Enhancement of the imprinting effect in cholesterol-imprinted microporous silica

A sol–gel method has been used to fabricate a cholesterol MIP for application in polar solutions. In this study, (cholesteryl propylcarbamate)triethoxysilane and tetraethyl orthosilicate were used as the hydrophobic monomer and crosslinker, respectively. The MIP had a larger pore volume when formation of the polymer was catalyzed at a higher pH than when it was formed at lower pH values, with the pore diameters being 3.5 nm and 2 nm, respectively for materials formed at high and low pH values. Both of these pore volumes were greater than those found for the respective control polymers formed without template. However, only the polymers formed at low pH values showed an imprinting effect. Compared with other methods explored, the sol–gel procedure gave only a small amount of non-specific binding for both the MIP and NIP when synthesized at low pH values. The largest imprinting-induced promotion of binding (IPB) value of the MIP (13 650%) was obtained with [HCl] = 0.01 M in the sol–gel solution. The MIP showed high selectivity towards cholesterol in comparison with other steroid hormones, and also to a lesser extent recognized vitamin D3 in methanol solution containing 5 vol.% water.