Attomolar detection of protein biomarkers using biofunctionalized gold nanorods with surface plasmon resonance

This paper describes an ultrasensitive surface plasmon resonance (SPR) detection method using biofunctionalized gold nanorods for the direct detection of protein biomarkers. Immunoglobulin E (IgE), which has separate antibody and DNA aptamer binding sites, was chosen as a model protein for which a sandwich assay platform was designed. Detection was achieved via the specific adsorption of unlabelled IgE proteins onto the surface immobilized aptamer followed by the specific adsorption of anti-IgE coated gold nanorods (Au-NRs). Using the biofunctionalized nanorods in conjunction with SPR, we were able to directly measure IgE proteins at attomolar concentrations. This is a remarkable 10 ⁸ enhancement compared to conventional SPR measurements of the same surface sandwich assay format 'anti-IgE/IgE/surface bound IgE-aptamer' in the absence of gold nanorod signal amplification.