Colorimetric detection of volatile organic compounds using a colloidal crystal-based chemical sensor for environmental applications

The detection of pollutants such as volatile organic compounds (VOCs) is of significant importance for environmental protection. However, conventional monitoring methods are often time consuming and require expensive equipments. In this study, a colloidal crystal-based colorimetric chemical sensor was developed for environmental applications. The device consists of a glass substrate with a three-dimensional colloidal crystal and poly(dimethylsiloxane) (PDMS) elastomer. Such a colloidal crystal was generated by infiltrating the voids within an opaline lattice of polystyrene nanoparticles with a liquid prepolymer to PDMS, followed by thermal curing. When a sample solution such as benzene, toluene, or xylene, capable of swelling the elastomer matrix, was applied to the surface of this crystal, the lattice constant and thus the wavelength of Bragg diffracted light was increased. On the basis of this mechanism, we demonstrated the colorimetric detection of VOCs. As a result, the colloidal crystal-based chemical sensor could be used to specifically determine VOC concentrations. Additionally, using this colloidal crystal-based chemical sensor, the change in the optical characteristics could be observed with the naked eye. Therefore, this chemical sensor can be applicable to on-site monitoring for environmental applications.