Photonic sensing of organic solvents through geometric study of dynamic reflection spectrum

Traditional photonic sensing based on the change of balanced reflection of photonic structures can hardly distinguish chemical species with similar refractive indices. Here a sensing method based on the dynamic reflection spectra (DRS) of photonic crystal gel has been developed to distinguish even homologues, isomers and solvents with similar structures and physical properties. There are inherent relationships between solvent properties, diffusion behaviour and evolution of reflection signals, so that the geometric characteristics of DRS pattern including ascending/descending, colour changes, splitting/merging and curvature of reflection band can be utilized to recognize different organic solvents. With adequate solvents being tested, a database of DRS patterns can be established, which provide a standard to identify an unknown solvent. Photonic sensing is a method for detecting individual chemical species, but can fail when they are sufficiently similar in physical properties. Here, the authors report a method that can distinguish even very closely related species, such as homologues and chemical isomers.