Label-free optical biosensor based on localized surface plasmon resonance of twin-linked gold nanoparticles electrodeposited on ITO glass.

A simple low-cost electrochemical approach has been used to directly deposit twin-linked gold nanoparticles (TGNPs) onto transparent indium tin oxide (ITO) coated film glass. The as-prepared TGNPs have a transverse localized surface plasmon resonance (LSPR) band at 540 nm and a longitudinal LSPR band at about 710 nm. The longitudinal LSPR band of TGNPs exhibits higher refractive index sensitivity (245 nm/RIU) than its transverse LSPR band. The resulting "clean" surface of the TGNPs is easy applied to the further modification. The subsequent bioconjugation of TGNP films with goat anti-mouse-immunoglobulin G (anti-m-IgG) is successfully employed for the detection of mouse-immunoglobulin G (m-IgG) in a model based on the specific binding affinity between the antigen and antibody. The spectrophotometric sensor shows concentration-dependent binding for m-IgG. This study reveals a simple and sensitive method to fabricate a label-free optical biosensor based on longitudinal LSPR band of TGNPs on ITO substrate.