SERS characteristics analysis of composite Ag/SiO₂ sinusoidal grating

In current microfluidic-SERS(surface-enhanced Raman scattering) detection fields, noble metal nanoparticle sols are commonly used but a limited number of hot spots exist per unit of its volume and the areas of these hot spots are very small. Another common SERS substrate, the noble metal nano-three-dimensional array, has a time-consuming fabrication process and is costly to manufacture, while also succumbing to the memory effect. In this paper, a composite Ag/SiO₂ sinusoidal grating SERS substrate structure integrated into a microchannel is proposed, which can be fabricated by laser interference photolithography and has no need for prefabricated photomasks. Large area and low-cost SERS substrates can be created simply and rapidly by using this method. The mathematical evaluation model of electric field enhancement near the composite sinusoidal grating surface is established with rigorous coupled wave analysis(RCWA). The mathematical model of the surface plasmon polaritons(SPP) coupling absorption is derived. The optimization matching relation of incident light, the composite sinusoidal grating structure and the dielectric constant of the external environment are analyzed. The optimal composite sinusoidal grating structure was obtained when the wavelength of incident light was 785 nm. The composite sinusoidal grating was prepared and its SERS performance was verified experimentally, proving that the SERS enhancement factor(EF) can reach 10⁴.