A ratiometric photoelectrochemical immunosensor based on g-C3N4@TiO2 NTs amplified by signal antibodies–Co3O4 nanoparticle conjugates

Abstract

Herein, we report a ratiometric photoelectrochemical (PEC) immunosensor coupled with secondary antibodies–Co₃O₄ nanoparticle conjugates (Ab₂–Co₃O₄ NPs) for signal amplification. The Ab₁-g-C₃N₄@TiO₂ NTs and BSA-g-C₃N₄@TiO₂ NTs act as the sensing and reference photoelectrodes, where Ab₁, BSA and TiO₂ NTs are the capture antibodies, bovine serum albumin and TiO₂ nanotube arrays, respectively. In the presence of target Ag, the sensing PEC photocurrent decreases due to the steric hindrance of Ab₁ molecules, which increases the inner resistance of the photoelectrode. The signal-off response is enhanced further using Ab₂–Co₃O₄ NP conjugates due to their steric hindrance effect and the consumption of electron donors by the Co₃O₄ NPs. Furthermore, the performance of the ratiometric PEC platform is tested using alpha-fetoprotein (AFP) as a model antigen. Under the optimal conditions, the concentration of AFP is detected in the range of 0.4 pg mL⁻¹ to 40 ng mL⁻¹ with a detection limit of 0.2 pg mL⁻¹. This ratiometric strategy is beneficial to improve the reliability and anti-interference ability of PEC immunosensors.