Analysis of bimetallic nanorod dimer biosensors for label-free molecule detection

Abstract

A bimetallic nanorod dimer biosensor based on localized surface plasmon resonance (LSPR) has been proposed in this thesis. Larger absorption and stronger electric eld coupling have been achieved when a gold (Au) core nanorod is coated with silver (Ag) shell layer (Au@Ag). The optical response, e.g., dielectric function of this bimetallic monomer has been modeled analytically with the help of Clausius-Mossotti equation. Using the developed model, the polarizability, dipole moment, and absorption crosssection of the Au@Ag nanorod dimer have been calculated. In order to investigate the molecular sensitivity, this bimetallic dimer has been simulated without and with the presence of label-free proteins using the nite di erence time domain (FDTD) technique. Lysozyme (Lys), human serum albumin (HSA), human -immunoglobulin (IgG), adenomatous polyposis coli (APC) and human brinogen (Fb) proteins have been used to calculate the resonance shifts from the FDTD simulations. In addition, e ects of physical parameters, orientations and environment of Au@Ag nanorods in the dimer system have also been studied through peak shifts for an APC protein sample. The shift values from the proposed structure have been found to be 6%{ 30% larger compared to the conventionally used Au dimer sensors. Therefore, better sensitivity performance of the Au@Ag nanorod dimers would pave the way for its extensive research in biochemical and pharmaceutical industries.