A piezoelectric quartz crystal sensor array self assembled calixarene bilayers for detection of volatile organic amine in gas

P-tert-butylcalix[n]arenes (n=4, 6, 8, abbreviated as CA[4], CA[6], CA[8], respectively) were immobilized on the Au surface of the piezoelectric quartz crystal by the reaction between CA[n] and the acid chloride terminated mercaptoacetic acid (MAA) self assembled monolayers to form MAA/CA[n] bilayers. The sensing films were not only immobilized easily and reproducibly, but also used to improve the reversibility of the sensor signal. The response characteristics show the response of CA to organic amine attributes to specific interaction between CA[n] (host) and organic amines (guest). The frequency shifts of n-butylamine and iso-butylamine are much larger than tert-butylamine and diethylamine because of shape-selection and hydrogen bonding. Compared to CA[6] and CA[4], CA[8] has highest sensitivity to organic amine due to having more flexibility to accommodate guest molecules. A sensor array with three-layer back-propagation neural network was applied to detect the binary mixture of n-butylamine in the range of 7.14–142 μl l⁻¹ and iso-butylamine in the range of 7.14–57 μl l⁻¹. The optimum values of learning rate (0.15) and momentum term (0.8) were determined by experiment. The best epoch of training was 1098. The root mean square error of prediction was 1.69 (μl l⁻¹) for n-butylamine, and 1.42 (μl l⁻¹) for iso-butylamine.