Colorimetric and luminescent determination of heparin based on assembly between a highly charged iridium(III) complex and gold nanoparticles

A highly charged water-soluble iridium(III) (Ir(III)) complex [(ppy) 2 Ir(bpy-N)] 3+ was designed, synthesized and characterized, and the crystal structure of it was determined by X-ray crystallography. The photophysical properties of complex in absence or presence of sodium heparin were studied by UV–vis absorption and photoluminescent spectroscopies. After addition of sodium heparin, the luminescent intensity of complex at ca. 656 nm was increased about 4.3-fold, without any observable color change in the solution. The new Ir(III) complex was also assembled with gold nanoparticles (AuNPs) for the dual-mode detection of sodium heparin, combined with colorimetric and luminescent methods. In this system, the luminescence of complex was quenched by AuNPs firstly with the red color of gold nano colloids transition into blue due to the aggregation. The color of the assembled system changed from blue to purple to red accompanying with the luminescent intensity of system restoring after increasing the concentrations of added sodium heparin. The sodium heparin was sensitively detected with LOD of 0.09 μg/mL. This work demonstrates a novel bifunctional sensing platform for sodium heparin, leveraging the unique photophysical properties of the Ir(III) complex and the plasmonic behavior of AuNPs, offering significant potential for sensitive and visual detection applications.