Abstract
This paper reports the work of developing one coplanar microfluidic sorter while using the electro-wetting on dielectrics (EWOD) technique. When connected with delivery capillary to receive sample solution containing micro-particles, this device can select about 10 micro-particles in high volume throughput of milliliter amount within 20 min, to potentially match the requirement of efficiently determining the low amounts of bacteria in concentrated food and environmental samples, of which the typical bacteria density is 10 colony forming unit or less, much smaller than that of clinical pathogen samples. This coplanar T-shape EWOD device contains two fluidic channels, one inlet channel and the other collection channel stemmed from the middle of inlet channel. When the solution droplet falls from the delivery capillary to the entrance end of inlet channel, the droplet is driven to the intersection of two channels. The droplet containing fluorescent particle will be diverted to the lower channel to collect. Otherwise, the non-fluorescent droplet keeps moving toward the other end of inlet channel to waste zone. The particle fluorescence is collected through microscope lens to detect with one photomultiplier tube. The detected signals trigger the personal computer control board to active each EWOD electrode to direct the droplet moving directions. When the solution of 1 mL containing about 10 fluorescent micro-particles is delivered into this sorting device, nearly all the particles were correctly directed into collection zone in 20 min.
Highlights
Unlike conventional miniaturized lab-on-a-chip (LOC) devices performing assays in continuous microchannel fluidics, the alternative systems, such as electrowetting-on-dielectrics (EWOD) platform, which move discrete droplets on a substrate, have recently attracted increasing attentions because of the benefits to control fluid without using pumps and valves [1]
In the snapshot II when the droplet was driven to the detection waste zone along the inlet channel of this EWOD device
We successfully develop one EWOD device to count the numbers of fluorescence microparticles that are contained in one sample of 1 mL
Summary
Unlike conventional miniaturized lab-on-a-chip (LOC) devices performing assays in continuous microchannel fluidics, the alternative systems, such as electrowetting-on-dielectrics (EWOD) platform, which move discrete droplets on a substrate, have recently attracted increasing attentions because of the benefits to control fluid without using pumps and valves [1]. Electrowetting is a phenomenon of altering the liquid wettability on a solid surface by applying external voltage to produce an electric field across the liquid-solid interface [6]. To balance the forces between γSL , γLG , and γSG , representing the interfacial tension between solid-liquid, liquid-gas, and solid-gas interfaces, respectively, existing at the edge of a sessile droplet, the contact angle θ becomes external voltage (V) dependent, as described by electrowetting equation, as follows, cos[θ(V)] = cos[θ(0)] + (CH /2γLG )V2
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