Bimodal 3D DNA nanomachines coupling with bioconjugates powered electrochemical and visual-driven dual-enzyme cascade sensing of Let-7a

A dual-enzyme self-powered biosensor utilizing bimodal 3D DNA nanomachines and gold nanoparticle (AuNPs)/ carbon/disulfide molybdenum hollow nanorods bioconjugates is developed for the electrochemical and visual detection of the tumor biomarker let-7a. DNA probes are immobilized on a flexible electrode substrate of AuNPs/ graphdiyne/carbon cloth to improve probe loading capacity and electron transfer efficiency. The presence of let7a initiates the work of dual-enzyme 3D DNA nanomachine, and the output DNA single strand cleaved by Nb. BbvCI is served as a bridge to connect glucose oxidase (GOD)-DNA conjugate. The GOD coordinates with the cathodic enzyme bilirubin oxidase and produces an increased open circuit voltage signal, which is attributed to the hexaammine ruthenium in the double-stranded adsorption system of the biocathode. By utilizing the H2O2 generated during the oxidation process of GOD, a linear relationship between the color of 3,3 ',5,5 '-tetramethylbenzidine and the concentration of let-7a is established, enhancing the reliability of the detection results through the independent signal conversion mechanisms of electrochemical/colorimetric modes. The results demonstrate a wide dynamic range of 0.0001-0.1 pM with detection limits of 31.04 aM (S/N=3) in electrochemical mode and 59.99 aM (S/N=3) in the colorimetric mode. This dual-mode biosensing strategy can be expanded to detect additional nucleic acid biomarkers, providing a promising support and reference for biological analysis and medical diagnosis.