Sensitive Fluorescent Detection of Heparin and Protamine Using a Propidium Iodide-Based Sensing System

Heparin and protamine are important biological macromolecules that play vital roles in the physiological processes and clinical medicine. The utilization of commercially available fluorescent probes for the quantitative detection of heparin and protamine circumvents the necessity for laborious organic synthesis, thereby facilitating a cost-effective, fast-response, and highly sensitive fluorescent detection. In this work, propidium iodide (PI) was selected as a fluorescent probe for the sensing of heparin and protamine. The results demonstrated that PI underwent aggregation on the heparin surface, driven by electrostatic interactions, resulting in fluorescence quenching. The fluorescence intensity exhibited a linear relationship with heparin concentration in the range of 0-6.67 μg/mL, with a detection limit of 0.12 μg/mL. Utilizing the electrostatic complex system of PI and heparin as a probe, the quantitative detection of protamine-the antidote to heparin-can be achieved, based on the high affinity between heparin and protamine. The PI-based detection of heparin and protamine has been demonstrated to be applicable not only in HEPES buffer but also in solutions containing 1% fetal bovine serum. This finding indicates its potential for use in complex media.