Z-Scheme Bismuth-Based Ternary Heterostructured Photoelectrochemical Sensor Integrated with Cu3P Nanoparticles as a Multifunctional Signal Probe for Quantifying Circulating Tumor Cells

Circulating tumor cells (CTCs) are widely acknowledged as critical biomarkers for early cancer diagnosis and prognosis, highlighting the urgent need for the development of sensitive and accurate detection methods for CTCs. Herein, a photoelectrochemical (PEC) sensor was developed based on dual Z-scheme Bi2S3/Bi2O2CO3/Zn0.5Cd0.5S heterojunctions as the high-efficiency photoactive material and Cu3P nanoparticles (Cu3P NPs) as the multifunctional signal probe, thereby achieving sensitivity and precise detection of MCF-7 cells. The Z-scheme heterojunction structure significantly enhances the photoelectric conversion efficiency, while Cu3P NPs can suppress the photocurrent through p-n semiconductor quenching and enzyme-mimetic catalytic precipitation, which involves the catalytic oxidation of 4-chloro-1-naphthol (4-CN) to form the insoluble precipitate benzo-4-chloro-hexadienone (4-CD). Coupled with aptamer-functionalized magnetic nanobeads (AptMUC1-MNs) for selective cell capture and enrichment, the PEC sensor achieved an ultrawide linear range (4 cells/mL to 3 × 105 cells/mL) and a remarkably low detection limit (LOD) of 1 cell/mL (S/N = 3), alongside good selectivity, stability, and reproducibility. Furthermore, the successful validation of MCF-7 in human serum samples demonstrates its clinical applicability, highlighting promising potential for early cancer diagnosis and liquid biopsy applications. This work provides a novel PEC sensing platform for sensitive detection of different biomarkers in clinical diagnosis.