Organic-Inorganic Hybrid Flower-Shaped Microspheres Applied in Photoelectrochemical Sensing

Organic-inorganic hybrid materials are rarely applied in photoelectrochemical (PEC) sensing because of the serious charge-carrier recombination in organic conjugated polymers. In this work, a series of poly(3,4-ethylenedioxythiophene) (PEDOT)/ZnIn₂S₄ hybrid flower-shaped microspheres were synthesized using ionic liquids (ILs) as the supporting electrolyte for EDOT electropolymerization and as the regulating reagent for controlling ZnIn₂S₄ growth, respectively. It was found that the hybrid material [HOEMIM]NTf₂-PEDOT/[HOEMIM]BF₄-ZnIn₂S₄ ([HOEMIM]⁺: 1-hydroxyethyl-3-methylimidazolium cation; NTf₂^-: bis(trifluoromethanesulfonyl)amide) was the optimal one, with a smooth, transparent, and continuous polymer film covering the uniform and ordered cross-linked nanosheet arrays. The hybrid material could produce a high anodic photocurrent, which was about 78 times as high as that produced by the [HOEMIM]BF₄-ZnIn₂S₄. The enhancement effect should be the highest among all the organic-inorganic hybrid materials reported so far. This was related to its unique micromorphology structure, p-n heterojunction, and the coexisting ILs, which restrained the charge-carrier recombination in PEDOT and enhanced PEDOT sensitization to ZnIn₂S₄. Then, a carcinoembryonic antigen PEC immunosensor was constructed based on the photoanodic sensing platform, and it exhibited good performance. Furthermore, the [HOEMIM]BF₄-ZnIn₂S₄ was treated with NaClO solution to create the [HOEMIM]NTf₂-PEDOT/[HOEMIM]BF₄-S-Zn_wIn_xS_yO_z general platform for both photoanodic and photocathodic sensing. As a proof of concept, L-cysteine and dissolved oxygen were used as models for photoanodic and photocathodic sensing, respectively. The results demonstrated that the general PEC platform was quite competent. This work opens up a window for the design of organic-inorganic hybrid PEC materials and will promote the application of such hybrid materials in PEC biosensing.