Probing sugar-lectin recognitions in the near-infrared region using glyco-diketopyrrolopyrrole with aggregation-induced-emission.

This study describes the construction of aggregation-induced-emission (AIE)-based glycosyl probes for the sensitive and selective detection of sugar-lectin interactions in the near-infrared (NIR) region. Mannosyl and galactosyl diketopyrrolopyrrole (DPP) derivatives were effectively synthesized by the Cu(I)-catalyzed azide-alkyne 1.3-dipolar cycloaddition reaction. We observed that these glycodyes had typical AIE behaviors in a semi-aqueous solution with a strong fluorescence (FL) emission in the NIR region. In a buffer solution, the glycosyl DPPs at the quenching state showed sharply increased FL upon addition of a selective lectin that recognizes the glycosyl moiety of the compounds with nanomolar limits of detection. In contrast, addition of unselective lectins, proteins and ions did not fluctuate the FL. Scanning electron microscopy analyses suggested that the FL generation could probably be a result of AIE of the glyco-DPPs upon complexation with lectins. These glyco-DPPs, to the best of our knowledge, represent the first fluorogenic AIE-based probes that can sense lectins in the NIR region, providing insights for the further extension towards low-background in vivo targeted imaging of tissues that express a lectin.