A self-assembled fusion protein-based surface plasmon resonance biosensor for rapid diagnosis of severe acute respiratory syndrome

A surface plasmon resonance (SPR)-based biosensor was developed for simple diagnosis of severe acute respiratory syndrome (SARS) using a protein created by genetically fusing gold binding polypeptides (GBPs) to a SARS coronaviral surface antigen (SCVme). The GBP domain of the fusion protein serves as an anchoring component onto the gold surface, exploiting the gold binding affinity of the domain, whereas the SCVme domain is a recognition element for anti-SCVme antibody, the target analyte in this study. SPR analysis indicated the fusion protein simply and strongly self-immobilized onto the gold surface, through GBP, without surface chemical modification, offering a stable and specific sensing platform for anti-SCVme detection. AFM and SPR imaging analyses demonstrated that anti-SCVme specifically bound to the fusion protein immobilized onto the gold-micropatterned chip, implying that appropriate orientation of bound fusion protein by GBP resulted in optimal exposure of the SCVme domain to the assay solution, resulting in efficient capture of anti-SCVme antibody. The best packing density of the fusion protein onto the SPR chip was achieved at the concentration of 10 μg mL⁻¹; this density showed the highest detection response (906 RU) for anti-SCVme. The fusion protein-coated SPR chip at the best packing density had a lower limit of detection of 200 ng mL⁻¹ anti-SCVme within 10 min and also allowed selective detection of anti-SCVme with significantly low responses for non-specific mouse IgG at all tested concentrations. The fusion protein provides a simple and effective method for construction of SPR sensing platforms permitting sensitive and selective detection of anti-SCVme antibody.