Self-Assembled Magnetic Colloids for DNA Separations in Microfluidic Devices

Theory of DNA electrophoresis (∼ 1999 –2002 ½)

“…The production of these devices is a sophisticated and costly procedure with little tunability after construction. A promising new alternative [86,87] is the use of quasi-regular arrays of columns, formed by the application of a homogeneous magnetic field (. 10 mT) to a suspension of superparamagnetic particles (with a diameter on the order of a few micrometers) confined between two parallel flat plates.…”

“…10 mT) to a suspension of superparamagnetic particles (with a diameter on the order of a few micrometers) confined between two parallel flat plates. Doyle et al [86] have employed such a medium composed of self-assembled posts of a The l-DNA electropherograms were reproducible within approximately 6% with each subsequent replacement of the sieving medium. The resolution ranged from 5.5 kbp for the 15-33.5 kbp samples to 11.6 kbp for the 33.5-48.5 kbp samples.…”

“…By comparing experiments and results from a mean field model, they indicated that the average post separation, d*, can be controlled by varying the height of the microchannel, L, and the ferrofluid volume fraction, and that in particular, post spacing is related to channel height via a power law of the form When DNA is placed in this array and an electric field is applied the polymer chain becomes hooked around a post in a pulley-like conformation, the escape time is dependent on the molecular weight of the DNA and separation is possible (inspired by [86]). …”

“…The use of self-assembled arrays of posts as a separation medium has several key advantages over existing microlithographic etched arrays: (i) the post separation, or effective pore size is tunable and reproducible to within about 5% [86] by modifying the strength of the applied magnetic field and/or the concentration of ferrofluid (typical post separations range from 1 to 100 mm); (ii) selfassembled arrays do not require costly and sophisticated techniques (such as lithography) in their construction, making this method feasible for many more researchers; (iii) suspensions of ferrofluids have low viscosity in the absence of a magnetic field and are well suited for injection into narrow channels; (iv) self-assembled arrays can be altered on the fly (e.g., by changing the magnetic field intensity, even during separation) for specific applications. This last point is unique to this system.…”

Double-Stranded DNA Diffusion in Slitlike Nanochannels

“…1,2 The potential for the use of small-channel devices in DNA mapping [3][4][5][6][7] and separation, [8][9][10][11][12][13] single biomolecule manipulation, 12 and even ion separation 14,15 has inspired interest in the static and dynamic response of individual molecules to confinement. [16][17][18] The proximity of the bounding walls offers a very powerful method to change the polymer equilibrium conformation through steric interactions as well as the polymer dynamics through modulation of hydrodynamic interactions (HI).…”