Dielectric film for biosensor application

The surface of dielectric barium strontium titanate (BST) film was modified by a self-assembled monolayer (SAM) of mono-dodecyl phosphate (DDPO4) from aqueous solutions of alkyl phosphate ammonium salts. The phosphate terminal groups were believed to anchor to the Ti atoms through oxygen bridges with the terminal methyl groups exposed outwardly, resulting in a highly hydrophobic surface with an advancing water contact angle (CA) of 99.8°, compared with the original CA 40.8° of the bare BST surface. X-ray photoelectron spectroscopy (XPS) showed the dense coverage of the SAM and immobilized BSA layer. The microscopic features and the biosensing properties were characterized by atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS) in the presence of [Fe(CN)6]3−/4− as a redox couple. AFM images revealed that bovine serum albumin (BSA) was well-immobilized on the DDPO4-modified BST surface. The EIS showed a significant increase in the electron-transfer resistance. Specific binding of anti-BSA on the immobilized BSA surface was evidenced by AFM imaging and EIS. It was demonstrated that the specific binding of anti-BSA can be quantitatively detected by measuring the electron-transfer resistance. The investigation indicated the potential application of the dielectric film for electrochemical biosensors.