Dual-photocathode array propelled lab-on-paper ratiometric photoelectrochemical sensing platform for ultrasensitive microRNA bioassay

In this work, a dual-photocathode array propelled lab-on-paper ratiometric photoelectrochemical (PEC) sensing platform integrated with DNA bridge nanostructure mediated electron-transfer tunneling distance regulation strategy was engineered for ultrasensitive assay of microRNA-141 (miRNA-141). Specifically, the spatial-resolved dual-photocathode array were comprised of a working electrode (PCE1) and internal reference electrode (PCE2), which were responsible for producing independent working signal (I-w) and internal reference signal (I-r). The dual-photocathode array was assembled with cascading multiple photosensitive structures consisting of pyramid-shaped Cu2O, graphene quantum dots, and AgI nanoparticles (NPs). With the proximity regulation of DNA hairpins H1 and H2, the amplified photocurrent signals were obtained on PCE1 and PCE2. When target existed, the output DNA probes from various concentrations of miRNA-141 induced duplex specific nuclease-catalyzed target recycling reactions were introduced onto PCE1, while the output DNA probes produced with a constant concentration of miRNA-141 were introduced onto PCE2, resulting in the formation of different amounts of DNA bridge nanostructures on PCE1 and PCE2. Those formed DNA bridge nanostructures with enhanced rigidity remarkably increased the electron-transfer tunneling distance between the sensing interface and AgI NPs immobilized on the terminals of H1 and H2, leading to noticeably decreased photocurrent signals. Based on the introduction of different amounts of target-induced output DNA probes on PCE1 and PCE2, the variable Iw and constant Ir were ultimately collected. By monitoring the ratio of Iw and Ir, the ultrasensitive bioassay of miRNA-141 was realized with high accuracy, selectivity, and practicability.