Ratiometric detection of nanomolar concentrations of heparin in serum and plasma samples using a fluorescent chemosensor based on peptides.

A peptidyl fluorescent chemosensor for heparin was synthesized by conjugating a pyrene fluorophore with the heparin-binding peptide. The fluorescent chemosensor (Py12; pyrene-RKRLQVQLSIRT) showed a highly sensitive ratio-metric response to nanomolar concentrations of heparin in aqueous solutions at physiological pH by increasing excimer emission intensity at 500 nm with a concomitant decrease in monomer emission intensity at 400 nm. Py12 showed a sensitive ratio-metric response to heparin over a wide pH range (1.5 <= pH <= 11.5) and exhibited high selectivity for heparin compared to other biological competitors, such as hyaluronic acid and chondroitin sulfate. Py12 sensitively and ratiometrically detected nanomolar concentrations of heparin in biologically relevant samples containing human serum and human plasma, respectively. The detection limit of Py12 was 34 pM (R-2 = 0.997) for heparin in an aqueous buffer solutions containing 5% human serum and 33 pM (R-2 = 0.994) for heparin in aqueous buffer solutions containing 5% human plasma. Py12 had sufficient sensitivity and selectivity for ratiometrically detecting a nanomolar concentration of heparin, indicating that the peptide-base chemosensor provides a potential tool for monitoring heparin levels in clinical plasma samples.