Pyrene Excimer-Based Peptidyl Chemosensors for the Sensitive Detection of Low Levels of Heparin in 100% Aqueous Solutions and Serum Samples

Fluorescent chemosensors (<b>1</b> and <b>2</b>, Py–(Arg)_<i>n</i>GlyGlyGly­(Arg)_<i>n</i>Lys­(Py)–NH₂, <i>n</i> = 2 and 3) bearing two pyrene (Py) labeled heparin-binding peptides were synthesized for the sensitive ratiometric detection of heparin. The peptidyl chemosensors (<b>1</b> and <b>2)</b> sensitively detected nanomolar concentrations of heparin in aqueous solutions and in serum samples via a ratiometric response. In 100% aqueous solutions at pH 7.4, both chemosensors exhibited significant excimer emission at 486 nm as well as weak monomer emission in the absence of heparin. Upon the addition of heparin into the solution, excimer emission increased with a blue shift (10 nm) and monomer emission at 376 nm decreased. The chemosensors showed a similar sensitive ratiometric response to heparin independent of the concentration of the chemosensors. The peptidyl chemosensors were applied to the ratiometric detection of heparin over a wide range of pH (1.5–11.5) using the excimer/momomer emission changes. In the presence of serum, <b>1</b> and <b>2</b> displayed significant monomer emission at 376 nm with relatively weak excimer emission and the addition of heparin induced a significant increase in excimer emission at 480 nm and a concomitant decrease in monomer emission. The enhanced ratiometric response to heparin in the serum sample was due to the interactions between the peptidyl chemosensors and serum albumin in the serum sample. The detection limits of <b>2</b> for heparin were less than 1 nM in 100% aqueous solutions and serum samples. The peptidyl chemosensors bearing two heparin-binding sites are a suitable tool for the sensitive ratiometric detection of nanomolar concentrations of heparin in 100% aqueous solutions and serum samples