A highly sensitive self-oscillating cantilever array for the quantitative and qualitative analysis of organic vapor mixtures

A setup for gas and liquid sensing applications was developed and operated which is based on both the frequency shifts and the bending of microcantilevers. To drive the cantilevers an electrostatic and magnetic actuation was developed with a closed feed-back loop which forces the cantilever to oscillate always at its resonance frequency. The oscillation is detected via the beam-deflection technique. By measuring the dc-signal of the photodiode the static bending of the cantilever can be monitored simultaneously. The closed feed-back loop propagates a very stable oscillation at the resonance frequency and gives a strong increase of the quality factor compared to the system without this feed-back loop. For the highly sensitive identification of gases and organic vapors the cantilevers are functionalized by polymer coatings to detect specific chemical interactions. The polymer coatings begin to swell after exposure to analyte vapor. Additionally to the mass increase, a change of surface stress between the coating and the cantilever surface occurs, resulting in a bending of the cantilever. With this setup it is possible to measure concentrations of analytes in the lower ppm-range. The data evaluation was done by multivariate data analysis. The sensor responses were used in principal component regression (partial least squares, PLS) for the qualitative and quantitative analysis and prediction of vapors under investigation. The results obtained with different volatile organic compounds (VOCs) are presented to introduce this promising approach for easy-to-use and highly sensitive sensor systems. (c) 2005 Elsevier B.V. All fights reserved.