Monodisperse

highly charged polystyrene colloidal particles with an average diameter of 170 nm were prepared by emulsifier-free emulsion polymerization.These particles spontaneously self-assemble into crystalline colloidal arrays (CCAs) in low ionic strength aqueous solutions due to long-range electrostatic repulsions among the particles.These CCAs diffract light

meeting the Bragg condition in the ultraviolet

visible and near-infrared spectral regions.CCAs were embedded into a polyacrylamide hydrogel to form polymerized crystalline colloidal arrays (PCCA) by adding acrylamide

N

N-methylenebisacrylamide and 2

2-diethoxyacetophene into the liquid CCAs

and then photopolymerizing the mixture of monomers to make a thin PCCA film.Modified PCCAs containing —NH2 groups were prepared via Mannich reaction with ethylenediamine.Hydrogel modified with ethyleneamide underwent a volume phase transition in response to the change in ionic strength of the solution.The biotinylation of the PCCA was achieved by chemical conjugation of the polymer gel with biotin after appropriate chemical modification of the gel.The interaction of the biotinylated PCCA with avidin led to a shrinkage in volume of the system caused by increased cross-linking in the hydrogels due to the binding between biotin and avidin.This volume change of the hydrogels altered the periodicity of the CCAs

resulting in a blue shift in the diffraction spectra.When excess biotin hydrazide was added

it was able to displace avidin bound to the biotinylated PCCA by the formation of a stronger complex with avidin.The disassociation of avidin from the PCCA led to the re-swelling of the hydrogels

corresponding to an increase in the interparticle distance in the PCCA and thus a red shift in the diffraction spectra.Our results demonstrated the response of a model sensor system made of biotinylated PCCA to the binding of an interacting protein

avidin.This may provide a basis for the sensing of protein molecules by functionalized PCCA systems.