Conjugated Polyelectrolytes as Light-Up Macromolecular Probes for Heparin Sensing

Two cationic poly(fluorene‐alt‐benzothiadiazole)s with different side chains are designed and synthesized. Both polymers show low fluorescence in aqueous solution due to the charge‐transfer character of the polymer's excited states. Fluorescence turn‐on biosensors for heparin detection and quantification are developed, taking advantage of complexation‐induced aggregation, which increases the polymer fluorescence in aqueous solution. It is found that good polymer water‐solubility is beneficial to the sensitivity and fluorescence contrast of the heparin turn‐on sensor as a result of the low fluorescence background. Moreover, stronger complexation between the polymer/heparin leads to a substantially larger fluorescence increase in the presence of heparin relative to that in the presence of its analog, hyaluronic acid (HA), allowing discrimination of heparin from HA. Heparin quantification with a practical calibration range covering the whole therapeutic dosing levels (0.2–8 U mL−1) is realized based on the polymer with good water‐solubility. This investigation provides a new insight for designing conjugated polymers with a light‐up signature for biomolecular sensing. Conjugated polyelectrolytes can be used as light‐up probes for chemical and biomolecular sensing. Cationic poly(fluorene‐alt‐benzothiadiazole)s have low fluorescence in aqueous solution and exhibit aggregation‐enhanced fluorescence, which make them macromolecular probes for heparin detection and quantification.