Comparison of spherical and rod-like morphologies of SBA-15 for enzyme immobilization

Mesoporous silica, namely SBA-15, has been used for enzyme immobilization to help improve thermal stability of the enzymes and, in some cases, increase the enzymatic activity. It has been shown that morphology of SBA-15 is one of the factors influencing kinetics of enzyme adsorption. We reported, here, the adsorption kinetics and peroxidase activity of cytochrome c (cytc) in spherical SBA-15 in comparison of three different rod-like (fibrous, fiber, and rope) SBA-15 samples. The experimental adsorption profile fitted much better to the pseudo-second order than the pseudo-first order model. The maximum loading capacity of cytc was 466, 423, 390, and 352 mg/g for fibrous, rope, fiber, and spherical SBA-15, respectively. The rate constant for cytc adsorption for spherical SBA-15 was 3 times slower than rope and fiber SBA-15, and 15 times slower than fibrous SBA-15. The activity of cytc after immobilization in SBA-15 samples depended on the amount of cytc loading. The cytc loading in all SBA-15 at lower than 10 mu mol/g showed higher activity than in free cytc in solution. The maximum activity of immobilized cytc was found in spherical SBA-15 at cytc loading of 1.00 mu mol/g (similar to 7 times higher than in free cytc). Finally, the Fe(III) at the heme group of cytc/SBA-15 samples with high activity was examined to contain high-spin state. The investigation in this work could suggest useful information for the preparation of SBA-15 for enzyme immobilization to appropriate applications, such as drug delivery.