A photoelectrochemical sensor based on In₂O₃/In₂S₃/ZnIn₂S₄ ternary Z-scheme heterojunction for ultrasensitive detection of dopamine in sweat

A novel ternary heterojunction material In₂O₃/In₂S₃/ZnIn₂S₄ was synthesized, and a photoelectrochemical sensor was fabricated for the non-invasive test of dopamine (DA) in sweat. In₂O₃ multihollow microtubules were synthesized and then In₂S₃ was formed on their surface to construct a type-I heterojunction between In₂S₃ and In₂O₃. ZnIn₂S₄ was further introduced to form a Z-scheme heterojunction between In₂S₃/ZnIn₂S₄. Under photoexcitation, the photogenerated holes of In₂O₃ transferred to the valence band of In₂S₃, superimposed with the holes produced by In₂S₃, leads to a significantly higher photocatalytic oxidation capacity of In₂O₃/In₂S₃/ZnIn₂S₄ ternary composites than that of In₂O₃/In₂S₃. The Z-scheme heterojunction accelerates the transfer of photogenerated electrons accumulated on the type-I heterojunction. In the presence of DA, it is rapidly oxidized into polydopamine (PDA) by In₂O₃/In₂S₃, and the benzoquinone groups of PDA compete for the photogenerated electrons to reduce the current in the external circuit, whereby DA determination is achieved. Owing to the combination of type-I and Z-scheme heterojunction, the sensor showed extremely high sensitivity, with a detection limit of 3.94 × 10⁻¹² mol/L. It is one of the most sensitive methods for DA detection reported and has been applied to the determination of DA in human sweat.