More and more diseases find their cause in malfunctioning genes. There is therefore still need for rapid, low-cost and direct methods to accurately perform genetic analysis. Currently the process takes a long time to complete and is very expensive. Briefly, once the chromosomes are isolated from the blood, they are sorted by flow sorting two at a time. Those under suspicion for mutations are further analysed. We are interested in particular chromosome mutations called translocations, where two chromosomes interchange parts, creating two new chromosomes. These kinds of mutations are responsible for various forms of cancer as well as for the well-known Down’s syndrome.
We are currently working on a system that will be able to isolate chromosome-carrying cells from blood, extract the chromosomes and sort them as well as perform whole genome amplification and analysis of the same chip. For cell sorting we are using a method called pinched-flow fractionation [1], by which the cells are separated using only flow in microfluidic channels. The chromosome-carrying cells are then isolated and lysed with the help of traps [2] and electric fields. The extracted chromosomes are taken further into the device for sorting, achieved using a combination of electrophoresis, dielectrophoresis and flow.
Although much is known about the genetic structure of chromosomes, practically no data exists on their physical parameters. Information such as size, dielectric properties and charge are necessary in order to get an idea of the magnitude of the various forces they are exposed to in DC and AC electric fields. We have been measuring the permittivity and conductivity of chromosomes in air and liquid using an AFM, as well as their mobility due to a DC field in various microchannels. We are also investigating the use of bumper arrays for further size sorting. All our structures are fabricated in glass using a two wafer structure, allowing optical and fluorescence observations to be made.
Both theoretical as well as experimental results for these structures will be presented and discussed.
[1] Masumi Yamada, Megumi Nakashima, and Minoru Seki, Anal. Chem. 76, 5465-5471, 2004
[2] Dino Di Carlo, Liz Y. Wu and Luke P. Lee, Lab Chip, 6, 1445-1449, 2006 |