Enzyme Entrapment in Silica Nanoparticles: Mediated by Single Walled Carbon Nanotubes-lysozyme for Biosensor Applications

Introduction Silica compounds are among the most extensively studied materials, especially those prepared by the sol−gel process [13]. A wide variety of proteins can catalyze the precipitation of silica and become encapsulated as the silica matrix forms. The reaction provides an efficient method for enzyme immobilization and provides significant mechanical stability to resulting silica matrix. Potential applications of Carbon nanotubes (CNTs) include development of different biosensing platforms such as single-walled carbon nanotubes (SWNT) based electrochemical biosensors [4-6], SWNTbased optical biosensors [7, 8] and SWNT-based electronic biosensors [9, 10]. Unfortunately most processes of (SWNT) syntheses produce large, aggregated bundles of SWNTs. These aggregated bundles often make processing difficult and mask the unique properties of individual tubes. Thus a number of covalent [11, 12] and noncovalent [13-15] methods of protein attachment have been developed to debundle these aggregates into individual tubes. However, covalent coupling normally damages the sidewalls of SWNTs and disrupts their unique electrical and optical properties [16, 17]. In contrast, noncovalent methods can allow for the electronic structure of the SWNTs [18, 19] to be retained but may in some cases lead to a loss of protein function [20]. Organophosphorus hydrolase (OPH) is an enzyme with unique capabilities of hydrolyzing wide spectrum of organophosphates (OPs), into much less toxic products such as p-nitrophenol and diethyl phosphate. Recent studies have demonstrated the remarkable versatility of a biomimetic silicification reaction as a means of enzyme immobilization [21]. Biosilicification is a rapid ambient precipitation of silica mediated by a biological catalyst. This work describes the approach to create a bio-nano interface suitable for direct electrochemistry of enzymes. Direct bioelectrocatalysis of paraoxon hydrolysis is demonstrated by entrapping OPH in silica composite obtained through SWNTLSZ catalyzed synthesis of silica.