Quantitative determination of protamine using a fluorescent protein chromophore-based AIE probe

An aggregation induced emission (AIE) fluorescent protein chromophore derivative CIC-FP for detecting protamine and heparin under physiological environment was designed and synthesized. CIC-FP exhibited good biocompatibility and a large stoke shift (91 nm), thus well attenuating the background interference, which could be used for quantitative detection of heparin and protamine. Since protamine has strong positively groups, it can interact with CIC-FP where bearing carboxyl through electrostatic interactions to form a tightly bound CIC-FP/protamine complex, thus showing superior fluorescence intensity response with a detection limit of 65.28 ng/mL. Because heparin has a stronger affinity with protamine, it would compete with CIC-FP on protamine, resulting in the release of CIC-FP and making CIC-FP change into free state with decreased fluorescence intensity. Besides, CIC-FP was successfully applied to detect spiked protamine in human serum samples. In summary, CIC-FP can be used to sensitive detection of protamine with good accuracy, which provides a new idea for designing protamine probes.