Electrochemical Chiral Recognition of Tryptophan Isomers Based on Nonionic Surfactant-Assisted Molecular Imprinting Sol–Gel Silica

A new molecularly imprinted SiO2 (MISiO2) film on the surface of indium tin oxide (ITO) electrode was prepared by the sol–gel method and was then applied successfully in the electrochemical chiral recognition of tryptophan (Trp) isomers. Owing to the high chemical stability, excellent rigidity, and low cost, the resultant sol–gel SiO2 is a good matrix material for molecular imprinting. Nonionic surfactant cicosaethylene glycol hexadecyl ether (Brij58) arranged directionally on the surface of the hydrophobic ITO electrode possesses a large amount of oxygen-containing functional groups and may induce the accumulation of template molecules (L-Trp) on the surface of ITO, resulting in L-MISiO2/ITO after the removal of L-Trp templates by calcination. The characterizations of the L-MISiO2/ITO reveal that the L-Trp templates could be successfully removed from the matrix, producing complementary cavities within the L-MISiO2/ITO. The resultant L-MISiO2/ITO exhibits greatly higher affinity toward L-Trp than D-Trp due to the three-point interaction mechanism, and therefore it exhibits good chiral recognition ability for the Trp isomers. In addition, the as-prepared L-MISiO2/ITO or D-MISiO2/ITO (D-Trp as the templates) can predict the ratio of L- and D-isomers in racemic mixture. Last, the MISiO2 films exhibited quick binding kinetics and good recognition reproducibility.