Natural oxidation of Ti3C2Tx to construct efficient TiO2/Ti3C2Tx photoactive heterojunctions for advanced photoelectrochemical biosensing of folate-expressing cancer cells

The rapid-charge carrier recombination and low conductivity are critical in devising an efficient photoelectrochemical (PEC) sensor. Herein, we propose partial oxidation of few-layered MXene (Ti3C2Tx) to construct a photo-active TiO2/Ti3C2Tx platform that could be configured for PEC sensing of folate receptors (FR), particularly, FR-expressing breast cancer cells (MDA-MB-231). MXene-Ti3C2Tx dispersion was oxidized in natural-open air conditions, where continuous exposure for six (06) days allowed for homogeneous in-situ growth of TiO2 over MXenes nanosheets (MX-06). This exposure enabled partial oxidation of MXene-sheets with a balanced TiO2 to MXene content that could exhibit improved photoresponsive characteristics owing to the synergism of redox-active TiO2 and highly conductive underlying Ti3C2Tx. The photoelectrode was then adapted for biorecognition by conjugating chitosan and folic acid (FA) networks, which permitted selective detection of FR-expressed cells with significant antifouling capabilities against common proteins such as bovine serum album (BSA), hemoglobin, and immunoglobulin G. (Ig G). The detection mechanism relies on FA's strong affinity for cancer cell folate receptors, which proportionally inhibited the photoelectrodes PEC oxidation response to ascorbic acid (AA)(mediator). The proposed inhibition strategy enabled sensitive detection of FR-expressed MDA-MB-231 cells in the concentration range of 1 × 102 to 2 × 107 cells/mL with a detection limit of 1.01 cells/mL (S/N = 3).