Highly Sensitive Detection of Isomers through Dynamic Reflection Spectroscopy Based on Simple Amorphous Photonic Crystals

Photonic band gaps of photonic crystals (PCs) are related to the effective refractive indices; therefore, it is quite difficult to detect homologues and isomers with similar reflection indices by PCs. Some researchers have tried to use some complex PCs for detecting homologues and isomers. However, there are few reports in trace detection of isomers (cis–trans isomers) and mixed isomers by using simple amorphous photonic crystals (APCs). Herein, dynamic reflection spectrum (DRS) patterns of APCs are obviously different by changing species of compounds, mixtures of two similar isomers, volatility temperatures, and diameters of SiO2. Isomers with a refractive index difference of only 0.001 and their mixtures could be distinguished based on different DRS patterns of simple APCs. For example, the difference in the refractive indices of cis-3-hexene and trans-3-hexene is only 0.001, and the difference of desorption balance time of APCs is 142 s. The method shows high sensitivity detection in isomers and cis–trans isomers.