Ultrasensitive Ratiometric Homogeneous Electrochemical MicroRNA Biosensing via Target-Triggered Ru(III) Release and Redox Recycling

A new label-free and enzyme-free ratiometric homogeneous electrochemical microRNA biosensing platform was constructed via target-triggered Ru­(III) release and redox recycling. To design the effective ratiometric dual-signal strategy, [Ru­(NH₃)₆]³⁺ (Ru­(III)), as one of the electroactive probes, was ingeniously entrapped in the pores of the positively charged mesoporous silica nanoparticle (PMSN), and another electroactive probe, [Fe­(CN)₆]^3– (Fe­(III)), was selected to facilitate Ru­(III) redox recycling due to its distinctly separated reduction potential and different redox properties. Owing to the liberation of the formed RNA–ssDNA complex from PMSN, the target miRNA triggered the Ru­(III) release and was quickly electroreduced to Ru­(II), and then, the in-site-generated Ru­(II) could be chemically oxidized back to Ru­(III) by Fe­(III). Thus, with the release of Ru­(III) and the consumption of Fe­(III), a significant enhancement for the ratio of electroreduction current [Ru­(NH₃)₆]³⁺ over [Fe­(CN)₆]^3– (<i>I</i>_Ru(III)/<i>I</i>_Fe(III)) value was observed, which was dependent on the concentration of the target miRNA. Consequently, a simple, accurate, and ultrasensitive method for the miRNA assay was readily realized. Furthermore, the limit of detection (LOD) of our method was down to 33 aM (S/N = 3), comparable or even superior to other approaches reported in literature. More importantly, it also exhibited excellent analytical performance in the complex biological matrix cell lysates. Therefore, this homogeneous biosensing strategy not only provides an ingenious idea for realizing simple, rapid, reliable, and ultrasensitive bioassays but also has a great potential to be adopted as a powerful tool for precision medicine