In this work, we first exposed that the application of p-type semiconductor, silver iodide-chitosan nanoparticle (SICNP), acted as peroxidase mimetic to catalyze the bioprecipitation reaction for signal-amplification photocathodic immunosensing of human interleukin-6 (IL-6). After immobilization of captured antibody onto a polyethylenimine-functionalized carbon nitride (CN) matrix, SICNPs as photoactive tags and peroxidase mimetics were labeled on secondary antibodies, which were subsequently introduced onto the sensing interface to construct sandwich immunoassay platform through antigen-antibody specific recognition. Due to the matched energy levels between CN and AgI, the photocurrent intensity and photostability of SICNP were dramatically improved with rapid separation and transportation of photogenerated carriers. Moreover, the insoluble product in effective biocatalytic precipitation reaction served as electron acceptor to scavenge the photoexcited electron, leading to great amplification of the photocurrent signal of SICNP again. With the help of multiamplification processes, this photocathodic immunosensor presented a turn-on photoelectrochemical performance for IL-6, which showed wide linear dynamic range from 10(-6) to 10 pg/mL with the ultralow detection limit of 0.737 ag/mL. This work also performed the promising application of SICNP in developing an ultrasensitive, cost-effective, and enzyme-free photocathodic immunosensor for biomarkers.

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A ternary hybrid was developed through interaction between a hierarchical-ordered TiO2 and a thiol group that was obtained by in situ chemical polymerization of L-cysteine on the carbon nanohorn (CNH) superstructure modified electrode. Herein, unique-ordered TiO2 superstructures with quasi-octahedral shape that possess high crystallinity, high porosity, oriented subunit alignment, very large specific surface area, and superior photocatalytic activity were first introduced as a photosensitizer element in the photoelectrochemical determination. Additionally, the assembly of hierarchical-structured CNHs was used to provide an excellent electron-transport matrix to capture and transport an electron from excited anatase to the electrode rapidly, hampering the electron-hole recombination effectively, resulting in improved photoelectrochemical response and higher photocatalytic activity in the visible light region. Owing to the dependence of the photocurrent signal on the concentration of electron donor, 4-methylimidozal, which can act as a photogenerated hole scavenger, an exquisite photoelectrochemical sensor was successfully fabricated with a wide linear range from 1 × 10(-4) to 1 × 10(-10) M, and the detection limit was down to 30 pM. The low applied potential of 0.2 V was beneficial to the elimination of interference from other reductive species that coexisted in the real samples. More importantly, the mesocrystal was first introduced in the fabricating of a biosensor, which not only opens up a new avenue for biosensors manufactured based on mesocrystal materials but also provides beneficial lessons in the research fields ranging from solar cells to photocatalysis.

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