Development of a miniature odour sensor for implantation in Mice

Abstract

Olfactory navigation is crucial for survival-related behaviours in animals, including lo cating food sources, evading predators, and selecting mates. There is increasing ev idence that suggests mice can process intermittent and fluctuating odour stimuli to extract spatial and temporal information for effective navigation. We have devised a custom-designed open-field behavioural arena(150cm×108 cm) to study odour-based navigation in mice. The arena features controlled airflow and visual isolation to have the animal focus exclusively on olfactory cues that are introduced via a custom-made odour delivery device. To gain a better understanding of the sensory input during navigation, we aim to develop a miniature, head-mounted odour sensor for real-time olfactory information recording in freely behaving animals. We evaluate various odour detection technologies, including a photoionisation detector (PID), an ethanol sensor, and a metal oxide (MOx) sensor. While a PID of fers high sensitivity and fast response times, their size and cost limit their applicability for head-mounted use. MOx sensors, particularly those incorporating microelectrome chanical systems (MEMS), are ideal due to their compact size, high sensitivity, and rapid response times. A metal oxide sensor, the Micro Chemical Sensor (MiCS) 6814 —which has three independent sensing elements — was determined to be the suit able sensor for the project due to its compact size and sensitivity to volatile organic compounds (VOCs). A significant challenge when using MOx sensors is their slow recovery time, which limits their ability to capture rapid odour concentration fluctuations in turbulent environments. By applying signal deconvolution with a rise-decay-sustain kernel, we were able to overcome the slow recovery of this sensor and produce signals using the MiCS that are comparable to a PID while capturing dynamic olfactory information. This paves the way to use this sensor as a chronic lightweight implant, allowing its integration into behavioural experiments with freely moving mice.