Molecular Recognition for Bile Acids Using a Molecularly Imprinted Overoxidized Polypyrrole Film

An electrochemical technique for preparation of a molecularly imprinted overoxidized polypyrrole (oPPy) film and its recognition property for bile acids are investigated, aiming for application to a bile acid sensor and clarification of the principle of the recognition mechanism with the quartz crystal microbalance. The molecularly imprinted oPPy has been prepared through a potentiodynamical overoxidation process in an alkaline solution from a taurocholate (TC) doped polypyrrole (PPy) film grown on an Au electrode. The molecularly imprinted film exhibited a high selectivity and sensitivity toward bile acids. Cholate, chenodeoxycholate, deoxycholate, TC, and artificially synthesized dehydrocholate showed a linear relationship between the resonance frequency and their logarithmic concentrations in a range from 10-9 to 10-5 M with detection limits for trace concentrations (~25 nM). The sensitivity of an oPPy film imprinted with TC increased in the sequence of TC (28.8 Hz/log concentration) < cholate (72.7) < chenodeoxycholate (73.8) < or = deoxycholate (73.7) < dehydrocholate (82.0), and was found to depend on the molecular volume of bile acids (increasing in the sequence TC > cholate > or = chenodeoxycholate , deoxycholate > dehydrocholate).