Towards Bio-inspired Photonic Vapour Sensors

Many highly-evolved bio-photonic structures, which tailor the propagation of light by coherent optical scattering, have been investigated. These natural designs, which have many diverse ecological functions, are becoming increasingly studied as sources of innovation and inspiration for a range of scientific, technological, and commercial applications. The brilliant blue colour reflected from the scales of the Morpho butterfly is just one example of nature’s ability to manipulate light and colour strongly. In this thesis, the photonic structure present in the scales of the Morpho butterfly is investigated as a source of bio-inspiration in the pursuit of high- performance photonic vapour sensors. The intention of this is to outperform classical sensor approaches which traditionally suffer from poor selectivity between chemical species. By measuring the change in reflectance from the iridescent scales of the Morpho butterfly, both a sensitive and, critically, a selective response to chemical vapours can be obtained. Here, the origin of this unique multivariable vapour-induced optical response is investigated, and this biological template is further explored as a source of innovation for the mature field of chemical sensing. By using synergy between experimental and theoretical techniques, a mechanism for the sensitive and selective response of the Morpho butterfly’s scales to different chemical vapour environments is elucidated. This mechanism arises from combined chemical and physical effects within the photonic nanostructure. Following this, demonstrations of this biological template’s vapour response attributes, which have large and desirable diversity in the optical responses, are made. These response attributes are visualised in the spectral changes associated with optical excitation conditions, such as from different angles and polarisation states, and also in the temporal response profiles. Finally, theoretical sensor designs that outperform the Morpho scales are described. Simple principles that might improve the currently unacceptable levels of selectivity in contemporary sensor implementations are outlined and the vapour response of a Morpho-inspired photonic structure is presented