Preparation of 3D flexible SERS substrates by mixing gold nanorods in hydrogels for the detection of malachite green and crystal violet.

A simple and cost-effective fabrication method of gold nanorods (AuNRs) nanoparticles hybridized with polyvinyl alcohol hydrogel (AuNR/PVA) for SERS substrate is described. The AuNR/PVA achieves the control of inter-particle nanogap by modulating the density of gold nanorods, and inter-particle nanogap by the spatial deformation of the hydrogel, and the reduction of the gap between the AuNRs deposited on hydrogel makes the SERS enhancement. In addition, the AuNR/PVA substrate maintains high SERS activity after more than 100 cycles of bending and storage in air for 30 days, and the substrate possesses high sensitivity and high reproducibility. Combining a flexible and transparent surface-enhanced Raman spectroscopy (SERS) substrate for in situ detection with a small portable Raman can be applied to scenarios such as environmental detection and hazardous materials detection. The substrate showed excellent SERS activity against malachite green (MG) and crystal violet (CV) with limits of detection of 1.18 × 10-13 M and 7.17 × 10-12 M, respectively. The usability of the proposed SERS substrate was demonstrated by detecting the above contaminants in aquatic water. This work not only utilizes a cost-effective method for mass production but also provides a reliable and convenient platform for the preparation of other noble metal flexible substrates.

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.

A novel "on-off" SERS nanoprobe based on sulfonated cellulose nanofiber-Ag composite for selective determination of NADH in human serum.

A novel S-CNF-based nanocomposite was created using sulfonated cellulose nanofiber (S-CNF) to enable the detection of NADH in serum by surface-enhanced Raman spectroscopy (SERS). The numerous hydroxyl and sulfonic acid groups on the S-CNF surface absorbed silver ions and converted them to silver seeds, which formed the load fulcrum. After adding a reducing agent, silver nanoparticles (Ag NPs) were firmly adhered to the S-CNF surface to form stable 1D "hot spots." The S-CNF-Ag NP substrate demonstrated outstanding SERS performance, including good uniformity with an RSD of 6.88% and an enhancement factor (EF) of 1.23 × 107. Owing to the anionic charge repulsion effect, the S-CNF-Ag NP substrate still maintains remarkable dispersion stability after 12 months of preservation. Finally, S-CNF-Ag NPs' surface was modified with 4-mercaptophenol (4-MP), a special redox Raman signal molecule, to detect reduced nicotinamide adenine dinucleotide (NADH). The results showed that the detection limit (LOD) of NADH was 0.75 µM; a good linear relationship (R2 = 0.993) was established in the concentration range 10-6 - 10-2 M. The SERS nanoprobe enabled rapid detection of NADH in human serum without any complicated sample pretreatment and provides a new potential to detect biomarkers.

Self-calibration SERS sensor with "core-satellite" structure for detection of hyaluronidase activity.

Hyaluronidase expression is known to be upregulated in various pathological conditions. A method based on a combination of ratiometric surface-enhanced Raman scattering (SERS) and magnetic separation is described for the determination of hyaluronidase (HAase) activity. Gold nanospheres (AuNPs) functionalized by 4-mercaptophenylboronic acid (4-MPBA) form stable cyclic esters with diol on hyaluronic acid (HA) by the boronic acid group, while Fe3O4@DTNB@Au modified with mercaptoethylamine (MEA) was used as a capture substrate to bind to the carboxyl group on the surface of HA, forming the "Au@4-MPBA@HA/Fe3O4@DTNB@Au@MEA" "core-satellite" structure. When HAase is present, HA is enzymatically disrupted, resulting in the destruction of the "core-satellite" structure, the SERS signal of 4-MPBA is subsequently weakened. The gold shell in the substrate protects the 5,5'-Dithio bis-(2-nitrobenzoic acid) (DTNB) from the external environment, which makes it become an ideal internal standard (IS) molecule for subsequent calibration. Under optimal conditions, the I1075/I1324 varied in the range of 10-3 - 10 U‧mL-1 HAase activity, with a limit of detection (LOD) of 0.32 mU‧mL-1，below the level of HAase in normal human body fluids. This method has been successfully applied to the determination of HAase activity in urine and is expected to provide a new method in disease detection, especially in the non-invasive detection of bladder cancer.