Aptamer-Gated Organic Photoelectrochemical Transistor Biosensor Based on a TiO ₂ -Embedded Vertically Ordered Mesoporous SiO ₂ Film for Sensitive Detection of Carcinoembryonic Antigen

This study developed an organic photoelectrochemical transistor (OPECT) biosensor based on TiO₂-embedded vertically ordered mesoporous silica film (VMSF) modified ITO electrode for ultrasensitive detection of carcinoembryonic antigen (CEA). The sensor uses VMSF as a molecular gate, with the complementary DNA (cDNA) of the CEA aptamer immobilized at the entrances of the mesoporous channels for specific target recognition. In the absence of CEA, cDNA and the aptamer form stable double-stranded DNA (dsDNA), blocking Ru(phen)₃²⁺ from entering the channels and suppressing the photoelectrochemical signal. When CEA is present, it triggers the release of cDNA, which is cleaved by exonuclease I (Exo I), opening the molecular gate and enhancing the photocurrent signal. The Exo I-assisted signal amplification strategy significantly improves the sensor's sensitivity. Additionally, TiO₂ nanoparticles are embedded in the VMSF channels, combining TiO₂'s photoelectrochemical properties with VMSF's molecular sieving function, optimizing charge separation and migration efficiency, and enhancing the photoelectrochemical signal. The energy level alignment between TiO₂ and Ru(phen)₃²⁺ promotes photoelectric conversion efficiency, while the negative charge on VMSF improves antifouling ability and selectivity. Furthermore, the positively charged Ru(phen)₃²⁺ can enters and accumulated in the mesopores of negatively charged VMSF through electrostatic interactions, thereby enhancing the detected signal output under light irradiation. The sensor has a detection range of 100 fg/mL to 500 ng/mL and a minimum detection limit of 0.031 pg/mL, significantly outperforming conventional sensors, demonstrating broad clinical application potential.