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.