Electrical impedance-spectroscopy particle detector for use in microanalysis systems

This paper describes a novel chromatographic detection method using an integrated electrical impedance spectroscopy particle detector fabricated using micromachining technologies for use in chemical and biological analysis systems such as liquid chromatography or field flow-fractionation systems. The design, theory, fabrication, and testing of the detector are described. Critical parameters of the detector such as detection limits, and the effects of flow rate and applied voltage on detector response are measured. Motivation for use of an on-chip impedance spectroscopy detector is given. Electrical impedance spectroscopy is performed by measuring the magnitude and phase of the electrical impedance over a range of frequencies and is used not only for detection, but also for particle size measurement. The demonstrated impedance detection system is simple, small, and flexible. The impedance detector consists of 20 mu m wide electrodes on the top and bottom surface of the separation channel giving a detection volume between 150 pL and 30 nL. Some of the advantages of the detector include simplicity of design, fabrication, and operation, fast response and short warm-up time, high signal-to-noise ratio, detection of a wide range of sample types, small size, and compatibility with micromachining processes. The fact that spectroscopy may be used to determine particle size and composition may be its biggest advantage.