Response kinetics of chemically-modified quartz piezoelectric crystals during odorant stimulation

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Abstract
When chemically-modified piezoelectric quartz crystals are used to detect odorous compounds in air the maximum frequency changes induced by odorants vary both within and between sensors. This variability is reduced when stimulation variables, such as flow rate, odorant concentration and duration, are closely controlled. Precise control of the stimulus allows time-dependent frequency responses to be observed as odorants interact with the sensor surface. The aim of the present experiments was to examine in detail the time-dependent frequency responses of sensors (functionalized with one of six different surface coatings) when exposed to one of 18 odorants. The results demonstrate that these time-dependent responses (termed ‘kinetic signatures’) were characteristic of each odorant–surface interaction. They were repeatable for each sensor and reproducible among sensors with inter-crystal variability reduced virtually to zero. Kinetic signatures were independent of the maximum frequency change induced by odorants and they appear to be useful as a new method of analysing odorant–surface interactions; an application for odorant discrimination using a six-sensor array and artificial neural network analysis is demonstrated.

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