Photonic crystal carbohydrate sensors: low ionic strength sugar sensing.

We developed a carbohydrate sensing material, which consists of a crystalline colloidal array (CCA) incorporated into a polyacrylamide hydrogel (PCCA) with pendent boronic acid groups. The embedded CCA diffracts visible light, and the PCCA diffraction wavelength reports on the hydrogel volume. This boronic acid PCCA responds to species containing vicinal cis diols such as carbohydrates. This PCCA photonic crystal sensing material responds to glucose in low ionic strength aqueous solutions by swelling and red shifting its diffraction as the glucose concentration increases. The hydrogel swelling results from a Donnan potential due to formation of boronate anion; the boronic acid pK(a) decreases upon glucose binding. This sensing material responds to glucose and other sugars at <50 microM concentrations in low ionic strength solutions.