Detection and Sizing of Single Droplets Flowing in a Microfluidic Device by Impedance Measurement

Abstract This article reports on the evaluation of the electrochemical noise technique consisting in measuring the fluctuations of the electrolyte resistance (ER, impedance at high frequency) between two metallic electrodes immerged in a conductive electrolyte to detect and characterize single particles circulating in a microfluidic device. Numerical simulations were performed with the finite element method to study the influence of the dimensions of the channel and the electrodes on the impedance. Excellent agreement was obtained between the theoretical and experimental results, which allowed the diameter of the oil droplets to be estimated with an accuracy of a few percents in the case of droplet diameters ranging from 60 to 100 μm. Developments of smaller microfluidic devices are under progress to detect and characterize particles of a few micrometers, such as biological cells for example.