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Bio-inspired gas sensors

Bio-inspired gas sensors are devices inspired by nature, e.g. bird feathers or insects cuticles or butterfly wings changing colour when in contact with liquid or vapour .

For example, the wing structure of well known blue Morpho butterfly is composed of chitin-and-air multilayers whose colour changes when exposed to different vapours. When vapour replaces the air in the cavities, there is a change in refractive index difference between two materials, which causes the colour to redshift in the optical wavelength. Colour change in the wings can be attributed to absorption of different vapours and/or different concentrations and outperform response of existing engineered photonic sensors. Another example is iridescent blue colour in scales of Hoplia coerulea beetle. The scales are are made of periodic porous multilayers and the colour changes from blue to green when in contact with water.

Production methods of bio-inspired multilayered polymer or metal-oxide sensors include self-assembly, coextrusion, or spin-coating, which makes them high-sensitivity and low-cost sensors. Available 'classic' gas and vapor sensors have a single-output and are used when response selectivity is not required. Photonic crystal sensors colour change is related to their photonic band structure, which depends on a refractive index and thickness of multilayers. The smallest change in one of the parameters will notably change reflected colour.

Metal-oxide gas-sensors are based on the change of the refractive index difference between two materials as the vapor or liquid enters the pores of the layers. Polymer-based gas sensors are devices made of polymer multilayers, sensitive to certain vapour (e.g. ethanol, acetone). Absorption of vapour causes swelling of the polymer layer. The change of layers thickness will induce the colour change in the multilayers, see: Distributed Bragg reflector.