April 3, 2006
Microfluidic Devices Advance Rapid On-Chip Gene Analysis
Rapid genetic analysis is one of the most promising applications of microfluidics for cancer research and clinical oncology. Being able to take a blood or tissue sample from a patient and identify cancer-related genes in a matter of hours, if not minutes, would enable oncologists to better design individualized therapy and even monitor how well that therapy is working. That dream is now closer to reality as a result of work published by two independent groups that have developed microfluidic designs that can rapidly concentrate DNA from biological samples.
Texas A&M investigator Victor Ugaz, Ph.D., and graduate student Faisal Shaikh, writing in the Proceedings of the National Academy of Science, described their strategy for concentrating, focusing and metering minute amounts of DNA within the confines of a microfluidic device. The heart of their device is an array of individually addressable microfabricated electrodes that can be turned on and off in such a way that charged biomolecules, such as DNA and most proteins, will be concentrated in a small volume with all other molecules and allowed to continue through the microfluidic device unimpeded. Once the sample is concentrated as needed, the electric field is used to propel the DNA to another part of the microfluidic chip for subsequent analysis by PCR or gene sequencing techniques.
By adjusting which electrodes are charged and in what order, the researchers are also able to separate and concentrate DNA according to its length. And unlike other devices that use electric fields to purify DNA, this one uses low voltage and does not require any mechanical pumping to move the sample through the microfluidic channels. As a result, this design should be readily adaptable for use in a clinical setting with little need for external equipment.
Meanwhile, James Landers, Ph.D., and his collaborators at the University of Virginia have developed a microfluidic design that integrates solid-phase extraction of DNA with PCR in a single chip. Writing in the journal Analytical Chemistry, the investigators describe how their device can concentrate the DNA present in 600 nanoliters of blood — less than a pinprick — and then run PCR on the concentrated DNA. In a demonstration of their device, the researchers identified anthrax DNA present in a nasal swab in only 25 minutes.
The work from Ugaz and Shaikh is detailed in a paper titled, “Collection, focusing, and metering of DNA in microchannels using addressable electrode arrays for portable low-power bioanalysis.” An abstract of this paper is available through PubMed.
The work from the Landers group is detailed in a paper titled, "A simple, valveless microfluidic sample preparation device for extraction and amplification of DNA from nanoliter-volume samples." An abstract is available through PubMed.