Thiourea functionalized hydrogel photonic crystal sensor for Cd2+ detection

Abstract

A new hydrogel photonic crystal (HPC) sensor utilizing thiourea as the recognition group for cadmium cation detection was developed. The sensor was fabricated by infiltrating a 3D contact polystyrene photonic crystal template with precursor solution of acrylamide, 1-allyl-2-thiourea and N,N′-methylenebisacrylamide, followed by a thermal polymerization using ammonium persulfate as initiator at room temperature. The resulting HPC sensor with periodic opal structure changed its volume and Bragg diffraction wavelength in response to the difference of the Cd²⁺ concentration. Shifts of diffraction peak were observed by using a fiber optic spectrometer and the measurements showed a function relationship between the blue-shift and aqueous Cd²⁺ concentrations in the range of 0.01 mmol L⁻¹ to 10 mmol L⁻¹ in a pH 4 buffer solution. The functionalized thiourea groups allowed HPC to recognize the analyte Cd²⁺ with high specificity. The maximum blue-shift reached 47 nm responding to Cd²⁺ but no significant shift responding to Zn²⁺ and Hg²⁺. The HPC sensor could be used to quantitatively determine Cd²⁺ concentrations in complex solutions such as natural water.