Silica Nanotubes Based on Needle-like Calcium Carbonate:  Fabrication and Immobilization for Glucose Oxidase

As an inorganic template for fabricating hollow silica nanotubes (SNTs), needle-like calcium carbonate particles consisting mainly of aragonite were obtained by carbonation in a high-gravity environment generated by rotating packed-bed reactor. Through orthogonally designed experiments, the optimal conditions for the fabrication of SNTs, i.e., reaction temperature (15 °C), SiO2/CaCO3 ratio (20 wt %), and cetyltrimethylammonium bromide (CTBA)/CaCO3 ratio (50 wt %), were obtained. The prepared SNTs were characterized by Brunauer−Emmett−Teller (BET) analysis, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A hollow nanotubular structure with open ends was revealed. The resulting SNTs were utilized as a support for the immobilization of glucose oxidase (GOx) by a simple physical adsorption method. FTIR spectra indicated that the protein secondary structure was maintained well in the immobilized molecules. The amount of protein immobilized on the SNTs and the enzymatic activity of the immobilized GOx were investigated in detail. It was observed that the enzymatic activity first increased and then decreased with increasing coverage of the SNT surface by GOx, indicating that the overlap and aggregation of GOx molecules can decrease the enzymatic activity of the adsorbed GOx molecules at high surface coverage.