Abstract:

A hydrogel photonic crystal (HPC) film was fabricated for the specific detection of cadmium ions. This sensing film was based on a combination of a photonic crystal and a responsive hydrogel. It was fabricated using a "sandwich" filling method with a polystyrene (PS) colloidal crystal template, acrylamide (AM) and 1-allyl-2-thiourea (ATU) monomers. The morphology and responsivity were investigated in detail. The sensing film had an ordered, inverse opal structure and produced an optical signal in response to changes in the concentration of Cd²⁺. The Bragg diffraction peaks from the sensing film were blue shifted with increasing concentrations of Cd²⁺, and the color changes were visible to the naked eye. When the optimum ratio of monomers, suitable pH and ionic strength were used, the maximum displacement of the diffraction peak reached 51.1 nm. The presence of other interfering metal ions did not affect the specific response to Cd²⁺, and the sensing film exhibited a fast response rate. The cyclic tests showed that the sensing films had suitable mechanical and chemical stability because of their highly cross-linked structure. Importantly, these sensing films were allowed for high efficiency and rapid detection of Cd²⁺ by a color change that was visible to the naked eye.

Key words: Photonic crystal, Hydrogel, 1-Allyl-2-thiourea, Cadmium ion, Blue shift, Naked eye