SERS Tags: Novel Optical Nanoprobes for Bioanalysis

Evaluating Receptor-Specific Fresh Specimen Staining for Tumor Margin Detection in Clinical Breast Specimens

PURPOSE

Reliable and rapid identification of tumor in the margins of breast specimens during breast-conserving surgery to reduce repeat surgery rates is an active area of investigation. Dual-stain difference imaging (DDSI) is one of many approaches under evaluation for this application. This technique aims to topically apply fluorescent stain pairs (one targeted to a receptor-of-interest and the other a spectrally distinct isotype), image both stains, and compute a normalized difference image between the two channels. Prior evaluation and optimization in a variety of preclinical models produced encouraging diagnostic performance. Herein, we report on a pilot clinical study which evaluated HER2-targeted DDSI on 11 human breast specimens.

PROCEDURES

Gross sections from 11 freshly excised mastectomy specimens were processed using a HER2-receptor-targeted DDSI protocol shortly after resection. After staining with the dual-probe protocol, specimens were imaged on a fluorescence scanner, followed by tissue fixation for hematoxylin and eosin and anti-HER2 immunohistochemical staining. Receiver operator characteristic curves and area under the curve (AUC) analysis were used to assess diagnostic performance of the resulting images. Performance values were also compared to expression level determined from IHC staining.

RESULTS

Eight of the 11 specimens presented with distinguishable invasive ductal carcinoma and/or were not affected by an imaging artifact. In these specimens, the DDSI technique provided an AUC = 0.90 ± 0.07 for tumor-to-adipose tissue and 0.81 ± 0.15 for tumor-to-glandular tissue, which was significantly higher than AUC values recovered from images of the targeted probe alone. DDSI values and diagnostic performance did not correlate with HER2 expression level, and tumors with low HER2 expression often produced high AUC, suggesting that even the low expression levels were enough to help distinguish tumor.

CONCLUSIONS

The results from this preliminary study of rapid receptor-specific staining in human specimens were consistent with prior preclinical results and demonstrated promising diagnostic potential.

A Ratiometric SERS Probe for Imaging the Macrophage Phenotypes in Live Mice with Epilepsy and Brain Tumor

Macrophage performs multiple functions such as pathogen phagocytosis, antigen presentation, and tissue remodeling by polarizing toward a spectrum of phenotypes. Dynamic imaging of macrophage phenotypes is critical for evaluating disease progression and the therapeutic response of drug candidates. However, current technologies cannot identify macrophage phenotypes in vivo. Herein, a surface-enhanced Raman scattering nanoprobe, AH1, which enables the accurate determination of physiological pH with high sensitivity and tissue penetration depth through ratiometric Raman signals is developed. Due to the phenotype-dependent metabolic reprogramming, AH1 can effectively identify macrophage subpopulations by measuring the acidity levels in phagosomes. After intravenous administration, AH1 not only visualizes the spatial distribution of macrophage phenotypes in brain tumors and epileptic regions of mouse models, but also reveals the repolarization of macrophages in brain lesions after drug intervention. This work provides a new tool for dynamically monitoring the disease-associated immune microenvironment and evaluating the efficacy of immune-therapeutics in vivo.

Electric Field Promoted Click Surface-Enhanced Raman Spectroscopy for Rapid and Specific Detection of DNA 2-Deoxyribose 5'-Aldehyde Oxidation Products in Plasma

Rapid identification of DNA oxidative damage sites is of great significance for disease diagnosis. In this work, electric field-regulated click reaction surface-enhanced Raman spectroscopy (e-Click-SERS) was developed aiming at the rapid and specific analysis of furfural, the biomarker of oxidative damage to the 5-carbon site of DNA deoxyribose. In e-Click-SERS, cysteamine-modified porous Ag filaments (cys@p-Ag) were prepared and used as electrodes, amine-aldehyde click reaction sites, and SERS substrates. Cysteamine was controlled as an "end-on" conformation by setting the voltage of cys@p-Ag at -0.1 V, which ensures its activity in participating in the amine-aldehyde click reaction during the detection of furfural. Benefiting from this, the proposed e-Click-SERS method was found to be sensitive, rapid-responding, and interference-resistant in analyzing furfural from plasma. The method detection limits of furfural were 5 ng mL-1 in plasma, and the whole "extraction and detection" procedure was completed within 30 min with satisfactory recovery. Interference from 13 kinds of common plasma metabolites was investigated and found to not interfere with the analysis, according to the exclusive adaptation of the amine-aldehyde click reaction. Notably, the e-Click-SERS technique allows in situ analysis of biological samples, which offers great potential to be a point-of-care testing tool for detecting DNA oxidative damage.

Four-Color SERS Monitoring of Size-dependent Nanoparticle Delivery in the Same Tumor

The physicochemical properties of nanoparticles (NPs) significantly influence their deposition at the disease site, ultimately impacting the overall therapeutic efficacy; however, precisely assessing the effects of various factors on NP accumulation within a single cell/tumor tissue is challenging due to the lack of appropriate labeling techniques. Surface-enhanced Raman spectroscopy (SERS) tag is a powerful encoding method that has recently been intensively employed for immunodetection of biomarkers. Herein, we introduce a multiplexed SERS tracking approach for systematic investigation of size-dependent accumulation and distribution of NPs within the same tumor. Four-sized (34, 60, 108, and 147 nm) NPs encoded with different SERS "colors" were fabricated, mixed, and incubated with monolayer tumor cells, multicellular tumor spheroids, or injected into mouse models bearing xenograft solid tumors in a single dose. Multicolor SERS detection of the specimens revealed that NP accumulation in tumor cells, tumor spheroids, and solid tumors was in the order of 34 nm > 60 nm > 108 nm > 147 nm, 60 nm > 34 nm > 108 nm > 147 nm, and 34 nm > 147 nm > 108 nm > 60 nm, respectively. Inductively coupled plasma mass spectroscopy determination performed in parallel samples were in alignment with the four-color SERS probing results, demonstrating the effectiveness of this multiplexed evaluation assay. Furthermore, in combination with fluorescence labeling of specific biomolecules, this method can be applied for the colocalization of different NPs in various pathological structures and provide additional information for analysis of the possible mechanisms.

Gap-enhanced gold nanodumbbells with single-particle surface-enhanced Raman scattering sensitivity

Gap-enhanced Raman tags (GERTs) have been widely used for surface-enhanced Raman scattering (SERS) imaging due to their excellent SERS performances. Here, we reported a synthetic strategy for novel gap-enhanced dumbbell-like nanoparticles with anisotropic shell coatings. Controlled shell growth at the tips of gold nanorods was achieved by using cetyltrimethylammonium bromide (CTAB) as a capping agent. A mechanism related to the shape-directing effects of CTAB was proposed to explain the findings. Optimized gap-enhanced gold dumbbells exhibited highly enhanced SERS responses compared to rod cores, with an enhancement ratio of 101.5. We further demonstrated that gap-enhanced AuNDs exhibited single-particle SERS sensitivity with an acquisition time as fast as 0.1 s per spectrum, showing great potential for high-speed SERS imaging.

Boosting the Brightness of Raman Tags Using Cyanostar Macrocycles

Raman probes have received growing attention for their potential use in super-multiplex biological imaging and flow cytometry applications that cannot be achieved using fluorescent probes. However, obtaining strong Raman scattering signals from small Raman probes has posed a challenge that holds back their practical implementation. Here, we present new types of Raman-active nanoparticles (Rdots) that incorporate ionophore macrocycles, known as cyanostars, to act as ion-driven and structure-directing spacers to address this problem. These macrocycle-enhanced Rdots (MERdots) exhibit sharper and higher electronic absorption peaks than Rdots. When combined with resonant broadband time-domain Raman spectroscopy, these MERdots show a ∼3-fold increase in Raman intensity compared to conventional Rdots under the same particle concentration. Additionally, the detection limit on the concentration of MERdots is improved by a factor of 2.5 compared to that of Rdots and a factor of 430 compared to that of Raman dye molecules in solution. The compact size of MERdots (26 nm in diameter) and their increased Raman signal intensity, along with the broadband capabilities of time-domain resonant Raman spectroscopy, make them promising candidates for a wide range of biological applications.

Fabrication of Ag-CaCO3 Nanocomposites for SERS Detection of Forchlorfenuron

In this study, Ag-CaCO3 nanocomposites were synthesized using silver nitrate as the precursor solution based on calcium carbonate nanoparticles (CaCO3 NPs). The synthesis involved the reaction of calcium lignosulphonate and sodium bicarbonate. The properties of Ag-CaCO3 nanocomposites were studied by various technologies, including an ultraviolet-visible spectrophotometer, a transmission electron microscope, and a Raman spectrometer. The results showed that Ag-CaCO3 nanocomposites exhibited a maximum UV absorption peak at 430 nm, the surface-enhanced Raman spectroscopy (SERS) activity of Ag-CaCO3 nanocomposites was evaluated using mercaptobenzoic acid (MBA) as the marker molecule, resulting in an enhancement factor of 6.5 × 104. Additionally, Ag-CaCO3 nanocomposites were utilized for the detection of forchlorfenuron. The results demonstrated a linear relationship in the concentration range of 0.01 mg/mL to 2 mg/mL, described by the equation y = 290.02x + 1598.8. The correlation coefficient was calculated to be 0.9772, and the limit of detection (LOD) was determined to be 0.001 mg/mL. These findings highlight the relatively high SERS activity of Ag-CaCO3 nanocomposites, making them suitable for analyzing pesticide residues and detecting toxic and harmful molecules, thereby contributing to environmental protection.

An interference-free SERS-based aptasensor for chlorpyrifos detection

In this study, we propose an interference-free SERS-based aptasensor for trace detection of chlorpyrifos (CPF) in real samples. In the aptasensor, gold nanoparticles coated with Prussian blue (Au@PB NPs) were employed as SERS tags to provide a sole and intense Raman emission at 2160 cm^-1, which could avoid overlapping with the Raman spectrum of the real samples in 600-1800 cm^-1 to improve the anti-matrix effect ability of the aptasensor. Under the optimum conditions, this aptasensor displayed a linear response for CPF detection in the range of 0.1-316 ng mL^-1 with a low detection limit of 0.066 ng mL^-1. In addition, the prepared aptasensor shows excellent application to determine CPF in cucumber, pear and river water samples. The recovery rates were highly correlated with high-performance liquid chromatography‒mass spectrometry (HPLC‒MS/MS). This aptasensor shows interference-free, specific and sensitive detection for CPF and offers an effective strategy for other pesticide residue detection.

Aggregation enhanced fluorescence and Raman signals for highly sensitive cancer detection

The implementation of early cancer detection benefits the treatment outcomes with remarkably improved survival rate through the detection of rare circulating biomarkers in body fluids. Spectroscopic technologies play a crucial role in sensitive biomarker measurements by outputting extremely strong signals. In particular, the aggregation enhanced fluorescence and Raman technologies feature the detection of targets down to single-molecule level, thereby demonstrating the great promise of early cancer detection. In this review, we focus on the aggregation-induced emission (AIE) and aggregation-related surface-enhanced Raman scattering (SERS) spectroscopic strategies for detecting cancer biomarkers. We discuss the AIE and SERS based biomarker detection using target-driven aggregation as well as the aggregated nanoprobes. Furthermore, we deliberate on the progress of developing AIE and SERS integrated platforms. Ultimately, we put forth the potential challenges and perspectives on the way to use these two spectroscopic technologies in clinical settings. It is expected this review can inspire the design of AIE and SERS integrated platform for highly sensitive and accurate cancer detection.

Flexible, stretchable, and single-molecule-sensitive SERS-active sensor for wearable biosensing applications

The development of wearable sensors for remote patient monitoring and personalized medicine has led to a revolution in biomedical technology. Plasmonic metasurfaces that enhance Raman scattering signals have recently gained attention as wearable sensors. However, finding a flexible, sensitive, and easy-to-fabricate metasurface has been a challenge for decades. In this paper, a novel wearable device, the flexible, stretchable, and single-molecule-sensetive SERS-active sensor, is proposed. This device offers an unprecedented SERS enhancement factor in the order of 1011, along with other long-desired characteristics for SERS applications such as a high scattering to absorption ratio (∼2.5) and a large hotspot volume (40 nm × 40 nm × 5 nm). To achieve flexibility, we use polydimethylsiloxane (PDMS) as the substrate, which is stable, transparent, and biologically compatible. Our numerical calculations show that the proposed sensor offers reliable SERS performance even under bending (up to 100° angles) or stretching (up to 50% stretch). The easy-to-fabricate and flexible nature of our sensor offers a promising avenue for developing highly sensitive wearable sensors for a range of applications, particularly in the field of personalized medicine and remote patient monitoring.

Emerging integrated SERS-microfluidic devices for analysis of cancer-derived small extracellular vesicles

Cancer-derived small extracellular vesicles (sEVs) are specific subgroups of lipid bilayer vesicles secreted from cancer cells to the extracellular environment. They carry distinct biomolecules (e.g., proteins, lipids and nucleic acids) from their parent cancer cells. Therefore, the analysis of cancer-derived sEVs can provide valuable information for cancer diagnosis. However, the use of cancer-derived sEVs in clinics is still limited due to their small size, low amounts in circulating fluids, and heterogeneous molecular features, making their isolation and analysis challenging. Recently, microfluidic technology has gained great attention for its ability to isolate sEVs in minimal volume. In addition, microfluidics allows the isolation and detection of sEVs to be integrated into a single device, offering new opportunities for clinical application. Among various detection techniques, surface-enhanced Raman scattering (SERS) has emerged as a promising candidate for integrating with microfluidic devices due to its ultra-sensitivity, stability, rapid readout, and multiplexing capability. In this tutorial review, we start with the design of microfluidics devices for isolation of sEVs and introduce the key factors to be considered for the design, and then discuss the integration of SERS and microfluidic devices by providing descriptive examples of the currently developed platforms. Lastly, we discuss the current limitations and provide our insights for utilising integrated SERS-microfluidics to isolate and analyse cancer-derived sEVs in clinical settings.

ReS2 Nanoflowers-Assisted Confined Growth of Gold Nanoparticles for Ultrasensitive and Reliable SERS Sensing

ReS₂, as a new member of transition metal dichalcogenides (TMDCs), has emerged as a promising substrate for semiconductor surface-enhanced Raman spectroscopy (SERS) due to its unique optoelectronic properties. Nevertheless, the sensitivity of the ReS₂ SERS substrate poses a significant challenge to its widespread application in trace detection. In this work, we present a reliable approach for constructing a novel ReS₂/AuNPs SERS composite substrate, enabling ultrasensitive detection of trace amounts of organic pesticides. We demonstrate that the porous structures of ReS₂ nanoflowers can effectively confine the growth of AuNPs. By precisely controlling the size and distribution of AuNPs, numerous efficient and densely packed "hot spots" were created on the surface of ReS₂ nanoflowers. As a result of the synergistic enhancement of the chemical and electromagnetic mechanisms, the ReS₂/AuNPs SERS substrate demonstrates high sensitivity, good reproducibility, and superior stability in detecting typical organic dyes such as rhodamine 6G and crystalline violet. The ReS₂/AuNPs SERS substrate shows an ultralow detection limit of 10^-10 M and a linear detection of organic pesticide molecules within 10^-6-10^-10 M, which is significantly lower than the EU Environmental Protection Agency regulation standards. The strategy of constructing ReS₂/AuNPs composites would contribute to the development of highly sensitive and reliable SERS sensing platforms for food safety monitoring.

An anisotropic nanobox based core-shell-satellite nanoassembly of multiple SERS enhancement with heterogeneous interface for stroke marker determination

Herein, A novel gold-silver alloy nanobox (AuAgNB)@SiO₂-gold nanosphere (AuNP) nanoassembly based on core-shell-satellite structure is fabricated and applied to the surface-enhanced Raman scattering (SERS) detection of S100 calcium-binding protein B protein (S100B). It contains an anisotropic hollow porous AuAgNB core with rough surface, an ultrathin silica interlayer labeled with reporter molecules, and AuNP satellites. The nanoassemblies were systematically optimized by tuning the reporter molecules concentration, silica layer thickness, AuAgNB size, and the size and number of AuNP satellite size. Remarkably, AuNP satellites are adjacent to AuAgNB@SiO₂, developing AuAg-SiO₂-Au heterogeneous interface. With the strong plasmon coupling between AuAgNB and AuNP satellites, chemical enhancement from heterogeneous interface, and the tip "hot spots" of AuAgNB, the SERS activity of the nanoassemblies was multiply enhanced. Additionally, the stability of nanostructure and Raman signal was significantly improved by the silica interlayer and AuNP satellites. Eventually, the nanoassemblies were applied for S100B detection. It demonstrated satisfactory sensitivity and reproducibility with a wide detection range of 10 fg/mL-10 ng/mL and a limit of detection (LOD) of 1.7 fg/mL. This work based on the AuAgNB@SiO₂-AuNP nanoassemblies with multiple SERS enhancements and favorable stability demonstrates the promising application in stroke diagnosis.

Microcavity- and Microlaser-Based Optical Barcoding: A Review of Encoding Techniques and Applications

Optical microbarcodes have recently received a great deal of interest because of their suitability for a wide range of applications, such as multiplexed assays, cell tagging and tracking, anticounterfeiting, and product labeling. Spectral barcodes are especially promising because they are robust and have a simple readout. In addition, microcavity- and microlaser-based barcodes have very narrow spectra and therefore have the potential to generate millions of unique barcodes. This review begins with a discussion of the different types of barcodes and then focuses specifically on microcavity-based barcodes. While almost any kind of optical microcavity can be used for barcoding, currently whispering-gallery microcavities (in the form of spheres and disks), nanowire lasers, Fabry-Pérot lasers, random lasers, and distributed feedback lasers are the most frequently employed for this purpose. In microcavity-based barcodes, the information is encoded in various ways in the properties of the emitted light, most frequently in the spectrum. The barcode is dependent on the properties of the microcavity, such as the size, shape, and the gain materials. Various applications of these barcodes, including cell tracking, anticounterfeiting, and product labeling are described. Finally, the future prospects for microcavity- and microlaser-based barcodes are discussed.

Surface enhanced Raman scattering active substrate based on hydrogel microspheres for pretreatment-free detection of glucose in biological samples

Determining glucose in biological samples is tedious and time-consuming due to sample pretreatment. The sample is usually pretreated to remove lipids, proteins, hemocytes and other sugars that interfere with glucose detection. A surface-enhanced Raman scattering (SERS) active substrate based on hydrogel microspheres has been developed to detect glucose in biological samples. Due to the specific catalytic action of glucose oxidase (GOX), the high selectivity of detection is guaranteed. The hydrogel substrate prepared by microfluidic droplets technology protects the silver nanoparticles from the surrounding environment and improves the stability and reproducibility of the assay. In addition, the hydrogel microspheres have size-adjustable pores that selectively allow small molecules to pass through. The pores block the entry of large molecules, such as impurities, enabling glucose detection through glucose oxidase etching without sample pretreatment. This hydrogel microsphere-SERS platform is highly sensitive and enables reproducible detection of different glucose concentrations in biological samples. The use of SERS to detect glucose provides clinicians with new diagnostic methods for diabetes and a new application opportunity for SERS-based molecular detection techniques.

Smart Design of Nanostructures for Boosting Tumor Immunogenicity in Cancer Immunotherapy

Although tumor immunotherapy has emerged as a promising therapeutic method for oncology, it encounters several limitations, especially concerning low response rates and potential off-targets that elicit side effects. Furthermore, tumor immunogenicity is the critical factor that predicts the success rate of immunotherapy, which can be boosted by the application of nanotechnology. Herein, we introduce the current approach of cancer immunotherapy and its challenges and the general methods to enhance tumor immunogenicity. Importantly, this review highlights the integration of anticancer chemo/immuno-based drugs with multifunctional nanomedicines that possess imaging modality to determine tumor location and can respond to stimuli, such as light, pH, magnetic field, or metabolic changes, to trigger chemotherapy, phototherapy, radiotherapy, or catalytic therapy to upregulate tumor immunogenicity. This promotion rouses immunological memory, such as enhanced immunogenic cell death, promoted maturation of dendritic cells, and activation of tumor-specific T cells against cancer. Finally, we express the related challenges and personal perspectives of bioengineered nanomaterials for future cancer immunotherapy.

Surface-Roughened SERS-Active Single Silver Nanowire for Simultaneous Detection of Intracellular and Extracellular pHs

The simultaneous and accurate detection of intracellular pH (pH_i) and extracellular pH (pH_e) is essential for studying the complex physiological activities of cancer cells and exploring pH-related therapeutic mechanisms. Here, we developed a super-long silver nanowire-based surface-enhanced Raman scattering (SERS) detection strategy for simultaneous sensing of pH_i and pH_e. A surface-roughened silver nanowire (AgNW) with a high aspect ratio is prepared at a nanoelectrode tip using a Cu-mediated oxidation process, which is then modified by pH-sensitive 4-mercaptobenzoic acid (4-MBA) to form 4-MBA@AgNW as a pH sensing probe. With the assistance of a 4D microcontroller, 4-MBA@AgNW is efficient in simultaneously detecting pH_i and pH_e in both 2D and 3D culture cancer cells by SERS, with minimal invasiveness, high sensitivity, and spatial resolution. Further investigation proves that the surface-roughened single AgNW can also be used in monitoring the dynamic variation of pH_i and pH_e of cancer cells upon stimulation with anticancer drugs or under a hypoxic environment.

A clinically feasible diagnostic spectro-histology built on SERS-nanotags for multiplex detection and grading of breast cancer biomarkers

Simultaneous detection of multiple biomarkers is always an obstacle in immunohistochemical (IHC) analysis. Herein, a straightforward spectroscopy-driven histopathologic approach has emerged as a paradigm of Raman-label (RL) nanoparticle probes for multiplex recognition of pertinent biomarkers in heterogeneous breast cancer. The nanoprobes are constructed by sequential incorporation of signature RL and target specific antibodies on gold nanoparticles, which are coined as Raman-Label surface enhanced Raman scattering (RL-SERS)-nanotags to evaluate simultaneous recognition of clinically relevant breast cancer biomarkers i.e., estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor2 (HER2). As a foot-step assessment, breast cancer cell lines having varied expression levels of the triple biomarkers are investigated. Subsequently, the optimized detection strategy using RL-SERS-nanotags is subjected to clinically confirmed, retrospective formalin-fixed paraffin embedded (FFPE) breast cancer tissue samples to fish out the quick response of singleplex, duplex as well as triplex biomarkers in a single tissue specimen by adopting a ratiometric signature RL-SERS analysis which enabled to minimize the false negative and positive results. Significantly, sensitivity and specificity of 95% and 92% for singleplex, 88% and 85% for duplex, and 75% and 67% for triplex biomarker has been achieved by assessing specific Raman fingerprints of the respective SERS-tags. Furthermore, a semi-quantitative evaluation of HER2 grading between 4+/2+/1+ tissue samples was also achieved by the Raman intensity profiling of the SERS-tag, which is fully in agreement with the expensive fluorescent in situ hybridization analysis. Additionally, the practical diagnostic applicability of RL-SERS-tags has been achieved by large area SERS imaging of areas covering 0.5-5 mm2 within 45 min. These findings unveil an accurate, inexpensive and multiplex diagnostic modality envisaging large-scale multi-centric clinical validation.

Exploring the generality of ligands for Silica-Encapsulated nanoclusters as SERS labels

The surface enhanced Raman scattering (SERS) reporters are rather limited, and the Raman peaks still overlap in varying degrees, making SERS multiplex coding a critical bottleneck in the exploration of SERS nanotechnology. Herein, we design a general strategy to expand the SERS probe scope to 26 probes of six types, which can be further expanded within a limited range, with stable performance and structure. By constructing (Au-aggregate)@Ag@silica and (Au-aggregate)@silica nanocomposites, we develop optimal enhancement strategies for each Raman molecules. Mixed signal-ligand SERS probes improve the complexity of Raman spectra and expand the coding capacity. By integrating the strategies, SERS inks are produced and applied in anti-counterfeiting. With these improvements, this work breaks the constrains of probe selection, bringing SERS one step closer to the sensor or anti-counterfeiting application.

Duplex Phenotype Detection and Targeting of Breast Cancer Cells Using Nanotube Nanoprobes and Raman Imaging

We designed, synthesized, and characterized a Raman nanoprobe made of dye-sensitized single-walled carbon nanotubes (SWCNTs) that can selectively target biomarkers of breast cancer cells. The nanoprobe is composed of Raman-active dyes encapsulated inside a SWCNT, whose surface is covalently grafted with poly(ethylene glycol) (PEG) at a density of ∼0.7% per carbon. Using α-sexithiophene- and β-carotene-derived nanoprobes covalently bound to an antibody, either anti-E-cadherin (E-cad) or anti-keratin-19 (KRT19), we prepared two distinct nanoprobes that specifically recognize biomarkers on breast cancer cells. Immunogold experiments and transmission electron microscopy (TEM) images are first used to guide the synthesis protocol for higher PEG-antibody attachment and biomolecule loading capacity. The duplex of nanoprobes was then applied to target E-cad and KRT19 biomarkers in T47D and MDA-MB-231 breast cancer cell lines. Hyperspectral imaging of specific Raman bands allows for simultaneous detection of this nanoprobe duplex on target cells without the need for additional filters or subsequent incubation steps. Our results confirm the high reproducibility of the nanoprobe design for duplex detection and highlight the potential of Raman imaging for advanced biomedical applications in oncology.

Resonant Raman-Active Polymer Dot Barcodes for Multiplex Cell Mapping

Resonance Raman spectroscopy is an efficient tool for multiplex imaging because of the narrow bandwidth of the electronically enhanced vibrational signals. However, Raman signals are often overwhelmed by concurrent fluorescence. In this study, we synthesized a series of truxene-based conjugated Raman probes to show structure-specific Raman fingerprint patterns with a common 532 nm light source. The subsequent polymer dot (Pdot) formation of the Raman probes efficiently suppressed fluorescence via aggregation-induced quenching and improved the dispersion stability of particles without leakage of Raman probes or particle agglomeration for more than 1 year. Additionally, the Raman signal amplified by electronic resonance and increased probe concentration exhibited over 10³ times higher relative Raman intensities versus 5-ethynyl-2'-deoxyuridine, enabling successful Raman imaging. Finally, multiplex Raman mapping was demonstrated with a single 532 nm laser using six Raman-active and biocompatible Pdots as barcodes for live cells. Resonant Raman-active Pdots may suggest a simple, robust, and efficient way for multiplex Raman imaging using a standard Raman spectrometer, suggesting the broad applicability of our strategy.

Metallic nanoparticles as effective sensors of bio-molecules

This work describes biologically important nanostructures of metals (AgNPs, AuNPs, and PtNPs) and metal oxides (Cu₂ONPs, CuONSs, γ-Fe₂O₃NPs, ZnONPs, ZnONPs-GS, anatase-TiO₂NPs, and rutile-TiO₂NPs) synthesized by different methods (wet-chemical, electrochemical, and green-chemistry methods). The nanostructures were characterized by molecular spectroscopic methods, including scanning/transmission electron microscopy (SEM/TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), photoelectron spectroscopy (XPS), ultraviolet-visible spectroscopy (UV-vis), dynamic light scattering (DLS), Raman scattering spectroscopy (RS), and infrared light spectroscopy (IR). Then, a peptide (bombesin, BN) was adsorbed onto the surface of these nanostructures from an aqueous solution with pH of 7 that did not contain surfactants. Adsorption was monitored using surface-enhanced Raman scattering spectroscopy (SERS) to determine the influence of the nature of the metal surface and surface evolution on peptide geometry. Information from the SERS studies was compared with information on the biological activity of the peptide. The SERS enhancement factor was determined for each of the metallic surfaces.

SERS-based immunomagnetic bead for rapid detection of H5N1 influenza virus

The surface-enhanced Raman scattering (SERS) has recently drawn attention in the detection of respiratory viruses, but there have been few reports of the direct detection of viruses. In this study, a sandwich immunomagnetic bead SERS was established for the rapid diagnosis of the H5N1 influenza virus. The detection limit was estimated to be 5.0 × 10-6 TCID50/ml. The method showed excellent specificity with no cross-reaction with H1N1, H5N6 or H9N2. The H5N1 influenza virus detection accuracy of the SERS method was 100% in chicken embryos. The results hold great promise for the utilization of SERS as an innovative approach in the diagnosis of influenza virus.

Functionalized MoS2: circular economy SERS substrate for label-free detection of bilirubin in clinical diagnosis

A one-pot hydrothermal synthesis of Fe-doped MoS₂ nanoflowers (Fe-MoS₂ NFs) has been developed as a surface-enhanced Raman spectroscopy (SERS) substrate. The Fe-MoS₂ NFs display high reproducibility, stability, and recyclability, which is beneficial for the development of the sustainable ecological environment. The SERS substrate provides a high enhancement factor of 10⁵, which can be ascribed to the inducing defects by doping Fe that can improve the charge transfer between probe molecules and MoS₂. The Fe-MoS₂ NFs have been used to detect bilirubin in serum. The Fe-MoS₂ NF SERS substrate exhibits a linear detection range from 10^-3 to 10^-9 M with a low limit of detection (LOD) of 10^-8 M. The substrate displays an excellent selectivity to bilirubin in the presence of other potentially interfering molecules (dextrose and phosphate). These results provide a novel concept to synthesize ultra-sensitive SERS substrates and open up a wide range of possibilities for new applications of MoS₂ in clinical diagnosis.

Open-sourced Raman spectroscopy data processing package implementing a baseline removal algorithm validated from multiple datasets acquired in human tissue and biofluids

SIGNIFICANCE

Standardized data processing approaches are required in the field of bio-Raman spectroscopy to ensure information associated with spectral data acquired by different research groups, and with different systems, can be compared on an equal footing.

AIM

An open-sourced data processing software package was developed, implementing algorithms associated with all steps required to isolate the inelastic scattering component from signals acquired using Raman spectroscopy devices. The package includes a novel morphological baseline removal technique (BubbleFill) that provides increased adaptability to complex baseline shapes compared to current gold standard techniques. Also incorporated in the package is a versatile tool simulating spectroscopic data with varying levels of Raman signal-to-background ratios, baselines with different morphologies, and varying levels of stochastic noise.

RESULTS

Application of the BubbleFill technique to simulated data demonstrated superior baseline removal performance compared to standard algorithms, including iModPoly and MorphBR. The data processing workflow of the open-sourced package was validated in four independent in-human datasets, demonstrating it leads to inter-systems data compatibility.

CONCLUSIONS

A new open-sourced spectroscopic data pre-processing package was validated on simulated and real-world in-human data and is now available to researchers and clinicians for the development of new clinical applications using Raman spectroscopy.

A Multilayered Mesoporous Gold Nanoarchitecture for Ultraeffective Near-Infrared Light-Controlled Chemo/Photothermal Therapy for Cancer Guided by SERS Imaging

Surface-enhanced Raman scattering (SERS) imaging has emerged as a promising tool for guided cancer diagnosis and synergistic therapies, such as combined chemotherapy and photothermal therapy (chemo-PTT). Yet, existing therapeutic agents often suffer from low SERS sensitivity, insufficient photothermal conversion, or/and limited drug loading capacity. Herein, a multifunctional theragnostic nanoplatform consisting of mesoporous silica-coated gold nanostar with a cyclic Arg-Gly-Asp (RGD)-coated gold nanocluster shell (named RGD-pAS@AuNC) is reported that exhibits multiple "hot spots" for pronouncedly enhanced SERS signals and improved near-infrared (NIR)-induced photothermal conversion efficiency (85.5%), with a large capacity for high doxorubicin (DOX) loading efficiency (34.1%, named RGD/DOX-pAS@AuNC) and effective NIR-triggered DOX release. This nanoplatform shows excellent performance in xenograft tumor model of HeLa cell targeting, negligible cytotoxicity, and good stability both in vitro and in vivo. By SERS imaging, the optimal temporal distribution of injected RGD/DOX-pAS@AuNCs at the tumor site is identified for NIR-triggered local chemo-PTT toward the tumor, achieving ultraeffective therapy in tumor cells and tumor-bearing mouse model with 5 min of NIR irradiation (0.5 W cm^-2 ). This work offers a promising approach to employing SERS imaging for effective noninvasive tumor treatment by on-site triggered chemo-PTT.

Tumor identification via in vivo portable Raman detection of sialic acid with a dual gold nanoprobe system

A dual gold nanoprobe system was designed for in vivo portable Raman detection of sialic acid (SA) for tumor identification. The dual gold nanoprobe system contained two gold nanoprobes, Au10-DTTC/PEG-PBA and Au40-PEG-SA. Au10-DTTC/PEG-PBA was constructed on a 10 nm gold nanoparticle modified with 3,3'-diethylthia tricarbocyanine iodide (DTTCI) as the Raman reporter and 3-aminophenylboronic acid (APBA) through a thiol PEG succinimidyl carboxymethyl ester (HS-PEG-NHS) linker for specific recognition of SA. Au40-PEG-SA was constructed on a 40 nm gold nanoparticle modified with SA through HS-PEG-NHS. For in vivo detection of SA, Au10-DTTC/PEG-PBA and Au40-PEG-SA were subsequently injected into tumor xenografted mice with optimal interval and retention times. Through the specific recognition between PBA and SA, the conjugates of Au10-DTTC/PEG-PBA and Au40-PEG-SA formed in the tumor region emitted strong SERS signals of DTTC, which could be detected by a portable Raman detector. This work provides a convenient and portable method to detect SA in tumor xenografted mice, which is useful for family-stay identification and clinical cleavage of tumors.

Surface-Enhanced Raman Spectroscopic Probing in Digital Microfluidics through a Microspray Hole

We report a novel approach for surface-enhanced Raman spectroscopy (SERS) detection in digital microfluidics (DMF). This is made possible by a microspray hole (μSH) that uses an electrostatic spray (ESTAS) for sample transfer from inside the chip to an external SERS substrate. To realize this, a new ESTAS-compatible stationary SERS substrate was developed and characterized for sensitive and reproducible SERS measurements. In a proof-of-concept study, we successfully applied the approach to detect various analyte molecules using the DMF chip and achieved micro-molar detection limits. Moreover, this technique was exemplarily employed to study an organic reaction occurring in the DMF device, providing vibrational spectroscopic data.

SERS "hot spot" enhance-array assay for misfolded SOD1 correlated with white matter lesions and aging

Misfolding of superoxide dismutase-1 (SOD1) has been correlated with many neurodegenerative diseases, such as Amyotrophic lateral sclerosis's and Alzheimer's among others. However, it is unclear whether misfolded SOD1 plays a role in another neurodegenerative disease of white matter lesions (WMLs). In this study, a sensitive and specific method based on SERS technique was proposed for quantitative detection of misfolded SOD1 content in WMLs. To fabricate the double antibodysandwich substrates for SERS detection, gold nanostars modified with capture antibody were immobilized on glass substrates to prepare active SERS substrates, and then SERS probes conjugated with a Raman reporter and a specific target antibody were coupled with active SERS substrates. This SERS substrates had been employed for quantitative detection of misfolded SOD1 levels in WMLs and exhibited excellent stability, reliability, and accuracy. Moreover, experimental results indicated that the level of misfolded SOD1 increased with the increase in age and the degree of WMLs. Hence, misfolded SOD1 may be a potential blood marker for WMLs and aging. Meanwhile, SERS-based gold nanostars have great clinical application potential in the screening, diagnosis and treatment of WMLs.

Guiding Epilepsy Surgery with an LRP1-Targeted SPECT/SERRS Dual-Mode Imaging Probe

Accurate identification of the resectable epileptic lesion is a precondition of operative intervention to drug-resistant epilepsy (DRE) patients. However, even when multiple diagnostic modalities are combined, epileptic foci cannot be accurately identified in ∼30% of DRE patients. Inflammation-associated low-density lipoprotein receptor-related protein-1 (LRP1) has been validated to be a surrogate target for imaging epileptic foci. Here, we reported an LRP1-targeted dual-mode probe that is capable of providing comprehensive epilepsy information preoperatively with SPECT imaging while intraoperatively delineating epileptic margins in a sensitive high-contrast manner with surface-enhanced resonance Raman scattering (SERRS) imaging. Notably, a novel and universal strategy for constructing self-assembled monolayer (SAM)-based Raman reporters was proposed for boosting the sensitivity, stability, reproducibility, and quantifiability of the SERRS signal. The probe showed high efficacy to penetrate the blood-brain barrier. SPECT imaging showed the probe could delineate the epileptic foci clearly with a high target-to-background ratio (4.11 ± 0.71, 2 h). Further, with the assistance of the probe, attenuated seizure frequency in the epileptic mouse models was achieved by using SPECT together with Raman images before and during operation, respectively. Overall, this work highlights a new strategy to develop a SPECT/SERRS dual-mode probe for comprehensive epilepsy surgery that can overcome the brain shift by the co-registration of preoperative SPECT and SERRS intraoperative images.

Label-Free Fluorescence Quantitative Detection Platform on Plasmonic Silica Photonic Crystal Microsphere Array

We have demonstrated the proof-of-concept of a label-free fluorescence quantitative detection platform based on gold nanoparticle (AuNP) enhancement intrinsic fluorescence of protein on the silica photonic crystal microsphere (SPCM) array. The label-free one-step competitive fluorescence immunoassay protocol has been proposed on the surface of the SPCM. Aflatoxin B₁ (AFB₁) as a model molecule was detected by the newly established method. AFB₁-bovine serum albumin and monoclonal antibodies (Abs) of anti-AFB₁ have been immobilized on the surfaces of SPCMs and AuNPs, respectively. AuNPs remarkably enhanced the intrinsic fluorescence of artificial antigens on the surface of the SPCM at near UV excitation. The simulation of electric field distribution showed that the maximum value of the near-field enhancement |E/E₀| of the SPCM with AuNPs could reach 20. The label-free fluorescence enhancement effect comes from the synergistic effects of photonic crystal effect and AuNP plasmon effect. Such a label-free fluorescence detection method can provide a linear detection range from 0.1 to 10 ng/mL with a limit of detection of 0.025 ng/mL and good specificity for AFB₁. The recovery rates in the spiked cereal samples were measured in the range of 84.07 ± 5.71%-101.02 ± 5.13%, which were consistent with that of the traditional enzyme linked immunosorbent assay method. The label-free detection platform displays great application potential in biology, medicine, agriculture, food industry, chemical industry, energy source, and environmental protection.

Microfluidic SERS devices: brightening the future of bioanalysis

A new avenue has opened up for applications of surface-enhanced Raman spectroscopy (SERS) in the biomedical field, mainly due to the striking advantages offered by SERS tags. SERS tags provide indirect identification of analytes with rich and highly specific spectral fingerprint information, high sensitivity, and outstanding multiplexing potential, making them very useful in in vitro and in vivo assays. The recent and innovative advances in nanomaterial science, novel Raman reporters, and emerging bioconjugation protocols have helped develop ultra-bright SERS tags as powerful tools for multiplex SERS-based detection and diagnosis applications. Nevertheless, to translate SERS platforms to real-world problems, some challenges, especially for clinical applications, must be addressed. This review presents the current understanding of the factors influencing the quality of SERS tags and the strategies commonly employed to improve not only spectral quality but the specificity and reproducibility of the interaction of the analyte with the target ligand. It further explores some of the most common approaches which have emerged for coupling SERS with microfluidic technologies, for biomedical applications. The importance of understanding microfluidic production and characterisation to yield excellent device quality while ensuring high throughput production are emphasised and explored, after which, the challenges and approaches developed to fulfil the potential that SERS-based microfluidics have to offer are described.

Detection and Characterization of Nodularin by Using Label-Free Surface-Enhanced Spectroscopic Techniques

Nodularin (NOD) is a potent toxin produced by Nodularia spumigena cyanobacteria. Usually, NOD co-exists with other microcystins in environmental waters, a class of cyanotoxins secreted by certain cyanobacteria species, which makes identification difficult in the case of mixed toxins. Herein we report a complete theoretical DFT-vibrational Raman characterization of NOD along with the experimental drop-coating deposition Raman (DCDR) technique. In addition, we used the vibrational characterization to probe SERS analysis of NOD using colloidal silver nanoparticles (AgNPs), commercial nanopatterned substrates with periodic inverted pyramids (Klarite^TM substrate), hydrophobic Tienta^® SpecTrim^TM slides, and in-house fabricated periodic nanotrenches by nanoimprint lithography (NIL). The 532 nm excitation source provided more well-defined bands even at LOD levels, as well as the best performance in terms of SERS intensity. This was reflected by the results obtained with the Klarite^TM substrate and the silver-based colloidal system, which were the most promising detection approaches, providing the lowest limits of detection. A detection limit of 8.4 × 10^-8 M was achieved for NOD in solution by using AgNPs. Theoretical computation of the complex vibrational modes of NOD was used for the first time to unambiguously assign all the specific vibrational Raman bands.

SERS combined with PCR as a potent tool for detecting mutations: a case study of tomato plants

Conventional methods of detecting economically essential mutations have several disadvantages. Even though fluorescence-based methods are still the best option, Surface-Enhanced Raman Spectroscopy (SERS) may soon emerge as an alternative to the current techniques for detecting these mutations, because of its ability to detect molecular vibrational signatures. We were able to identify and develop a PCR-based SERS assay that can relentlessly differentiate between different types of indels, and SNPs as demonstrated in the case of tomato genome related to tomato yellow leaf curl virus and root-knot nematodes, diseases that are economically significant to the global agriculture industry and where the selection of resistant crops is the best solution. This tri-primer assay utilizes mutation-specific forward primers and SERS probes tagged with FAM and Cy3 dyes, specific for each allele of a particular gene (Ty-3 and Mi-1). The unique Raman spectral features of these dyes enabled to perform of multiplexing, which made it possible to detect not only the indel type but also the zygosity in a single experiment. Moreover, this technique successfully differentiated between two different SNP-based alleles. Therefore, due to its efficient multiplexing capability and lack of the need for quenchers, it has the potential to become a powerful onsite and offsite screening tool in the not-too-distant future.

Single-step controlled synthesis of flower-like gold nanoparticles stabilized by chitosan for sensitive detection of heparin using a surface-enhanced Raman scattering method

A novel single-step and template-free procedure, including controlled synthesis of gold flowers (AuNFs), conjugation to a 4-MBA reporter, and stabilization with chitosan, is proposed to develop the SERS tags-based nanoparticles for trace detection of heparin. This SERS detection assay is based on the aggregation/non-aggregation balance of AuNFs-4-MBA@chitosan nanoparticles, which was induced by adding a very low concentration of heparin in the as-synthesized colloidal solutions. SERS-tag colloids are prepared by mixing chitosan with HAuCl4 and 4-mercapto benzoic acid before being reduced with ascorbic acid under appropriate pH conditions. The formed AuNFs-4-MBA@chitosan nanoparticles were positively charged with high stability and well-dispersed in aqueous media. Based on understanding each reaction component's role in the preparation of the SERS tag colloid, we aim to simplify the controlled synthesis and Raman probe conjugation process. The average size of AuNFs is below 90 nm, fine-tuned in shape and effectively conjugated to the Raman reporter molecules 4-MBA. These as-prepared SERS tag-based AuNFs have good biocompatibility and are virtually non-toxic, as studied with fibroblast and MCF-7 cells. Through these SERS-tag colloids, the trace detection of heparin is improved, with a wide detection window (0.01 to 100 ppm), high reproducibility (RSD value of 3.56%), limit of detection (LOD) of 0.054 ppm, and limit of quantification (LOQ) of 0.17 ppm. Comparison experiments show that the SERS-tag colloids possess good selectivity over other ions, and organic and amino acid substances. The results provide the capability and the potential for application under complex biological conditions and future biosensing based on SERS signal amplification.

Contributions of vibrational spectroscopy to virology: A review

Vibrational spectroscopic techniques, both infrared absorption and Raman scattering, are high precision, label free analytical techniques which have found applications in fields as diverse as analytical chemistry, pharmacology, forensics and archeometrics and, in recent times, have attracted increasing attention for biomedical applications. As analytical techniques, they have been applied to the characterisation of viruses as early as the 1970 s, and, in the context of the coronavirus disease 2019 (COVID-19) pandemic, have been explored in response to the World Health Organisation as novel methodologies to aid in the global efforts to implement and improve rapid screening of viral infection. This review considers the history of the application of vibrational spectroscopic techniques to the characterisation of the morphology and chemical compositions of viruses, their attachment to, uptake by and replication in cells, and their potential for the detection of viruses in population screening, and in infection response monitoring applications. Particular consideration is devoted to recent efforts in the detection of severe acute respiratory syndrome coronavirus 2, and monitoring COVID-19.

A Background-Free SERS Strategy for Sensitive Detection of Hydrogen Peroxide

The accurate and sensitive detection of biomolecules by surface-enhanced Raman spectroscopy (SERS) is possible, but remains challenging due to the interference from biomolecules in complex samples. Herein, a new SERS sensor is developed for background-free detection of hydrogen peroxide (H₂O₂) with an ultralow detection limit (1 × 10^-10 mol/L), using a Raman-silent strategy. The Au microparticles (Au-RSMPs) resembling rose-stones are devised as SERS substrates with a high enhancement effect, and 4-mercaptophenylboronic acid (4-MPBA) is selected as an H₂O₂-responsive Raman reporter. Upon the reaction with H₂O₂, the phenylboronic group of 4-MPBA was converted to a phenol group, which subsequently reacted with 4-diazonium-phenylalkyne (4-DP), an alkyne-carrying molecule via the azo reaction. The formed product exhibits an intense and sharp SERS signal in the Raman-silent region, avoiding interference of impurities and biomolecules. As a proof-of-concept demonstration, we show that this SERS sensor possesses significant merits towards the determination of H₂O₂ in terms of broad linear range, low limit of detection, and high selectivity, showing promise for the quantitative analysis of H₂O₂ in complicated biological samples.

Robust, reliable and quantitative sensing of aqueous arsenic species by Surface-enhanced Raman Spectroscopy: The crucial role of surface silver ions for good analytical practice

Arsenic speciation analysis is important for pollution and health risk assessment. Surface-enhanced Raman Spectroscopy (SERS) is supposed to be a promising detection technology for arsenic species owing to the unique fingerprints. However, further application of SERS is hampered by its poor repeatability. Herein, the role of surface silver ions on colloidal Ag was revealed in SERS analysis of arsenic species. Arsenic species were adsorbed on Ag nanoparticles (Ag NPs) driven by surface silver ions and were simultaneously sensed by the SERS "hot spots" generated from the aggregation of Ag NPs. So, the inconsistent SERS activities of Ag NPs synthesized from different batches can be significantly improved by modifying external silver ions onto Ag NPs (AgNPs@Ag⁺), Specific binding affinity of surface silver ions to arsenic species generated higher sensitivity (detection limit, 4.0 × 10^-11 mol L^-1 for arsenite, 8.0 × 10^-11 mol L^-1 for arsenate), wider linear range, faster response, cleaner spectra background and better reproducibility. Batch-to-batch reproducibility was significantly improved with a variation below 3.1%. The method was also demonstrated with drinking and environmental water with adequate recovery and high interference resistance. Our findings displayed good analytical practice of the surface silver ions derived SERS method and its great potential in the rapid detection of hazardous materials.

Lateral Flow Immunoassays for Detecting Viral Infectious Antigens and Antibodies

Abundant immunological assays currently exist for detecting pathogens and identifying infected individuals, making detection of diseases at early stages integral to preventing their spread, together with the consequent emergence of global health crises. Lateral flow immunoassay (LFIA) is a test characterized by simplicity, low cost, and quick results. Furthermore, LFIA testing does not need well-trained individuals or laboratory settings. Therefore, it has been serving as an attractive tool that has been extensively used during the ongoing COVID-19 pandemic. Here, the LFIA strip's available formats, reporter systems, components, and preparation are discussed. Moreover, this review provides an overview of the current LFIAs in detecting infectious viral antigens and humoral responses to viral infections.

Raman Spectroscopy for Chemical Biology Research

In chemical biology research, various fluorescent probes have been developed and used to visualize target proteins or molecules in living cells and tissues, yet there are limitations to this technology, such as the limited number of colors that can be detected simultaneously. Recently, Raman spectroscopy has been applied in chemical biology to overcome such limitations. Raman spectroscopy detects the molecular vibrations reflecting the structures and chemical conditions of molecules in a sample and was originally used to directly visualize the chemical responses of endogenous molecules. However, our initial research to develop "Raman tags" opens a new avenue for the application of Raman spectroscopy in chemical biology. In this Perspective, we first introduce the label-free Raman imaging of biomolecules, illustrating the biological applications of Raman spectroscopy. Next, we highlight the application of Raman imaging of small molecules using Raman tags for chemical biology research. Finally, we discuss the development and potential of Raman probes, which represent the next-generation probes in chemical biology.

An Alkyne-Mediated SERS Aptasensor for Anti-Interference Ochratoxin A Detection in Real Samples

Avoiding interference and realizing the precise detection of mycotoxins in complex food samples is still an urgent problem for surface-enhanced Raman spectroscopy (SERS) analysis technology. Herein, a highly sensitive and specific aptasensor was developed for the anti-interference detection of Ochratoxin A (OTA). In this aptasensor, 4-[(Trimethylsilyl) ethynyl] aniline was employed as an anti-interference Raman reporter to prove a sharp Raman peak (1998 cm-1) in silent region, which could avoid the interference of food bio-molecules in 600-1800 cm-1. 4-TEAE and OTA-aptamer were assembled on Au NPs to serve as anti-interference SERS probes. Meanwhile, Fe3O4 NPs, linked with complementary aptamer (cApts), were applied as capture probes. The specific binding of OTA to aptamer hindered the complementary binding of aptamer and cApt, which inhibited the binding of SERS probes and capture probes. Hence, the Raman responses at 1998 cm-1 were negatively correlated with the OTA level. Under the optimum condition, the aptasensor presented a linear response for OTA detection in the range of 0.1-40 nM, with low detection limits of 30 pM. In addition, the aptasensor was successfully applied to quantify OTA in soybean, grape and milk samples. Accordingly, this anti-interference aptasensor could perform specific, sensitive and precise detection of OTA in real samples, and proved a reliable reference strategy for other small-molecules detection in food samples.

Functionalized silver nanoparticles for SERS amplification with enhanced reproducibility and for ultrasensitive optical fiber sensing in environmental and biochemical assays

Plasmonic sensors have broad application potential in many fields and are promising to replace most bulky sensors in the future. There are various method-based chemical reduction processes for silver nanoparticle production with flexible structural shapes due to their simplicity and rapidity in nanoparticle fabrication. In this study, self-assembled silver nanoparticles (Ag NPs) with a plasmon peak at 424 nm were successfully coated onto -NH2-functionalized glass and optical fiber sensors. These coatings were rapidly produced via two denaturation reactions in plasma oxygen, respectively, and an APTES ((3-aminopropyl)triethoxysilane) solution was shown to have high strength and uniformity. With the use of Ag NPs for surface-enhanced Raman scattering (SERS), excellent results and good stability with the detection limit up to 10-10 M for rhodamine B and 10-8 M for methylene blue, and a signal degradation of only ∼20% after storing for 30 days were achieved. In addition, the optical fiber sensor with Ag NP coatings exhibited a higher sensitivity value of 250 times than without coatings to the glycerol solution. Therefore, significant enhancement of these ultrasensitive sensors demonstrates promising alternatives to cumbersome tests of dye chemicals and biomolecules without any complicated process.

Design of Ag/TiO2/Ag Composite Nano-Array Structure with Adjustable SERS-Activity

How to fabricate large area controllable surface-enhanced Raman scattering (SERS) active nanostructure substrates has always been one of the important issues in the development of nanostructure devices. In this paper, nano-etching technology and magnetron sputtering technology are combined to prepare nanostructure substrate with evolvable structure, and Ag/TiO₂/Ag composites are introduced into the evolvable composite structure. The activity of SERS is further enhanced by the combination of TiO₂ and Ag and the electron transfer characteristics of TiO₂ itself. Deposition, plasma etching, and transfer are carried out on self-assembled 200 nm polystyrene (PS) colloidal sphere arrays. Due to the shadow effect between colloidal spheres and the size of metal particles introduced by deposition, a series of Ag/TiO₂/Ag nanostructure arrays with adjustable nanostructure substrates such as nano-cap (NC), nano cap-star (NCS), and nano particle-disk (NPD) can be obtained. These nanoarrays with rough surfaces and different evolutionary structures can uninterruptedly regulate optical plasmon resonance and reconstruct SERS hotspots over a large range, which has potential application value in surface science, chemical detection, nanometer photonics, and so on.

Hydrophobic plasmonic silver membrane as SERS-active catcher for rapid and ultrasensitive Cu(II) detection

The rapid and selective identification of heavy metal ions is crucial for environmental water safety. In this study, a novel surface-enhanced Raman scattering (SERS)-active catcher was designed for Cu(II) detection using a hydrophobic hydroxyoxime-mediated plasmonic silver membrane (HOX@Ag-PVDF). Uniformly dispersed Ag nanoparticles (ca. 80 nm) and hydroxyoxime molecules were synchronously decorated on the skeleton of the polyvinylidene fluoride membrane via an in situ interfacial assembly strategy. HOX@Ag-PVDF shows excellent SERS activity (EF = 2.5 × 10⁷), high reproducibility (~8% RSD), and long-term stability (50 days) for detecting 4-nitrothiophenol (4-NTP). Moreover, HOX@Ag-PVDF can serve as a new platform for rapid and dry-free SERS detection of Cu(II) owing to its strong affinity and surface hydrophobicity. Cu(II) ions can be rapidly captured in 5 s and selectively recognized by SERS signals without interference from other metal ions. HOX@Ag-PVDF exhibits linear SERS response signals at low concentrations ranging from 10^-6 to 10^-10 mol/L Cu(II) (R² = 0.9893) with a low detection limit (LOD) of 52.0 pmol/L. This hydrophobic plasmonic membrane, with its simple sampling and rapid SERS response characteristics, provides ultrasensitive recognition and heavy metal detection for practical applications.

Application of SERS in the Detection of Fungi, Bacteria and Viruses

In this review, we report the recent advances of SERS in fungi, bacteria, and viruses. Firstly, we briefly introduce the advantage of SERS over fluorescence on virus identification and detection. Secondly, we review the feasibility analysis of Raman/SERS spectrum analysis, identification, and fungal detection on SERS substrates of various nanostructures with a signal amplification mechanism. Thirdly, we focus on SERS spectra for nucleic acid, pathogens for the detection of viruses and bacteria, and furthermore introduce SERS-based microdevices, including SERS-based microfluidic devices, and three-dimensional nanostructured plasmonic substrates.

Chiral molecular imprinting-based SERS detection strategy for absolute enantiomeric discrimination

Chiral discrimination is critical in environmental and life sciences. However, an ideal chiral discrimination strategy has not yet been developed because of the inevitable nonspecific binding entity of wrong enantiomers or insufficient intrinsic optical activities of chiral molecules. Here, we propose an "inspector" recognition mechanism (IRM), which is implemented on a chiral imprinted polydopamine (PDA) layer coated on surface-enhanced Raman scattering (SERS) tag layer. The IRM works based on the permeability change of the imprinted PDA after the chiral recognition and scrutiny of the permeability by an inspector molecule. Good enantiomer can specifically recognize and fully fill the chiral imprinted cavities, whereas the wrong cannot. Then a linear shape aminothiol molecule, as an inspector of the recognition status is introduced, which can only percolate through the vacant and nonspecifically occupied cavities, inducing the SERS signal to decrease. Accordingly, chirality information exclusively stems from good enantiomer specific binding, while nonspecific recognition of wrong enantiomer is curbed. The IRM benefits from sensitivity and versatility, enabling absolute discrimination of a wide variety of chiral molecules regardless of size, functional groups, polarities, optical activities, Raman scattering, and the number of chiral centers.