Impedance Detection Of Droplets In Microfluidic Chip

In this article, the microfluidic chip for impedance detection of droplets was designed. An impedance detector for droplets which is convenient and can adjust frequency was set up. Droplets were generated based on the shear principle. The content concentration, size, speed and other important characteristics of droplets in the microfluidic chip were studied. The main contents are as following:A theoretical model of microfluidic droplets for impedance detection was established. The internal equivalent model when the droplets pass through the electrodes was analyzed and the calculation formula for the impendence was given. The corresponding relationship between the impedance and concentration of droplets was discussed.At first, we fabricated the droplets based microfluidic chip which was integrated thin-film metal (Pt) microelectrode. Using the molding method, we manufactured the chip of PDMS containing micro-channel of droplets. We integrated thin-film microelectrode on the glass. Taking advantage of oxygen plasma to deal with the chip of PDMS and glass, we use a micro-assembly equipment of self-development to carry out precious positioning. Finally, the chip of PDMS and glass was bonded together.Based on the shear principle, the droplets were generated in the micro-channel. We utilize fluid-focusing method to generate droplets in cross micro-channel. Besides, we make use of COMSOL4.2to optimize simulation about boundary conditions of droplets generation. In this way, we can make sure that droplets can be generated stably. The influence of surface modification of glass channel on the stable generation of droplets was discussed. In addition, We analyzed the effect that surfactants did on the interfacial tension between oil and water phases.We have integrated the experiment platform for droplets impedance detection. The design of signal generating circuit and conditioning circuit had been made. An impedance detector for droplets which is convenient and can adjust frequency was set up. We completed the microfluidic chip and testing platform for droplets impedance detection, and researched the concentration, size, speed and other important characteristics of droplets. Combining the optical signals with electrical signals, we can obtain the speed and volume of droplets accurately. Detecting5μmol/L to200μmol/L concentration of droplets’inclusion, the correspondence between the output voltage and the concentrations of inclusion was analyzed. The liner equations and regression coefficients of different range of concentration of droplets and its output voltage were calculated.