Synthesis of novel gold mesoflowers as SERS tags for immunoassay with improved sensitivity

Immunoassays: Analytical and Clinical Performance, Challenges, and Perspectives of SERS Detection in Comparison with Fluorescent Spectroscopic Detection

Immunoassays (IAs) with fluorescence-based detection are already well-established commercialized biosensing methods, such as enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassay (LFIA). Immunoassays with surface-enhanced Raman spectroscopy (SERS) detection have received significant attention from the research community for at least two decades, but so far they still lack a wide clinical commercial application. This review, unlike any other review that we have seen, performs a three-dimensional performance comparison of SERS IAs vs. fluorescence IAs. First, we compared the limit of detection (LOD) as a key performance parameter for 30 fluorescence and 30 SERS-based immunoassays reported in the literature. We also compared the clinical performances of a smaller number of available reports for SERS vs. fluorescence immunoassays (FIAs). We found that the median and geometric average LODs are about 1.5-2 orders of magnitude lower for SERS-based immunoassays in comparison to fluorescence-based immunoassays. For instance, the median LOD for SERS IA is 4.3 × 10-13 M, whereas for FIA, it is 1.5 × 10-11 M. However, there is no significant difference in average relative standard deviation (RSD)-both are about 5-6%. The analysis of sensitivity, selectivity, and accuracy reported for a limited number of the published clinical studies with SERS IA and FIA demonstrates an advantage of SERS IA over FIA, at least in terms of the median value for all three of those parameters. We discussed common and specific challenges to the performances of both SERS IA and FIA, while proposing some solutions to mitigate those challenges for both techniques. These challenges include non-specific protein binding, non-specific interactions in the immunoassays, sometimes insufficient reproducibility, relatively long assay times, photobleaching, etc. Overall, this review may be useful for a large number of researchers who would like to use immunoassays, but particularly for those who would like to make improvements and move forward in both SERS-based IAs and fluorescence-based IAs.

Facile synthesis of gold nanocages with silver nanocubes templates dual metal effects enabled SERS imaging and catalytic reduction

Silver (Ag) nanomaterials featuring a cubic shape particularly represent supreme class of advance nanomaterials. This work explored a new precursor and its effect on morphological features of silver (Ag) nanocubes (NCs) serving as sacrificial templates for facile synthesis of gold NCs. The AgNCs were initially prepared utilizing sodium thiosulphate (Na2S2O3) as relatively stable S2- producing species along with a soft etchant source KCl. The effects of different potassium halides were evaluated to grasp control over seed mediated growth of Ag nanocubes. Taking the advantages of dual metallic properties, Ag@4MBA@AuNCs nanostructure was synthesized using 4-mercaptobenzoic acid (4MBA) as a Raman reporter molecule. This nanostructure showed 1010-times enhancement in surface enhanced Raman scattering (SERS) signal, leading to a highly sensitive imaging probe for the detection of even three breast cancer cells (MCF-7 cells) in vitro. Subsequently, the oxidative nanopeeling well accompanied by incorporation of Au/Ag alloy nanoparticles on AuNCs corona assembly was achieved, which facilitated the catalytic reduction of toxic nitrophenol to eco-friendly aminophenol. Such sophisticated and engineered nanoassemblies possess broad applications in bioanalysis.

Surface-enhanced Raman spectroscopy for drug discovery: peptide-RNA binding

The ever-growing demand for new drugs highlights the need to develop novel cost- and time-effective techniques for drug discovery. Surface-enhanced Raman spectroscopy (SERS) is an emerging ultrasensitive and label-free technique that allows for the efficient detection and characterization of molecular interactions. We have recently developed a SERS platform for detecting a single protein molecule linked to a gold substrate (Almehmadi et al. Scientific Reports 2019). In this study, we extended the approach to probe the binding of potential drugs to RNA targets. To demonstrate the proof of concept, two 16-amino acid residue peptides with close primary structures and different binding affinities to the RNA CUG repeat related to myotonic dystrophy were tested. Three-microliter solutions of the RNA repeat with these peptides at nanomolar concentrations were probed using the developed approach, and the binding of only one peptide was demonstrated. The SER spectra exhibited significant fluctuations along with a sudden strong enhancement as spectra were collected consecutively from individual spots. Principal component analysis (PCA) of the SER spectral datasets indicated that free RNA repeats could be differentiated from those complexed with a peptide with 100% accuracy. The developed SERS platform provides a novel opportunity for label-free screening of RNA-binding peptides for drug discovery. Schematic representation of the SERS platform for drug discovery developed in this study.

Exploring Sensitive Label-Free Multiplex Analysis with Raman-Coded Microbeads and SERS-Coded Reporters

Suspension microsphere immunoassays are rapidly gaining attention in multiplex bioassays. Accurate detection of multiple analytes from a single measurement is critical in modern bioanalysis, which always requires complex encoding systems. In this study, a novel bioassay with Raman-coded antibody supports (polymer microbeads with different Raman signatures) and surface-enhanced Raman scattering (SERS)-coded nanotags (organic thiols on a gold nanoparticle surface with different SERS signatures) was developed as a model fluorescent, label-free, bead-based multiplex immunoassay system. The developed homogeneous immunoassays included two surface-functionalized monodisperse Raman-coded microbeads of polystyrene and poly(4-tert-butylstyrene) as the immune solid supports, and two epitope modified nanotags (self-assembled 4-mercaptobenzoic acid or 3-mercaptopropionic acid on gold nanoparticles) as the SERS-coded reporters. Such multiplex Raman/SERS-based microsphere immunoassays could selectively identify specific paratope–epitope interactions from one mixture sample solution under a single laser illumination, and thus hold great promise in future suspension multiplex analysis for diverse biomedical applications.

Proximity hybridization induced DNA assembly for label-free surface-enhanced Raman spectroscopic detection of carcinoembryonic antigen

In our research, label-free and surface-enhanced Raman dyes-free Raman spectroscopy which was used to detect carcinoembryonic antigen (CEA) according to poly adenine (Poly A)-regulated self-assembly methods was developed and studied. CEA induced partial hybridization of Ab-H2 and Ab-H1, and Ab-H1-CEA-Ab-H2 (a sandwich proximity CEA-DNA complex) was formed, which unfolded molecular beacon 1 (MB1) and modified the substrate. Subsequently, MB2-AuNPs were hybridized with MB1, and Ab-H1-CEA-Ab-H2 was released via toehold regulated displacements of DNA strands. Therefore, hybridization processes of MB2 and MB1 were induced and promoted by CEA-DNA complexes which worked as catalysts. The misplaced target then induced a next round of strand exchange, and the signals for determination of CEA were amplified by AuNPs absorbed on the substrate. It was indicated that the spectral characteristics of adenine at 736 cm^-1 were consistent with the SERS spectrum of DNA. Adenine acted as an internal marker for label-free SERS detection of CEA. Moreover, satisfactory stability and reproducibility were found. Meanwhile, the antibody could specifically recognize the corresponding antigen. Since adenine was dominant in SERS spectra, which was also proximal to Au surface, the sensitivity of the novel method was high without modifications. The analytical performance of this method in determining serum CEA was satisfactory.

Gap-Dependent Surface-Enhanced Raman Scattering (SERS) Enhancement Model of SERS Substrate-Probe Combination Using a Polyelectrolyte Nanodroplet as a Distance Controller

The development of surface-enhanced Raman scattering (SERS) biosensor platforms based on the sandwich combination of an SERS substrate and Raman reporter coated gold nanoparticle (AuNP) labeled with antibody has been widely performed for highly sensitive detection of biomolecules. The size of biomolecules located between these SERS-active materials dictates the sensitivity enhancement of the sensor. However, no suitable molecular size is provided. In this study, we report the gap-dependent SERS enhancement model using the combination of two SERS-active materials of 2D arrays of gold core-silver shell nanoparticles (Au@Ag core-shell NPs) as SERS-active substrates and mercaptobenzoic acid (MBA)-labeled AuNPs as SERS probes. The distance between these two materials is finely tuned using layer-by-layer assembled polyelectrolyte multilayer films. The morphology of the polyelectrolyte spacer is controlled into a droplet nanostructure, which is assumed to have a comparable shape with globular biomolecules. The well-controlled height or thickness of polyelectrolyte nanodroplet was achieved by changing number of deposition cycles. By increasing the thickness of the polyelectrolyte nanodroplet, MBA SERS intensities gradually decreased until at 40 nm-thick nanodroplet film and maintained afterward. This spacer thickness defined the limit of plasmonic coupling effect from this SERS probe-substrate combination. The SERS enhancement capability of this model was compared to conventional SERS immunoassay using three different antigen-antibody complex sizes of prostate-specific antigen, carcinoembryonic antigen, and carbohydrate antigen 19-9. Good agreement of the limitation of plasmon coupling as a function of the distance between the SERS substrate-probe combination using this developed model and SERS immunoassay was found. The finding provides valuable guidelines for immune-system selection in SERS immunosensors based on SERS substrate-probe combination.

AuNP array coated substrate for sensitive and homogeneous SERS-immunoassay detection of human immunoglobulin G

Owing to the high sensitivity, fast responsiveness and high specificity, immunoassays using surface-enhanced Raman scattering (SERS) as the readout signal displayed great potential in disease diagnosis. In this study, we developed a SERS-immunoassay method for the detection of human immunoglobulin G (HIgG). Upon involving well-ordered AuA on a SERSIA substrate, the LSPR effect was further enhanced to generate a strong and uniform Raman signal through the formation of sandwich structure with the addition of target HIgG and SERSIA tag. Optimization of the assay provided a wide linear range (0.1–200 μg mL⁻¹) and low limit of detection (0.1 μg mL⁻¹). In addition, the SERS-immunoassay method displayed excellent specificity and was homogeneous, which guaranteed the practical use of this method in the quantitative detection of HIgG. To validate this assay, human serum was analysed, which demonstrated the potential advantages of SERS-immunoassay technology in clinical diagnostics.

An AuNP array coated substrate was developed for the SERS-immunoassay detection of human immunoglobulin G.

Metal Nanoparticles/MoS2 Surface-Enhanced Raman Scattering-Based Sandwich Immunoassay for α-Fetoprotein Detection

The detection of cancer biomarkers at an early stage of tumor development is vital for effective diagnosis and treatment of cancer. Current diagnostic tools can often detect cancer only when the biomarker levels are already too high, so that the tumors have spread and treatments are less effective. It is urgent therefore to develop highly sensitive assays for the detection of such biomarkers at the lowest possible concentration. In this context, we developed a sandwich immunoassay based on surface-enhanced Raman scattering (SERS) for the ultrasensitive detection of α-fetoprotein (AFP), which is typically present in human serum as a biomarker indicative of early stages of hepatocellular carcinoma. In the immunoassay design, molybdenum disulfide (MoS2) modified with a monoclonal antibody was used as a capture probe for AFP. A secondary antibody linked to an SERS-encoded nanoparticle was employed as the Raman signal reporter, that is, the transducer for AFP detection. The sandwich immunocomplex "capture probe/target/SERS tag" was deposited on a silicon wafer and decorated with silver-coated gold nanocubes to increase the density of "hot spots" on the surface of the immunosensor. The developed SERS immunosensor exhibits a wide linear detection range (1 pg mL-1 to 10 ng mL-1) with a limit of detection as low as 0.03 pg mL-1 toward AFP with good reproducibility (RSD < 6%) and stability. These parameters demonstrate that the proposed immunosensor has the potential to be used as an analytical platform for the detection of early-stage cancer biomarkers in clinical applications.

Effect of Varying Expression of EpCAM on the Efficiency of CTCs Detection by SERS-Based Immunomagnetic Optofluidic Device

Simple Summary

In this work we present a magnetically supported SERS-based immunoassay based on solid SERS-active support for the detection of circulating tumor cells. The SERS response in our optofluidic device was correlated with the level of EpCAM expression. The level of EpCAM cell expression in four cell lines with relatively high (human metastatic prostate adenocarcinoma cells (LNCaP)), medium (human metastatic prostate adenocarcinoma cells (LNCaP)), weak (human metastatic prostate adenocarcinoma cells (LNCaP)), and no EpCAM expressions (cervical cancer cells (HeLa) has been estimated using Western Blot method supported by immunochemistry and correlated with responses of immunomagnetic SERS-based analysis. The capture efficiency of developed assay was investigated in metastatic lung cancer patients. The assay demonstrates the capability to detect circulating tumor cells from blood samples over a broad linear range (from 1 to 100 cells/mL) reflecting clinically relevant amount of CTCs depending on the stage of metastasis, age, applied therapy.

Abstract

The circulating tumor cells (CTCs) isolation and characterization has a great potential for non-invasive biopsy. In the present research, the surface–enhanced Raman spectroscopy (SERS)-based assay utilizing magnetic nanoparticles and solid SERS-active support integrated in the external field assisted microfluidic device was designed for efficient isolation of CTCs from blood samples. Magnetic nanospheres (Fe₂O₃) were coated with SERS-active metal and then modified with p-mercaptobenzoic acid (p-MBA) which works simultaneously as a Raman reporter and linker to an antiepithelial-cell-adhesion-molecule (anti-EpCAM) antibodies. The newly developed laser-induced SERS-active silicon substrate with a very strong enhancement factor (up to 10⁸) and high stability and reproducibility provide the additional extra-enhancement in the sandwich plasmonic configuration of immune assay which finally leads to increase the efficiency of detection. The sensitive immune recognition of cancer cells is assisted by the introducing of the controllable external magnetic field into the microfluidic chip. Moreover, the integration of the SERS-active platform and p-MBA-labeled immuno-Ag@Fe₂O₃ nanostructures with microfluidic device offers less sample and analytes demand, precise operation, increase reproducibly of spectral responses, and enables miniaturization and portability of the presented approach. In this work, we have also investigated the effect of varying expression of the EpCAM established by the Western Blot method supported by immunochemistry on the efficiency of CTCs’ detection with the developed SERS method. We used four target cancer cell lines with relatively high (human metastatic prostate adenocarcinoma cells (LNCaP)), medium (human metastatic prostate adenocarcinoma cells (LNCaP)), weak (human metastatic prostate adenocarcinoma cells (LNCaP)), and no EpCAM expressions (cervical cancer cells (HeLa)) to estimate the limits of detection based on constructed calibration curves. Finally, blood samples from lung cancer patients were used to validate the efficiency of the developed method in clinical trials.

SERS based protocol using flow glass-hemostix for detection of neuron-specific enolase in blood plasma

An inexpensive and disposable lateral flow glass-hemostix (FGH) has been developed as an immunoassay, in which surface-enhanced Raman scattering (SERS) is utilized for sensing signal transduction.

Recent Progress on Liquid Biopsy Analysis using Surface-Enhanced Raman Spectroscopy

Traditional tissue biopsy is limited in understanding heterogeneity and dynamic evolution of tumors. Instead, analyzing circulating cancer markers in various body fluids, commonly referred to as "liquid biopsy", has recently attracted remarkable interest for their great potential to be applied in non-invasive early cancer screening, tumor progression monitoring and therapy response assessment. Among the various approaches developed for liquid biopsy analysis, surface-enhanced Raman spectroscopy (SERS) has emerged as one of the most powerful techniques based on its high sensitivity, specificity, tremendous spectral multiplexing capacity for simultaneous target detection, as well as its unique capability for obtaining intrinsic fingerprint spectra of biomolecules. In this review, we will first briefly explain the mechanism of SERS, and then introduce recently reported SERS-based techniques for detection of circulating cancer markers including circulating tumor cells, exosomes, circulating tumor DNAs, microRNAs and cancer-related proteins. Cancer diagnosis based on SERS analysis of bulk body fluids will also be included. In the end, we will summarize the "state of the art" technologies of SERS-based platforms and discuss the challenges of translating them into clinical settings.

Proximity hybridization triggered rolling-circle amplification for sensitive electrochemical homogeneous immunoassay

A new homogeneous electrochemical immunoassay strategy was developed for ultrasensitive detection of carcinoembryonic antigen (CEA) based on target-induced proximity hybridization coupled with rolling circle amplification (RCA). The immobilization-free detection of CEA was realized by the use of an uncharged peptide nucleic acid (PNA) probe labeled with ferrocene (Fc) as the electroactive indicator on a negatively charged indium tin oxide (ITO) electrode. In the presence of a target protein and two DNA-labeled antibodies, the proximate complex formed in homogeneous solution could unfold the molecular beacon, and a part of the unfolded molecular beacon as a primer hybridized with the RCA template to initiate the RCA process. Subsequently, the detection probe modified Fc (Fc-PNAs) hybridized with the long amplified DNA products. The consumption of freely diffusible Fc-PNAs (neutrally charged) resulted in a significant reduction of the Fc signal due to the fact that long amplified DNA/Fc-PNA products were electrostatically repelled from the ITO electrode surface. The reduction of the electrochemical signal (signal-off) could indirectly provide the CEA concentration. Under the optimal conditions, CEA detection was implemented in a wide range from 1 pg mL^-1 to 10 ng mL^-1, with a low detection limit of 0.49 pg mL^-1. The proposed strategy exhibited advantages of good selectivity, high sensitivity, acceptable accuracy, and favorable versatility of analytes. Moreover, the practical application value of the system was confirmed by the assay of CEA in human serums with satisfactory results.

Graphene oxide wrapped with gold nanorods as a tag in a SERS based immunoassay for the hepatitis B surface antigen

A composite consisting of graphene oxide and gold nanorods (GO-GNRs) was designed for the trace determination of hepatitis B surface antigen (HBsAg) using surface enhanced Raman spectroscopy (SERS). GO contains numerous carboxy and hydroxy groups on its surface and therefore can serve as the substrate for decoration with GNRs and for immobilizing antibody against HBsAg. The GNRs (carrying the SERS probe 2-mercaptopyridine) exhibit high SERS activity, and this improves the sensitivity of the biosensor. The antibody on the GO-GNRs binds HBsAg with high specificity, and it results in excellent selectivity. The SERS signal (measured at 1002 cm^-1) increases in the 1-1000 pg·mL^-1 HBsAg concentrations range, and the limit of detection is 0.05 pg·mL^-1 (at an S/N ratio of 3). The immunoassay achieves the sensitive and selective determination of HBsAg in serum and expands the potential application of GO-GNR based SERS tag in clinical research. Graphical abstract A novel graphene oxide-gold nanorod (GO-GNRs) based surface-enhanced Raman scattering (SERS) tag for immunoassay was designed. It allows for sensitive and selective determination of HBsAg in serum. The method is expected to expand the potential application in the environment, in medicine and in food analysis.

Plasmonic Heterodimers with Binding Site-Dependent Hot Spot for Surface-Enhanced Raman Scattering

A novel plasmonic heterodimer nanostructure with a controllable self-assembled hot spot is fabricated by the conjugation of individual Au@Ag core-shell nanocubes (Au@Ag NCs) and varisized gold nanospheres (GNSs) via the biotin-streptavidin interaction from the ensemble to the single-assembly level. Due to their featured configurations, three types of heterogeneous nanostructures referred to as Vertice, Vicinity, and Middle are proposed and a single hot spot forms between the nanocube and nanosphere, which exhibits distinct diversity in surface plasmon resonance effect. Herein, the calculated surface-enhanced Raman scattering enhancement factors of the three types of heterodimers show a narrow distribution and can be tuned in orders of magnitude by controlling the size of GNSs onto individual Au@Ag NCs. Particularly, the Vertice heterodimer with unique configuration can provide extraordinary enhancement of the electric field for the single hot spot region due to the collaborative interaction of lightning rod effect and interparticle plasmon coupling effect. This established relationship between the architecture and the corresponding optical properties of the heterodimers provides the basis for creating controllable platforms which can be exploited in the applications of plasmonic devices, electronics, and biodetection.

A gold nanoflower-based traceable drug delivery system for intracellular SERS imaging-guided targeted chemo-phototherapy

Accurate and effective drug delivery in tumor cells significantly improves the curative effect with high drug delivery efficiency, low toxicity and side effects and has become an urgent demand for anticancer therapy. In this paper, a novel traceable and targeted drug delivery nanosystem (i.e. AuNF-nanocarriers) with high drug encapsulation and pH-controlled release was prepared based on gold nanoflowers (AuNFs) for efficient intracellular SERS imaging-guided chemo-phototherapy. SERS-active flower-like gold nanoparticles with large surface area were synthesized first and then modified with Raman and RGD molecules in sequence to prepare bright, traceable and targeted SERS tags of A549 human lung cancer cells. Furthermore, thiolated-PAA (PAA-SH) was synthesized and utilized for the first time to modify the SERS tags with a layer of negative charges for efficient pH-dependent loading and release of the anticancer drug doxorubicin. Based on the A549 human lung cancer cell model, the availability of the proposed AuNF-nanocarriers for efficient intracellular SERS imaging-guided chemo-phototherapy was studied and the results indicate that the AuNF-based drug delivery system exhibited attractive characteristics such as good stability, efficiency and pH-controlled drug loading and release, traceable and targeted delivery, as well as SERS imaging and chemo-phototherapy functions, and shows great potential for powerful SERS-imaging and as a theranostic candidate for precision nanomedicine that could achieve sensitive and accurate tumor detection and therapy.

Cavity-Type DNA Origami-Based Plasmonic Nanostructures for Raman Enhancement

DNA origami has been established as addressable templates for site-specific anchoring of gold nanoparticles (AuNPs). Given that AuNPs are assembled by charged DNA oligonucleotides, it is important to reduce the charge repulsion between AuNPs-DNA and the template to realize high yields. Herein, we developed a cavity-type DNA origami as templates to organize 30 nm AuNPs, which formed dimer and tetramer plasmonic nanostructures. Transmission electron microscopy images showed that high yields of dimer and tetramer plasmonic nanostructures were obtained by using the cavity-type DNA origami as the template. More importantly, we observed significant Raman signal enhancement from molecules covalently attached to the plasmonic nanostructures, which provides a new way to high-sensitivity Raman sensing.

SERS-based immunoassay on 2D-arrays of Au@Ag core–shell nanoparticles: influence of the sizes of the SERS probe and sandwich immunocomplex on the sensitivity

The sensitivity of immunoassay performed on SERS-active substrates can be improved by optimizing the size of SERS probes and also by decreasing the size of sandwich immunocomplex.

Quantitative and multiplex dot-immunoassay using gap-enhanced Raman tags

A highly specific, quantitative, and multiplex dot immunoassay has been developed. The immunoassay utilizes functionalized plasmonic gap-enhanced Raman tags (GERTs) as labels and nitrocellulose membrane as a substrate.

A promising magnetic SERS immunosensor for sensitive detection of avian influenza virus

Avian influenza viruses infect a great number of global populations every year and can lead to severe epidemics with high morbidity and mortality. Facile, rapid and sensitive detection of viruses is very crucial to control the viral spread at its early stage. In this work, we developed a novel magnetic immunosensor based on surface enhanced Raman scattering (SERS) spectroscopy to detect intact but inactivated influenza virus H3N2 (A/Shanghai/4084T/2012) by constructing a sandwich complex consisting of SERS tags, target influenza viruses and highly SERS-active magnetic supporting substrates. The procedure of sample pretreatment could be significantly simplified since the magnetic supporting substrates allowed the enrichment and separation of viruses from a complex matrix. With a portable Raman spectrometer, the immunosensor could detect H3N2 down to 10²TCID₅₀/mL (TCID₅₀ refers to tissue culture infection dose at 50% end point), with a good linear relationship from 10² to 5×10³ TCID₅₀/mL. Considering its time efficiency, portability and sensitivity, the proposed SERS-based magnetic immunoassay is very promising for a point-of-care (POC) test in clinical and diagnostic praxis.

Embedding Raman Tags between Au Nanostar@Nanoshell for Multiplex Immunosensing

Novel Raman tags with various reporter molecules embedded in between gold nanostar (AuNS) and gold nanoshell are developed, showing significantly enhanced surface-enhanced Raman scattering intensity compared to gold nanoparticle-based composites. Immunoassay using these AuNS@tag@shell structures is highly specific with sensitivity down to 0.1 pg mL^-1 , and is capable of multiplex detection, making them highly promising for biosensing applications.

Nanostructure-based surface-enhanced Raman scattering biosensors for nucleic acids and proteins

Detection of nucleic acid and protein targets related to human health and safety has attracted widespread attention. Surface-enhanced Raman scattering (SERS) is a powerful tool for biomarker detection because of its ultrahigh detection sensitivity and unique fingerprinting spectra. In this review, we first introduce the development of nanostructure-based SERS-active substrates and SERS nanotags, which greatly influence the performance of SERS biosensors. We then focus on recent advances in SERS biosensors for DNA, microRNA and protein determination, including label-free, labeled and multiplex analyses as well as in vivo imaging. Finally, the prospects and challenges of such nanostructure-based SERS biosensors are discussed.

Combination assay of lung cancer associated serum markers using surface-enhanced Raman spectroscopy

A highly sensitive and specific SERS-based combination assay of lung cancer associated serum markers is reported, and the LODs of CEA and NSE in human serum specimens are 1.48 pg mL⁻¹ and 2.04 pg mL⁻¹, respectively.

Highly uniform indicator-mediated SERS sensor platform for the detection of Zn2+

An indicator-mediated surface-enhanced Raman scattering (SERS) sensor platform with highly uniform SERS sensitivity was fabricated by modifying 4-mercaptopyridine (4-MPY) molecules as an indicator onto the surface of Ag nanoparticles that were anchored onto a silicon wafer.

Gold nanoflowers with tunable sheet-like petals: facile synthesis, SERS performances and cell imaging

Gold nanoflowers with tunable sheet-like petals were controllably synthesized, and their SERS performances as well as their application in cell imaging were studied.

A SERS protocol as a potential tool to access 6-mercaptopurine release accelerated by glutathione-S-transferase

The developed method for monitoring GST, an important drug metabolic enzyme, could greatly facilitate researches on relative biological fields.