Infrared detection in Melanophila acuminata (2001)

The progression of science has often included mimicry of nature, inherent in which lies the solution of many seemingly insurmountable technical obstacles. One limitation humans have sought to overcome through arti cial means is their range of visual sensitivity, which is con ned to a small band of the electromagnetic radiation spectrum. Nature has given us two biological models for detection of infrared wavelengths: snakes and insects. The insects include Buprestid beetles of the species Melanophila acuminata (Coleoptera: Buprestidae), that can detect infrared radiation emitted from forest res with bilateral thoracic pit organs. Investigation of the pit organ of Melanophila beetles may lead to the development of a new class of highly-sensitive detectors that operate at ambient temperatures. The sensitivity threshold of infrared detection in Melanophila beetles was established using standard electrophysiological techniques and precise control of radiant ux dosimetry. These experiments determined the distance from which the beetles detect forest res and pointed to olfaction as the sense responsible for long-range orientation. Moreover, the response characteristics of action and generator potentials recorded from the infrared pit organ were measured. A tunable infrared ultrafast laser was used to measure the spectral sensitivity of the pit organ. The bulk optical and thermal properties of the organ tissue were examined with integrating sphere measurements and scanning probe microscopy, respectively. The material properties together with the action spectrum indicate that the pit vii organ may utilize its tissue properties speci cally to sense wavelengths in the mid-infrared atmospheric window (2{5 m). Two experiments were designed to provide physical evidence that the beetle infrared pit organ functions via a photo-thermal-mechanical transduction mechanism. In the rst mechanism experiment, a ber-based di erential-phase optical low coherence re ectometer was used to measure sub-wavelength displacement of the organ. Although the displacement upon absorption of infrared light is not unique to the organ tissue, the complex morphology of the displacement waveform supports the photo-thermalmechanical hypothesis. In the second mechanism experiment, the sensitivity as a function of pit organ temperature was measured with electrophysiological techniques. No dependence upon static temperature was found, which indicates that the beetle responds only to rapid temperature changes brought about, for example, by absorption of infrared light by the pit organ. Novel electrode assemblies were designed and built to record an infrared response from the interganglionic connectives in the thorax of the beetle. These electrophysiological experiments veri ed the conveyance of infrared information through speci c pathways to rostrally-situated sites in the nervous system of the beetle. These experiments were designed to determine the manner in which Melanophila beetles sense infrared light. Although many questions remain, the information gained may provide suggestions to aid in the development of new solid-state infrared detectors.