Ceramic Materials for Mass-Sensitive Sensors - Detection of VOCs and Monitoring Oil Degradation
Inorganic frameworks obtained by the sol-gel route can be templated by a molecular imprinting (MIP) approach to generate functional cavities. Such MIP ceramics show highly appreaciable properties for chemical sensor applications, because they are inherently chemically and thermally robust. In combination with mass-sensitive devices (e.g. quartz crystal micro balance – QCM, surface transverse wave oscillator - STW), they yield highly selective and sensitive chemical sensors. Gas phase measurements with volatile organic compounds (VOCs) e.g. lead to sensitivities below 1 ppm. Sensitivity can be tuned by the sol-gel-precursor: when hydrolysing more bulky alkoxides, this leads to enhanced sensitivity by increasing porosity as a consequence of slower solvent evaporation. By adding products of oxidative oil degradation to the sol-gel mixture, we succeeded in generating sensors for degradation processes in these complex matrices. This allows parallelly monitoring both the chemical state of oil and changes in viscosity. Sensitivity is enhanced according to the Sauerbrey equation by going from 10 MHz QCM transducers to higher frequencies either by etching the quartz substrates and so reducing the resonator thickness or by applying STWs.
P. A. Lieberzeit et al., "Ceramic Materials for Mass-Sensitive Sensors - Detection of VOCs and Monitoring Oil Degradation", Advances in Science and Technology, Vol. 45, pp. 1799-1802, 2006