Volatile alcohol-responsive visual sensors based on P(HEMA-co-MA)-infiltrated SiO2 inverse opal photonic crystals

Abstract

Functional molecule-infiltrated inverse opal photonic crystals can exhibit reversible photonic stopband shifts as a response to the external environment, which enables them to be promising chemical or biochemical sensors. The present study reports on a copolymer, poly(2-hydroxyethyl methacrylate-co-methyl acrylate), infiltrated SiO₂ inverse opal as visual sensor for the detection of volatile alcohols vapors. The constructed sensor generates remarkable stopband red-shifts when exposed to an atmosphere of volatile alcohols. Particularly for isopropanol and butanol, a red-shift of more than 85 nm can be obtained and the color of the sensor changes from green to red, which can be observed by the naked eye. This can be attributed to the increased effective refractive index of the inverse opal caused by the diffusion and adsorption of alcohol molecules into the pores. This is based on a combination of a three-dimensional macroporous structure of the inverse opal and strong affinity of the copolymer to alcohols. The exposure to air can reactivate the sensor because of the volatilization and desorption of alcohols. The selectivity, sensitivity and the reusability of the sensor have been investigated by monitoring the reflectance spectra. The results demonstrate that the prepared sensor can be used as a promising candidate as visual sensors for detecting volatile alcohol vapors.