A pyrene-based fluorescent sensor for ratiometric detection of heparin and its complex with heparin for reversed ratiometric detection of protamine in aqueous solution

•Pyrene-based sensor, IPy, shows fluorescent ratiometric responses to heparin.•The strong heparin-binding affinity endows IPy with high sensitivity and selectivity.•IPy/heparin complex shows reversed ratiometric responses to protamine.•Protamine competes with IPy to bind with heparin and release IPy back to solution.•Both ratiometric detection processes can be performed in serum solutions.

An imidazolium-modified pyrene derivative, IPy, was used for ratiometric detection of heparin, and its complex with heparin was used for reversed ratiometric detection of protamine in both aqueous solution and serum samples. The cationic fluorescent probe could interact with anionic heparin via electrostatic interaction to bring about blue-to-green fluorescence changes as monomer emission significantly decreases and excimer increases. The binary combination of IPy and heparin could be further used for green-to-blue detection of protamine since heparin prefers to bind to protamine instead of the probe due to its stronger affinity with protamine. The cationic probe shows high sensitivity to heparin with a low detection limit of 8.5 nM (153 ng/mL) and its combination with heparin displays high sensitivity to protamine with a detection limit as low as 15.4 nM (107.8 ng/mL) according to the 3σ IUPAC criteria. Moreover, both sensing processes are fast and can be performed in serum solutions, indicating possibility for practical applications.

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