Biomimetic Preparation Of Nanosilica For Enzyme Encapsulation

Encapsulation is demonstrated to be an effective method for enzyme immobilization. Compared to traditional encapsulation method, the biomimetic approach, which occurs under mild conditions, can create benign microenvironment for the immobilized enzyme and improve the stability of enzyme. The method offers a new program for the immobilized enzyme technology, and further expands the application of biomimetic mineralization. The study discusses biomimetic method for the preparation of nanosilica for enzyme encapsulation. The details in this study were summarized as follows:Firstly, polyethyleneimine-mediated silica formation was used to immobilize horseradish peroxidase (HRP) under room temperature and neutral pH for the removal of phenol. SEM image showed that the immobilized HRP particles were near-spherical and homogeneous ranging from 200-500 nm. FT-IR spectra indicated that HRP was successfully encapsulated within the silica matrix. The results showed that 65.3% of HRP was immobilized and 70.8% of its initial activity could be retained. As well, the immobilized HRP exhibited improved thermal, pH and storage stabilities. The resulting silica-encapsulated HRP was used into the reaction of phenol removal. The phenol removal rate could reach 73.1%. After 5 repeated cycles, almost 51.7% of its initial activity was retained.Secondly, papain was immobilizated through the biomimetic silicification process. This method made use of the silicification activity of papain itself. By incubating papain in a silica precursor solution, the papain-silica composite formed rapidly, and papain was encapsulated simultaneously. The results showed that the encapsulation efficiency and the recovery activity were 82.6% and 83.1%, respectively. The mechanism of papain encapsulation was tentatively proposed. Furthermore, the encapsulated papain exhibited enhanced thermal, pH, recycling and storage stabilities. Kinetic analysis showed that the biomimetic silica matrix did not significantly hinder the mass transport of substrate or the release of product.Finally, an approach combining biomimetic mineralization with Fe3O4 magnetic particles (MNPS) was proposed to prepare immobilized papain that was easily separated from reaction mixture. FT-IR spectra showed that aminosilane-modified MNPS was synthesized, and EMNPS was coated with biosilica. SEM suggested that the silica layer increased the average size and disperasion of the sample. The study indicated the loading of papain was 0.24 mg-mg-1 MNPS and the activity of EMNPS and EMNPS/SiO2 were 3.72 and 3.66 u-mg-1 MNPS, respectively. Furthermore, the stability of EMNPS/SiO2 was better than EMNPS. Compared with free papain, EMNPS has slightly higher affinity, and EMNPS/SiO2 has lower affinity with substrate.