Microstructural modifications induced by the entrapped glucose oxidase in cross-linked polyacrylamide microgels used as glucose sensors

Glucose oxidase (GOx) has been immobilized in cross-linked polyacrylamide microgels using the concentrated emulsion polymerization method. The immobilization of the enzyme is effective when the number of cross-links is equal or greater than 0.021 mol/g. The swelling of the microgels is not affected by the entrapped enzyme but decreases with increasing the number of cross-links. The glass transition temperature of microgels with GOx presents considerable differences with that of the empty microgels, which are explained on base of the competition between the plasticizer effect of the encapsulated enzyme and the chain mobility restrictions imposed by the microgel cross-linking content. Immobilization of GOx slightly modifies the X-ray diffraction patterns of the microgels; however, the diffraction profiles of cross-linked microgels suggest the formation of bis(acrylamide) aggregates in the outer layers of the microgel particles.