Colloidal crystals based portable chromatic sensor for butanol isomers and water mixtures detection

In this work, we report on a structurally-colored composite colloidal crystal able to change its color in presence of different polar solvents such as butanol and to distinguish its isomers. Herein, polydimethylsiloxane (PDMS) infiltrated polystyrene opals are fabricated by means of a two steps approach and their final structure exhibits a green opalescence, the diffraction peak wavelength position changes as a function of the analytes spotted on the surface. In fact, the realized composites present a colorimetric variation in their response, since a remarkable red-shift of the diffraction peak is observed. An analytical model has been proposed and validated in order to assess the optical chromatic response, according to which the changing of the filling factor is the main element that produces the variation in the optical response. The selectivity, sensitivity and the reusability of the sensor have been investigated by monitoring the static reflectance spectra considering a mixture of 2-Methylpropan-2-ol (TerB) and water. Dynamic reflection spectra have been employed as an appropriate technique for the recognition of butanol isomers such as TerB, Butan-1-ol (NB) and Butan-2-ol (2B). The results demonstrate that the prepared photonic crystal sensing material and the interrogation approach used are a suitable tool for the development of low cost, portable sensors for homologues and isomers.