Mannose-substituted conjugated polyelectrolyte and oligomer as an intelligent energy transfer pair for label-free visual detection of concanavalin A

Mannose-substituted blue-fluorescent cationic conjugated polyelectrolyte (P1) and yellow- fluorescent neutral conjugated oligomer (6) are synthesized via the combination of Suzuki coupling polymerization and click chemistry. The spectral overlap between the emission of P1 and the absorption of 6 allows one to blend them to form an intelligent fluorescence resonance energy transfer (FRET) pair for multicolor protein sensing. Despite the nonspecific-interaction- induced perturbation in the polymer emission, strong specific binding between mannose and Concanavalin A (ConA) is able to result in protein-selective FRET from P1 to 6. The fluorescence of 6/P1 blend in the presence of ConA is dominated by yellow emission, while it remains blue in the presence of other six nonspecific proteins. The 6/P1 blend thus serves as a multicolor bicomponent FRET probe for label-free visual detection of ConA in a high-contrast and convenient manner. In addition, its linear ratiometric fluorescence response toward ConA enables effective protein quantification with a low limit of detection of ∼1.5 nM. This study demonstrates the importance of molecular engineering in conjugated polyelectrolyte based label-free chemical and biological sensing.