The structure and morphology of silver SERS substrates of the nanoisland-type have been optimized to obtain high-intensity surface-enhanced Raman scattering of light. This optimization was carried out by searching the thickness of the sprayed silver layer, the deposition rate, the material sample weight, methods of chemical preparation of the surface before deposition, and changing the annealing regimes after deposition. Due to the formation of a developed surface and obtaining reproducibly small gaps between the metal granules, it was possible to create a SERS structure with a high-Q plasma absorption circuit near a wavelength of 560 nm and therefore efficiently working both at the input resonance at the wavelength of the exciting laser radiation at 532 nm and at the output resonance in the wavelength range of 532-590 nm. The gain of Raman light scattering upon excitation by a laser with a wavelength of 532 nm was 108. In addition, the parameters of protein adsorption, traditionally used in the solid-phase immunochemical analysis as a blocking agent, were studied on these substrates, and bovine serum albumin and casein were chosen as optimal for these purposes. It has been shown that during the adsorption interaction of proteins and the SERS surface based on nanoisland silver and silicon oxide, the laws described in the classical adsorption theory apply. The amplified optical response spectra were measured using an EnSpectr SERS R532 Raman spectrometer with a wide output laser beam with a wavelength of 532 nm and, accordingly, a low power density, which, on the one hand, provides signal averaging over a large area and, on the other hand, prevents the burnout of the investigated substances. It is possible to create various types of highly sensitive and highly specific biosensors for detecting low concentrations of protein molecules (viruses, bacteria, and toxins) on the base of optimized SERS substrates with a high gain and high sorption capacity.
The pictures below show the mechanism for changing the optical properties of substrates and the mechanism for adjusting plasma absorption to a laser wavelength of 532 nm and the output resonance at the Stokes frequency component of Raman light scattering due to a change in the morphology of nanoparticles on the surface of the substrate with changing annealing and deposition parameters.
