Bio-inspired Gas Sensor 

Morpho butterfly-inspired photonic structures have been explored for use in gas-, vapor-, infrared-, and temperature sensor applications. In addition, selective response to diverse vapors makes butterfly-wing structures potentially useful for gas sensor applications. A single photonic structure has various differential reflectance spectra with different vapors and highly selective responses to individual vapors. The critical analysis of the data suggested that the optical response is mainly due to a combination of physical adsorption and capillary condensation of gas molecules in the gaps of the lamellae. This detection of gases or vapors was achieved by the principal component analysis (PCA) method based on the masses of collected spectral data. There is a gradient of polarity on the surface of the Morpho butterfly scales. Once the Morpho scales are exposed to vapors and gas molecules, a scale with a high polarity gradient gives a strong reflection peak at visible wavelengths. Furthermore, it was concluded that the spectral change is caused by the change in lamella thickness and refractive index because there was a thin layer of vapors and gas molecules on the structure's surface. 

In the present work, Morpho butterfly-inspired structures are fabricated by multi-photon lithography (MPL) using the crosslinkable photopolymer IP-Dip (Nanoscribe). Structural characterization is performed by scanning electron microscopy (SEM). A home-built optical characterization system is developed for optically characterizing butterfly structures at wavelengths of 1.3 μm to 1.7 m in the infrared. Optical characterization results reveal a reflection peak about 1500 nm as expected, given that the fabricated structures are scaled up relative to the feature size found in the nature butterflies.