Photocurrent polarity reversal induced by CuBi2O4 for sensitive photoelectrochemical detection of circulating tumor cells.

Circulating tumor cells (CTCs) are tumor cells that shed from solid tumor lesions and enter the peripheral blood circulation. As a critical contributor to tumor metastasis, their sensitive and accurate detection is of significant importance. Herein, a novel photoelectrochemical (PEC) sensing platform was designed for the detection of CTCs, based on CuBi2O4 induced "photocurrent polarity switching" and catalytic hairpin assembly (CHA) for signal amplification. The MCF-7 breast cancer cell line was used as the model target for evaluation. Specifically, complementary capture DNA (cDNA) were hybridized with EpCAM aptamer (AptEpCAM) and immobilized onto magnetic nanoparticles (MNs). In the presence of MCF-7 cells, the stronger affinity between AptEpCAM and MCF-7 cells led to the release of cDNA via magnetic separation, thereby initiating the subsequent CHA reaction. Importantly, plenty of CuBi2O4 were bound to the surface of CdS quantum dots (QDs) attributed to CHA process, causing the photocurrent polarity switching from anodic photocurrent to cathodic photocurrent, while achieving signal amplification. Based on this, the proposed PEC sensor demonstrated excellent performance in the detection of MCF-7 cells, showing a wide linear detection range from 7 to 1×106 cells/mL and a low detection limit (LOD) of 2 cells/mL (S/N=3). Moreover, the sensor exhibited superior specificity, stability, and reproducibility, along with favorable analytical performance in human serum samples, highlighting its significant potential for application in the biomedical field.