Surface-enhanced Raman Scattering Detection Research Articles

Microfluidics for disease diagnostics based on surface-enhanced raman scattering detection.

This review reports diverse microfluidic systems utilizing surface-enhanced Raman scattering (SERS) detection for disease diagnosis. Integrating SERS detection technology, providing high-sensitivity detection, and microfluidic technology for manipulating small liquid samples in microdevices has expanded the analytical capabilities previously confined to larger settings. This study explores the principles and uses of various SERS-based microfluidic devices developed over the last two decades. Specifically, we investigate the operational principles of documented SERS-based microfluidic devices, including continuous-flow channels, microarray-embedded microfluidic channels, droplet microfluidic channels, digital droplet channels, and gradient microfluidic channels. We also examine their applications in biomedical diagnostics. In conclusion, we summarize the areas requiring further development to translate these SERS-based microfluidic technologies into practical applications in clinical diagnostics.

Cellulose Nanofiber Films with Gold Nanoparticles Electrostatically Adsorbed for Facile Surface-Enhanced Raman Scattering Detection.

Cellulose nanofiber (CNF) holds great promise in applications such as surface-enhanced Raman scattering (SERS), catalysis, esthesia, and detection. This study aimed to build novel CNF-based SERS substrates through a facile synthetic method. Citrate-reduced gold nanoparticles (AuNPs) were adsorbed on the cationized CNF surface due to electrostatic interactions, and uniform AuNPs@(2,3-epoxypropyl trimethylammonium chloride)EPTMAC@CNF flexible SERS substrates were prepared by a simple vacuum-assisted filtration method. The probe molecule methylene blue was chosen to assess the performance of the CNF-based SERS substrate with a sensitivity up to 10-9 M, superior signal reproducibility (relative standard deviation (RSD) = 4.67%), and storage stability (more than 30 days). Tensile strength tests indicated that the CNF-based films had good mechanical properties. In addition, CNF-based substrates can easily capture and visually identify microplastics in water. These results demonstrate the potential application of the flexible, self-assembled AuNPs@EPTMAC@CNF flexible SERS substrate for prompt and sensitive detection of trace substances.

Microfluidic-SERS Technologies for CTC: A Perspective on Clinical Translation.

Enumeration and phenotypic profiling of circulating tumor cells (CTCs) provide critical information for clinical diagnosis and treatment monitoring in cancer. To achieve this goal, an integrated system is needed to efficiently isolate CTCs from patient samples and sensitively evaluate their phenotypes. Such integration would comprise a high-throughput single-cell processing unit for the isolation and manipulation of CTCs and a sensitive and multiplexed quantitation unit to detect clinically relevant signals from these cells. Surface-enhanced Raman scattering (SERS) has been used as an analytical method for molecular profiling and in vitro cancer diagnosis. More recently, its multiplexing capability and power to create distinct molecular signatures against their targets have garnered attention. Here, we share our insights into the combined power of microfluidics and SERS in realizing CTC isolation, enumeration, and detection from a clinical translation perspective. We highlight the key operational factors in CTC microfluidic processing and SERS detection from patient samples. We further discuss microfluidic-SERS integration and its clinical utility as a paradigm shift in clinical CTC-based cancer diagnosis and prognostication. Finally, we summarize the challenges and attempt to look forward to what lies ahead of us in potentially translating the technique into real clinical applications.

Plasmonic Au@Ag Core-Shell Nanoisland Film for Photothermal Inactivation and Surface-Enhanced Raman Scattering Detection of Bacteria.

Plasmonic metal nanomaterials have been extensively investigated for their utilizations in biomedical sensing and treatment. In this study, plasmonic Au@Ag core-shell nanoisland films (Au@AgNIFs) were successfully grown onto a glass substrate using a seed-mediated growth procedure. The nanostructure of the Au@AgNIFs was confirmed through scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM). The UV-Vis spectra of the Au@AgNIFs exhibited a broad absorption in the visible range from 300 to 800 nm because of the surface plasmon absorption. Under simulated sunlight exposure, the temperature of optimal Au@AgNIF was increased to be 66.9 °C to meet the requirement for photothermal bacterial eradication. Furthermore, the Au@AgNIFs demonstrated a consistent photothermal effect during the cyclic on/off exposure to light. For photothermal therapy, the Au@AgNIFs revealed superior efficiency in the photothermal eradication of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). With their unique nanoisland nanostructure, the Au@AgNIFs exhibited excellent growth efficiency of bacteria in comparison with that of the bare glass substrate. The Au@AgNIFs were also validated as a surface-enhanced Raman scattering (SERS) substrate to amplify the Raman signals of E. coli and S. aureus. By integrating photothermal therapy and SERS detection, the Au@AgNIFs were revealed to be a potential platform for bacterial theranostics.

Metal-Organic Framework-Enabled Trapping of Volatile Organic Compounds into Plasmonic Nanogaps for Surface-Enhanced Raman Scattering Detection.

Utilizing electromagnetic hotspots within plasmonic nanogaps is a promising approach to create ultrasensitive surface-enhanced Raman scattering (SERS) substrates. However, it is difficult for many molecules to get positioned in such nanogaps. Metal-organic frameworks (MOFs) are commonly used to absorb and concentrate diverse molecules. Herein, we combine these two strategies by introducing MOFs into plasmon-coupled nanogaps, which has so far remained experimentally challenging. Ultrasensitive SERS substrates are fabricated through the construction of nanoparticle-on-mirror structures, where Au nanocrystals are encapsulated with a zeolitic imidazolate framework-8 (ZIF-8) shell and then coupled to a gold film. The ZIF-8 shell, as a spacer that separates the Au nanocrystal and the Au film, can be adjusted in thickness over a wide range, which allows the electric field enhancement and plasmon resonance wavelength to be varied. By trapping Raman-active molecules within the ZIF-8 shell, we show that our plasmon-coupled structures exhibit a superior SERS detection performance. A range of volatile organic compounds at the concentrations of 10-2 mg m-3 can be detected sensitively and reliably. Our study therefore offers an attractive route for synergistically combining plasmonic electric field enhancement and MOF-enabled molecular enrichment to design and create SERS substrates for ultrasensitive detection.

Dual-functional Au-porous anodic alumina (PAA) sensors for enrichment and label-free detection of airborne virus with surface-enhanced Raman scattering

The development of a rapid and sensitive method for the enrichment and direct detection of airborne viruses has become urgently needed to prevent their spread. We have developed a dual-functional, label-free platform for the enrichment and optical identification of airborne viruses. This platform allows for the on-site enrichment and identification of airborne viruses through a virus enrichment component combined with surface-enhanced Raman scattering (SERS). In this work, we created an Au-porous anodic alumina (PAA) composite film, by ion sputtering Au nanoparticles (Au NPs) on a porous structure. The Au-PAA serves as a dual-functional sensor: it combines ultrafiltration through the vertical nanopores in the PAA for virus enrichment and constitutes a plasmonic substrate due to the surface plasmon near-field enhancements within the nanochannel structure. This sensor demonstrates an extraordinary enrichment efficiency (about 98 %) of obtained bioaerosols and enables simultaneous, sensitive detection at the single-virus level. Finite-difference time-domain (FDTD) simulations evidenced the electric field intensity and charge distribution of the Au-PAA. This Au-PAA composite film offers a powerful system for on-site, label-free viral particle enrichment and SERS detection. Contaminated air containing viruses can be collected in a few minutes and analyzed immediately by our platform, which is particularly beneficial for timely monitoring of viruses in the air of large public spaces. Additionally, this platform can be applied to evaluate the indoor air quality.

SERS substrate based on COF@Ag for detecting amoxicillin in honey and lake water

This study presents the design of a Surface-enhanced Raman scattering (SERS) substrate, COF@Ag, for the sensitive detection of Amoxicillin (AMX) in lake water and honey. Furthermore, the study investigates the role of covalent organic frameworks (COFs) in SERS detection. The characterization results demonstrate the capability of COFs to efficiently enrich Ag nanoparticles (AgNPs), resulting in a more concentrated distribution of hotspots and an enhanced electromagnetic field on the substrate. By employing density functional theory (DFT) simulation, the frontier electronic orbitals of COFs and AMX were analyzed, and the chemical bonds and weak interactions in the system were examined using the Interaction Region Indicator (IRI) method to propose potential enhancement mechanisms. In aqueous solutions, the linear range is 1 μg/L-30 μg/L, with a limit of detection (LOD) 0.279 μg/L. In lake water, the linear range span from 100 μg/L to 500 μg/L, with a detection limit of 8.244 μg/L. For honey, the linear range extend from 20 ng/g to 100 ng/g, with a detection limit of 2.917 ng/g. This method holds key significance in facilitating the rapid detection of amoxicillin and advancing the application of COFs in SERS.

Reversible Thermoelectric Regulation of Electromagnetic and Chemical Enhancement for Rapid SERS Detection.

Actively controlling surface-enhanced Raman scattering (SERS) performance plays a vital role in highly sensitive detection or in situ monitoring. Nevertheless, it is still challenging to achieve further modulation of electromagnetic enhancement and chemical enhancement simultaneously in SERS detection. In this study, a silver nanocavity structure with graphene as a spacer layer is coupled with thermoelectric semiconductor P-type gallium nitride (GaN) to form an electric-field-induced SERS (E-SERS) for dual enhancement. After applying the electric field, the intensity of SERS signals is further enhanced by over 10 times. The thermoelectric field enables fast and reproducible doping of graphene, thereby modulating its Fermi level over a wide range. The thermoelectric field also regulates the position of the plasmon resonance peak of the silver nanocavity structure, rendering synchronous dual electromagnetic and chemical regulation. Additionally, the method enables the trace detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A detailed theoretical analysis is performed based on the experimental results and finite-element calculations, paving the way for the fabrication of high-efficient E-SERS substrates.

Raman and Surface-Enhanced Raman Scattering Detection in Flowing Solutions for Complex Mixture Analysis.

Raman scattering provides a chemical-specific and label-free method for identifying and quantifying molecules in flowing solutions. This review provides a comprehensive examination of the application of Raman spectroscopy and surface-enhanced Raman scattering (SERS) to flowing liquid samples. We summarize developments in online and at-line detection using Raman and SERS analysis, including the design of microfluidic devices, the development of unique SERS substrates, novel sampling interfaces, and coupling these approaches to fluid-based chemical separations (e.g., chromatography and electrophoresis). The article highlights the challenges and limitations associated with these techniques and provides examples of their applications in a variety of fields, including chemistry, biology, and environmental science. Overall, this review demonstrates the utility of Raman and SERS for analysis of complex mixtures and highlights the potential for further development and optimization of these techniques. Expected final online publication date for the Annual Review of Analytical Chemistry, Volume 17 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Biomimetic-Membrane-Protected Plasmonic Nanostructures as Dual-Modality Contrast Agents for Correlated Surface-Enhanced Raman Scattering and Photoacoustic Detection of Hidden Tumor Lesions.

Optical imaging and spectroscopic modalities are of considerable current interest for in vivo cancer detection and image-guided surgery, but the turbid or scattering nature of biomedical tissues has severely limited their abilities to detect buried or occluded tumor lesions. Here we report the development of a dual-modality plasmonic nanostructure based on colloidal gold nanostars (AuNSs) for simultaneous surface-enhanced Raman scattering (SERS) and photoacoustic (PA) detection of tumor phantoms embedded (hidden) in ex vivo animal tissues. By using red blood cell membranes as a naturally derived biomimetic coating, we show that this class of dual-modality contrast agents can provide both Raman spectroscopic and PA signals for the detection and differentiation of hidden solid tumors with greatly improved depths of tissue penetration. Compared to previous polymer-coated AuNSs, the biomimetic coatings are also able to minimize protein adsorption and cellular uptake when exposed to human plasma without compromising their SERS or PA signals. We further show that tumor-targeting peptides (such as cyclic RGD) can be noncovalently inserted for targeting the ανβ3-integrin receptors expressed on metastatic cancer cells and tracked via both SERS and PA imaging (PAI). Finally, we demonstrate image-guided resections of tumor-mimicking phantoms comprising metastatic tumor cells buried under layers of skin and fat tissues (6 mm in thickness). Specifically, PAI was used to determine the precise tumor location, while SERS spectroscopic signals were used for tumor identification and differentiation. This work opens the possibility of using these biomimetic dual-modality nanoparticles with superior signal and biological stability for intraoperative cancer detection and resection.

Simultaneous detection of SARS-CoV-2 S1 protein by using flexible electrochemical and Raman enhancing biochip

Flexible laser-scribed graphene (LSG) substrates with gold nanoislands have been developed as biochips for in situ electrochemical (EC) and surface-enhanced Raman scattering (SERS) biodetection (biomolecules and viral proteins). A flexible biochip was fabricated using CO2 laser engraving polyimide (PI) films to form a 3D porous graphene-like nanostructure. Gold nanoislands were deposited on the LSG substrates to enhance the intensity of the Raman signals. Moreover, the addition of auxiliary and reference electrodes induced a dual-function EC-SERS biochip with significantly enhanced detection sensitivity. The biochip could selectively and easily capture SARS-CoV-2 S1 protein through the SARS-CoV-2 S1 antibody immobilized on EC-SERS substrates using 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The grafted antibody specifically bound to SARS-CoV-2, resulting in a significant increase in the SERS signal of the target analyte. The limit of detection (LOD) of the SARS-CoV-2 S1 protein was 5 and 100 ng/mL by using EC and SERS detection, respectively. Although the LOD of the SARS-CoV-2 S1 protein detected using SERS is only 100 ng/mL, it can provide fingerprint information for identification. To improve the LOD, EC detection was integrated with SERS detection. The three-electrode detection chip enables the simultaneous detection of SERS and EC signals, which provides complementary information for target identification. The dual-functional detection technology demonstrated in this study has great potential for biomedical applications, such as the rapid and sensitive detection of SARS-CoV-2.

High energy facet-dominated TiO2−X facet heterojunction with excellent carrier utilization for ultrasensitive SERS sensing and efficient degradation of antibiotic residues

Realizing efficient utilization of photogenerated carriers is crucial to boosting the photophysical and photochemical performances of semiconductors. Herein, (101) and (001) facets co-exposed anatase TiO2−X facet heterojunction with abundant oxygen vacancies was developed as a new surface-enhanced Raman scattering (SERS) substrate and also as an excellent photocatalyst for synchronous detection and degradation of antibiotic residues in actual water system. Due to the efficient carrier separation induced by facet heterojunction and the efficient charge migration derived from exposure of more high energy (001) facets, the TiO2−X facet heterojunction exhibits an ultrahigh SERS enhancement factor of 1.07 × 107 for non-resonant Raman probe, with excellent spectral reproducibility and stability. More meaningfully, the developed substrate can realize an ultrasensitive detection for different kinds of antibiotic residues in real river water, even a comprehensive identification for multicomponent residues. Moreover, TiO2−X facet heterojunction can also execute an efficient photocatalytic degradation for residue pollutants in actual water system. And, the developed multi-function substrate possesses an excellent recyclability not only in SERS detection but also in photocatalysis.

Application of Nanohybrid Substrates with Layer-by-Layer Self-Assembling Properties to High-Sensitivity Surface-Enhanced Raman Scattering Detection.

The present study was conducted to prepare and investigate large-area, high-sensitivity surface-enhanced Raman scattering (SERS) substrates. Organic/inorganic nanohybrid dispersants consisting of an amphiphilic triblock copolymer (hereafter referred to simply as "copolymer") and graphene oxide (GO) were used to stabilize the growth and size of gold nanoparticles (AuNPs). Ion-dipole forces were present between the AuNPs and copolymer dispersants, while the hydrogen bonds between GO and the copolymer prevented the aggregation of GO, thereby stabilizing the AuNP/GO nanohybrids. Transmission electron microscopy (TEM) revealed that the AuNPs had particle sizes of 25-35 nm and a relatively uniform size distribution. The AuNP/GO nanohybrids were deposited onto the glass substrate by using the solution drop-casting method and employed for SERS detection. The self-assembling properties of two-dimensional sheet-like GO led to a regular lamellar arrangement of AuNP/GO nanohybrids, which could be used for the preparation of large-area SERS substrates. Following removal of the copolymer by annealing at 300 °C for 2 h, measurements were obtained under scanning electron microscopy. The results confirmed that 2D GO nanosheets were capable of stabilizing AuNPs, with the final size reaching approximately 40 nm. These AuNPs were adsorbed on both sides of the GO nanosheets. Because the GO nanosheets were merely 5 nm-thick, a good three-dimensional hot-junction effect was generated along the z-axis of the AuNPs. Lastly, the prepared material was used for the SERS detection of rhodamine 6G (R6G), a commonly used highly fluorescent dye. An enhancement factor (EF) of up to 3.5 × 106 was achieved, and the limit of detection was approximately 10-10 M. Detection limits of 10-10 M and < 10-10 M were also observed with the detection of Direct Blue 200 and the biological molecule adenine. It is therefore evident that AuNP/copolymer/GO nanohybrids are large-area flexible SERS substrates that hold great potential in environmental monitoring and biological system detection applications.

Chemically renewable SERS sensor for the inspection of H2O2 residue in food stuff

Hydrogen peroxide (H2O2) residue in foodstuffs will bring great harm to human health. We immobilize the composite of the reduced polyaniline (PANIR) modified gold nanoparticles on the surface of ITO (ITO/AuNPs/PANIR) to develop surface-enhanced Raman scattering (SERS) sensor for H2O2.detection. The principle is that PANIR is oxidized by H2O2 to generate a new SERS peak at 1460 cm−1 for realizing quantitative analysis of H2O2. Fe2+-Fenton reaction is introduced to catalytically react with H2O2 to hydroxyl radical, which speeds up the oxidation of PANIR. Before SERS detection, acidic treatment could guarantee the reduced state of PANIR in composite. Limit of detection of ITO/AuNPs/PANIR-based SERS assay for H2O2 is down to 1.78 × 10−12 mol/L and a good linear relationship from 1 × 10−10 to 3.16 × 10−7 mol/L is achieved. Furthermore, the SERS sensor could be regenerated by acidic treatment. As a scenario, the renewable SERS sensor is utilized to monitor H2O2 residues in food and environmental samples.

Three-Phase Catassembly of 10 nm Au Nanoparticles for Sensitive and Stable Surface-Enhanced Raman Scattering Detection.

Interfacial self-assembly with the advantage of providing large-area, high-density plasmonic hot spots is conducive to achieving high sensitivity and stable surface-enhanced Raman scattering (SERS) sensing. However, rapid and simple assembly of highly repeatable large-scale multilayers with small nanoparticles remains a challenge. Here, we proposed a catassembly approach, where the "catassembly" means the increase in the rate and control of nanoparticle assembly dynamics. The catassembly approach was dropping heated Au sols onto oil chloroform (CHCl3), which triggers a rapid assembly of plasmonic multilayers within 15 s at the oil-water-air (O/W/A) interface. A mixture of heated sol and CHCl3 constructs a continuous liquid-air interfacial tension gradient; thus, the plasmonic multilayer film can form rapidly without adding functional ligands. Also, the dynamic assembly process of the three-phase catassembly ranging from cluster to interfacial film formation was observed through experimental characterization and COMSOL simulation. Importantly, the plasmonic multilayers of 10 nm Au NPs for SERS sensing demonstrated high sensitivity with the 1 nM level for crystal violet molecules and excellent stability with an RSD of about 10.0%, which is comparable to the detection level of 50 nm Au NPs with layer-by-layer assembly, as well as breaking the traditional and intrinsic understanding of small particles of plasmon properties. These plasmonic multilayers of 10 nm Au NPs through the three-phase catassembly method illustrate high SERS sensitivity and stability, paving the way for small-nanoparticle SERS sensing applications.

Three-Dimensional MXene-AgNP Hollow Spheres for In Situ Surface-Enhanced Raman Scattering Detection of Catalysis Reactions.

MXenes are attractive candidates in the fields of surface-enhanced Raman scattering (SERS) and catalysis. However, most of the current studies on MXenes are based on blocks and nanosheets, limiting their SERS and catalytic properties. Herein, we have prepared 3D MXene hollow spheres wrapped with silver nanoparticles (Ti3C2-AgNP HSs) using a sacrificial template method, which exhibits excellent sensitivity with a low detection limit due to good light-trapping capability of the hollow sphere and strong localized surface plasmon resonance (LSPR) effect of AgNPs. Furthermore, it shows outstanding photocatalytic performance and realizes in situ SERS monitoring of the 4-nitrobenzenethiol (4-NTP) to 4-aminothiophenol (4-ATP) catalysis reaction. The finite-difference time-domain (FDTD) simulations confirm that 3D Ti3C2-AgNP hollow structures have stronger hot spots than 3D solid structures and higher SERS sensitivity for molecule detection. Therefore, it promises to be an excellent bifunctional material for highly sensitive SERS detection and the in situ monitoring of catalytic reactions.

A fluorescence and SERS dual-mode sensing on tetracycline antibiotics based on Ag@NH2-MIL-101(Al) nanoprobe

Antibiotic residues are becoming more and more concern due to the increasingly serious resistance from bacteria to organism. On-site and accurate evaluation on antibiotics is necessary and urgent to effectively solve such public issue. To provide point-of-care-test (POCT) ideas for antibiotic accurate evaluation, a fluorescence (FL)-surface-enhanced Raman scattering (SERS) dual-mode detection of tetracycline antibiotic (TCs) was realized for the first time. Based on the inner filter effect in Ag@NH2-MIL-101(Al) nanoprobe, the fluorescence quenching was induced and the SERS signal was swiftly turn on through π-π interaction and hydrogen bonding in the presence of TCs. This FL-SERS dual mode sensor displayed excellent detection limits (FL in ∼10−3 ppm, SERS in ∼10−5 ppm), and achieved a reliable detection of TCs in honey with a recovery rate of 84.45%−112.08%. This method combines the advantages of FL and SERS detection, meanwhile, two techniques verified against each other to achieve highly sensitive and specific FL-SERS dual-mode sensor for TCs. We believe that such antibody-or aptamer-independent FL and SERS complementary nanoprobe can be applied to fast, direct and multiple sensing in environment and food hazards.

Long-lived SERS Matrix for Real-Time Biochemical Detection Using "Frozen" Transition State.

For the long-time tracking of biological events, maintaining the bioactivity of the analytes during the detection process is essential. Here, we show a versatile surface-enhanced Raman Scattering (SERS) platform, termed a superwettable-omniphobic lubricous porous SERS (SOLP-SERS) substrate. The SOLP-SERS substrate could generate a three-dimensional liquid "hotspots" matrix with an ultra-long lifetime (tens of days) by confining tiny amounts of liquids within the gaps between nanoparticles. Then, the analytes are trapped in the uniform liquid "hotspots", whose bioactivity can be well maintained over a long period of time during SERS detection. Limits of detection down to femtomolar levels were achieved for various molecules. More importantly, SERS signals were uniform within the substrate and remained stable for more than 30 days. As a proof-of-concept experiment, the dynamic detection of the polymerization of Aβ peptides into amyloids was monitored by the SOLP-SERS substrate within 48 h. Moreover, the exosomes secreted by breast cancer cells, an important biomarker of cancer, were also measured. These results demonstrate that the SOLP-SERS platform will provide new insights into the development of real-time biochemical sensors with ultrahigh sensitivity.

Magnetic MOF Substrates for the Rapid and Sensitive Surface-Enhanced Raman Scattering Detection of Uranyl.

With the widespread use of uranium in the nuclear industry, achieving rapid and sensitive detection of uranium contaminants is critical for reducing environmental pollution. Surface-enhanced Raman scattering (SERS), with its high sensitivity and unique fingerprint properties, has been used for the analysis of uranyl. However, the weak affinity of Au for uranyl remains a challenge in the development of spherical Au-based SERS substrates. The metal-organic framework (MOF) material ZIF-8 exhibits excellent adsorption capacity for uranyl and could overcome this limitation. In this study, ZIF-8 porous structures were modified on a magnetic SERS substrate, Fe3O4@SiO2@Au (FA), for the rapid and sensitive detection and analysis of the uranyl species. Uranyl was adsorbed by ZIF-8, allowing ready access to the hot spots in the interstices of Au nanoparticles (AuNPs). Symmetrically stretched vibrating bonds of O═U═O were detected at 829 cm-1 as the characteristic peak of uranyl by surface plasmon resonance between the AuNPs. The ZIF-8 coating had minimal influence on target detection as the detection limit for 4-MPY was only half an order of magnitude lower than before modification. The enhancement factor for uranyl reached 106. The substrate showed excellent sensing performance in a neutral or alkaline environment. It was used to detect uranyl in tap water and river water; rapid separation of the species from the water samples was achieved using an external magnet to extract radioactive waste. The proposed substrate offers a route for monitoring and detecting uranyl contamination and an approach for achieving rapid on-site detection, providing a promising application for environmental contaminant detection.

A Review on Non-Noble Metal Substrates for Surface-Enhanced Raman Scattering Detection

Surface-enhanced Raman scattering (SERS), a powerful spectroscopic technique owing to its abundant vibrational fingerprints, has been widely employed for the assay of analytes. It is generally considered that one of the critical factors determining the SERS performance is the property of the substrate materials. Apart from noble metal substrates, non-noble metal nanostructured materials, as emerging new substrates, have been extensively studied for SERS research by virtue of their superior biocompatibility, good chemical stability, outstanding selectivity, and unique physicochemical properties such as adjustable band structure and carrier concentration. Herein, in this review, we summarized the research on the analytical application of non-noble metal SERS substrates from three aspects. Firstly, we started with an introduction to the possible enhancement mechanism of non-noble metal substrates. Then, as a guideline for substrates design, several main types of materials, including carbon nanomaterials, transition metal dichalcogenides (TMDs), metal oxides, metal-organic frameworks (MOFs), transition metal carbides and nitrides (MXenes), and conjugated polymers were discussed. Finally, we especially emphasized their analytical application, such as the detection of pollutants and biomarkers. Moreover, the challenges and attractive research prospects of non-noble metal SERS substrates in practical application were proposed. This work may arouse more awareness of the practical application of the non-noble metal material-based SERS substrates, especially for bioanalysis.