Lab-on-a-Chip by Digital Microfluidics
lab on a chip, microfluidics, MEMS, microTAS
Digital Microfluidics is a method of processing liquids in droplet forms. Realizing that typical biochemical laboratory equipments and procedures, either technician-run or robot-run, are operated with discrete amounts of liquids through bottles, pipettes, well plates, etc., we consider aliquot treatment of liquid a more natural fit to build a lab-on-a-chip. While there are several candidate actuation mechanisms to handle liquid droplets, we have converged to electrowetting-on-dielectric (EWOD) in recent years for its efficient driving mechanism, simple fabrication, and low power consumption. Easily automated, digital microfluidics can be used as a discrete, randomly accessed, multi-analyte analyzer, in which reagents or samples, compartmentalized into droplets, can be processed in any desired order in parallel fashion. The principle behind digital microfluidics can be shown by introducing various ways of transporting liquid droplet through modulation of surface tension and demonstrating how to implement them for function. We first show droplets can be created from a reservoir (i.e., digitized), driven (i.e., pumped), divided, and merged using EWOD actuation, either in air or immersed in oil. Following these four basic droplet manipulation functions, we further show that the driving voltage can be lowered (as low as 15 V), multiple droplets can be simultaneously manipulated on an MxN grid, and even the difficult issue of microfluidic mixing can be solved. To demonstrate the simplicity of EWOD microfluidics for system development, we report a stand-alone portable microfluidic system complete with a battery pack. A few more advanced technologies will be unveiled, including electronic tracking of droplets, in-droplet particle separation, sample dilution and concentration, and handling of various biofluids, thus expanding the functionality of digital microfluidics for biomedical applications. Finally, we report on-chip sample processing for MALDI-Mass Spectroscopy as one example of how digital microfluidics are used for specific applications.
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Nanotech 2005 Conference Program Abstract