A semiconductor photoelectrochemical (PEC) aptamer sensor has been widely researched in recent years because of its broad application prospects. However, a universal PEC sensor has not been achieved, and its sensing mechanism based on a photogenerated carrier transfer process has yet to be elucidated. Herein, a novel hydrogen-treated TiO2 nanorod array one-dimensional (1D)/Ti2CO X MXene two-dimensional (2D) (H-TiO2/Ti2CO X ) PEC aptamer sensor is presented, which achieved a record detection range of 10–9–103 μg/L and a limit of detection (LOD) of 1 fg/L for microcystic toxins-LR detection. Besides, the PEC sensor can also test serotonin (5-HT), aflatoxin-B1, and prostate-specific antigen (PSA) with high performance by changing the aptamers, exhibiting favorable application universality. Furthermore, a new phenomenon of a switchable enhanced/suppressed photocurrent detection signal was discovered from H-TiO2/Ti2CO X PEC aptamer sensors through the variation of the length of the TiO2 nanorod. Meanwhile, it reveals that the steric hindrance effect determines the photogenerated hole transfer and depolarization processes, which is proposed for the first time as the predominant mechanism of the switchable enhanced/suppressed photocurrent signal for PEC sensors, giving possibilities to develop PEC sensors with higher efficiency.

The stability enhancement mechanism of honeycomb borophene on a typical MXene material, known as Ti 2 C, was investigated systematically by theoretical energetic and kinetic studies. On this basis, the epitaxial growth model has been proposed by comparative total energy calculations of boron adatoms and islands. Our results reveal that the planar honeycomb borophene layer is energetically favorable on a Ti 2 C substrate with desirable kinetic and thermodynamic stability. Strong substrate-induced interactions, including charge redistribution, orbital hybridization, and covalent bond formation, are crucial factors for enhanced stability. Boron adatoms easily migrate and form clusters along hollow sites on the surface due to the limit of the potential energy surface, resulting in the formation of six-membered boron islands as the local minimum. Adatoms are preferred to bond with dangling bonds at the step edge of clusters, leading to the spread or combination of islands. Our calculating results indicate that Ti 2 C is a potential substrate for the epitaxial growth of honeycomb borophene, which may provide important insights into searching potential two-dimensional substrates.

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