Target-Induced Tandem Built-In Electric Fields in the Hollow SnS ₂ /ZIS@ZnS Heterojunction for the Photoelectrochemical Immunoassay

Both sluggish charge transfer and rapid recombination of photogenerated carriers lead to low photoelectric conversion efficiency, still presenting challenges for the photoelectrochemical (PEC) immunoassay. Herein, an innovative PEC sensing platform was proposed based on hollow surface immobilized SnS 2 –ZnIn 2 S 4 shell-ZnS core (SnS 2 /ZIS@ZnS) heterojunctions with a tandem built-in electric field (BIEF). To begin with, Sn(IV)-ZIS@ZnS featuring a hollow core–shell structure was fabricated via lateral epitaxy and adsorption methods. Following the release of H 2 S, after carcinoembryonic antigen (CEA) was specifically recognized via a sandwich-type immune reaction, the released H 2 S reacted with Sn(IV)-ZIS@ZnS to form dual S-scheme heterojunction SnS 2 /ZIS@ZnS. Owing to the inherent differences in work function among these three heterocomponents, a tandem BIEF was established within the heterojunction. The tandem BIEF effectively facilitated charge transfer and enhanced the photoelectric conversion efficiency, ultimately enhancing the photocurrent signal. Benefiting from the pronounced variation in photocurrent, the proposed PEC sensing platform enables highly sensitive detection of CEA, exhibiting a linear detection range from 0.02 to 50 ng/mL with a detection limit as low as 3.5 pg/mL. This work provides a promising avenue to develop a high-performance PEC sensing platform based on BIEF as a signal modulation mechanism for clinical diagnostics.