A New Method For High-throughput Generation Of Droplet Arrays Based On Surface Tension Confinement

Surface-tension-confined droplet microfluidics has a wide range of applications in the fields of biology and chemistry.Facile microdroplet generation method is the focus of recent research in the field of surface-tension-confined droplet microfluidics.The high-throughput measurements can be achieved through droplet-based assays,such as single cell culture and analysis,high-throughput assay of enzyme activity and so on.In this article,on the basis of surface-tension-confined droplet microfluidics technology,a simple and controllable method for the preparation of oil-covered droplet arrays is proposed,and based on this method,the encapsulation of microparticles and single-cell capture,culture and monitoring were realized.Polydimethylsiloxane(PDMS)is a heat-resistant,non-toxic polymer organic material,in the article,the PDMS prepolymer was coated on silicon column arrays,and after heating and curing,a PDMS stencil was obtained,and more than 10,000 micro-holes were evenly arranged on the stencil.By covering the PDMS stencil on a hydrophobic glass substrate,selective plasma etching can be achieved,resulting in a glass substrate with a hydrophilic lattice pattern.When the plasma treatment time is controlled at 10 seconds,the size of the hydrophilic patterns on the substrate is basically the same as the size of the holes on the PDMS stencil.By guiding liquids sliding along the hydrophilic-in-hydrophobic patterned substrates,oil-covered droplet arrays with uniformly sized and regularly shaped picoliter droplets were successfully generated on the patterned substrates.More than ten thousand 31 p L droplets were generated in five seconds with the generation frequency up to 3 k Hz.By covering the droplet arrays with oil during generation,on the one hand the droplets are isolated from each other,on the other hand effectively prevent the evaporation of droplets and it was found that the oil-covered droplet arrays can be stored for three days with less than 35% volume loss.In addition,through the measurement of the contact angle,the physical process and the principle of the formation of the oil-covered droplet arrays is discussed in detail based on the principle of wettability.Based on the proposed droplet arrays preparation method,single polystyrene(PS)microspheres and single cells were successfully captured and encapsulated in the droplet arrays,and the distribution of PS spheres in the droplet array was observed to follow the Poisson distribution rule.Using a suitable concentration of Escherichia coli-containing bacterial culture fluid to prepare the oil-covered droplet arrays,droplets containing a single E.coli can be obtained.After 3 days of cultivation,the E.coli in the droplets successfully grew and proliferated,and the dynamic changes in the number and morphology of E.coli in the droplets were also observed.The droplet arrays generation method is proved to be high-throughput,facile,efficient and low-costing,and the prepared droplet array will be of enormous potential for chemical and biological assays.