Ultrasensitive Photoelectrochemical Assay with PTB7-Th/CdTe QDs Sensitized Structure as Signal Tag and 4-CD Precipitate as Efficient Quencher.

Herein, an ultrasensitive photoelectrochemical (PEC) assay was developed for the monitoring of microRNA-141 (miRNA-141) based on poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-bldithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl}/CdTe quantum dots ( PTB7-Th/CdTe QDs) sensitized structure as signal tag and the benzo-4-chlorohexadienone (4-CD) precipitate as efficient quencher. PTB7-Th and CdTe QDs were successively modified on the electrode surface to form a novel sensitized structure with eminent photovoltaic performances and surpassing film-forming ability. The PTB7-Th/CdTe QDs sensitized structure served as signal tag for achieving a strong initial PEC signal. Besides, a tiny amount of target (miRNA-141) could be transformed into numerous DNA products via enzyme assisted target cycling procedure, which further triggered the formation of a DNA supersandwich structure on the electrode surface for loading abundant manganese porphyrin (MnPP). Thereafter, MnPP as mimetic enzyme could catalyze 4-chloro-1-naphthol (4-CN) to generate 4-CD precipitate on the sensing interface in the presence of H2O2, which could efficiently block electron transfer, leading to a significantly quenched PEC signal for determination of miRNA-141. The designed PEC biosensor performed a wide detection range from 0.1 fM to 1 nM with a low detection limit of 33 aM for miRNA-141, which paved a new avenue for highly accurate and ultrasensitive monitoring of multifarious analytes in bioanalysis and clinical diagnosis.