Particle concentration sensor using control volume between double electrical sensing zones

We present a novel flow-rate independent cell concentration sensor using a fixed control volume between double electrical sensing zones. Compared to Hemacytometer [L.M. Prescott, J.P. Harley, D.A. Klein, Microbiology, McGraw-Hill, New York, 2002.] and Coulter Counter [M. Koch, A.G.R. Evans, A. Brunnschweiler, Design and fabrication of a micromachined coulter counter, J. Micromech. Microeng. 9 (1999) 159–161] requiring an accurate fluid volume measurement or precision flow-rate control, the present cell concentration sensor offers the flow-rate independent method for the cell concentration measurement with counting cells in a fixed control volume of 0.423 μl. In the experimental study, we have used the RBC samples of three different concentrations and compared the results obtained from the present device with those from Hemacytometer. Using the fabricated devices, we have made two different cell concentration measurements: (1) with single electrical sensing at a fixed flow-rate of 1.2 μl/min; (2) with double electrical sensing with a known control volume of 0.423 ± 0.01 μl. Compared to Hemacytometer, the single and double sensing methods show the maximum concentration errors of 8.7% and 10.3%, which are in the measurement error range of Hemacytometer. We also measure the cell concentration within the maximum concentration errors of 10.3% in two cases: (1) two different flow-rates of 5 and 0.5 μl/min, (2) the varying flow-rates from 2 to 1 μl/min, respectively. Therefore, we verify the flow-rate independent measurement capability of the present device. Finally, we conclude that the present sensor can measure cell concentration without the accurate control and measurement of flow-rate.