Beyond the classical lock/key-recognition-based approach used in the bio-analytical field, an electronic tongue or nose device (eT/eN) is an assembly of non-specific sensors. Following a long story around the imaging of biological interactions of biomolecules by surface plasmon resonance imaging, we recently extended this approach to the non-specific interactions studies in gas phase giving rise to a new optical-nose generation. The signals resulting from the binding of VOCs on an array of bioinspired receptors can be seen as 3D continuous dynamic images or movies. Finally, complex data obtained from odors are analyzed as simple images via a specific database. This flexible and straightforward approach allowed a downscaling of the device and a new miniaturized portable and generic opto-nose, Neose, was recently launched also based on silicon integrated photonic technologies (Mach-Zehnder interferometers array). The translation of a smell into an image could be seen as a first step to open up the merging of the olfactory and visual senses.
The sensitive, selective and real-time detection of odors, in the form of volatile organic compounds (VOCs), remains an important challenge in modern science. As a result, in the field of artificial olfaction, subsequent advances in sensor technologies have given rise to a variety of gas sensors spanning to address a large plethora of applications such as medical diagnostics, quality control, environmental monitoring and etc. Currently, however, the development of electronic nose (eN) technology has garnered the most attention with its biomimetic approach of multi-sensor systems. This study focuses on such an opto-eN system, which utilises Surface Plasmon Resonance Imaging (SPRI) as its transduction technique, operating in gas phase. The immediate requirement, therein, lies on the robustness of these system, especially in their ability to produce reliable measurement during in situ/on field applications. In this regard, temperature and humidity variations, regionally and seasonally, have shown to cause the most significant impact. Their influence on the signal is integrated, with chemical and physical contributions arising from both the immobilized sensing receptors and the metallized SPRI prism, responsible for the plasmonic behavior. Accordingly, we began by optimizing the prism metallization through a complete numerical study on metal layer configurations and thickness choices. The chosen structures were then experimentally compared for optimum performance and stability. Finally, the selected Chromium/Gold (Cr/Au) prism sample was used to test the effect of humidity and temperature. The developed numerical model was demonstrated to be a useful technique, which was experimentally coupled at various temperatures to obtain a fundamental understanding of the adsorption of water on gold surfaces. We believe that the comprehension of this phenomenon and its possible implications will be transferable and thereby useful for sensors beyond the opto-eN application.
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