Highly sensitive and selective microRNA photoelectrochemical assay with magnetic electron donor–acceptor covalent organic framework as photoactive material and ZnSe QDs as photocurrent-polarity-switching factor

Herein, taking microRNA-138 (miRNA-138) as a model due to its important role in pre-diagnosis and therapy of Alzheimer's disease, a highly sensitive and selective photoelectrochemical (PEC) sensor was developed based on the magnetic electron donor–acceptor (D–A) covalent organic framework (COF), Fe3O4 @D–A COF, as the photoactive material and ZnSe quantum dots (QDs) as the photocurrent-polarity-switching factor. Fe3O4 @D–A COF, which contained the structure of D–A with a fast separation and transportation of photogenerated carriers, showed a large cathodic photocurrent. ZnSe QDs, as a photosensitive material, matched with D–A COF in energy level and could change the photocurrent polarity of D–A COF. Finally, the obtained Fe3O4 @D–A COF-hairpin DNA1/ZnSe QDs-hairpin DNA2 complex, which was formed through the miR-138-induced catalytic hairpin assembly (CHA) reaction, was adsorbed magnetically on the surface of the magnetic indium tin oxide electrode, producing a large anodic photocurrent. Based on the CHA reaction amplification, magnetic separation, D–A structure of COF and photocurrent-polarity-switching strategy, miRNA-138 was selectively and sensitively assayed (linear range, 1 fM to 10 nM; detection limit, 45 aM). The proposed sensor shows its great prospects in clinical analysis and early diagnosis of disease. [Display omitted] •A highly sensitive and selective PEC sensor was designed to detect microRNA.•The donor–acceptor covalent organic framework was used as photoactive material.•The photocurrent polarity of D–A COF was switched by introducing ZnSe QDs.