We report the development of a novel sensing material that reports on analyte concentrations via diffraction of visible light from a polymerized crystalline colloidal array (PCCA). The PCCA is a mesoscopically periodic crystalline colloidal array (CCA) of spherical polystyrene colloids polymerized within a thin, intelligent polymer hydrogel film. CCAs are brightly colored, and they efficiently diffract visible light meeting the Bragg condition. The intelligent hydrogel incorporates chemical molecular recognition agents that cause the gel to swell in response to the concentration of particular analytes; the gel volume is a function of the analyte concentration. The color diffracted from the hydrogel film is, thus, a function of analyte concentration: the swelling of the gel changes the periodicity of the CCA, which results in a shift in the diffracted wavelength. We have fabricated a sensor, utilizing a crown ether as the recognition agent, that detects Pb2+ in the 0.1 μM-20mM (∼20 ppb-∼4000 ppm) concenration range. We have also fabricated glucose and galactose sensors, utilizing glucose oxidase or â-D-galactosidase as the recognition elements. The glucose oxidase sensor detects glucose in the 0.1-0.5 mM (18-90 ppm) concentration range in the presence of oxygen and detects as little as 10-12 M glucose (0.18 ppt) in the absence of oxygen. In addition, this sensor reports on dissolved oxygen concentration from ∼1 to 6 ppm in the presence of constant glucose concentrations.