Self-Assembled Glycobis(acrylamide)-Stabilized Gold Nanoparticles for Fluorescent Turn-on Sensing of Lectin and Escherichia coli

Gold nanoparticles (AuNPs) with shelf lives of more than 6 months at 25 °C were synthesized by in situ reduction and stabilization using a d-glucose-based bis(acrylamide) solution. Transmission electron microscopy (TEM) images support the homogeneous coating of AuNPs by Glc-bis. In the process, intrinsic emission of self-assembled glycobis(acrylamide) (Glc-bis) was quenched by AuNPs, and the resultant system, Glc-bis@AuNPs, can work as a turn-on sensor, wherein the quenched emission was restored upon the addition of lectin, Concanavalin A (Con A). The aggregation of Glc-bis@AuNPs upon interaction with Con A was pragmatic from the TEM images. The quenching as well as recovery of the emission based on the proximity of AuNPs with Glc-bis in Glc-bis@AuNPs was further confirmed by steady-state as well as fluorescence lifetime measurements. The Glc-bis@AuNPs system was found to be stable up to 1 M NaCl concentration, a factor that fulfills the requirement for biosensing applications. The binding constant of Glc-bis@AuNPs toward Con A was 9.8 × 10⁴ M^-1, while the limit of detection was 1.6 nM. The interaction of Glc-bis@AuNPs with a FimH-positive, pathogenic K12 strain of Escherichia coli resulted in restoration of the emission, but experiments with the FimH-negative TOP10 strain did not yield any emission.