In Situ Nanoplasmonic Probing of Enzymatic Activity of Monolayer-Confined Glucose Oxidase on Colloidal Nanoparticles

In situ probing protein-particle interactions and activities of proteins on colloidal nanopartide (NP) surfaces is a long-standing key challenge in understanding the nanobio interfaces and virtually important for a variety of biological and biomedical applications. The interactions of NPs with proteins, for instance, are known to form NP bioconjugates or protein coronas; protein surface immobilization and molecular layer-by-layer deposition techniques are widely used, but a clear understanding of the confinement effect on protein activity by molecular coating, at the monolayer level, remains poorly understood. We explore here a novel approach, using colloidal plasmonic nano-complexes coated with glucose oxidase (GOx) as self-sensing nanoprobes for in situ optical probing of surface-confined enzymatic activity, which is at least 1-2 orders of magnitude more sensitive than standard colorimetric assays for detecting GOx activity. We found that enzymatic activity of monolayer-confined GOx on colloidal NPs was significantly enhanced as compared with free GOx (also proved by conformational changes from circular dichroism studies), with a low apparent Michaelis-Menten constant K-m of similar to 0.115 mM and high turnover k(cat)/K-m of similar to 8394 M-1.s(-1); compared with the anchored-type suspending GOx , the outmost polyelectrolyte monolayer-protected sandwiched type GOx exhibits significantly improved enzymatic activities toward higher temperatures and wider pH range. This finding is of fundamental important and instructive for safe use of such nanomaterials for bioapplications.