Research On Droplet Generation Drive And Detection Technology Based On Digital Microfluidic Chip

The droplet-based microfluidic system can perform ultra-small volume and ultra-high throughput reaction,measurement and analysis,and has been increasingly used to perform complex chemical and biological experiments.At present,droplet-based microfluidic technology is mainly divided into continuous microfluidic technology and digital microfluidic technology.The continuous microfluidic technology is mainly generated and transported by two immiscible fluids based on structured microchannels.Liquid droplets,while digital microfluidic technology mainly applies a voltage to a patterned electrode array to perform a series of manipulations of nanoliter to microliter droplets.In order to track the reaction process and the extent of the reaction,real-time detection of the state and content of the droplets in the above reaction becomes crucial.The droplet size has a great influence on the reaction process,the degree and the detection effect,so higher requirements are put forward for the uniformity of the droplet size in the microfluidic chip.Continuous microfluidic technology uses the mechanical action of continuous and discrete terms to generate relatively uniform droplets.However,due to the limitation of its driving mechanism in digital microfluidic technology,the uniformity generation of droplets poses certain challenges.Therefore,this article has carried out research on the generation and detection technology of droplets,and carried out the uniformity generation of droplets based on digital microfluidic technology and the improvement of droplet detection sensitivity.The specific research content is as follows:(1)In order to eliminate the influence of different droplet sizes on droplet detection,a new pattern of droplet generation electrode,the necked curved quadrilateral electrode,is proposed.It is found that the necked curved quadrilateral electrode can fix the necked position in the process of droplet generation,so as to improve the droplet generation efficiency The uniformity of the system.In the digital microfluidic chip,the droplet moves along the direction of the voltage applied to the driving electrode,and the edge of the droplet basically coincides with the edge of the electrode,so the volume of the droplet is related to the size of the electrode.In this paper,three groups of necked curved quadrilateral electrodes with different sizes are fabricated.The volume of droplet formation increases with the increase of the electrode.However,when the electrode shrinks,the electrowetting force decreases,the droplet formation speed slows down,and the electrode processing becomes more difficult.Therefore,in this paper,the problem of uniformity of droplet formation is well solved by using the necked quadrilateral electrode with curved edges(the major axis of ellipse is 1.5mm,the minor axis is 0.62mm).Through the comparison between the traditional square electrode and the necked curved quadrilateral driving electrode,it is found that the average error of droplet volume generated by the square driving electrode is 12.54%,and the average error of droplet volume generated by the necked curved quadrilateral driving electrode is 3.25%.The necked curved quadrilateral driving electrode can effectively improve the uniformity of droplet formation.(2)In this paper,a coplanar inclined interdigital electrode is designed to improve the sensitivity of capacitance detection.The coplanar electrode was obtained by etching ITO glass with the self-made soft lithography process,and the passivation layer was spin coated on the surface of the electrode to avoid pollution.When the droplet in the microfluidic channel enters the sensing region of coplanar electrode,its capacitance will change,and then it can be used to detect the number,flow rate and content of droplets.The experimental results show that the detection sensitivity of the designed coplanar oblique interdigital electrode is better than that of the traditional coplanar single pair of parallel electrodes.The average capacitance of the coplanar oblique interdigital electrode is about19.4% higher than that of the coplanar single pair of parallel electrodes when oil: water =1:1;about 24% higher than that of the coplanar single pair of parallel electrodes when oil:water = 2:1;about 6.5% higher than that of the coplanar single pair of parallel electrodes when oil: water = 3:1.(3)In this paper,the number,size,content and flow rate of micro droplets in microfluidic chip were studied.The capacitance of fluid with different dielectric constant is different.According to the capacitance of fluid in microchannel,the type of known fluid in microchannel can be detected.When the solute concentration of a fluid sample is known to be different,the capacitance value is also different,so the concentration of such droplets can be detected by the change of capacitance value.According to the waveform of capacitance detection,the number,size and flow rate of droplets can also be obtained through analysis and calculation.