Photoelectrochemical detection of human epidermal growth factor receptor 2 based on Co.sub.3O.sub.4-ascorbic acid oxidase as multiple signal amplifier

A sensitive photoelectrochemical (PEC) sensor based on hexagonal carbon nitride tubes (HCNT) as photoactive material was prepared for the detection of human epidermal growth factor receptor 2 (HER2). Magnetic Fe.sub.3O.sub.4 nanospheres (MNs) modified with anti-HER2 antibodies were employed for highly efficient capture of HER2 from serum sample, and Co.sub.3O.sub.4 nanoparticles (Co.sub.3O.sub.4 NPs) modified with ascorbic acid oxidase (AAO) as well as HER2 aptamer were used for signal amplification. When the aptamer-Co.sub.3O.sub.4-AAO probe was captured onto the electrode surface through the specific binding of the aptamer with HER2, the photocurrent intensity decreased. This was because Co.sub.3O.sub.4 NPs competed with HCNT for consumption of the excitation energy. As a consequence AAO catalyzed the oxidation of the electron donor (AA), and the aptamer-Co.sub.3O.sub.4-AAO probe increased the steric hindrance at the electrode surface, leading to significant photocurrent intensity decrease, thus realizing multiple signal amplification. Based on this signal amplification strategy, at 0 V (vs Ag/AgCl), the PEC sensor shows a wide linear response ranging from 1 pg mL.sup.-1 to 1 ng mL.sup.-1 with a low detection limit of 0.026 pg mL.sup.-1 for HER2. Importantly, the prepared PEC sensor was applied for detection of HER2 in human serum samples with recoveries between 98.8 and 101%. Graphical abstract