Self-assembled film of hydrophobins on gold surfaces and its application to electrochemical biosensing

Hydrophobins are small fungal proteins which self-assemble on interfaces and significantly change the surface wettability. The self-assembled film of hydrophobin HFBI on a gold surface improved the surface hydrophilicity with water contact angle changing from 73.8 ± 1.8° to 45.3 ± 1.4°. A quartz crystal microbalance (QCM) analysis indicated that the HFBI coverage density on a gold surface was 588 ng cm−2, and the self-assembled film remained stable under different pH values ranging from 1 to 13. A hydrophilic protein such as choline oxidase (ChOx) was then successfully immobilized on the HFBI modified gold surface. To evaluate the bioactivity of immobilized enzyme, an amperometric choline biosensor was constructed based on the Gold/HFBI/ChOx electrode, which produced as large as 4578.27 nA response current by 0.238 μg immobilized ChOx, when saturated by choline substrate. Comparing with our choline biosensors previously reported, the HFBI self-assembled film exhibited excellent capability to preserve the bioactivity of ChOx, hence a great potential in electrochemical biosensing is suggested.