Chemical sensors respond to the presence of a specific analyte in a variety of ways. One of the most convenient is a change in optical properties, and in particular a visually perceptible colour change. Here we report the preparation of a material that changes colour in response to a chemical signal by means of a change in diffraction (rather than absorption) properties. Our material is a crystalline colloidal array of polymer spheres (roughly 100 nm diameter) polymerized within a hydrogel that swells and shrinks reversibly in the presence of certain analytes (here metal ions and glucose). The crystalline colloidal array diffracts light at (visible) wavelengths determined by the lattice spacing, which gives rise to an intense colour. The hydrogel contains either a molecular-recognition group that binds the analyte selectively (crown ethers for metal ions), or a molecular-recognition agent that reacts with the analyte selectively. These recognition events cause the gel to swell owing to an increased osmotic pressure, which increases the mean separation between the colloidal spheres and so shifts the Bragg peak of the diffracted light to longer wavelengths. We anticipate that this strategy can be used to prepare 'intelligent' materials responsive to a wide range of analytes, including viruses.

Polymerized colloidal crystal hydrogel films as intelligent chemical sensing materials

We report the development of a novel sensing material that reports on analyte concentrations via diffraction of visible light from a polymerized crystalline colloidal array (PCCA). The PCCA is a mesoscopically periodic crystalline colloidal array (CCA) of spherical polystyrene colloids polymerized within a thin, intelligent polymer hydrogel film. CCAs are brightly colored, and they efficiently diffract visible light meeting the Bragg condition. The intelligent hydrogel incorporates chemical molecular recognition agents that cause the gel to swell in response to the concentration of particular analytes; the gel volume is a function of the analyte concentration. The color diffracted from the hydrogel film is, thus, a function of analyte concentration:  the swelling of the gel changes the periodicity of the CCA, which results in a shift in the diffracted wavelength. We have fabricated a sensor, utilizing a crown ether as the recognition agent, that detects Pb2+ in the 0.1 μM−20mM (∼20 ppb−∼4000 ppm) concenra...

Intelligent Polymerized Crystalline Colloidal Arrays: Novel Chemical Sensor Materials

Studies on cation-exchange membranes having permselectivity between cations in electrodialysis

Application of macrocyclic compounds in chemical analysis

Publisher Summary This chapter describes the physical organic aspects of crown-ether chemistry It discusses the thermodynamic and kinetic stabilities of crown-ether complexes and describes the chemical reactivity of the complexes The term macrocyclic polyether refers to cyclic compounds having at least one oxygen donor atom The unique ability of crown ethers to form stable complexes with various cations has been used to advantage in diverse processes, such as isotope separations, the transport of ions through artificial and natural membranes, and the construction of ion-selective electrodes Because of their lipophilic exterior, crown ether complexes are often soluble even in apolar solvents This property has been successfully exploited in liquid–liquid and solid–liquid phase-transfer reactions

Stability and reactivity of crown-ether complexes

Calorimetric titration study of the interaction of some uni- and bivalent cations with benzo-15-crown-5, 18-crown-6, dibenzo-24-crown-8, and dibenzo-27-crown-9 in methanol-water solvents, at 25.degree.C and .mu. = 0.1

Y. Chan

Papers

Calorimetric titration study of the interaction of some uni- and bivalent cations with benzo-15-crown-5, 18-crown-6, dibenzo-24-crown-8, and dibenzo-27-crown-9 in methanol-water solvents, at 25.degree.C and .mu. = 0.1