Plasmon management in index engineered 2.5d hybrid nanostructures for surface-enhanced raman scattering

Leaky mode resonance (LMR) and optical standing waves (SWs) generated in suitably illuminated vertically aligned supported nanowires (NWs) were demonstrated to enhance the plasmonic electric (E) field behavior of silver nanoparticles (AgNPs) dispersed on the wires. The combination of LMR and SW can significantly enhance the local plasmonic E field around highdensity AgNPs. The results of the finite difference time domain (FDTD) calculations were experimentally verified by comparing the surface-enhanced Raman scattering (SERS) sensitivity, which is directly dependent on the E field, in AgNP-coated silicon, germanium and silver NWs. As LMR and SW are functions of the substrate optical index (n, k), an engineering of the indices predicted a (3.88, 0) theoretical value to maximize the plasmonic E-field on the hybrid scaffold at a given AgNP density. These SERS substrates were utilized for the detection of marine toxins, L-BMAA (2-amino-3-(methylamino) propionic acid hydrochloride) and Malachite green, which are used extensively in seafood. AgNP-decorated silicon NWs, whose index (3.88, 0.02) lies close to the theoretically predicted value, exhibit at least pico-molar sensitivity toward those marine toxins. A plasmon management strategy is developed that could assist in lowering the detection level of environmental toxins by SERS.