Perpetuating enzymatically-induced spatiotemporal pH and catalytic heterogeneity of a hydrogel by nanoparticles

Abstract

Attainment of spatiotemporally inhomogeneous chemical and physical properties in a system is gaining attention across disciplines due to their resemblance in environmental and biological heterogeneity. Notably, origin of natural pH gradient and how it has been incorporated in cellular system is one of the most important questions in understanding the prebiotic origin of life. Herein, we have demonstrated spatiotemporal pH gradient formation pattern in a hydrogel surface, employing two different enzymatic reactions, namely, glucose oxidase (pH decreasing) and urease (pH increasing). We found here the generic pattern of spatiotemporal change in pH and proton transfer catalytic activity completely altered in a cationic gold nanoparticle containing hydrogel. In absence of the nanoparticle, the gradually generated macroscopic pH gradient slowly diminished with time; whereas presence of nanoparticle helped to enhance and even perpetuates the generated gradient effect. This behavior is due to the differential responsiveness of the interface of the cationic nanoparticle in temporally changing surroundings with increasing or decreasing pH or ionic contents. Moreover, the catalytic proton transfer ability of the nanoparticle showed concerted kinetic response following the spatiotemporal pH dynamics in the gel matrix. Notably, nanoparticle-driven spatiotemporally resolved gel matrix will have the applicability in the area of membrane-free generation and controlling of spatially segregated chemistry in macroscopic scale.