Highly sensitive determination of CA19-9 using a polydopamine-quenched ZnPc/Ti3C2 Schottky junction-based photoelectrochemical immunosensor

Carbohydrate antigen 19-9 (CA19-9) is a key biomarker for early diagnosis of various malignancies, including lung cancer. Herein, a ZnPc/Ti 3 C 2 heterojunction photosensitive material was synthesized via a novel one-pot strategy and utilized for the first time to construct a photoelectrochemical sandwich immunosensor. Taking advantage of the reducing property of Ti 3 C 2 , gold nanoparticles (AuNPs) were in-situ generated on ZnPc/Ti 3 C 2 to form ZnPc/Ti 3 C 2 /AuNPs nanocomposite, which was then immobilized onto a fluorine-doped tin oxide (FTO) electrode. The AuNPs provided a large surface area and biocompatible interface for efficient loading of capture antibody (Ab1). Upon target CA19-9 recognition, the polydopamine-labeled detection antibody (PDA-Ab2) was introduced, triggering a dual photocurrent quenching mechanism through which PDA acted as an electron trap, capturing photoelectrons from ZnPc/Ti 3 C 2 /AuNPs, while the bulky immunocomplex competed with the electrode for light absorption, reducing irradiation of the photosensitive material. This synergistic quenching enabled highly sensitive CA19-9 detection with a linear range of 0.001–200 U/mL and a detection limit of 0.53 mU/mL. The proposed sensor was successfully applied to CA19-9 determination in serum samples with a relative error within 10% compared with hospital reference values, demonstrating its potential for clinical diagnostics.