Easy to optimize: dynamic combinatorial libraries of metal-dye complexes as flexible sensors for tripeptides

A dynamic combinatorial library (DCL) of dye complexes of Cu2+ and Ni2+ was used to sense the sequence isomeric tripeptides His-Gly-Gly, Gly-His-Gly, and Gly-Gly-His. The DCL sensor was obtained by mixing buffered aqueous solution of three commercially available dyes together with CuCl2 and NiCl2. The addition of the peptide analytes resulted in characteristic changes in the UV-vis spectrum of the mixture, which allowed the identification of the peptide. Due to the modular nature of the sensor, it was possible to optimize the sensor by variation of the amounts and ratio of its constituent building blocks. The composition of the best sensor was found to vary substantially, depending on the sensing problem to be addressed. Whereas a Cu2+/Ni2+ ratio of 1:3 gave the best differentiation for Gly-His-Gly and Gly-Gly-His, a sensor containing exclusively Cu2+ was found to provide the best discrimination between His-Gly-Gly and Gly-Gly-His.