Synthesis and characterization of water-soluble conjugated glycopolymer for fluorescent sensing of concanavalin A.

A neutral polyfluorene derivative that contains 20 mol% 2,1,3-benzothiadiazole (BT) is synthesized by Suzuki cross-coupling polymerization. A cationic conjugated polymer A and an alpha-mannose-bearing polymer B are subsequently obtained through different post-polymerization methods. As a result of the charged pendant groups or sugar-bearing groups attached to the polymer side chains, both A and B show good water-solubility. The titration of Concanavalin A (Con A) into polymer aqueous solution leads to different fluorescent responses for polymers A and B. Polymer A does not show any obvious fluorescence change upon interaction with Con A, whereas polymer B shows fluorescence increase in BT emission intensity when Con A is added. This is because of the specific interaction between alpha-mannose and Con A, which induces polymer aggregation, and then facilitates energy transfer from the phenylene-fluorene segments to the BT units. A practical calibration curve ranging from 1 nM to 250 nM is obtained by correlating the changes in BT emission intensity with Con A concentration. The advantage of polymer B-based Con A macromolecular probe is that it shows signal increase upon Con A recognition, which is significantly different from other conjugated polymer-based fluorescence quenching assays.