<p>MBene is a 2D material stripped from a ternary transition metal boride (MAB). In recent years, attention has gradually shifted from the stripping of MBene to its application. Here, we prepared 2D Mo₂B₂ by treating HCl/H₂O₂ solution for MoAlB, and Mo₂B₂/In₂S₃ photoelectroactive material was fabricated by hydrothermal method to construct a photoelectrochemical (PEC) assay for dengue fever virus DNA (DENVD) detection. Hairpin DNA1 (H₁) was linked to the electrode surface by the Au–S bond. In the presence of DENVD, it opened the end of H₁ and introduced Fc-modified hairpin DNA2 (H₂) and hairpin DNA3 (H₃) onto the electrode surface. The Y-shaped DNA was formed by catalytic hairpin assembly (CHA) reaction, and Fc enhances the PEC signal. Fc is oxidized to Fc⁺ to provide electrons for holes, reducing the combination of electrons and holes of Mo₂B₂/In₂S₃, and enhancing the PEC response. The PEC assay had a detection range of 1.0 aM–1.0 fM and provided a low detection limit of 0.5 aM. Moreover, it also has good specificity, reproducibility, and stability indicating its promising potential in clinical diagnosis. In addition, this study provides a new idea for the application of 2D MBene materials.</p> Graphical Abstract <p></p>