Photoelectrochemical immunoassay of alpha-fetoprotein based on a SnO2/In2S3 heterojunction and an enzyme-catalyzed precipitation strategy

Abstract

We report the sensitive photoelectrochemical (PEC) sandwich-type immunosensing of alpha-fetoprotein (AFP) by using SnO₂/In₂S₃ as a novel heterojunction material and horseradish peroxidase (HRP)–CeO₂ as an efficient biolabel. A SnO₂/In₂S₃/fluorine-doped tin oxide (FTO) photoanode was fabricated by hydrothermally synthesizing SnO₂/In₂S₃ and cast-coating it on a FTO slice. A HRP–CeO₂–secondary antibody–bovine serum albumin complex was immunologically immobilized on the photoanode, and the PEC immunoassay of AFP was realized by the HRP and mimetic enzyme CeO₂ catalyzed oxidation of 3-amino-9-ethylcarbazole by H₂O₂ to generate a precipitate with a steric hindrance effect. Under optimized conditions, the value of photocurrent decrease was linear with the common logarithm of AFP concentration from 500 fg mL⁻¹ to 50 ng mL⁻¹, and the limit of detection (S/N = 3) is 0.15 pg mL⁻¹.