Luong Truc Quynh Ngan

SEM morphology of hierarchical AgNFs/Si and the corresponding SERS fingerprint spectrum of fixed S. aureus cells, demonstrating the potential of the substrate for label-free bacterial detection.

Surface-enhanced Raman scattering (SERS) is a powerful technique for detecting trace amounts of chemicals due to its capacity to significantly amplify the Raman signal of the molecules of these substances. This is particularly relevant in food systems where monitoring antibiotic residues is critical for food safety. Traditional SERS substrates typically utilize colloidal silver nanospheres (AgNSs), but anisotropic silver nanoparticles with numerous sharp tips can further enhance SERS sensitivity, enabling lower detection limits suitable for food safety regulations. In this study, we describe a straightforward synthesis of colloidal silver triangular nanoplates (AgTNPls), featuring multiple sharp tips, using only four common reagents: silver nitrate, trisodium citrate, sodium borohydride (NaBH₄) and hydrogen peroxide (H₂O₂), all at room temperature. By carefully controlling the sequence of reagent addition, specifically introducing H₂O₂ after NaBH₄, we achieved a two-step synthesis. In the first step, AgNSs seeds form, and in the second, these seeds convert into AgTNPls, resulting in a colloid of relatively uniform AgTNPls with an edge length of approximately 52 nm. The resulting AgTNPls colloid, combined with an aluminum foil, produced an SERS substrate with high enhancement factor of 3.2 × 10⁹ (using rhodamine 6G as a test molecule). Applied to enrofloxacin (an antibiotic widely used in livestock and aquaculture) detection, this substrate achieved a detection limit as low as 0.39 µg/L (0.39 ppb), with enrofloxacin detectable at concentrations down to 5 µg/L. This highly sensitive SERS substrate holds great promise for rapid, accurate detection of antibiotic residues in food products, aiding regulatory compliance and food safety assurance.

3D urchin-like TiO₂@Gr-AuNPs (UT@Gr-AuNPs) architecture on silicon substrate was used as a SERS substrate for detection and photocatalytic degradation of R6G under UV light irradiation.

Wool roll-like silver nanoflowers of different sizes were obtained by reducing AgNO ₃ with ascorbic acid in the presence of citric acid in a mixed ethanol/water solution with different volume ratios.

Surface-Enhanced Raman Scattering (SERS) is a technique currently widely used in the identification and quantification of organic and biological molecules at low concentrations, in which an important application is the detection of pesticide residues in food. To accomplish this task, SERS substrates with high Raman enhancement factor and good reproducibility are required. One of the most commonly used SERS substrates is the SERS substrate made of silver nanoparticles immobilized on a solid substrate. In this report we first present the results of electrochemical deposition of silver nanoparticles on the silicon surface using ethanol electrolyte solution. Thanks to both factors, electrochemical deposition (instead of electroless) and ethanol electrolyte (instead of aqueous), under optimal conditions, on the surface of silicon a monolayer of silver nanoparticles grew, which are uniform in shape and size and are arranged very close to each other with nanometer separation. Next we report on the use of fabricated arrays of silver nanoparticles in the role of a SERS substrate. To test the performance of the SERS substrate, the probe molecules used were molecules of difenoconazole, a well-known fungicide. Results showed that difenoconazole could be detected with a detection limit of 0.023 ppm (5.6 × 10⁻⁸ M).

Metal-assisted chemical etching of silicon is a commonly used method to fabricate vertical aligned silicon nanowire arrays. In this report we show that if in the above method the chemical etching is replaced by the electrochemical one, we can also produce silicon nanowire arrays, but with a special characteristic-extremely strong photoluminescence. Further research showed that the huge photoluminescence intensity of the silicon nanowire arrays made by metal-assisted electrochemical etching is related to the anodic oxidation of the silicon nanowires which has occurred during the electrochemical etching. It is most likely that the luminescence of the silicon nanowire arrays made with metal-assisted electrochemical etching is the luminescence of silicon nanocrystallites (located on the surface of silicon nanowire fibers) embedded in a silicon oxide matrix, similar to that in a silicon rich oxide system.