Tubular and Spherical SiO2 Obtained by Sol Gel Method for Lipase Immobilization and Enzymatic Activity

Abstract

A wide range of hybrid biomaterials has been designed in order to sustain bioremediation processes by associating sol-gel SiO2 matrices with various biologically active compounds (enzymes, antibodies). SiO2 is a widespread, chemically stable and non-toxic material; thus, the immobilization of enzymes on silica may lead to improving the efficiency of biocatalysts in terms of endurance and economic costs. Our present work explores the potential of different hybrid morphologies, based on hollow tubes and solid spheres of amorphous SiO2, for enzyme immobilization and the development of competitive biocatalysts. The synthesis protocol and structural characterization of spherical and tubular SiO2 obtained by the sol gel method were fully investigated in connection with the subsequent immobilization of lipase from Rhizopus orizae. The immobilization is conducted at pH 6, lower than the isoelectric point of lipase and higher than the isoelectric point of silica, which is meant to sustain the physical interactions of the enzyme with the SiO2 matrix. The morphological, textural and surface properties of spherical and tubular SiO2 were investigated by SEM, nitrogen sorption, and electrokinetic potential measurements, while the formation and characterization of hybrid organic-inorganic complexes were studied by UV-VIS, FTIR-ATR and fluorescence spectroscopy. The highest degree of enzyme immobilization (as depicted from total organic carbon) was achieved for tubular morphology and the hydrolysis of p-nitrophenyl acetate was used as an enzymatic model reaction conducted in the presence of hybrid lipase–SiO2 complex.

SiO2-Based Materials for Immobilization of Enzymes

“…Briefly, hybrid complex material consisting in lipase-inorganic support (SiO 2 Tt, AuSiO 2 Tt) was obtained according to the previous reported work [17] concerning the generation of biocatalyst lipase-SiO 2 matrices. Lipase (Rhizopus oryzae, Sigma-Aldrich) in phosphate buffer (pH 6.3) was mixed with SiO 2 and Au/SiO 2 powder (0.02 g) also dispersed in phosphate buffer and magnetically stirred 24 h (100°C).…”

“…The textural properties of tubular and spherical silica, correlated with total organic carbon measurement on their lipase derivative hybrid complex, were previously evaluated and reported [17].…”

“…SiO 2 veils have been also obtained, and their composites have been used as support for platinum electrocatalyst [11].Improvement of in situ generated template-assisted SiO 2 synthesis and appropriate post-synthesis treatments allowed us to obtain nanotubes with intrinsic photo-and electrochemical activity due to high density of oxygen-related lattice defects [12,13] but also to reveal the distinctive capacity of highly defected SiO 2 and its composite SiO 2 -TiO 2 to generate reactive oxygen species (ROS) with potential applications in biology and medicine [14].SiO 2 materials (nanotubes) have been proven to be biologically active for bioremediation processes, showing bactericidal and bacteriostatic effects on halotolerant microorganisms [15]. These type of materials have been successfully used as inorganic carriers in hybrid complex with enzymes [16], the enzymatic activity of the complex being dependent on morphological and textural properties of SiO 2 matrices [17].Generally, sol-gel synthesis of tubular SiO 2 materials was conducted in line with Nakamura and Matsui's work [18], modifications of synthetic procedure being done in respect to particular applications.Thin and larger SiO 2 nanotubes in addition to spherical SiO 2 are meant to function as inorganic host for immobilized enzymes, and, accordingly, their previously synthesis has been reported [7,17]. Better control of synthesis conditions allowed an optimization of their morphology and structure, in order to be appropriate for an inorganic carrier.…”

“…SiO 2 materials (nanotubes) have been proven to be biologically active for bioremediation processes, showing bactericidal and bacteriostatic effects on halotolerant microorganisms [15]. These type of materials have been successfully used as inorganic carriers in hybrid complex with enzymes [16], the enzymatic activity of the complex being dependent on morphological and textural properties of SiO 2 matrices [17].…”

“…Thin and larger SiO 2 nanotubes in addition to spherical SiO 2 are meant to function as inorganic host for immobilized enzymes, and, accordingly, their previously synthesis has been reported [7,17]. Better control of synthesis conditions allowed an optimization of their morphology and structure, in order to be appropriate for an inorganic carrier.…”