A photoelectrochemical sensor based on InO/InS/ZnInS ternary Z-scheme heterojunction for ultrasensitive detection of dopamine in sweat.

A novel ternary heterojunction material InO/InS/ZnInS was synthesized, and a photoelectrochemical sensor was fabricated for the non-invasive test of dopamine (DA) in sweat. InO multihollow microtubules were synthesized and then InS was formed on their surface to construct a type-I heterojunction between InS and InO. ZnInS was further introduced to form a Z-scheme heterojunction between InS/ZnInS. Under photoexcitation, the photogenerated holes of InO transferred to the valence band of InS, superimposed with the holes produced by InS, leads to a significantly higher photocatalytic oxidation capacity of InO/InS/ZnInS ternary composites than that of InO/InS. 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 InO/InS, 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 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.