Shell-Switchable SERS Blocking Strategy for Reliable Signal-On SERS Sensing in Living Cells: Detecting an External Target without Affecting the Internal Raman Molecule

Generalized ratiometric surface-enhanced Raman scattering biosensor for okadaic acid in food based on Au-triggered signal amplification

BACKGROUND

Reliability and robustness have been recognized as key challenges for Surface-enhanced Raman scattering (SERS) analytical techniques. Quantifying the concentration of an analyte using a single characteristic peak from SERS has been a controversial topic because the Raman signal is susceptible to highly concentrated electromagnetic hotspots, inhomogeneity of SERS substrate, or non-standardization of measurement conditions. Ratiometric SERS strategies have been demonstrated as a promising solution to effectively balance and compensate for signal fluctuations caused by matrix heterogeneity. However, it is not easy to construct ratiometric SERS sensors with monitoring the ratio of two different signal intensities for target analysis.

RESULTS

An attempt has been made to develop a novel ratiometric biosensor that can be applied to detect okadaic acid (OA). Aptamer-anchored magnetic particles were first combined with gold-tagged short complementary DNA (Au-cDNA) to create heterogeneous nanostructures. When the target was present, the Au-cDNA was dissociated from nanostructures, and 4-nitrothiophenol (4-NTP) was initiated to reduce to 4-aminothiophenol (4-ATP) in the presence of hydrogen sources. The SERS ratio change of 4-NTP and 4-ATP was finally detected by AuNPs-coated film. OA was successfully quantified, and the detection limit was as low as 2.4524 ng/mL. The constructed biosensor had good stability and reproducibility with a relative standard deviation of less than 4.47%. The proposed method used gold nanoparticles as an intermediate to achieve catalytic signal amplification and subsequently increased the sensitivity of the biosensor.

SIGNIFICANCE AND NOVELTY

Catalytic reaction-based ratiometric SERS biosensors combine the multiple advantages of catalytic signal amplification and signal self-calibration and provide new insights into the development of stable, reproducible, and reliable SERS detection techniques. This ratiometric SERS technique offered a universal method that is anticipated to be applicable for the detection of other targets by substituting the aptamer.

Ultrasensitive Hierarchical AuNRs@SiO2@Ag SERS Probes for Enrichment and Detection of Insulin and C-Peptide in Serum

Introduction

Insulin and C-peptide played crucial roles as clinical indicators for diabetes and certain liver diseases. However, there has been limited research on the simultaneous detection of insulin and C-peptide in trace serum. It is necessary to develop a novel method with high sensitivity and specificity for detecting insulin and C-peptide simultaneously.

Methods

A core-shell-satellites hierarchical structured nanocomposite was fabricated as SERS biosensor using a simple wet-chemical method, employing 4-MBA and DTNB for recognition and antibodies for specific capture. Gold nanorods (Au NRs) were modified with Raman reporter molecules and silver nanoparticles (Ag NPs), creating SERS tags with high sensitivity for detecting insulin and C-peptide. Antibody-modified commercial carboxylated magnetic bead@antibody served as the capture probes. Target materials were captured by probes and combined with SERS tags, forming a "sandwich" composite structure for subsequent detection.

Results

Under optimized conditions, the nanocomposite fabricated could be used to detect simultaneously for insulin and C-peptide with the detection limit of 4.29 × 10-5 pM and 1.76 × 10-10 nM in serum. The insulin concentration (4.29 × 10-5-4.29 pM) showed a strong linear correlation with the SERS intensity at 1075 cm-1, with high recoveries (96.4-105.3%) and low RSD (0.8%-10.0%) in detecting human serum samples. Meanwhile, the C-peptide concentration (1.76 × 10-10-1.76 × 10-3 nM) also showed a specific linear correlation with the SERS intensity at 1333 cm-1, with recoveries 85.4%-105.0% and RSD 1.7%-10.8%.

Conclusion

This breakthrough provided a novel, sensitive, convenient and stable approach for clinical diagnosis of diabetes and certain liver diseases. Overall, our findings presented a significant contribution to the field of biomedical research, opening up new possibilities for improved diagnosis and monitoring of diabetes and liver diseases.

Face-to-face Assembly Strategy of Au Nanocubes: Induced Generation of Broad Hotspot Regions for SERS-Fluorescence Dual-Signal Detection of Intracellular miRNAs

While designing anisotropic noble metal nanoparticles (NPs) can enhance the signal intensity of Raman dyes, more sensitive surface-enhanced Raman scattering (SERS) probes can be designed by oriented self-assembly of noble metal nanomaterials into dimers or higher-order nanoclusters. In this study, we engineered a self-assembly strategy in living cells for real-time fluorescence and SERS dual-channel detection of intracellular microRNAs (miRNAs), using Mg2+-dependent 8-17E DNAzyme sequences as the driving motors, gold nanocubes (AuNCs) as the driver components, and three-branched double-stranded DNA as the linking tool. The assembly selects adenine in DNA as a reporter molecule, simplifying the labeling process of Raman reporter molecules and reducing the synthesis process. In addition, adenine is stably distributed between the faces of AuNCs and the wide hotspot region gives good reproducibility of the adenine SERS signal. In this strategy, the SERS channel was consistently stable and more sensitive compared to the fluorescence channel. Among them, the detection limit of the SERS channel was 2.1 pM and the coefficient of variation was 1.26% in the in vitro liquid phase and 1.49% in MCF-7 cells. The strategy successfully achieved accurate tracking and quantification of miRNA-21 in cancer cells, showing good reproducibility in complex samples as well as cells. The reported strategy provides ideas for exploring intracellular specific triggering of nanoparticles for precise control of self-assembly.

Constructing Ultra-Strong SERS Tags in the Cellular Raman-Silent Region by Orthogonal Array Testing Strategy

Surface-enhanced Raman spectroscopy (SERS) tags have the advantages of unique fingerprint vibration spectrum, ultranarrow spectral line widths, and weak photobleaching effect, showing great potential for bioimaging. However, SERS imaging is still hindered for further application due to its weak spontaneous Raman scattering, biomolecular signal interference, and long acquisition times. Here, we develop a novel SERS tag of the core (Au)-shell (N-doped graphene) structure (Au@NGs) with ultrastrong and stable Raman signal (2180 cm-1) in the cellular Raman-silent region (1800-2800 cm-1) through base-promoted oxidative decarboxylation of amino acids. Exploring the factors (metal salts, amino acids, catalysts, temperature, etc.) to obtain Au@NGs with the strongest Raman signal commonly requires more than 100,000 separate experiments, while that using an orthogonal array testing strategy is reduced to 56. The existence of deep charge transfer between the Au surface and C≡N-graphene is proved by theoretical calculations, which means the ultrastrong signal of Au@NGs is the joint effect of electromagnetic and chemical enhancement. The Au@NGs have a detection sensitivity down to a single-nanoparticle level, and high-speed and high-resolution cellular imaging (4453 pixels) is obtained within 10 s by global Raman imaging. The combination of Au@NGs-based tags with ultrastrong intrinsic Raman imaging capability and global imaging technology holds great promise for high-speed Raman imaging.

Pt-Decorated Gold Nanoflares for High-Fidelity Phototheranostics: Reducing Side-Effects and Enhancing Cytotoxicity toward Target Cells

Functionalized with the Au-S bond, gold nanoflares have emerged as promising candidates for theranostics. However, the presence of intracellular abundantly biothiols compromises the conventional Au-S bond, leading to the unintended release of cargoes and associated side-effects on non-target cells. Additionally, the hypoxic microenvironment in diseased regions limits treatment efficacy, especially in photodynamic therapy. To address these challenges, high-fidelity photodynamic nanoflares constructed on Pt-coated gold nanoparticles (Au@Pt PDNF) were communicated to avoid false-positive therapeutic signals and side-effects caused by biothiol perturbation. Compared with conventional photodynamic gold nanoflares (AuNP PDNF), the Au@Pt PDNF were selectively activated by cancer biomarkers and exhibited high-fidelity phototheranostics while reducing side-effects. Furthermore, the ultrathin Pt-shell catalysis was confirmed to generate oxygen which alleviated hypoxia-related photodynamic resistance and enhanced the antitumor effect. This design might open a new venue to advance theranostics performance and is adaptable to other theranostic nanomaterials by simply adding a Pt shell.

MnO2 nanoparticles decorated with Ag/Au nanotags for label-based SERS determination of cellular glutathione

A novel stimulus-responsive surface-enhanced Raman scattering (SERS) nanoprobe has been developed for sensitive glutathione (GSH) detection based on manganese dioxide (MnO₂) core and silver/gold nanoparticles (Ag/Au NPs). The MnO₂ core is not only capable to act as a scaffold to amplify the SERS signal via producing "hot spots", but also can be degraded in the presence of the target and thus greatly enhance the nanoprobe sensitivity for sensing of GSH. This approach enables a wide linear range from 1 to 100 µM with a 2.95 µM (3σ/m) detection limit. Moreover, the developed SERS nanoprobe represents great possibility in both sensitive detection of intracellular GSH and even can monitor the change of intracellular GSH level when the stimulant occurs. This sensing system not merely offers a novel strategy for sensitive sensing of GSH, but also provides a new avenue for other biomolecules detection.

Material design, development, and trend for surface-enhanced Raman scattering substrates

Surface-enhanced Raman scattering (SERS) is a powerful and non-invasive spectroscopic technique that can provide rich and specific chemical fingerprint information for various target molecules through effective SERS substrates. In view of the strong dependence of the SERS signals on the properties of the SERS substrates, design, exploration, and construction of novel SERS-active nanomaterials with low cost and excellent performance as the SERS substrates have always been the foundation and the top priority for the development and application of the SERS technology. This review specifically focuses on the extensive progress made in the SERS-active nanomaterials and their enhancement mechanism since the first discovery of SERS on the nanostructured plasmonic metal substrates. The design principles, unique functions, and influencing factors on the SERS signals of different types of SERS-active nanomaterials are highlighted, and insight into their future challenge and development trends is also suggested. It is highly expected that this review could benefit a complete understanding of the research status of the SERS-active nanomaterials and arouse the research enthusiasm for them, leading to further development and wider application of the SERS technology.

Construction of a novel nano-enzyme for ultrasensitive glucose detection with surface-enhanced Raman scattering

Fabricating more sensitive, stable and low-cost nanomaterials for the detection of glucose is important for the disease diagnosis and monitoring. Herein, we established a nanocomposite (polypyrrole bridging GO@Au@MnO₂) as a novel surface-enhanced Raman scattering (SERS) nanoprobe for the quantitative detection of glucose in trace serum. Each component in the nanocomposites played an irreplaceable role in SERS detection of glucose. Polypyrrole (PPy) could act as Raman signal and extra SERS signal molecules didn't need to be introduced; Graphene oxide (GO) and gold nanoparticles (Au NPs) could enhance Raman signal of PPy; Au NPs also acted as glucose oxidase, which can oxidize glucose to produce gluconic acid and hydrogen peroxide(H₂O₂); Manganese oxide (MnO₂) further enhanced Raman signal of PPy and responded to hydrogen peroxide, which will induce the decrease of Raman intensity of PPy. Thus, glucose can be quantified according to Raman signal output of PPy, which displayed a liner range from 1 to 10 μM, with detectable limit of 0.114 μM. Because of the merits in sensitivity, convenience and versatility, the novel method shows large potential space for disease-related substance detection in the future.

Competitive Ratiometric Aptasensing with Core-Internal Standard-Shell Structure Based on Surface-Enhanced Raman Scattering

Reproducibility and stability are important indicators for the evaluation of quantitative sensing methods based on surface-enhanced Raman scattering (SERS) technology. Developing a SERS substrate with self-calibration capabilities is vital for effectively quantifying targets. In this work, a competitive ratiometric SERS aptasensor was developed. 4-Aminothiophenol as an internal standard (IS) was embedded in the substrate followed by gradually loading with the aptamer and methylene blue functionalizing of the complementary sequences of the aptamer (MB-cDNA). Recognition and binding of the target to the aptamer resulted in the shedding of MB-cDNA after magnetic separation reducing the SERS signal of MB, allowing for the ratiometric determination of the target based on the constant intensity from the IS. For the selective detection of okadaic acid (OA), a good negative correlation was achieved between the SERS ratiometric intensity and OA concentration in the range of 0.5-100 ng/mL. The magnetic separation strategy effectively simplifies the production steps of the aptasensor, and the ratiometric strategy effectively improved the reproducibility and stability of the OA sensing. This ratiometric aptasensor has been successfully employed to detect OA in food and environmental samples and is expected to be extended to detect other targets.

AuNPs-COFs Core-Shell Reversible SERS Nanosensor for Monitoring Intracellular Redox Dynamics

The redox homeostasis in living cells is greatly crucial for maintaining the redox biological function, whereas accurate and dynamic detection of intracellular redox states still remains challenging. Herein, a reversible surface-enhanced Raman scattering (SERS) nanosensor based on covalent organic frameworks (COFs) was prepared to dynamically monitor the redox processes in living cells. The nanosensor was fabricated by modifying the redox-responsive Raman reporter molecule, 2-Mercaptobenzoquione (2-MBQ), on the surface of gold nanoparticles (AuNPs), followed by the in situ coating of COFs shell. 2-MBQ molecules can repeatedly and quickly undergo reduction and oxidation when successively treated with ascorbic acid (AA) and hypochlorite (ClO^-) (as models of reductive and oxidative species, respectively), which resulted in the reciprocating changes of SERS spectra at 900 cm^-1. The construction of the COFs shell provided the nanosensor with great stability and anti-interference capability, thus reliably visualizing the dynamics of intracellular redox species like AA and ClO^- by SERS nanosensor. Taken together, the proposed SERS strategy opens up the prospects to investigate the signal transduction pathways and pathological processes related with redox dynamics.

In Situ Assay of Interfacial Interaction between ZnO Nanoparticles and Live Cell Disturbed by Surfactants

The interfacial interaction between pollutants and organisms is a critical process in controlling the environmental fates of pollutants; however, in situ assay of the interaction is still a great challenge. Here, in situ determination of dissociation constants (K_d) for ZnO nanoparticles (ZnO NPs) from live algal cells disturbed by different-charged surfactants was established using microscale thermophoresis (MST). Moreover, in situ measurement of the adhesion force between the ZnO NPs probe and live single cell was performed using an atomic force microscope (AFM). Results showed that the cationic cetyltrimethylammonium chloride (CTAC) and anionic sodium dodecylbenzenesulfonate (SDBS) increased but nonionic Triton X-100 (TX-100) decreased the adhesion of ZnO NPs on cells. However, the force signature exhibited a smooth single retracted peak at short distances in the SDBS- and TX-100-treated groups, distinguished from the "see-saw" pattern peak in the CTAC-treated groups. The extended Derjaguin-Landau-Verway-Overbeek (XDLVO) calculation further confirmed that SDBS and TX-100 mainly disturbed the short-range hydration on the NP-cell interface, while CTAC reduced the long-range electrostatic repulsion. Furthermore, an excellent linear correlation between Zn bioaccumulation and two parameters (K_d and adhesion force) indicated that NP-cell interfacial interactions affected Zn bioaccumulation. Thus, in situ assay provides a quantitative basis for the pollutant-organism interfacial interaction to evaluate the environmental fate and ecological risk of pollutants.

Surface Filtration in Mesoporous Au Films Decorated by Ag Nanoparticles for Solving SERS Sensing Small Molecules in Living Cells

For surface-enhanced Raman spectroscopy (SERS) sensing of small molecules in the presence of living cells, biofouling and blocking of plasmonic centers are key challenges. Here, we have developed a mesoporous Au (AuM) film coated with a Ag nanoparticles (NPs) as a plasmonic sensor (AuM@Ag) to analyze aromatic thiols, which is an example of a small molecule, in the presence of a living cell strain (e.g., MDA-MB-231) as a model living system. The resulting AuM@Ag provides 0.1 nM sensitivity and high reproducibility for thiols sensing. Simultaneously, the AuM@Ag film filters large biomolecules, preventing Raman signals from overlapping produced by large biomolecules. After analysis, the AuM@Ag film undergoes recycling by the full dissolution of the Ag-thiol layer and removal of thiols from AuM. Furthermore, fresh AgNPs are formed for further SERS analysis, which circumvents the Ag oxidation issue. The ease of the AgNPs deposition allows up to 12 cycles of on-demand recycling and sensing even after utilization as a sensor in multicomponent media without enhancement and sensitivity loss. The reported mesoporous film with surface filtering ability and prominent recycling procedure promises to offer a new strategy for the detection of various small molecules in the presence of living cells.

Flexible surface-enhanced Raman scatting substrates: recent advances in their principles, design strategies, diversified material selections and applications

Surface-enhanced Raman scattering (SERS) is widely used as a powerful analytical technology in cutting-edge areas such as food safety, biology, chemistry, and medical diagnosis, providing ultra-fast, ultra-sensitive, nondestructive characterization and achieving ultra-high detection sensitivity even down to the single-molecule level. Development of Raman spectroscopy is strongly dependent on high-performance SERS substrates, which have long evolved from the early days of rough metal electrodes to periodic nanopatterned arrays building on solid supporting substrates. For rigid SERS substrates, however, their applications are restricted by sophisticated pretreatments for detecting solid samples with non-planar surfaces. It is therefore essential to reassert the principles in constructing flexible SERS substrates. Herein, we comprehensively review the state-of-the-art in understanding, preparing and using flexible SERS. The basic mechanisms behind the flexible SERS are briefly outlined, typical design strategies are highlighted and diversified selection of materials in preparing flexible SERS substrates are reviewed. Then the recent achievements of various interdisciplinary applications based on flexible SERS substrates are summarized. Finally, the challenges and perspectives for future evolution of flexible SERS and their applications are demonstrated. We propose new research directions focused on stimulating the real potential of SERS as an advanced analytical technique for commercialization.

Ultrasensitive detection of plant hormone abscisic acid-based surface-enhanced Raman spectroscopy aptamer sensor

Abscisic acid (ABA), as the most common plant hormone in the growth of wheat, can greatly affect the yield when its levels deviate from normal. Therefore, highly sensitive and selective detection of this hormone is greatly needed. In this work, we developed an aptamer sensor based on surface-enhanced Raman spectroscopy (SERS) and applied it for the high sensitivity detection of ABA. Biotin-modified ABA aptamer complement chains were modified on ferrosoferric oxide magnetic nanoparticles (Fe₃O₄MNPs) and acted as capture probes, and sulfhydryl aptamer (SH-Apt)-modified silver-coated gold nanospheres (Au@Ag NPs) were used as signal probes. Through the recognition of the ABA aptamer and its complementary chains, an aptamer sensor based on SERS was constructed. As SERS internal standard molecules of 4-mercaptobenzoic acid (4-MBA) were encapsulated between the gold core and silver shell of the signal probes; the constructed aptamer sensor generated a strong SERS signal of 4-MBA after magnetic separation. When there were ABA molecules in the detection system, with the preferential binding of ABA aptamer and ABA molecule, the signal probes were released from the capture probes, after magnetic separation, leading to a linear decrease in SERS intensity of 4-MBA. Thus, the detection response was linear over a logarithmic concentration range, with an ultra-low detection limit of 0.67 fM. In addition, the practical use of this assay method was demonstrated in ABA detection from fresh wheat leaves, with a relative error (RE) of 5.43-8.94% when compared with results from enzyme-linked immunosorbent assay (ELISA). The low RE value proves that the aptamer sensor will be a promising method for ABA detection.

Core-Shell Plasmonic Nanomaterials toward: Dual-Mode Imaging Analysis of Glutathione and Enhanced Chemodynamic Therapy

A simple process, rich information, and intelligent response are the goals pursued by cancer diagnosis and treatment. Herein, we developed a core-shell plasmonic nanomaterial (Au@MnO₂-DNA), which consisted of a AuNP core with an outer shell MnO₂ nanosheet decorated with fluorophore modified DNA, to achieve the aforementioned aims. On the basis of the unique optical properties of plasmonic nanoparticles and the oxidability of the shell MnO₂, scattering signal and fluorescence (FL) signal changes were both related to the expression level of glutathione (GSH), for which a dual-mode imaging analysis was successfully achieved on single optical microscope equipment with one-key switching. Meanwhile, the product of Mn²⁺ from the reaction between MnO₂ and GSH not only served as a smart chemodynamic agent to initiate Fenton-like reaction for achieving chemodynamic therapy (CDT) of cancer cells but also relieved the side effect of intracellular GSH in cancer therapy. Therefore, the core-shell plasmonic nanomaterials with dual modal switching features and diagnostic properties act as excellent probes for achieving bioanalysis of aberrant levels of intracellular GSH and simultaneously activating the CDT of cancer cells based on the in situ reactions in cancer cells.

SERS Sensors Based on Aptamer-Gated Mesoporous Silica Nanoparticles for Quantitative Detection of Staphylococcus aureus with Signal Molecular Release

This work describes a simple and novel biosensor for the quantitative determination of Staphylococcus aureus (S. aureus) based on target-induced release of signal molecules from aptamer-gated aminated mesoporous silica nanoparticles (MSNs) coupled with surface-enhanced Raman scattering (SERS) technology. MSNs were synthesized and then modified with amino groups by (3-aminopropyl) triethoxysilane to make them positively charged. Next, signal molecules (4-aminothiophenol, 4-ATP) were loaded into the pores of MSNs. Then, negatively charged aptamers of S. aureus were assembled on the surface of MSNs through electrostatic interactions. Upon the addition of S. aureus, the assembled aptamers were specifically bound to the bacteria. Consequently, the "gates" were opened, resulting in the release of 4-ATP from the pores of MSNs. The released molecules were measured by a Raman spectrometer, and the intensity of 4-ATP at 1071 cm^-1 was linearly related to the S. aureus concentration. A silver nanoflower silica core-shell structure (Ag NFs@SiO₂) was prepared and it served as a SERS substrate. Under optimized experimental conditions, a good linear relationship (y = 2107.93 + 1536.30x, R² = 0.9956) in the range from 4.7 × 10 to 4.7 × 10⁸ cfu/mL was observed with a limit of detection of 17 cfu/mL. The method was successfully applied for the analysis of S. aureus in fish samples and the recovery rate was 91.3-109%.

Covalent Amide-Bonded Nanoflares for High-Fidelity Intracellular Sensing and Targeted Therapy: A Superstable Nanosystem Free of Nonspecific Interferences

A nanoflare, a conjugate of Au nanoparticles (NPs) and fluorescent nucleic acids, is believed to be a powerful nanoplatform for diagnosis and therapy. However, it highly suffers from the nonspecific detachment of nucleic acids from the AuNP surface because of the poor stability of Au-S linkages, thereby leading to the false-positive signal and serious side effects. To address these challenges, we report the use of covalent amide linkage and functional Au@graphene (AuG) NP to fabricate a covalent conjugate system of DNA and AuG NP, label-rcDNA-AuG. Covalent coating of abundant amino groups (-NH₂) onto the graphitic shell of AuG NP efficiently facilitates the coupling with carboxyl-labeled capture DNA sequences through simple, but strong, amide bonds. Importantly, such an amide-bonded nanoflare possesses excellent stability and anti-interference capability against the biological agents (nuclease, DNA, glutathione (GSH), etc.). By accurately monitoring the intracellular miR-21 levels, this covalent nanoflare is able to identify the positive cancer cells even in a mix of cancer and normal cells. Moreover, it allows for efficient photodynamic therapy of the targeted cancer cells with minimized side effects on normal cells. This work provides a facile approach to develop a superstable nanosystem showing promising potential in clinical diagnostics and therapy.

Multiplexed SERS Detection of Microcystins with Aptamer-Driven Core-Satellite Assemblies

We describe surface-enhanced Raman spectroscopy (SERS) aptasensors that can indirectly detect MC-LR and MC-RR, individually or simultaneously, in natural water and in algal culture. The sensor is constructed from nanoparticles composed of successive layers of Au core-SERS label-silver shell-gold shell (Au@label@Ag@Au NPs), functionalized on the outer Au surface by MC-LR and/or MC-RR aptamers. These NPs are immobilized on asymmetric Au nanoflowers (AuNFs) dispersed on planar silicon substrates through DNA hybridization of the aptamers and capture DNA sequences with which the AuNFs are functionalized, thereby forming core-satellite nanostructures on the substrates. This construction led to greater electromagnetic (EM) field enhancement of the Raman label-modified region, as supported by finite-difference time-domain (FDTD) simulations of the core-satellite assembly. In the presence of MC-LR and/or MC-RR, the aptamer-functionalized NPs dissociate from the AuNFs because of the stronger affinity of the aptamers with the MCs, which decreases the SERS signal, thus allowing indirect detection of the MCs. The improved SERS sensitivity significantly decreased the limit of detection (LOD) for separate MC-LR detection (0.8 pM) and for multiplex detection (1.5 pM for MC-LR and 1.3 pM for MC-RR), compared with other recently reported SERS-based methods for MC-LR detection. The aptasensors show excellent selectivity to MC-LR/MC-RR and excellent recoveries (96-105%). The use of these SERS aptasensors to monitor MC-LR production over 1 week in a culture medium of M. aeruginosa cells demonstrates the applicability of the sensors in a realistic environment.

Determination of NADH by Surface Enhanced Raman Scattering Using Au@MB@Ag NPs

Nicotinamide adenine dinucleotide (NADH) is an important coenzyme involved in various metabolic processes of living cells. As an important biomarker, NADH is associated with breast cancer and Alzheimer’s disease. In this paper, silver plated gold core–shell nanoparticles containing Raman signal molecules were synthesised on the basis of bare gold. Using the Raman peak corresponding to the 4-mercaptobenzonitrile (MB) silent region C≡N vibration for quantification, while avoiding competition with the precious metal surface binding site to be measured, it can also be free from the interference of endogenous biomolecules. On the one hand, it can correct the working curve, on the other hand, it can avoid competing with the binding site. Compared with the core–shell structure prepared here, the limit of detection (LOD) for NADH was only 10−5 M for bare gold and the LOD for the core–shell structure prepared on the basis of bare gold was 3.3 × 10−7 M. In terms of correction, with Rhodamine 6G (R6G) as a Raman signalling molecule, the R2 value before SERS detection and correction is only 0.9405, and the R2 value after correction increases to 0.9853. The unique fingerprint peak of SERS was used to realise the quantitative detection of NADH, which realizes the detection of NADH in complex biological samples of serum and provides the possibility for expanding the early diagnosis of breast cancer.