Droplet Three-dimension Manipulation On Slippery Liquid-infused Porous Surface

With the development of Micro Electromechanical System(MEMS)technology,digital microfluidic technology based on electrowetting on dielectric effect,due to its precise,efficient and fast micro-droplet control mode,has shown a good application prospect in chemical reaction,drug synthesis,sample analysis,biological detection and other fields.Digital microfluidic not only has a simple chip structure and strong system scalability,but also controls the directional movement of droplets without any micro-mechanical devices such as micro-pumps,micro-valves and micro-fluidic channels.However,the current digital microfluidic technology still has problems such as high continuous driving voltage(about 70 V to 150V),high voltage breakdown of dielectric layer,complex electrode structure,low parallelism and poor stability,etc.,and its driving mode of square wave pulse,sinusoidal pulse and AC signal largely restricts the application range of digital microfluidic technology.Aiming at the problems that high continuous driving voltage,high voltage breakdown of dielectric layer and complex electrode structure in current digital microfluidic technology,this paper reports a two-dimensional manipulation platform of droplet on the open electrode chip,with the use of polarity-dependent low-voltage electrowetting phenomenon on a perfluorinated silane modified slippery liquid infused porous surface(SLIPS),the performance of droplet manipulation on several modified SLIPS samples with different vertically placed times and silicon oil viscosities was studied,and the optimal condition for preparing a modified SLIPS membrane was obtained.Finally,the efficient and accurate continuous manipulation of the droplets on a loop of 16 square electrodes was achieved.Interestingly,unlike the traditional asymmetric electrowetting actuation,the droplet actuation velocity was almost not limited by the contact angle saturation effect and increased with the applied voltage on modified SLIPS.The threshold voltage of droplet continuous driving was decreased to only 8 V,which exhibited at least a 15-fold decrease compared to that of an unmodified SLIPS membrane.Compared to the typical configuration of open EWOD droplet manipulation,we reduced the number of electrodes to half.In addition,the modified SLIPS membrane exhibited good robustness with 1 k V breakdown voltage and is self-repairing.In order to improve the velocity of droplet actuation,enhance the equipment integration,and improve the speed and sensitivity of biochemical analysis,this paper constructed a parallel liquid infused membrane plates structure with patterned electrodes.Through programmable control of the direct current signals,the asymmetric electrowetting behavior of droplets between parallel liquid infused membrane plates and the vertical transport process of the droplet under the action of electrostatic force were studied,and the dynamic transport model of droplet vertical motion was established.In addition,the operating voltage range of a 0.5 ?L droplet with different plate spacing was obtained.Finally,we demonstrated the three-dimensional manipulation of the droplet in a parallel liquid infused membrane plates by means of mixed forces,namely,a horizontal asymmetric electrowetting force and a vertical electrostatic force.The 3D manipulation of droplets on the modified SLIPS provides a promising solution for high-throughput analysis and high-density integrated devices on digital microfluidic chip.