Study of surface enhanced Raman scattering of IR-780 Iodide molecules using Au-Ag bimetallic nanostructures with blunt and sharp sprouts.

Au-Ag bimetallic nanostructures with blunt and sharp sprouts are synthesized using a high yield one-step synthesis process. For the first time, these nanostructures are obtained at different growth times in the same synthesis process. The synthesized nanostructures are characterized using a field emission-scanning electron microscope, transmission electron microscope, energy dispersive X-ray analyzer, and UV-Visible spectrometer. The plasmon-active substrates are fabricated using synthesized nanostructures with ease. The Raman probe (IR-780 Iodide) molecules are dispersed on the surface of plasmon-active substrates by drop-casting 10 μl of dye solution of concentration ranging from 1 μM to 1 picomolar (pM) on the substrates. The surface enhanced Raman scattering (SERS) spectra are recorded for each concentration. The nanostructures with blunt sprouts are found useful only up to 100 pM. However, this limitation is brought down to 1 pM using nanostructures with sharp sprouts. The normal Raman scattering spectra of molecules and microcrystals are also recorded and compared with the SERS spectra of molecules. The experimental SERS enhancement factor (EF) is found around 1 × 10 for the Raman probe solution with 1 pM concentration. Finite Element Method (FEM) simulations are performed for estimating the possible single molecule SERS enhancement.