A molecularly imprinted photonic polymer (MIPP) sensor for respective detection of tetracycline, oxytetracycline and chlortetracycline is developed based on the combination of a colloidal crystal templating method and a molecular imprinting technique. Colloidal crystal templates are prepared from monodisperse polystyrene colloids. The molecularly imprinted polymer, which is embodied in the colloidal crystal templates, is synthesized with acrylic acid and acrylamide as monomers, N,N′-methylene bisacrylamide as a cross-linker and tetracyclines (TCs) as imprinting template molecules. After removal of the colloidal crystal template and the molecularly imprinted template, the resulted MIPP consists of a three-dimensional, highly ordered and interconnected macroporous array with a thin hydrogel wall, where nanocavities complementary to analytes in shape and binding sites are distributed. The response of MIPP to TCs stimulants in aqueous solution is detected through a readable Bragg diffraction red-shift, which is due to the lattice change of MIPP structures responding to their rebinding to the target TCs molecules. A linear relationship was found between the Δλ and the concentration of TCs in the range from 0.04 μM to 0.24 μM. With this sensory system, direct and selective detection of TCs has been achieved without using label techniques and expensive instruments. The developed method has been applied successfully to detect tetracycline in milk and honey samples.

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.

We developed a simple method based on molecularly imprinted photonic polymers (MIPPs) for sensing of sulfonamides in egg white samples. The fabrication of MIPPs mainly involved a photonic crystal template method integrated with a molecular imprinting technique. Firstly, an opal photonic crystal template was self-assembled from monodisperse polystyrene colloids. And then the template was embedded with molecularly imprinted polymers, which was synthesized with acrylic acid and acrylamide as monomers, N,N′-methylenebisacrylamide as a cross-linker and sulfamerazine (SM1) or sulfamethazine (SM2) as imprinting molecules. After removal of the photonic crystal template and the imprinted molecules, the resultant MIPP sensor accommodated an inverse opal photonic crystal structure embedded in hydrogels. By using the as-prepared MIPP sensor, sulfonamides were sensitively and specifically recognized via a molecular imprinting technique and the recognition was detected through the readable Bragg diffraction shift from the photonic crystal structure. A 70 nm maximum Bragg diffraction blue-shift of the MIPP was observed with the concentrations of the sulfamerazine or sulfamethazine varying from 3.8 μM to 22.8 μM and function relationships were found between blue-shifts and the concentrations of sulfonamides in pH 5 acetic acid–sodium acetate buffer solution. The developed method has been applied successfully to detect sulfonamides in egg white samples without using labelling techniques and expensive instruments.