Encapsulation of biomolecules for bioanalytical purposes: Preparation of diclofenac antibody-doped nanometer-sized silica particles by reverse micelle and sol-gel processing

In recent years, the sol-gel technique has attracted increasing interest as a unique approach to immobilize biomolecules for bioanalytical applications as well as biochemical and biophysical studies. For this purpose, crushed biomolecule-doped sol-gel glass monoliths have been widely used. In the present work, for the first time, the encapsulation of anti-diclofenac antibodies in silica nanoparticles was carried out by a combination of reverse micelle and sol-gel technique. Cyclohexane was used for the preparation of the microemulsion as organic solvent, while surfactant Igepal CO-520 was found to be the optimal stabilizer. The antibody source was a purified IgG fraction originating from a polyclonal rabbit antiserum. Tetramethyl orthosilicate (TMOS) was used as precursor. Rather uniform, monodispersed and spherical silica particles of about 70 nm diameter size were fabricated, as was demonstrated by transmission electron microscopy (TEM) and scanning electron microscopy/energy dispersive X-ray fluorescence analysis (SEM/EDX). The biological activity of the encapsulated antibodies was evaluated by incubation of the nanoparticles with a diclofenac standard solution and analysis of the filtrate and followed washing solutions by a highly sensitive enzyme-linked immunosorbent assay (ELISA), using non-doped particles as blanks. While only about 6% of the added diclofenac was nonspecifically retained by the blank, the corresponding amount of about 66% was much higher with the antibody-doped particles. An obvious advantage of this approach is the general applicability of the developed technique for a mild immobilization of different antibody species.