Coacervate-Based Plexcitonic Assembly toward Peroxidase-like Activity and Ultrasensitive Glucose Sensing

Inbuilt catalytic centers anchored inside the confined architecture of artificial nanoreactors have gained tremendous attention owing to their vast applicability in various catalytic transformations. However, designing homogeneously distributed catalytic units with exposed surfaces in confined environment is a challenging task. Here, we have utilized quantum dot (QD)-embedded coacervate droplets (QD-Ds) as a confined compartment for the in situ synthesis of gold nanoparticles (Au NPs) without any additional reducing agent. High-resolution transmission electron microscopy images reveal homogeneous distribution of 5.6 ± 0.2 nm-sized Au NPs inside the QD-Ds (Au@QD-Ds). The in situ synthesized Au NPs are found to be stable over a period of 28 days without any agglomeration. Control experiments reveal that the free surface carboxylic acid groups of embedded QDs simultaneously act as reducing and stabilizing agents for Au NPs. Notably, these Au@QD-Ds exhibit superior peroxidase-like activity compared to bulk aqueous Au NPs and Au@QDs under similar experimental conditions. The observed peroxidase-like activity follows the classical Michaelis-Menten model inside the Au@QD-Ds via the fast electron-transfer pathway. The enhanced peroxidase-like activity has been explained by considering confinement, mass action, and the ligand-free surface of embedded Au NPs. The present plexcitonic nanocomposites exhibit excellent recyclability over several consecutive cycles without any compromise in their catalytic activity. Finally, a cascade reaction with glucose oxidase (GOx)-loaded Au@QD-Ds have been utilized for colorimetric detection of glucose with a limit of detection of 272 nM in solution as well as on filter paper. The present work highlights a facile and robust methodology for the fabrication of optically active functional hybrid plexcitonic assemblies and may find importance in various fields including bioanalytical chemistry and optoelectronics.