Spectral dependence of gold nanorods on the optical properties of substrates and adsorption of polypeptides

Gold nanorods (NRs) wrapped with poly(styrene sulfonate) were fixed on glass or indium tin oxide (ITO) substrates that had been modified with polycationic polymer or 3-aminopropyltrimethoxysilane layers. The spectral properties of the NRs were affected by the refractive indices of the substrates and their surface conditions. Surface modification with poly(styrene sulfonate) and avidin molecules shifted the longitudinal surface plasmon (SP) bands to longer wavelength when the substrates were placed in air. In water and a buffered solution, red shifts of the SP bands were also observed, but the shift shifts were not as large as that in the air. It was found that refractive indices around the polymer-wrapped NRs were sensitive to the adsorption of organic molecules even in the aqueous media.