Combining vapour sensors into arrays is an accepted compromise to mitigate poor selectivity of conventional sensors. Here we show individual nanofabricated sensors that not only selectively detect separate vapours in pristine conditions but also quantify these vapours in mixtures, and when blended with a variable moisture background. Our sensor design is inspired by the iridescent nanostructure and gradient surface chemistry of Morpho butterflies and involves physical and chemical design criteria. The physical design involves optical interference and diffraction on the fabricated periodic nanostructures and uses optical loss in the nanostructure to enhance the spectral diversity of reflectance. The chemical design uses spatially controlled nanostructure functionalization. Thus, while quantitation of analytes in the presence of variable backgrounds is challenging for most sensor arrays, we achieve this goal using individual multivariable sensors. These colorimetric sensors can be tuned for numerous vapour sensing scenarios in confined areas or as individual nodes for distributed monitoring.

Significance Morpho butterflies are a brilliant spectacle of nature’s capability for photonic engineering. Their conspicuous appearance arises from the interference and diffraction of light within tree-like nanostructures on their scales. Scientific lessons learned from these butterflies have already inspired designs of new displays, fabrics, and cosmetics. This study reports a vertical surface polarity gradient in these tree-like structures. This biological pattern design may be applied to numerous technological applications ranging from security tags to self-cleaning surfaces, gas separators, protective clothing, and sensors. Here it has allowed us to unveil a general mechanism of selective vapor response in photonic Morpho nanostructures and to demonstrate attractive opportunities for chemically graded sensing units for high-performance sensing.

We study regular wavelength scale arrays of metallic dimers. By employing dimers made up of two different sized discs, we are able to couple to array-based collective surface lattice resonances of both bright and dark, that is symmetric and antisymmetric, dimer modes and to show that the degree of asymmetry can be used to control the relative strength of the two surface-lattice modes. The collective nature of these excitations can even lead to an antisymmetric surface-lattice resonance that is stronger than the symmetric one; this is in stark contrast to the dark and bright nature of the underlying modes of the individual dimers. We verify these experimental findings, derived from extinction measurements, by comparison with both analytical and numerical modeling.

Abstract:The science of light and colour manipulation continues to generate interest across a range of disciplines, from mainstream biology, across multiple physics-based fields, to optical engineering. Furthermore, the study of light production and manipulation is of significant value to a variety of industrial processes and commercial products. Among the several key methods by which colour is produced in the biological world, this review sets out to describe, in some detail, the specifics of the method involving photonics in animal and plant systems; namely, the mechanism commonly referred to as structural colour generation. Not only has this theme been a very rapidly growing area of physics-based interest, but also it is increasingly clear that the biological world is filled with highly evolved structural designs by which light and colour strongly influence behaviours and ecological functions.

Mesozoic lepidopteran wing scales shed light on the early evolution of moths and structural colors.