Electrical conductivity particle detector for use in biological and chemical micro-analysis systems

Abstract

This work introduces an integrated electrical detector for use as a conductivity or impedance based detection system for miniaturized biochemical analysis systems such as liquid chromatography or field flow-fractionation systems. Motivation for use of an on-chip conductivity detector is given. The design, fabrication, and characterization of the detector in the conductivity-based detection mode are described. Critical parameters of the conductivity detector, such as time constants, detection limits, and the effects of flow rate and applied voltage on detector response, are measured. In addition, the on-chip detector is compared to a conventional off-chip, UV-based detection system. The conductivity detector was fabricated by creating low impedance electrodes on the top and bottom surface at the end of a typical separation channel. The detector was shown to easily detect particles in the working concentration range of a typical separation system at low applied voltages. The measured time constants averaged approximately 2 seconds and changed slightly with flow rate through the detector. This time constant is acceptable for typical separations that take minutes to complete. The detector was also shown to dramatically improve resolution and reduce peak broadening for the system when compared to an off-chip detector.