Fabrication of Ag–ZnO NRs SERS substrates for abamectin detection: the effect of Ag sputtering times and ZnO sol concentrations in seed layer preparation on SERS performance

In this study, a surface-enhanced Raman scattering (SERS) substrate based on uniform silver nanoparticles/ZnO nanorods arrays (Ag–ZnO NRs) is prepared by combining of hydrothermal synthesis and magnetron sputtering method. The Ag sputtering time and ZnO sol concentrations in seed layer preparation affect significantly on SERS enhancement. At the optimal condition, the average size of the Ag NPs is about 30 nm and uniform distribution on the surface of the ZnO NRs which are beneficial to the sensitivity of the SERS signal. ZnO NRs arrays which have the uniform size, vertical orientation, and evenly distribution also contribute to an enhancement of Raman signal. The electromagnetic hot spots originated from individual Ag particles, the nanogaps spacing between the Ag particles on the single ZnO nanorod, the gaps between the Ag particles on the adjacent ZnO nanorods, and Ag/ZnO interface are main reasons determining the sensitivity of SERS substrate. For abamectin detection, the Ag–ZnO NRs substrate has exhibited sensitivity as low concentration as 1 ppm. The vibrations peaks of abamectin molecules are identified and investigated.