Synthesis and functionalization of gold nanorods and their application for plasmonic biosensors

Abstract

Gold nanorods, the anisotropic nanostructured plasmonic materials, are attractive for a number of applications in various fields due to their unique optical properties based on the localized surface plasmon resonance (LSPR). In this study, a modified seed-mediated synthesis of gold nanorods (GNRs) with various aspect ratios, functionalization, and their application for plasmonic bionsensors are described. In the synthesis of gold nanorods, variations in reaction conditions have led to the changes of the aspect ratio of gold nanorods. In the presence of silver ions, high yield of gold nanorods in low aspect ratio (3~4) was synthesized while high aspect ratio nanorods were grown in high yield by adding nitric acid. The effect of pH in the growth solution on the aspect ratio was also investigated. In addition, fine-tuning of the aspect ratio was achieved by additional growth of gold nanorods in the presence of gold ions at high temperature. To utilize short gold nanorods as molecular probes, a new strategy that functionalizes gold nanorods through molecular biomimetics was developed using gold-binding polypeptide (GBP)-fused protein A. The fusion protein with a high affinity to the surface of gold successfully functionalized gold nanorods via the in situ extraction of the unbound cetyltrimethylammonium bromide (CTAB) molecules in the gold nanorod solution. GBP-fused protein A molecules were adsorbed on the surface of gold, partially replacing the CTAB bilayer on the gold nanorods. In order to fabiricate gold nanorod molecular probes (GMPs), anti-C-reactive protein (anti-CRP) was conjugated with gold nanorods through the binding interaction between the protein A domain and the non-antigenic site of antibodies. The longitudinal plasmon absorption band of gold nanorods is highly sensitive to the refractive index of the environment, which can be changed by the events on the gold surface such as molecular adsorption on the surface. By using this feature were ...