A novel photoelectrochemical aptasensor for alpha-fetoprotein assay based on a 3D self-supporting TiO2/CdS/BiOI Z-scheme heterojunction

Alpha-fetoprotein (AFP) is a characteristic marker of liver cancer, and its accurate detection is of great significance for the early detection of liver cancer. This study utilizes visible light as the excitation light source, employs electrochemical measurement, and incorporates the AFP aptamer as the biorecognition element to construct a photoelectrochemical (PEC) biosensor for the highly sensitive detection of AFP. A Z-scheme heterostructure is constructed via a two-step hydrothermal method, and CdS nanoparticles are anchored on TiO₂NRA and BiOI nanosheets with high specific surface areas. The photocurrent response of the BiOI/CdS/TiO₂NRA composite material is 4.5 times that of TiO₂NRA. By analyzing the energy band positions, the electron transfer mechanisms of Z-scheme heterojunctions in CdS/TiO₂NRA and BiOI/CdS photoactive materials were elucidated. Subsequently, the AFP aptamer was immobilized on the base electrode surface via the CN structure to fabricate a self-supporting sensing platform. The PEC biosensor demonstrates excellent detection performance within the linear range of 1 nM ∼ 250 nM, exhibiting high selectivity and the detection limit is 0.59 nM (S/N = 3). It has been effectively utilized for the detection of AFP in blood, providing a practical method for early detection and prevention of liver cancer, and also offering new insights for the design of other similar characteristic marker biosensors.