Three-dimensional photonic crystal sensors

Photonic crystal templating of optically active hydrogel sensors is a topic of growing interest in materials chemistry. When interactions between a mesostructured hydrogel and analyte molecules cause a reversible dimensional change of the hydrogel, the corresponding shift in optical diffraction can be detected either spectroscopically or visually. Using poly(styrene) photonic crystals as templates, we synthesized inverse opal hydrogels through photopolymerization of 2-hydroxyethylmethacrylate and various functional monomers, and demonstrated the ability to sense pH and glucose at different ionic strengths and other experimental conditions. The diffraction of the pH sensitive hydrogel shifted from 544 run to 850 nm when the pH was increased from 4 to 7, while the diffraction of the glucose sensitive hydrogel changed from 599 run to 719 run when the glucose concentration was raised from 0 mM to 100 mM. Diffraction response kinetics on the order of similar to30 minutes were observed, which may be attributed to diffusion of analyte molecules through the thin (12-24 mum) hydrogel samples. These mechanically robust inverse opal hydrogel sensors-may form a starting point for chemical and biological sensing using diffractive three-dimensional mesostructures.