Modifying Fluorescent Protein Chromophore to Detect Protamine and Application in Real Serum Samples

As effective methods to accurately and rapidly detect protamine remains a major challenge, here we present a fluorescent protein chromophore‐based probe (IDL‐FP) utilizing twisted‐intramolecular charge transfer (TICT) to detect protamine. The introduction of an electron‐donor group 4‐dimethylaminobenzaldehyde extends the emission wavelength of IDL‐FP to the red region. The deprotection of t‐butyloxy carbonyl groups can then generate an electronegative carboxyl group, which promotes the binding to protamine via electrostatic attraction. Thus, IDL‐FP is sensitive and specific towards protamine and can serve as a highly selective detector for protamine with a detection limit as low as 8.87 ng/mL. As IDL‐FP exhibited good stability in physiological pH environment, we successfully apply IDL‐FP to detect spiked‐in protamine in human serum. In summary, probe IDL‐FP is a promising tool for the quantitative determination of protamine. In this research, a new TICT probe (IDL‐FP) was designed for sensitive detection of protamine. The introduction of indole‐3‐carboxaldehyde and 4‐dimethylaminobenzaldehyde gave IDL‐FP both an electron‐donor and electron‐acceptor, which urged the complete intramolecular charge transfer and a large stokes shift, allowing IDL‐FP to process minimal background noise and excellent biocompatibility. Additionally, protamine can directly induce the aggregation of IDL‐FP caused by electrostatic attraction. In this way, the turn‐on detection of protamine was achieved and the detection limit was as low as 8.87 ng mL−1, which showed a better sensitivity and higher stability. As IDL‐FP exhibited good stability in physiological pH environment, we successfully applied IDL‐FP to detect spiked‐in protamine in human serum. In summary, probe IDL‐FP is a promising tool for the quantitative determination of protamine for potential clinical usage.