Research Progress of SERS Sensors Based on Hydrogen Peroxide and Related Substances

Hydrogen peroxide (H2O2) has an important role in living organisms, and its detection is of great importance in medical, chemical, and food safety applications. This review provides a comparison of different types of Surface-enhanced Raman scattering (SERS) sensors for H2O2 and related substances with respect to their detection limits, which are of interest due to high sensitivity compared to conventional sensors. According to the latest research report, this review focuses on the sensing mechanism of different sensors and summarizes the linear range, detection limits, and cellular applications of new SERS sensors, and discusses the limitations in vivo and future prospects of SERS technology for the detection of H2O2.

Smartphone-based on-site detection of hydrogen peroxide in milk by using a portable ratiometric fluorescent probe

The on-site detection of hydrogen peroxide (H₂O₂) is important for maintaining food safety as the ingestion of H₂O₂ can lead to serious pathological conditions. However, most reported fluorescent probes require a fluorometer to ensure readable signal output and reliable detection result. Consequently, the fluorescent detection of H₂O₂ can be realized only within a standard laboratory setting. Herein, we report a novel supramolecular strategy that can successfully convert the typical off-on response to H₂O₂ into a ratiometric response, which allows the on-site detection of H₂O₂ when used in conjunction with a smartphone-based 3D-printed miniaturized testing system. This method has acceptable sensitivity, good anti-interference ability, and desirable accuracy compared to a standard detection method. More importantly, this portable ratiometric method can be used to detect H₂O₂ residue in commercial milk samples with the simple testing apparatuses.

Dual Function of 4-Aminothiophene in Surface-Enhanced Raman Scattering Application as an Internal Standard and Adsorbent for Controlling Au Nanocrystal Morphology

The sensitivity and quantitative accuracy of surface-enhanced Raman scattering (SERS) are the main factors that restrict its application. Here, novel Au nanoscale convex polyhedrons (Au NCPs) were designed and fabricated to solve these problems via an embedded standard, including eight pods and six small protrusions. Spherical Au seeds regrew into different sizes of Au NCPs with a face-centered cubic structure. This morphology is due to the dual mechanism of the 4-aminothiophene (4-ATP) molecule that serves as an internal standard and a surface ligand regulator combined with the regulatory role of hexadecyl trimethyl ammonium chloride. The results show that Au NCPs were enclosed by high-index {12 9 1} facets, which greatly improved the local plasma resonance and reduced the lowest SERS detectable concentration of pyrene in standard seawater to 0.5 nM. An effective reference was produced by embedding 4-ATP with a relative standard deviation value less than 2.97% (in the same batch) and 3.92% (between different batches). Our research offers a new strategy for morphological regulation of metal nanocrystals, which is useful for the preparation of highly sensitive SERS substrates and trace analysis.

Au-NP-Decorated Cotton Swabs as a Facile SERS Substrate for Food-Safety-Related Molecule Detection

Recently, food safety has received considerable attention, and various analytical techniques have been employed to monitor food quality. One of the promising techniques in this domain is the surface-enhanced Raman scattering (SERS) technique. This study developed a facile, cost-effective SERS method by supporting a wipe-type substrate with a small-head cotton swab. We fabricated Au-nanoparticle (NP)-decorated cotton swabs (CS-Au NP) via the dropwise addition of gold colloid on the cotton fibers. These swabs exhibit reduced gold colloid consumption and a compact fiber structure, allowing for the uniform distribution of Au NPs and easy capture of molecular signals. Experiments were conducted to obtain a CS-Au NP wiper performance optimized for cotton swab selection, NaCl concentration, and Au NP layers. The Raman reporter molecule 4-mercaptopyridine was detected at a concentration of 1 × 10^-8 M and a relative standard deviation of ≤10%. The proposed SERS platform enables the facile and reliable detection of food-safety-related molecules such as malachite green on the surface of fruits and vegetables. This paper describes the development of an easy, cost-effective, and environment-friendly method of detecting food-safety-related molecules on various food surfaces through SERS.

Au@Ag nanostructures for the sensitive detection of hydrogen peroxide

Hydrogen peroxide (H₂O₂) is an important molecule in biological and environmental systems. In living systems, H₂O₂ plays essential functions in physical signaling pathways, cell growth, differentiation, and proliferation. Plasmonic nanostructures have attracted significant research attention in the fields of catalysis, imaging, and sensing applications because of their unique properties. Owing to the difference in the reduction potential, silver nanostructures have been proposed for the detection of H₂O₂. In this work, we demonstrate the Au@Ag nanocubes for the label- and enzyme-free detection of H₂O₂. Seed-mediated synthesis method was employed to realize the Au@Ag nanocubes with high uniformity. The Au@Ag nanocubes were demonstrated to exhibit the ability to monitor the H₂O₂ at concentration levels lower than 200 µM with r² = 0.904 of the calibration curve and the limit of detection (LOD) of 1.11 µM. In the relatively narrow range of the H₂O₂ at concentration levels lower than 40 µM, the LOD was calculated to be 0.60 µM with r² = 0.941 of the calibration curve of the H₂O₂ sensor. This facile fabrication strategy of the Au@Ag nanocubes would provide inspiring insights for the label- and enzyme-free detection of H₂O_2.

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.

A novel electrochemical immunosensor based on PdAgPt/MoS2 for the ultrasensitive detection of CA 242

Dynamic monitoring of tumor markers is an important way to the diagnosis of malignant tumor, evaluate the therapeutic effect of tumor and analyze the prognosis of cancer patients. As a tumor marker of digestive tract, CA242 is often used to Assess the therapeutic effect of colorectal cancer and pancreatic cancer. In this study, immunosensor technology was used to detect CA242. PdAgPt nanocomposites, which have great advantages in biocompatibility, electrical conductivity and catalytic properties, were prepared by hydrothermal synthesis method. The prepared PdAgPt nanocomposites were loaded onto the surface of molybdenum disulfide (MoS₂) with large surface area, and the new nanocomposites were synthesized. Using PdAgPt/MoS₂ as signal amplification platform, the label-free CA242 electrochemical immunosensor has a wide detection range that extends from 1*10⁻⁴ U/ml to 1*10² U/ml and a low detection limit (LOD, 3.43*10⁻⁵ U/ml) after optimization of experimental conditions. In addition, the CA242 immunosensor designed in this study also performed well in the evaluation of repeatability, selectivity and stability, and was successfully used for the detection of CA242 in human serum sample. Therefore, the label-free electrochemical immunosensor constructed in this study has a broad application prospect in the detection of clinical biomarkers.

SERS and Indicator Paper Sensing of Hydrogen Peroxide Using Au@Ag Nanorods

The detection of hydrogen peroxide and the control of its concentration are important tasks in the biological and chemical sciences. In this paper, we developed a simple and quantitative method for the non-enzymatic detection of H₂O₂ based on the selective etching of Au@Ag nanorods with embedded Raman active molecules. The transfer of electrons between silver atoms and hydrogen peroxide enhances the oxidation reaction, and the Ag shell around the Au nanorod gradually dissolves. This leads to a change in the color of the nanoparticle colloid, a shift in LSPR, and a decrease in the SERS response from molecules embedded between the Au core and Ag shell. In our study, we compared the sensitivity of these readouts for nanoparticles with different Ag shell morphology. We found that triangle core-shell nanoparticles exhibited the highest sensitivity, with a detection limit of 10^-4 M, and the SERS detection range of 1 × 10^-4 to 2 × 10^-2 M. In addition, a colorimetric strategy was applied to fabricate a simple indicator paper sensor for fast detection of hydrogen peroxide in liquids. In this case, the concentration of hydrogen peroxide was qualitatively determined by the change in the color of the nanoparticles deposited on the nitrocellulose membrane.

Light responsive Fe-Tcpp@ICG for hydrogen peroxide detection and inhibition of tumor cell growth

In this work, we synthesized Fe-Tcpp@ICG(ICG, Indocyanine green) with light stimuli-response through 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (Fe-Tcpp) loaded ICG by electrostatic adsorption. The morphology and properties of Fe-Tcpp and Fe-Tcpp@ICG were characterised by ultraviolet-visible absorption spectrometer, X-ray diffraction, thermogravimetric analyzer and transmission electron microscope, respectively. A non-enzymatic photoelectrochemical sensor based on Fe-Tcpp@ICG was constructed to quantitatively detect hydrogen peroxide in tumor microenvironment. Under the optimal conditions, the linear range of detecting hydrogen peroxide was 0.01-50 mmol/L with detection limit of 0.2 μmol/L (S/N = 3). This sensor proposed a simple, fast, sensitive and label-free method for the detection of hydrogen peroxide. Moreover, the results also showed that the Fe-Tcpp@ICG can catalyze the decomposition of hydrogen peroxide to generate singlet oxygen, which can kill tumor cells. These indicated that this material was expected to be used for detecting hydrogen peroxide and inhibition of tumor cell growth.

Hierarchically Assembled Plasmonic Metal-Dielectric-Metal Hybrid Nano-Architectures for High-Sensitivity SERS Detection

In this work, we designed and prepared a hierarchically assembled 3D plasmonic metal-dielectric-metal (PMDM) hybrid nano-architecture for high-performance surface-enhanced Raman scattering (SERS) sensing. The fabrication of the PMDM hybrid nanostructure was achieved by the thermal evaporation of Au film followed by thermal dewetting and the atomic layer deposition (ALD) of the Al₂O₃ dielectric layer, which is crucial for creating numerous nanogaps between the core Au and the out-layered Au nanoparticles (NPs). The PMDM hybrid nanostructures exhibited strong SERS signals originating from highly enhanced electromagnetic (EM) hot spots at the 3 nm Al₂O₃ layer serving as the nanogap spacer, as confirmed by the finite-difference time-domain (FDTD) simulation. The PMDM SERS substrate achieved an outstanding SERS performance, including a high sensitivity (enhancement factor, EF of 1.3 × 10⁸ and low detection limit 10^-11 M) and excellent reproducibility (relative standard deviation (RSD) < 7.5%) for rhodamine 6G (R6G). This study opens a promising route for constructing multilayered plasmonic structures with abundant EM hotspots for the highly sensitive, rapid, and reproducible detection of biomolecules.

Optimization of Surface-Enhanced Raman Spectroscopy Detection Conditions for Interaction between Gonyautoxin and Its Aptamer

This study aimed to optimize the detection conditions for surface-enhanced Raman spectroscopy (SERS) of single-stranded DNA (ssDNA) in four different buffers and explore the interaction between gonyautoxin (GTX1/4) and its aptamer, GO18. The influence of the silver colloid solution and MgSO₄ concentration (0.01 M) added under four different buffered conditions on DNA SERS detection was studied to determine the optimum detection conditions. We explored the interaction between GTX1/4 and GO18 under the same conditions as those in the systematic evolution of ligands by exponential enrichment technique, using Tris-HCl as the buffer. The characteristic peaks of GO18 and its G-quadruplex were detected in four different buffer solutions. The change in peak intensity at 1656 cm⁻¹ confirmed that the binding site between GTX1/4 and GO18 was in the G-quadruplex plane. The relative intensity of the peak at 1656 cm⁻¹ was selected for the GTX1/4–GO18 complex (I₁₆₅₆/I₁₀₉₉) to plot the ratio of GTX1/4 in the Tris-HCl buffer condition (including 30 μL of silver colloid solution and 2 μL of MgSO₄), and a linear relationship was obtained as follows: Y = 0.1867X + 1.2205 (R² = 0.9239). This study provides a basis for subsequent application of SERS in the detection of ssDNA, as well as the binding of small toxins and aptamers.

Horseradish peroxidase-repeat assay based on tyramine signal amplification for highly sensitive H2O2 detection by surface-enhanced Raman scattering

A new and simple surface-enhanced Raman scattering (SERS) biosensor based on the tyramine signal amplification (TSA)-triggered formation of horseradish peroxidase (HRP) repeats on a gold sensing chip was designed for the highly sensitive detection of hydrogen peroxide (H₂O₂). Initially, gold wafers were functionalized with HRP as sensing chips. Then, the HRP immobilized on the chips triggers the TSA reaction to transform the tyramine-HRP conjugate into a tyramine-HRP repeat array. With the aid of the target H₂O₂, the HRP repeats catalyze the oxidation of o-phenylenediamine (OPD) and produce an enzyme catalytic product with a different chemical structure, thus altering the fingerprint of the SERS spectra from that of OPD. H₂O₂ can be quantitatively analyzed according to the change in SERS signal intensity. On the basis of the TSA strategy, the proposed method allows the detection of H₂O₂ with a limit of detection (LOD) of 0.8 × 10^-8 M. The as-prepared SERS sensor can achieve high-sensitivity H₂O₂ detection with a small amount of sample for each analysis. Therefore, this sensor exhibits significant potential for application in bioanalysis.

Therapeutic Applications of Nanozymes in Chronic Inflammatory Diseases

Since the discovery of horseradish peroxidase-like activity of magnetite nanoparticles in 2007, many researchers have investigated different types of nanoparticles that show enzyme-like activities, namely, nanozymes. Nanozymes possess high efficiency, stability, and low production costs compared to natural enzymes. Thus, nanozymes have already been widely studied in various domains including medical science, food industry, chemical engineering, and agriculture. This review presents the utilization of nanozymes in medicine and focuses particularly on their therapeutic applications in chronic inflammatory diseases because of their antioxidant-like activity. Furthermore, the treatment of chronic inflammatory diseases with nanozymes of different materials was introduced emphatically.

Rapid, ultrasensitive and non-enzyme electrochemiluminescence detection of hydrogen peroxide in food based on the ssDNA/g-C3N4 nanosheets hybrid

Hydrogen peroxide (H2O2) is usually used as a fungicide in food, it is carcinogenic, accelerates aging or inducing toxic effects such as cardiovascular disease. Herein, to meet the demand for effective and fast detection of H2O2 in food, a novel non-enzymatic electrochemiluminescence (ECL) sensor based on single-stranded DNA (ssDNA)/g-C3N4 nanosheets (NS) was established. The ssDNA/g-C3N4 NS hybrid was prepared by simple mixing g-C3N4 NS and ssDNA solution together. The prepared ssDNA/g-C3N4 NS exhibited improved peroxidase-like activity and was modified on a glassy carbon electrode to catalyze the ECL reaction of luminol-H2O2 to amplify the luminescence signal. Under the optimized conditions, the proposed sensor exhibits high sensitivity with a limit of detection (LOD) as low as 33 aM H2O2, which is much lower than the vast majority of reported methods. This method enables the reliable responding to H2O2 from the milk samples within 1 min.

A ferrocene-linked metal-covalent organic polymer as a peroxidase-enzyme mimic for dual channel detection of hydrogen peroxide

A novel ferrocene-linked metal-covalent organic polymer (MCOP-NFC) was synthesized through the Claisen-Schmidt condensation reaction of 1,1'-diacetyl ferrocene and tris(4-formylphenyl)amine. MCOP-NFC acts as a highly efficient artificial enzyme for mimicking peroxidase, and shows good stability in harsh chemical environments including strong bases and acids, and boiling water. Based on the peroxidase-like activity of MCOP-NFC, a highly sensitive dual channel detection method for hydrogen peroxide was developed. For the colorimetric detection strategy, the limit of detection (LOD) reached 2.1 μM, while the limit of detection was found to be as low as 0.08 μM based on the electrochemical detection channel. This study offers a new strategy for the development of an enzyme mimetic on the basis of the covalent assembly of nanostructures, and the proposed electrochemical-colorimetric sensor for H₂O₂ detection has great potential for applications in biology and biomedicine.