Digital Droplet Micro-jetting Prepared Microfluidic Chip Technology And Its Experimental Research

Microfluidic chip as a kind of forefront technology in modern analytical science is the main research direction of micro total analysis systems (μ-TAS). It will bring revolutionary impact on the life science, environmental science, medicine and chemistry. The microfluidic chip integrated channels, reaction zones, detectors and other micro elements in an area as small as a square inch to realize sampling, diluting, sample injecting, reacting, separating, detecting and other operating functions. Combing with certain external devices, it could achieve "sample in and data out", rapid, and automated chemical analysis or biochemical analysis.Photolithography and etching is commonly used for the preparation of microfluidic chips. However, they require expensive equipment, clean laboratories and skilled production ability and it is inconvenience to be promoted in general biochemistry laboratories. Microfluidic chip processing technology could not meet the needs of the current rapid development of microfluidic science, for example sealing of the glass microfluidic chips is difficult and low integration, preparation of male mold for the polymer chips is complex, high aspect ratio and three-dimensional microstructures are rarely reported, and fabrication process of paper microfluidic chip is complicated. Aiming at the preparation technology of microfluidic chip, in this paper, the preparation of paper and polydimethylsiloxane (PDMS)microfluidic chips based on the digitized liquid micro-injection technology is systematically studied and applications of the prepared microfluidic chips are experimentally researched.The flow of the fluid in the glass nozzle driving by the friction coupling of fluid and solid wall in the boundary layer caused by the pulse inertia force was theoretically analyzed. The influence of system parameters on the flow motion in the glass nozzle driving by pulse inertia force was obtained by solving the viscous group equations of continuum fluid. The formation processes of main and satellite droplets were simulated using fluent of Ansys 13.0 based on the calculating result. The digital liquid ejection process of was observed by a home-made stroboscope.The fabrication process for the glass nozzle based on thermal deformation was studied according the structural requirement of digital liquid ejection. A glass nozzle fabrication apparatus integrated pulling and forging process for 0.5mm-2.0mm nozzle and a glass nozzle fabrication apparatus for 4.0mm-7.5mm nozzle were designed, and the influence of heating time and voltage on the pulling and forging process was experimentally studied. The glass nozzle fabrication apparatus for 0.5mm-2.0mm nozzle integrated pulling and forging process. The glass nozzle with outlet diameter of 6.5mm enlarged the capacity of liquid in the nozzle and raised the ability for high viscosity liquid, and this supplied an glass nozzle basis for the digital liquid ejection.The influence of system parameters on the stability and ejection droplet volume of digital liquid ejection was experimentally studied. Result showed that, the ejection distance, driving voltage, driving frequency, the height of the liquid in the nozzle should cooperate with each other to realize steady ejection, and the droplet size could be controlled by adjusting the system parameters. It supplied an experimental basis to determine the system parameters to control the droplet size, avoid the satellite droplet and increase the stability and consistency of micro ejection. The droplet impact process was theoretically studied and the main influence factors for the maximum spreading diameter were obtained. The impact process of 100μm droplet was simulated by fluent, and the speed and surface tension coefficient of the droplet on the impact was studied. The formation of liquid line based on digital liquid ejection was analyzed, the concept of droplet overlapping degree was raised and this provide a theoretical basis for the wax line on the paper or glass substrate.A novel method for the preparation of paper and PDMS microfluidic devices was proposed respectively based on the digital droplet ejection technology. The wax droplets were ejected with a PZT actuator and a 6.5 mm borosilicate glass micro-nozzle on filter paper and glass sheet, linked with each other and formed into wax patterns used in the microfluid chips. And then, after thermal treating the wax droplets were melted and penetrated into the filter paper to become paper microfluidic chip,and with the wax mold formed on the glass sheet the PDMS microfluid chip was prepared by replication and other process.Multi-assay of glucose, protein, and PH were realized on paper microfluidic device with cross-shaped wax pattern, and concentration gradient of glucose,protein solution, PH were tested with circular micro reaction array, and micro reaction of phenolphthalein and NaOH was realized with prepared square and Y-shaped paper microfluidic devices.A micro mixing of blue and yellow dye was realized with the prepared PDMS microfluidic devices.Result showed that the microfluid chips could be applied in the biochemical analyzing experiments.The wax material has the advantage of low cost and easy available, and the glass nozzle had advantages of easy made, cheap, good chemical resistance,low friction and simple.The wax pattern is formed directly without multiple printing steps or templates and the filter paper does not need to contact with anything but the wax droplets which could avoid contamination.The wax mold used in the PDMS microfluid chips was formed directly and a high aspect ratio wax mold could be realized. The wax droplet generating system supplied a low-cost, simple, easy-to-use and fast fabrication method for paper and PDMS microfluidic device.