Seth fraden
Many of the artistic images in this article are kindly provided by Albert Folch, Professor of Bioengineering at the University of Washington, also Art Editor of the journal Lab on a Chip. The work of his lab has been showcased at BAIT: Bringing Art into Technology
18 Focus
Greg Cooksey & Albert Folch
separate even when they are flowing side by side, it is also very hard to get them to mix. Stirring is not an option because the channels are too narrow. Designers of microfluidic devices have to find ingenious ways to introduce turbulent flow and force mixture, such as building sharp bends into the channels, or using microvalves or micropumps. The potential of microfluidics to facilitate the work of research scientists and medical professionals has led to rapid and exciting developments in the field. Personalised medicine, rapid disease identification, forensic evidence from tiny sample; these technologies may seem decades away from realisation, but the development of lab-on-a-chip devices has helped to bring them closer to reality. These applications depend on identifying genetic material, in particular the exact sequence that builds up a DNA strand. For example, to identify a bacterial cell unambiguously, you need to make a comparison between the DNA sequence of that cell and the sequence of a known bacterium. In many cases, the amount of genetic material available is small. In order to carry out tests, the DNA extracted from the cell of interest needs to be ‘amplified’ by a process called polymerase chain reaction (PCR). In PCR, the original DNA sample passes through three specific temperature stages for a large number of cycles. First, a high temperature stage breaks apart the double helix of DNA in a ‘melting’ process, yielding two single-strand molecules. The temperature is lowered in the next stage, where the building blocks of DNA adhere to the single chains in a sequencespecific manner. Finally, the temperature is kept low while the building blocks are linked into a strand of DNA by an enzyme, yielding two copies of the original double helix. Through repeating many such cycles, this doubling process can exponentially amplify
Professor Seth Fraden is visiting from Brandeis University in Massachusetts. He specialises in soft condensed matter physics and is currently spending four months collaborating with members of the Department of Chemistry and Cavendish Laboratory in Cambridge. In America, his group has developed a new protein crystallisation technology using microfluidics, culminating in a device called the Phase Chip. He talks to BlueSci writer Vivek Thacker about his current work and future plans. What started your interest in microfluidics? SF: My background is in biological materials, looking at liquid crystals of viruses. Work on microfluidics began in my last sabbatical—at the time I was very impressed with the technological advances being made by Stephen Quake’s group at Caltech. He had developed a suite of microfluidic tools to synthesise small amounts of materials on a valve-based network, and he showed that it was a very scalable technology. I saw that as an advance to study my liquid systems in a very efficient manner, and decided to pick this up in my upcoming sabbatical. Is it easy to scale up from a microfluidic system to a bulk system? SF: No! Because the physics is different, you do not want to have the intention of scaling up. But the technology is scalable. Microfluidic valves are made photo-lithographically, like printing, so the effort to make a hundred is the same. It is like semiconductor manufacturing—once you’ve learnt to make one transistor, you can make ten million of them on the same wafer. Easter2011