ZnO/Ag nanostructures for surface-enhanced Raman spectroscopy: effect of wedge microcavity

Zinc oxide (ZnO) nanostructures with deposited silver (Ag) nanoparticles (NPs) exhibit exceptional opportunities for highly sensitive molecular diagnostics by means of the surface-enhanced Raman spectroscopy(SERS). Here we use the well known method of the hydrothermal synthesis of arrays of ZnO nanorods (NRs), followed with deposition of Ag-NPs by facile photochemical reduction under UV-light illumination to obtain ZnO-NRs/Ag-NPs hybrid structures with superior SERS activity. SERS spectra of a probe analyte, i.e. Rhodamine R6G molecules absorbed in an optimized ZnO-NRs/Ag-NPs structures, are detected in a wide range of the analyte concentration from 10^-6to 10^-14M. Numerical simulations of the light scattering in ZnO-NRs/Ag-NPs structures allow us to show that the wedge-like morphology of ZnO-NRs plays a crucial role in the 3D electromagnetic enhancement of the SERS signal, which can be as high as 3•10⁸for the lowest analyte concentration. The revealed high SERS activity of the obtained ZnO/Ag hybrid nanostructures together with the simplicity of their preparation open new prospects for their application in analytical chemistry, sensorics and photonics.