Fig. 4.

Optical signatures of the response of hybrid gelatin films with 30 μm thickness to distinct volatile organic compounds (VOCs) at 12%–15% (v/v) in the sensors chamber. Examples are given for four distinct VOCs (hexane, diethyl ether, acetone, and ethanol), showing the typical profile of the signals obtained during exposure and recovery cycles in the electronic nose (left side), as well as the corresponding optical and morphological changes observed in the hybrid gels by polarized optical microscopy with 90° crossed polarizers (top) and 45° crossed polarizers (bottom).