Binding activity of avidin to the biotin within mesoporous silica materials for bioanalytical applications

It has been reported that the activity of protein improved when it was adsorbed inside the pores of mesoporous silica (MPS). The current study investigated the activity of immobilized avidin to the biotin on MPS with various pore sizes (diameter = 2.4–45.0 nm). The binding amount of immobilized avidin to biotin is 123 to 160 ng biotin/10 μg avidin on 2.7- to 5.4-nm pore MPS, but that on 12- to 45-nm pore MPS was markedly decreased (33–42 ng biotin/10 μg). Moreover, the binding amount was approximately 2- and 3-fold higher on the glycidoxypropyl (Gly)-functionalized 5.4- and 45-nm pore MPS in comparison with methyl (Me)-functionalized 5.4- and 45-nm pore MPS, respectively. Furthermore, avidin immobilized in native and Gly-grafted 45-nm pore MPS retained more than 70% and 50% binding activity to biotin, respectively, after incubating at 90 °C for 3 h. In contrast, the activity was greatly reduced in the native and Gly-grafted 5.4-nm pore MPS under the same conditions (<36.9%). The immobilization also protected against effects of 0.01 M HCl and 50% MeOH; all of immobilized avidin proteins showed high activity (>50%) with biotin compared with that observed with free avidin (MeOH [<18.2%] and HCl [<32.7%]).