A photoelectrochemical sensor based on In 2 O 3 /In 2 S 3 /ZnIn 2 S 4 ternary Z-scheme heterojunction for ultrasensitive detection of dopamine in sweat.

A novel ternary heterojunction material In 2 O 3 /In 2 S 3 /ZnIn 2 S 4 was synthesized, and a photoelectrochemical sensor was fabricated for the non-invasive test of dopamine (DA) in sweat. In 2 O 3 multihollow microtubules were synthesized and then In 2 S 3 was formed on their surface to construct a type-I heterojunction between In 2 S 3 and In 2 O 3 . ZnIn 2 S 4 was further introduced to form a Z-scheme heterojunction between In 2 S 3 /ZnIn 2 S 4 . Under photoexcitation, the photogenerated holes of In 2 O 3 transferred to the valence band of In 2 S 3 , superimposed with the holes produced by In 2 S 3 , leads to a significantly higher photocatalytic oxidation capacity of In 2 O 3 /In 2 S 3 /ZnIn 2 S 4 ternary composites than that of In 2 O 3 /In 2 S 3 . 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 In 2 O 3 /In 2 S 3 , 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.