Mesoporous Silica Photonic Crystals for Colorimetric Concentration Detection

Colorimetric concentration detection based on photonic crystals has attracted considerable attention owing to the substantial color changes in response to external stimuli. In general, photonic crystals for colorimetric detection are carefully designed by introducing tailored recognition sites into an ordered structure. These materials are widely used in the detection of trace substances. However, the traditional photonic crystal assembled by colloid particles was rarely applied in concentration detection since the solute tends to occupy the interparticle voids, causing reduced refractive index contrasts and closed bandgaps at higher concentrations. Consequently, the development of a more convenient and universal concentration detection material is an urgent requirement. Herein, photonic crystals assembled by mesoporous SiO 2 particles ( m -SiO 2 –PC) were prepared and used as a colorimetric indicator of solution concentration for nonvolatilized substances. The solute preferentially occupied the mesopores of m -SiO 2 particles, yielding an increase in reflection index, a shift in reflection peak, and considerable color contrasts on the m -SiO 2 –PC film after the evaporation of solvent. The relation between wavelength shifts and solution concentrations could be used for quantitative concentration detection. A colorimetric concentration indicator based on m -SiO 2 –PC film provides a more efficient and universal method that is applicable for a variety of solutions.