Coating silver tree-like fractal structure with silica layer for inhibiting chemical reactions of analytes in surface-enhanced Raman scattering

Silica coating is performed onto silver tree-like fractal structures, which are self-grown in a solution, through a wet process using tetraethyl orthosilicate. Surface-enhanced Raman scattering (SERS) of para-aminothiophenol (p-ATP) is measured on the silver tree-like fractal structures with/without silica layer at the excitation wavelength of 532 nm. p-ATP is chemically transformed into dimercaptoazobenzene (DMAB) on the non-coated silver tree-like fractal structures, where DMAB peaks are clearly observed, during the SERS measurements. The DMAB peaks decrease/disappear on the silica-coated ones although the p-ATP peaks are observed. In the results, it is indicated that the chemical transformation is inhibited on the silica-coated ones. The sensitivity is decreased by half compared to the non-coated silver tree-like fractal structures, where the lower detection limit is estimated to be ≈2 × 10${}^{-5}$ mol L${}^{-1}$ for p-ATP. The silica coating is advantageous for inhibiting chemical transformations of analytes, enabling identification/estimation of chemicals in unknown sample with SERS similarly to conventional Raman spectroscopy. (© 2023 Wiley‐VCH GmbH)