A reagent containing intelligent polymerized crystalline colloidal arrays that colorimetrically indicate levels of pH, temperature and Pb²⁺ concentrations in solutions has been designed by researchers at the University of Pittsburgh.

According to a report in the Nov. 1 issue of Analytical Chemistry, the arrays comprise monodisperse, highly charged colloidal particles enveloped in hydrogel networks that change the arrays' volume in response to attached chemical recognition elements. Carboxylate functional groups are used for pH and ionic strength detection; a crown ether for Pb²⁺; and N-isopropylacrylamide, for temperature detection. When the volume changes, the diffraction wavelength shifts and the observed diffraction color changes.