(320a) Ratchet Nanofiltration of DNA

We have created a DNA filter that takes advantage of the nonlinear dependence of the electrophoretic mobility on applied electric field in the “nanofilter” array geometry to create a temporal asymmetry ratchet. The nanofilter array is a separation device that is made of a series of thin slits, typically 60 nm deep, which impedes DNA motion and leads to size-based separation of DNA [1].  However, it is not actually a filter. Instead, it acts as a gel-like sieving matrix with an electrophoretic mobility that depends nonlinearly on the electric field.  It has been shown theoretically and in simulations that such devices can enact a ratchet-like behavior in DNA by periodically alternating between two different magnitude electric fields in opposite directions [2,3].  Running the nanofilter in this manner allows the device to act as a filter, only permitting DNA below a desired size through the array while not clogging like a traditional filter. 

We will present experimental proof of the nanofilter array ratchet. Moreover, we will show that (i) the cutoff molecular weight for the filter can be adjusted by changing the electric field strength and/or pulse times without making a new device and (ii) the ratchet mode can be used to enhance the resolution of a separation. One could imagine collecting one set of the fragments then changing the electric fields to collect the second and so on to completely fractionate the mixture. This DNA filter is made using standard silicon microfabrication techniques, which lends itself to being integrated as a filtration step in a larger lab-on-a-chip type device for DNA processing.     

REFERENCES: 

1. J. Fu, P. Mao, and J. Han. Appl. Phys. Lett. 87, 263902 (2005).
2. G. W. Slater, H. L. Guo, and G. I. Nixon. Phys. Rev. Lett. 78, 1170 (1996).
3. F. Tessier and G. W. Slater.  Appl. Phys. A 75, 285 (2002)