Gold Nanoparticles Assembled on Amine-Functionalized Na−Y Zeolite:  A Biocompatible Surface for Enzyme Immobilization

Development of simple and reliable protocols for the immobilization of enzymes is an important aspect of biotechnology. Gold nanoparticles are known to bind enzymes, but reuse characteristics of the gold nano−enzyme bioconjugates has hitherto been poor. In this paper, we demonstrate that gold nanoparticles bound at high surface coverage on 3-aminopropyltrimethoxysilane (APTS)-functionalized Na−Y zeolites are excellent candidates for the immobilization of pepsin. The assembly of gold nanoparticles on the zeolite surface occurs through the amine groups present in APTS. Pepsin was then bound to the Na−Y zeolite (core)−Au nano (shell) structures via interaction with the gold nanoparticles leading to a new class of biocatalyst. A highlight of the new biocatalyst wherein the enzyme is supported by a more massive biocompatible surface is the ease with which separation from the reaction medium may be achieved by simple sedimentation. The catalytic activity of pepsin in the bioconjugate was comparable to that of the free enzyme in solution. The pepsin−gold nano−zeolite bioconjugate material exhibited excellent activity over seven successive reuse cycles as well as enhanced pH and temperature stability.