Trapping DNA with a high throughput microfluidic device

Abstract

Long strands of DNA can be trapped and concentrated near the inlet of a microfluidic channel by applying a pressure gradient and an opposing electric field. The mechanism for trapping involves a migration of DNA perpendicular to both the fluid flow and the electric field. Migration leads to a highly nonuniform distribution of DNA within a cross section of the channel, with the bulk of the DNA concentrated in a thin (10 μm) layer next to the walls of the channel. This highly concentrated layer generates an electrophoretic flux toward the inlet to the device, despite the much larger fluid flow in the opposite direction. In this paper, the extent to which DNA can be trapped and concentrated by this means has been characterized by fluorescence measurements. At short times (<2 hours) nearly all the incoming DNA remains trapped within the device until the electric field is turned off. The DNA largely accumulates near the inlet, but after 30-60 minutes additional DNA starts to accumulate deeper into the channel. Eventually DNA leaks from the device itself, but ≈80% of the incoming DNA can be retained for up to 5 hours. Optimizing the electric field strength can increase the amount of DNA that can be trapped, but the efficiency is not affected by the channel cross-section.

Recent advances in direct current electrokinetic manipulation of particles for microfluidic applications

“…They attributed the phenomena to the shear‐induced extra lift that arises from the nonlinear coupling between particle electrophoresis and the local fluid flow . Interestingly, cross‐stream migrations were also reported for DNA molecules in capillary electrophoresis with an applied Poiseuille flow though the moving direction seems also opposite to those of particles . In addition, Yoda's group observed near‐wall self‐assembly of submicron polystyrene particles into streamwise bands in a countercurrent Poiseuille and electroosmotic flow.…”

Transverse migration and microfluidic concentration of DNA using Newtonian buffers

“…Electrodes placed in each of the reservoirs were connected to a DC voltage source that generated a potential difference of up to 400 V. The potential drop occurs almost entirely across the 18 mm length of the channel, due to its small cross section relative to the other portions of the microchip and the tubing. 4,5 For each setting of ΔH, the rate of concentration was maximized at a potential field of f ¼ f m as listed in Table II for the 0.25Â TE solution with 0.5 wt. % PVP (solution 8).…”

“…The measurements agree with previous experiments that utilized the same buffer solution. 4,5 Table II also lists the velocity at the centerline, v 0 , due to the pressure-driven flow and the electrophoretic velocity, v E , for each set of conditions. These velocities were calculated from measurements of the DNA motion within the channel in response to independently applied fields.…”

“…The computer controlled shutter limited illumination of the sample to a total of 4 s over the course of any one experiment, reducing the effect of photobleaching on the measured intensities to less than 10%. 5 Example images showing the increase in DNA concentration with time are shown in Fig. 2(a).…”

“…1(a). 4,5 This microfluidic process has potential utility as a unit operation in the preprocessing of DNA samples in micrototal analysis systems. Microfluidic processing of biological samples for the purpose of extracting and purifying DNA would have many advantages over traditional methods.…”