Mechanical Engineering Faculty Research

Title

An Impedimetric Approach for Accurate Particle Sizing using a Micro Coulter Counter

Document Type

Article

Publication Date

3-2011

Abstract

In this paper, we present the design, impedimetric characterization and testing of a microfabricated Coulter counter for particle size measurement that uses a pair of thin film coplanar Au/Ti electrodes. An electrical equivalent circuit model of the designed device is analyzed. Accurate measurement of particle size was achieved by operating the device at a frequency for which the overall impedance is dominated by the channel resistance. A combination of design features, including the use of a pair of sensing electrodes with a surface area of 100 µm by 435 µm, a spacing of 1785 µm between the two sensing electrodes and a 350 µm long microchannel, ensures that this resistance dominates over a range of relatively low frequencies. The device was characterized for NaCl electrolyte solutions with different ionic concentrations ranging from 10−5 to 0.1 M. Results proved that the resistive behavior of the sensor occurs over a range of relatively low frequencies for all tested concentrations. The Coulter counter was then used to detect 30 µm polystyrene particles at a selected excitation frequency. Testing results demonstrated that the device can accurately measure particle sizes with small error. The design can be extended to ac Coulter counters with sub-micron sensing channels. Analysis of three designs of ac Coulter counters including sub-micron sensing channels using the electrical equivalent circuit model predicts that they can be operated at even lower frequencies, to accurately size nanoscale particles.

Publication Title

Journal of Micromechanics and Microengineering

Volume

21

Issue

4

First Page

045036