Photonic multilayers for ultrasensitive millisecond colorimetric discrimination between benzene, toluene, and xylene

Responsive photonic crystals (RPCs) have been used as real-time colorimetric sensors for the detection of various analytes. Herein, reusable one-dimensional photonic crystal (1D PC) polymeric films are used for the ultrafast and distinct colorimetric discrimination between benzene, toluene, and xylene (BTX). The 1D polymeric films are prepared via the alternate spin-coating of photo-cross-linkable poly(para-methyl styrene-co-benzophenone acrylate) (P(MS-co-BPA)) as a high refractive index polymer and poly(methyl acrylate-co-benzophenone acrylate) (P(MA-co-BPA) as a low refractive index polymer onto a glass substrate. Millisecond traffic light discrimination between BTX is achieved when these films are immersed in each BTX solution. The visibility in discrimination is further improved by controlling the thickness and crosslinking density of the P(MA-co-BPA) layers. The high efficiency of the BTX discrimination is attributed to the difference in miscibility between the low-refractive-index polymer and each BTX. This discrimination process is repeated several times, and the reusability of the films over multiple cycles is demonstrated. In addition, the 1D polymeric films are applied to the discrimination of commercial gasolines from adulterated samples, thus demonstrating a practical contribution to environmental protection.