Biosensing Using SERS Active Gold Nanostructures.

Surface-enhanced Raman spectroscopy (SERS) has become a powerful tool for biosensing applications owing to its fingerprint recognition, high sensitivity, multiplex detection, and biocompatibility. This review provides an overview of the most significant aspects of SERS for biomedical and biosensing applications. We first introduced the mechanisms at the basis of the SERS amplifications: electromagnetic and chemical enhancement. We then illustrated several types of substrates and fabrication methods, with a focus on gold-based nanostructures. We further analyzed the relevant factors for the characterization of the SERS sensor performances, including sensitivity, reproducibility, stability, sensor configuration (direct or indirect), and nanotoxicity. Finally, a representative selection of applications in the biomedical field is provided.

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 × 109 for the Raman probe solution with 1 pM concentration. Finite Element Method (FEM) simulations are performed for estimating the possible single molecule SERS enhancement.