Designing Microreactors Resembling Cellular Microenvironment via Polyamine-Mediated Nanoparticle-Assembly for Tuning...

Spatial confinement of glucose oxidase (GOx) in the hollow interior of a bioinspired matrix via polyamine mediated silica nanoparticle assembly under environmentally benign conditions is demonstrated herein. In a similarity to the biosilicification processes in diatoms, we use poly(allylamine hydrochloride) (PAH) to direct the assembly of silica nanoparticles on CaCO₃ spheres as the removable core. When this assembly process is performed on the CaCO₃ spheres, which are preloaded with GOx in a postsynthesis method, microspheres encapsulating GOx are formed. Interestingly, the encapsulated GOx in these microreactors exhibits activity with a Michaelis-Menten constant ( K_M) that is 2- to 3-fold less compared with the free enzyme in the solution. While the microenvironment of the organic (PAH)-inorganic (silica) hybrid system can be advantageous for the substrate to interact with enzyme, the effective pH in the vicinity of the entrapped enzyme may also be accountable for the improved activity, resulting in the lower apparent K_M and enhanced specificity constant ( k_cat/ K_M). A 2-fold higher thermal stability of the encapsulated GOx compared with free GOx in solution further demonstrates the efficacy of the integrated architecture. Additionally, the PAH by virtue of its buffering capability allows the microspheres in imparting pH stability to the encapsulated GOx. Therefore, the method is not only a greener process for performing enzyme immobilization but also anticipated to aid in designing microreactors for enhanced enzyme activity.