Homogeneous molecular iridium catalysts with peroxidase-like activity and luminescence outperforming nanozymes in multimodal respiratory syncytial virus biosensing.

Traditional nanozymes have been widely used in biosensing, but their intrinsic heterogeneity and poorly defined active sites hinder the rational modulation of catalytic and optical properties. Herein, three cationic iridium (III) complexes bearing distinct primary ligands (Ir-1, Ir-2, and Ir-3) were designed and investigated as structurally defined molecular catalysts for multimodal biosensing. These complexes were systematically evaluated in terms of their peroxidase-like catalytic activity, photoluminescence properties, and luminol electrochemiluminescence-enhancing ability. Their structure-activity relationships were further elucidated by comprehensive experimental characterization together with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. As a proof of concept, Ir-3 incorporating an N-heterocyclic carbene (NHC) ligand was employed as a versatile signal transducer to construct a multimodal biosensor integrating fluorescence (FL), electrochemiluminescence (ECL), ultraviolet-visible (UV-vis) colorimetry, and smartphone-assisted colorimetric readouts for the detection of respiratory syncytial virus (RSV). The multiple readouts enabled mutual signal validation and improved the reliability of RSV detection, with limits of detection (LOD) of 38.54 cps/μL in FL mode, 21.35 cps/μL in ECL mode, 48.42 cps/μL in UV-vis mode, and 657.30 cps μL in smartphone-assisted colorimetric mode. This work highlights the advantages of homogeneous and tunable iridium-based molecular catalysts in overcoming the inherent limitations of nanozymes for advanced biosensing applications.