Screening of Ruthenium Complexes as the Protein Light Switches for Protein Detection

Ruthenium(II)–dipyrido[3,2-a:2′,3′-c] phenazine (dppz) complexes (Ru–dppz complexes) can function as the molecular light switches for DNA assay, but their applications to protein detection remain a challenge because proteins possess more structural complexity than nucleic acids. Herein, we develop for the first time a computational virtual screening strategy to screen light switches for protein detection. We find that the binding affinity between Ru–dppz complexes and proteins relies on the structure and ratio of auxiliary and dppz ligands, and it plays a key role in light-switching performance. We discover that [Ru(dppz)2dip]2+ (dip = 4,7-diphenyl-1,10-phenanthroline) can function as the human serum albumin (HSA) light switch, and it exhibits strong hydrophobic and π-cation interactions with HSA to achieve a 280.0-fold luminescence enhancement, which is 2 orders of magnitude higher than the parent complex [Ru(dip)3]2+. Moreover, [Ru(dppz)2dip]2+ displays a rapid response time (<1 s), a large Stokes shift, and high sensitivity for HSA assay with a limit of detection of 0.0093 mg/L. We further develop a smartphone-integrated point-of-care device based on [Ru(dppz)2dip]2+ for rapid detection of HSA. Notably, this strategy can be extended to screen the β-lactoglobulin light switch that exhibits a 346.1-fold luminescence enhancement. This research provides a universal approach for the discovery of high-performance protein light switches with promising applications in biomedical research and clinical diagnostics.