Molecular Crowding and a Minimal Footprint at a Gold Nanoparticle Support Stabilize Glucose Oxidase and Boost its Activity

Abstract

Enzymes conjugated to nanomaterials are used in the design of various biotechnologies. In development of biosensors, surface modifications with the enzyme glucose oxidase (GOx) serve to aid the detection of blood glucose. In order to optimize sensor effectiveness, the enzyme tertiary structure needs to be preserved upon immobilization to retain the enzyme´s catalytic activity. Due to the nature of GOx, it suffers from tendency to denature when immobilized at a solid surface, methods to optimize enzyme stability are of great importance. Here, we introduce the study of the interaction of GOx to the highly curved surface of 20 nm gold nanoparticles (AuNP) that shows how placing a monolayer of enzyme where the enzyme spreads thin at the AuNP surface still provides stable catalytic performance up to14 days compared to enzymes free in solution. Moreover, by increasing enzyme density and creating a molecularly crowded environment at the highly curved nanoparticle surface, which limits the size of the enzyme footprint for attachment, the activity per enzyme can be enhanced up to 300%. This is of great importance for implementing stable and sensitive sensor technologies that are constructed by enzyme-based nanoparticle scaffolds. Here, we show by using the conditions that maintain GOx structure and function when limiting the enzyme coating to an ultra-thin layer, the design and construction of ultrafast responding diagnostic sensor technology for glucose can be achieved, which is crucial for monitoring rapid fluctuations of for instance, glucose in the brain.

Interactions of Catalytic Enzymes with n-Type Polymers for High-Performance Metabolite Sensors

“…It has the lowest amount of enzyme with the largest footprint (after P-0), suggesting that the enzyme has an expanded conformation on this surface which we found to be highly negatively charged. Overall, these calculated footprints are generally larger than the theoretical footprint of GOx predicted from its crystal structure (21, 67, or 195 nm 2 ) 37,41,42 but are in line with other reported values on Au (between 528 and 823 nm 2 ) 6 and Au nanoparticles (between 250 and 300 nm 2 ), 43 suggesting that GOx flattens out to some degree during adsorption. 44,45 Note that the native GOx dimensions are those of a deglycosylated GOx molecule, thus implying a larger structure for the protein in solution.…”

“…Proteins tend to lose the α-helical content and gain the β-sheets and random coil/irregular content upon adsorption on surfaces. 15,53 CD studies of GOx adsorbed or entrapped on various substrates, such as the Au nanoparticles, 43 Nafion matrix, 54 and self-assembled monolayers, 37,45,55 revealed a characteristic increase in the β-sheet content with a decrease in the αhelical content upon biohybrid formation. The α-helical content of GOx is closely linked to its activity.…”