A protein A modified Au-graphene oxide composite as an enhanced sensing platform for SPR-based immunoassay.

A sensitive and selective wavelength modulation surface plasmon resonance (SPR) biosensor is reported with Au nanoparticle decorated graphene oxide (GO) as an enhanced sensing platform. GO sheets possess favourable water dispersibility, good biocompatibility and high loading capacity. An Au-GO composite with the Au spheres size of 15-20 nm was synthesized and modified with staphylococcal protein A (SPA). The as-prepared composite assembles directly onto the Au film surface of the SPR sensor. Meanwhile, SPA specifically recognizes and binds the Fc portion of antibodies, contributing to highly oriented antibody immobilization on the chip surface without any antibody modification. Consequently, the biosensor based on the SPA modified Au-GO composite exhibits a satisfactory response to rabbit IgG in the concentration range of 0.1-50 μg mL(-1), while the biosensor based on the sole SPA layer for antibody immobilization shows a response in the concentration range of 1.6-50 μg mL(-1). Experimental results show that the SPA modified Au-GO composite can be successfully used for the signal amplification of immunosensors, thereby improving the sensitivity and obviating the need of chemical modification of the antibody.