinical signs, laboratory parameters, or microbial cultures and suffer from delays and inaccuracies. Therefore, there is a pressing need for novel diagnostic tools that can rapidly and accurately identify sepsis. This review highlights advances in biosensor development that could ultimately lead to faster and more accurate sepsis diagnostics. The focus is on nanomaterial-based optical approaches that promise rapid diagnostics without the need for large equipment or trained personnel. An overview of sepsis is provided, highlighting potential molecular targets and the challenges they present for assay development. The requirements for an ideal point-of-care test (POC) are discussed, including speed, simplicity, and cost-effectiveness. Different nanomaterials suitable for various optical detection methods are reviewed and innovative nanosensors are discussed for sepsis diagnostics, focusing on chemical design and approaches to increase selectivity by multiplexing.

Surface-Enhanced Raman Spectroscopy for Nitrite Detection

Nitrite is an important chemical intermediate in the nitrogen cycle and is ubiquitously present in environmental and biological systems as a metabolite or additive in the agricultural and food industries. However, nitrite can also be toxic in excessive concentrations. As such, the development of quick, sensitive, and portable assays for its measurement is desirable. In this review, we summarize the working principles and applications of surface-enhanced Raman spectroscopy (SERS) as a rapid, portable, and ultrasensitive method for nitrite detection and showcase its applicability in various water, food, and biological samples. The challenges and opportunities for future developments are also discussed.

Utilizing a synergistic strategy that combines electromagnetic and chemical enhancement to analyze the SERS effect of the Fe3O4@GO@Ag on PAHs detection

A comprehensive understanding of the enhancement mechanism of the substrate material is crucial to ensure the repeatability and functionality of SERS detection technology. Therefore, this study introduces a theoretical analysis method that integrates electromagnetic and chemical enhancement to achieve a comprehensive understanding of the SERS effect on the magnetic composite substrate. The visual model is employed in this study to comprehensively analyze and illustrate the electric field enhancement and optical effects of composite substrate materials. The study also elucidated the adsorption and charge transfer between the substrate material and target molecules. Based on this theory, Fe3O4@GO@Ag material was prepared and used to detect hydrophobic organic molecules such as polycyclic aromatic hydrocarbons (PAHs), with a concentration as low as 0.5 nM. This study comprehensively analyzed the SERS enhancement effect of the composite substrate for the first time, and prepared a magnetic composite substrate material for the detection of hydrophobic organic molecules, opening up a new avenue for theoretical guidance and experimental exploration in SERS detection and analysis.

Metallo-Supramolecular Helicates as Surface-Enhanced Raman Scattering (SERS) Substrates with High Tailorability

The exploration of novel functionalized supramolecular coordination complexes (SCCs) can enable new applications in domains that include purification and sensing. In this study, employing a coordination-driven self-assembly strategy, we designed and prepared a series of benzochalcogenodiazole-based metallohelicates as high-efficiency charge-transfer surface-enhanced Raman scattering (SERS) substrates, expanding the range of applications for these metallohelicates. Through structural modifications, including the substitution of single heteroatoms on ligands, replacement of coordinating metals, and alteration of ligand framework linkages, the Raman performance of these metallohelicates as substrates were systematically optimized. Notably, the SERS enhancement factors (EFs) of the metallohelicate-based SERS substrates were significantly enhanced to levels as high as 1.03×107, which rivals the EFs of noble metals devoid of "hot spots". Additionally, the underlying Raman enhancement mechanisms of these metallohelicates have been investigated through a combination of control experiments and theoretical calculations. This study not only demonstrates the utility of metallohelicates as SERS substrates but also offers insights and materials for the development of high-efficiency new charge-transfer SERS substrates.

A critical review on metal organic frameworks (MOFs)-based sensors for foodborne pathogenic bacteria detection

The pervasive threat of foodborne pathogenic bacteria necessitates advancements in rapid and reliable detection methods. Traditional approaches suffer from significant limitations including prolonged processing times, limited sensitivity and specificity. This review comprehensively examines the integration of metal organic frameworks (MOFs) with sensor technologies for the enhanced detection of foodborne pathogens. MOFs, with their unique properties such as high porosity, tunable pore sizes, and ease of functionalization, offer new avenues for sensor enhancement. This paper provides a comprehensive analysis of recent developments in MOFs-based sensors, particularly focusing on electrochemical, fluorescence, colorimetric, and surface-enhanced Raman spectroscopy sensors. We have provided a detailed introduction for the operational principles of these sensors, highlighting the role of MOFs play in enhancing their performance. Comparative analyses demonstrate MOFs' superior capabilities in enhancing signal response, reducing response time, and expanding detection limits. This review culminates in presenting MOFs as transformative materials in the detection of foodborne pathogens, paving the way for their broader application in ensuring food safety.

In situ surface-enhanced Raman spectroscopy for membrane protein analysis and sensing

Membrane proteins are involved in a variety of dynamic cellular processes and exploration of the structural basis of membrane proteins is of significance for a better understanding of their functions. In situ analysis of membrane proteins and their dynamics is, however, challenging for conventional techniques. Surface-enhanced Raman spectroscopy (SERS) is powerful in protein structural characterization, allowing for sensitive, in-situ and real-time identification and dynamic monitoring under physiological conditions. In this review, the applications of SERS in probing membrane proteins are outlined, discussed and prospected. It starts with a brief introduction to membrane proteins, SERS theories and SERS-based strategies that commonly-used for membrane proteins. How to assemble phospholipid biolayers on SERS-active materials is highlighted, followed by respectively discussing about direct and indirect strategies for membrane protein sensing. SERS-based monitoring of protein-ligand interactions is finally introduced and its potential in biomedical applications is discussed in detail. The review ends with critical discussion about current challenges and limitations of this research field, and the promising perspectives in both fundamental and applied sciences.

Detection of low-level fentanyl concentrations in mixtures of cocaine, MDMA, methamphetamine, and caffeine via surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) was utilized to measure low-level fentanyl concentrations mixed in common cutting agents, cocaine, 3,4-methylenedioxymethamphetamine (MDMA), methamphetamine, and caffeine. Mixtures were prepared with a fentanyl concentration range of 0-339 μM. Data was initially analyzed by plotting the area of a diagnostic peak (1026 cm-1) against concentration to generate a calibration model. This method was successful with fentanyl/MDMA samples (LOD 0.04 μM) but not for the other mixtures. A chemometric approach was then employed. The data was evaluated using principal component analysis (PCA), partial least squares (PLS1) regression, and linear discriminant analysis (LDA). The LDA model was used to classify samples into one of three designated concentration ranges, low = 0-0.4 mM, medium = 0.4-14 mM, or high >14 mM, with fentanyl concentrations correctly classified with greater than 85% accuracy. This model was then validated using a series of "blind" fentanyl mixtures and these unknown samples were assigned to the correct concentration range with an accuracy >95%. The PLS1 model failed to provide accurate quantitative assignments for the samples but did provide an accurate prediction for the presence or absence of fentanyl. The combination of the two models enabled accurate quantitative assignment of fentanyl in binary mixtures. This work establishes a proof of concept, indicating a larger sample size could generate a more accurate model. It demonstrates that samples, containing variable, low concentrations of fentanyl, can be accurately quantified, using SERS.

Aggregated gold nanoparticles rich in electromagnetic field "hotspots" for surface enhanced Raman scattering

A simple method for one-step synthesis of aggregated gold nanoparticles (a-AuNPs) using single-layer carbon dots (s-CDs) as the capping agents has been proposed. The obtained a-AuNPs are mainly composed of several spherical AuNPs of 20-25 nm sized, which aggregate to form nanogaps of ∼1 nm. Furthermore, the obtained a-AuNPs produce a strong localized surface plasmon resonance (LSPR) absorption band centered at around 640 nm, which is quite close to the wavelength of the commonly used 633 nm laser in surface enhanced Raman scattering (SERS). Thus, under the irradiation of 633 nm laser, a lot of electromagnetic field "hot spots" are formed at around the nanogaps, and strong SERS activity is achieved. The obtained a-AuNPs are dropped on tin-foil wafers to fabricate SERS substrates, which show the advantages of high sensitivity, fast response, good repeatability and satisfactory stability. On the basis, a sensitive SERS sensor is developed to detect malachite green in aquaculture water, with a low detection limit of 1 × 10-9 mol/L.

Study of two-dimensional information writing, reading and error correction at micro/nanoscale based on gold nanosphere arrays

Surface plasmon driven photocatalytic reactions have great potential for information encryption as well as information security. In this paper, explored the detection concentrations of dye molecule Rhodamine6G (R6G) on three substrates, where complete original Raman spectra signals were still obtained at a concentration of 10-8 M. Utilized photosensitive molecules to investigate the photocatalytic characteristics of 4-nitrobenzenethiol (4-NBT) on three substrates. Excitation light at a wavelength of 633 nm enables local photocatalytic for information signals writing, while 785 nm wavelength excitation light combined with two-dimensional Mapping technology is used for information signal reading. Read information signals are often prone to reading errors due to their own lack of resolution or strong interference from back bottom signals, so error correction processing of information signals is essential. Through comparative exploration, it is found that the ratio method can obtain high-precision and high-resolution information signals, and the interference of the background signals were well suppressed. Leveraging the advantages of Raman fingerprint spectra at the micro/nanoscale, it solves the challenge of incomplete information signals presentation at smaller scales. Additionally, through error correction processing of the information signals, high precision and high-resolution information signals are obtained.

An overview on plasmon-enhanced photoluminescence via metallic nanoantennas

In the realm of nanotechnology, the integration of quantum emitters with plasmonic nanostructures has emerged as an innovative pathway for applications in quantum technologies, sensing, and imaging. This research paper provides a comprehensive exploration of the photoluminescence enhancement induced by the interaction between quantum emitters and tailored nanostructure configurations. Four canonical nanoantennas (spheres, rods, disks, and crescents) are systematically investigated theoretically in three distinct configurations (single, gap, and nanoparticle-on-mirror nanoantennas), as a representative selection of the most fundamental and commonly studied structures and arrangements. A detailed analysis reveals that the rod gap nanoantenna configuration achieves the largest photoluminescence enhancement factor, of up to three orders of magnitude. The study presented here provides insights for the strategic design of plasmonic nanoantennas in the visible and near-IR spectral range, offering a roadmap for these structures to meet specific requirements in plasmon-enhanced fluorescence. Key properties such as the excitation rate, the quantum yield, the enhanced emitted power, or the directionality of the emission are thoroughly reviewed. The results of this overview contribute not only to the fundamental understanding of plasmon-enhanced emission of quantum emitters but also set the basis for the development of advanced nanophotonic devices with enhanced functionalities.

Surface-enhanced Raman scattering-based strategies for tumor markers detection: A review

The presence of malignant tumors poses a significant threat to people's life and well-being. As biochemical parameters indicate the occurrence and development of tumors, tumor markers play a pivotal role in early cancer detection, treatment, prognosis, efficient monitoring, and other aspects. Surface-enhanced Raman scattering (SERS) is considered a potent tool for the detection of tumor markers owing to its exceptional advantages encompassing high sensitivity, superior selectivity, rapid analysis speed, and photobleaching resistance nature. This review aims to provide a comprehensive understanding of SERS applications in the detection of tumor markers. Firstly, we introduce the SERS enhancement mechanism, classification of active substrates, and SERS detection techniques. Secondly, the latest research progress of in vitro SERS detection of different types of tumor markers in body fluids and the application of SERS imaging in biomedical imaging are highlighted in sections of the review. Finally, according to the current status of SERS detection of tumor markers, the challenges and problems of SERS in biomedical detection are discussed, and insights into future developments in SERS are offered.

Versatile, reusable and highly sensitive SERS-based point-of-care testing microplatform for reliable ATP detection

The advancement in miniaturized Raman spectrometers, coupled with the single-molecule-level sensitivity and unique fingerprint identification capability of surface-enhanced Raman scattering (SERS), offers great potential for point-of-care testing (POCT). Despite this, accurately quantifying analyte molecules, particularly in complex samples with limited sample volumes, remains difficult. Herein, we present a versatile and reusable SERS microplatform for highly sensitive and reliable quantitative detection of adenosine triphosphate (ATP) in biological fluids. The platform utilizes gold-Prussian blue core-shell nanoparticles modified with polyethyleneimine (Au@PB@PEI NPs), embedded within gold nanoparticle-immobilized capillary-based silica monolithic materials. PB acts as an internal standard, while PEI enhances molecular capture. The periodic, bimodal porous structure of the silica monolithic materials provides uniform and abundant sites for nanoparticle attachment, facilitating rapid liquid permeation, intense SERS enhancement, and efficient enrichment. The platform regulates ATP capture and release through magnesium ions in the liquid phase, eliminating matrix interferences and enabling platform reuse. Integrating efficient molecular enrichment, separation, an interference-free internal standard, a liquid flow channel, and a detection chamber, our platform offers simplicity in operation, exceptional sensitivity and accuracy, and rapid analysis (∼10 min). Employing PB as an internal calibration standard, ratiometric Raman signals (I732/I2123) facilitate precise ATP quantification, achieving a remarkable limit of detection down to 0.62 pM. Furthermore, this platform has been proven to be highly reproducible and validated for ATP quantification in both mouse cerebrospinal fluid and human serum, underscoring its immense potential for POCT applications.

Label-Free Exosome Analysis by Surface-Enhanced Raman Scattering Spectroscopy with Laser-Ablated Silver Nanoparticle Substrate

Early diagnostics of breast cancer is crucial to reduce the risk of cancer metastasis and late relapse. Exosome, which contains distinct information of its origin, can be the target object as a liquid biopsy. However, its low sensitivity and inadequate diagnostic tools interfere with the point-of-care testing (POCT) of the exosome. Recently, Surface-enhanced Raman Scattering (SERS) spectroscopy, which amplifies the Raman scattering, has been proved as a promising tool for exosome detection. However, the fabrication process of SERS probe or substrate is still inefficient and far from large-scale production. This study proposes rapid and label-free detection of breast cancer-derived exosomes by statistical analysis of SERS spectra using silver-nanoparticle-based SERS substrate fabricated by selective laser ablation and melting (SLAM). Employing silver nanowires and optimizing laser process parameters enable rapid and low-energy fabrication of SERS substrate. The functionalities including sensitivity, reproducibility, stability, and renewability are evaluated using rhodamine 6G as a probe molecule. Then, the feasibility of POCT is examined by the statistical analysis of SERS spectra of exosomes from malignant breast cancer cells and non-tumorigenic breast epithelial cells. The presented framework is anticipated to be utilized in other biomedical applications, facilitating cost-effective and large-scale production performance.

Highly sensitive SERS detection of melamine based on 3D Ag@porous silicon photonic crystal

The stability, reproducibility and engineering of SERS substrate faces a great challenge in melamine SERS assay. In this work, a simple, highly sensitive, stable and cost-efficient SERS detection platform for melamine was established based on its Raman fingerprints spectrum. The Ag@ porous silicon photonic crystal (Ag@PPC) was prepared as the 3D SERS substrate by electrochemical etching and magnetron sputter technology. The main influence factors for the preparation of SERS substrate were investigated in detail. The analytical enhancement factor of the 3D SERS substrate can reach to 2.6 × 108. The 3D SERS detection platform showed a wide linear detection range of 10-4∼10 mg L-1 and a low limit of detection of 0.1 μg L-1 for melamine. Moreover, such detection platform showed good stability, high reproducibility and high recovery rates for melamine. The 3D Ag@PPC SERS substrate can be easily prepared and engineered, displaying a great potential application in food safety field.

Multiplexed SERS Detection of Serum Cardiac Markers Using Plasmonic Metasurfaces

Surface-enhanced Raman spectroscopy (SERS) possesses exquisite molecular-specific properties with single-molecule sensitivity. Yet, translation of SERS into a quantitative analysis technique remains elusive owing to considerable fluctuation of the SERS intensity, which can be ascribed to the SERS uncertainty principle, a tradeoff between "reproducibility" and "enhancement". To provide a potential solution, herein, an integrated multiplexed SERS biosensing strategy is proposed, which features two distinct advantages. First, a subwavelength-structured plasmonic metasurface consisting of alternately stacked metal-dielectric pyramidal meta-atoms is fabricated and could provide simultaneously enhanced electric and magnetic fields to enable spatially extended and weakly wavelength-dependent SERS. Second, nanomechanical perturbations are harnessed to transduce signals in the form of SERS frequency shifts, which are not directly affected by the SERS uncertainty principle. By also employing 3D printing methods, a proof-of-concept study of multiplexed detection of a panel of serum cardiac biomarkers for acute myocardial infarction is provided. Success in the development of both the electric and magnetic fields-active plasmonic metasurfaces could transform future designs of SERS substrates with newly endowed functionalities, and frequency shift-based SERS multiplexing could open new opportunities to develop innovative quantitative optical techniques for applications in chemistry, biology, and medicine.