Exploring a New Ruthenium(II) Complex with High DNA Binding Ability as a Novel Efficient Luminescent Intercalation Agent to Construct a Label-Free ECL/PL Dual-Mode Biosensor

Ruthenium(II) complexes with special ligands have been widely recognized in numerous fields and attributed to their outstanding DNA binding capacity. Hybridization chain reaction (HCR), as an enzyme-free amplification technique, forms long double-stranded DNA (dsDNA) structures, which provides an intercalation platform for these complexes and obtains an effective enhancement of luminescent signals to a significant extent and enhances the sensitivity of detection. Hence, Ru(dip)2(tpphz) [dip = 4,7-diphenyl-1,10-phenanthroline, tpphz = tetrapyrido[3,2-a:2′,3′-c:3″,2″-h:2‴,3‴-j]phenazine] confirmed to possess high DNA binding capacity via UV–vis absorption spectroscopy and AutoDock theoretical simulation calculations was synthesized as a luminescence probe. As a proof of concept, the label-free ECL/PL dual-mode biosensor was further constructed. In this design, magnetic silica spheres with trigger DNA were amplified by HCR with hairpin DNA, forming large amounts of dsDNA on the surface, and Ru(dip)2(tpphz) was incorporated to generate robust signals. Trigger DNA was cleaved owing to the activation of Cas12a cleavage ability in the presence of the target, HCR amplification disappeared, and the signals reduced. The biosensor exhibited high selectivity, and the LOD was as low as 69 fM (S/N = 3). The results proved that Ru(dip)2(tpphz) has excellent DNA binding ability and ECL and PL dual properties, which has huge potential to establish label-free dual-mode biosensors and simultaneously offers a tremendous prospect in the fields of anticancer, gene therapy, and molecular probes beyond label-free biosensors in the future.