Toward bioinspired nanostructures for selective vapor sensing: diverse vapor-induced spectral responses within iridescen
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Toward bioinspired nanostructures for selective vapor sensing: diverse vaporinduced spectral responses within iridescent scales of Morpho butterflies Timothy A. Starkey1, Peter Vukusic1 and Radislav A. Potyrailo2* 1 2
Natural Photonics Group, School of Physics, University of Exeter, EX4 4QL, UK. GE Global Research, 1 Research Circle, Niskayuna, NY 12309, USA.
* Corresponding author: [email protected] ABSTRACT The iridescent colors of Morpho butterflies have captured scientific intrigue for over a century. However, only recently photonic structures of the wing scales of Morpho butterflies have inspired new ideas in the diverse areas of technology including sensing. In this study, we performed theoretical and experimental evaluation of vaporinduced reflectance changes of the Morpho scales. These experiments provided additional details of the origin and the magnitude of vapor response selectivity in these natural photonic nanostructures and facilitated our design and fabrication of highly selective biomimetic photonic nanostructures. INTRODUCTION The practical uses of chemical sensors are realized in a vast number of applications, such as in industrial processes, environmental studies, agriculture, clinical settings, and military technologies [1]. These applications stimulate growth in research into all aspects of high performance sensing. Whilst significant advances in receptor and transduction principles have been made, the ability to detect multiple volatiles and trace level molecules in real time remains challenging [2]. The biological world is known to contain a suite of ideas that stimulate technological applications, the most widely known commercial success is VelcroTM whose design was inspired by the barbs from the burdock plant [3]. Naturally evolved structures that manipulate light, which are commonly observed in animals [4]–[6] and plants [7], [8], are becoming increasingly studied to yield new ideas for technological exploitation. Recently, the naturally formed photonic structures present in the wing scales of tropical Morpho butterflies have begun to provide novel bio-inspiration within the sensing community [9], [10]. The nanostructure present in scales that adorn the wings of iridescent Morpho butterflies comprises multi-layered thin film reflecting layers which interact with light through interference and diffraction phenomena [11] to reflect an often vivid blue color. Figure 1 shows the metallic reflection of two Morpho butterflies, and an example of the nanostructure responsible for this color appearance. In our recent study we have shown that the local chemical environment within the iridescent scales of the Morpho butterfly strongly influences the reflectivity upon lowconcentration vapor exposures [12]. The combined role of this chemical environment, a gradient of surface polarity from the polar tops of ridges to the less polar bottoms, within the photonic structure of these scales allows the spectral transduction of volatile organic compounds (VOCs) due to their preferential adsorption [12]. T
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