Robust Single-Molecule Enzyme Nanocapsules for Biosensing with Significantly Improved Biosensor Stability

The present study demonstrates the use of highly stable single-molecule enzyme nanocapsules (SMENs) instead of traditional native enzyme as biorecognition element in enzyme-based biosensors. The main purpose of this study is to resolve the major obstacle and challenge in the biosensor field, i.e., the poor stability of enzyme-based biosensors, including thermal stability, organic solvent tolerance, long-term operational stability, etc. Highly active and robust SMENs of glucose oxidase (GOx, as a model enzyme) were synthesized (nGOx) using an in situ polymerization strategy in an aqueous environment. The particle-size distribution, transmission electron microscopic (TEM) images, and UV–vis spectral characterization revealed the formation of a thin polymer layer around each enzyme molecule. The polymer shell effectively stabilized the GOx enzyme core while enabling rapid substrate transportation, resulting in a new class of biocatalytic nanocapsules. Multiple covalent attachments between a thin polymer layer and an enzyme molecule strengthened the encapsulated GOx molecule. Encapsulation created a favorable microenvironment to avoid any structural dissociation at high temperature and helped to retain essential water during the organic solvent operation. The present work reports a study implementing nGOx SMENs as highly stable nano(bio)sensors for point-of-care diagnostic applications. Prepared nGOx SMENs manifested significantly improved thermal stability (even at 65 °C) and organic solvent tolerance without any compromise in biocatalytic activity. For example, the native GOx-based biosensor lost its catalytic activity for glucose after 4 h of incubation at high temperature (65 °C), while the nGOx/N-CNTs-Chi/GCE nano(bio)sensor maintained ∼56% of its original catalytic activity for glucose oxidation. The proposed SMENs-based nano(bio)sensors with robust stability in variable working environment could promote the development and applications of biosensors in point-of care diagnostics, biomedical detection, wearable devices, implantable equipment, and biofuel cells.