Photonic crystal pH and metal cation sensors based on poly(vinyl alcohol) hydrogel

A facile strategy for the preparation of poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAA) photonic crystal materials with pH and metal cation responses is presented. A solvent-assisted freeze-thaw method is used to form a physically cross-linked PVA gelated crystalline colloidal array (GCCA) photonic crystal. The PVA hydrogel-based photonic crystal sensors were prepared by the introduction of environmentally sensitive components responding to pH and cations into the GCCA system. The photonic crystal pH sensor shows good durability, a large stopband shift, and good adjustability. Further functionalization of 8-hydroxyquinoline makes the interpenetrating networks respond to metal cation concentrations which could be determined from the diffraction color change or precisely monitored by diffraction wavelength shifting using a spectrophotometer. The PVA hydrogel-based photonic crystal sensors could be fabricated in any size and geometry as needed because there is no requirement for a thin sample to allow for penetration of UV light and its processing time is greatly reduced compared with the use of colloidal crystal templates, which has an important significance in the large-scale industrial production in the future.