Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published July 2008 | public
Journal Article

Resonance impedance sensing of human blood cells


A challenging problem in alternating current (AC) impedance sensing of particles (e.g., blood cells in plasma) with micro electrodes is that with the shrinking of electrode surface area the electrode double layer capacitance decreases. This double-layer capacitor dominates the system impedance in lowfrequency range, while the parallel stray capacitor dominates the system impedance in high frequency range. Hence the sensitivity for particle sensing for micro impedance sensors decreases over a wide frequency range. In this paper, we propose an approach to solve the problem. The idea is to use resonant sensing by connecting an external parallel inductor to the system. At the resonant frequency, the capacitive components in the system are nullified by the inductor, leaving the channel impedance (including the particle impedance) to be a major component in the system impedance. We then successfully demonstrate this idea by sensing 5 µm polystyrene beads. More important, this technique is extended to sensing blood cells in diluted human whole blood and leukocyte-rich plasma. The sensitivity can be improved by two orders of magnitude over more than three decades in frequency domain. The measured signal peak height histogram at low frequency matches well with known volume distribution of erythrocytes and leukocytes.

Additional Information

© 2007 Elsevier B.V. Received 31 May 2007; received in revised form 5 October 2007; accepted 6 October 2007. Available online 23 October 2007. This work is supported by the National Space Biomedical Research Institute through NASA NCC9-58. The authors would like to thank other members of the Caltech Micromachining Laboratory for their valuable assistance.

Additional details

August 22, 2023
October 20, 2023