Building fluorescent sensors by template polymerization: The preparation of a fluorescent sensor for L-tryptophan

The development of fluorescent sensors for organic molecules is of great pr actical importance in chemical, biological, and pharmaceutical sciences. Us ing L-tryptophan as an example, we have studied a new way of making polymer ic fluorescent sensors using template polymerization or molecular imprintin g techniques. The fluorescent polymers were prepared using functional monom ers with a fluorescent probe attached to it. The fluorescence of this polym er could be quenched by 4-nitrobenzaldehyde. Addition of the template molec ules, L-tryptophan, increased the fluorescence intensity of the imprinted p olymer/quencher mixture in a concentration-dependent fashion, presumably th rough the displacement of the quencher from the binding sites by L-tryptoph an. This fluorescence intensity change upon mixing with L-tryptophan allows the binding event to be detected easily. The sensor also exhibited enantio selectivity for the template molecules. For example, the effect of D-trypto phan on the fluorescence intensity of the polymer is about 70% that of its L-enantiomer. Furthermore, the effect of L-phenylalanine and L-alanine on t he fluorescence intensity change is much smaller than that of L-tryptophan. Because the approach used does not require the de novo design of the compl ementary binding site and does not rely on any specific structural features of the template molecule or prior knowledge of its three-dimensional struc ture, the same principle could potentially be useful for the future constru ction of practical fluorescent sensors for many other compounds. (C) 1999 A cademic Press.