Detection and sizing of single droplets flowing in a lab-on-a-chip device by measuring impedance fluctuations

Abstract

International audienceThis paper is devoted to the evaluation of the electrochemical noise technique consisting in measuring the fluctuations of the electrolyte resistance (ER) between two metallic electrodes immerged in a conductive electrolyte to detect and characterize single particles circulating in a microfluidic device, without the help of optical measurements that require good visibility of the detection region. Numerical simulations were performed with the finite element method to study the influence of the dimensions of the channel and the electrodes on the ER. Measurements of the ER variations due to the passage of oil droplets and plugs passing between the electrodes were carried out. Excellent agreement was obtained between the theoretical and experimental ER transients, which allowed the velocity and 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 m. According to the numerical simulations and the amplitude of the background noise, oil droplets of diameter larger than 20-25 m can be detected in the microchannel used (cross section of 100 m  100 m and 100 m  100 m electrodes separated by a gap of 100 m). Developments of smaller microfluidic devices are under progress to detect and characterize particles of a few micrometers, such as biological cells for example

Electrical impedance microflow cytometry with oxygen control for detection of sickle cells

“…Electrical impedance spectroscopy has been utilized in combination with microfluidics as an emerging label-free technology with good efficiency and sensitivity [19,20] to differentiate cell populations [21–24], single droplets [25], and diseased blood cells [26,27] as well as to monitor cellular pathological conditions [28]. This method is based on cellular dielectric properties [19], size and composition [26,29,30] and does not require any biochemical and fluorescence markers.…”

A flow focusing microfluidic device with an integrated Coulter particle counter for production, counting and size characterization of monodisperse microbubbles

“…Additionally, capacitive sensing using interdigital electrode geometry has been demonstrated for the detection of 900 μm water-in-oil emulsions produced by flow focusing42. Yakdi et al reported detecting and sizing oil droplets greater than 50 μm in diameter generated by a T-junction by measuring impedance fluctuations 37 .…”

How to Choose a Proper Theoretical Analysis Model Based on Cell Adhesion and Nonadhesion Impedance Measurement

“…The structure of the electrode system for nonadhesion cells is the same as that for adhesion cells (see Figure a–h). ,, First, the electrode systems (see Figure a,b) designed for cell population measurement cannot accurately detect many cell biophysical properties such as cell number and cell size, because those electrode systems generally measure the changes in solution resistance produced by the release of ionic metabolites from live cells (see Figure c) . Therefore, they may be used for cell metabolism measurement.…”

“…Sensing electrodes can be designed on both sides of a microchannel (see Figure 3d) 42 or only on one side of a microchannel (see Figure 3e). 46 Those two electrode systems can realize cell counting; however, they cannot extract any biophysical information on individual cells, such as cell size, membrane capacitance, and cytoplasm conductivity, because cell position in the microchannel (>cell size) greatly affects the measurement of nonadhesive cells.…”