Label-free optical diagnosis of hepatitis B virus with genetically engineered fusion proteins.

A simple biosensing strategy for the diagnosis of patients with hepatitis B virus (HBV) was developed. This study can be divided into two themes, both of which utilized gold-binding polypeptide (GBP) fusion proteins: HBV surface antigen PreS2 (HBsAg) detection with GBP-fused single chain antibody (GBP-ScFv) and anti-HBsAg detection with GBP-HBsAg. These GBP-fusion proteins can directly bind onto the gold surface via the high binding affinity between the GBP and the gold surface, while at the same time, orient the recognition sites toward the sample for target binding. This one-step immobilization strategy, which greatly simplifies a fabrication process as well as maintaining biological activity of the recognition elements, can be applied to optical analytical methods, such as surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR).