Fractionation of Macro-Molecules Using Asymmetric Pulsed Field Electrophoresis

Abstract

A method and apparatus for fractionation of charged macro-molecules such as DNA is provided. DNA solution is loaded into a matrix including an array of obstacles. An alternating electric field having two different fields at different orientations is applied. The alternating electric field is asymmetric in that one field is stronger in duration or intensity than the other field, or is otherwise asymmetric. The DNA molecules are thereby fractionated according to site and are driven to a far side of the matrix where the fractionated DNA is recovered. The fractionating electric field can be used to load and recover the DNA to operate the process continuously.

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       27 . An apparatus for continuously fractionating charged macro-molecules comprising:
 an array of obstacles;   asymmetrically alternating electric fields applied to the array to separate the molecules into a plurality of bands sorted according to size along a horizontal direction of the array, each band containing molecules of substantially the same size; and   a plurality of locations along a bottom edge of the array for collecting separated molecules, shorter molecules separated towards a first side of the bottom edge and longer molecules separated towards a second side of the bottom edge opposite the first side.   
   
   
       28 . The apparatus of  claim 27  wherein the asymmetrically alternating electric fields comprise:
 an electric field which is alternating in direction as a function of time at a location in the matrix, and which has a time average of an electric field vector over many cycles, whereby the time integral of the vector at the same location over a part of the cycles when the electric field is instantaneously pointing to one side of the vector is not spatially symmetric about the vector with the time integral of the vector over another part of the cycles at the same location when the electric field is instantaneously pointing to another side of the vector.   
   
   
       29 . The apparatus of  claim 27  wherein the asymmetrically alternating electric fields comprise:
 time-dependent electric fields Ē(t) whose odd-order integrals over time, ∫|Ē(t)| n Ē(t)dt, are not at the time-average field orientation for every n, where n is any positive even integer.   
   
   
       30 . The apparatus of  claim 27  wherein the asymmetrically alternating electric fields comprise:
 first and second electric pulses of first and second waveforms;   the integral over time of one of the first or second pulses' amplitude larger than that of the other pulse;   the orientation of the first electric pulse varies between a first orientation and second orientation, and the orientation of the second electric pulse varying between a third orientation and forth orientation.   
   
   
       31 . The apparatus of  claim 30  wherein the first and second waveforms are square pulses. 
   
   
       32 . The apparatus of  claim 31  wherein one of the square pulses is of higher amplitude than the other. 
   
   
       33 . The apparatus of  claim 31  wherein one of the square pulses is of longer duration than the other. 
   
   
       34 . The apparatus of  claim 27  wherein the asymmetrically alternating electric fields comprise:
 first and second alternating electric pulses of first and second waveforms;   the integral over time of one of the first or second pulses' amplitudes larger than that of the other pulse;   the first and second electric pulses applied at first and second fixed orientations.   
   
   
       35 . The apparatus of  claim 34  wherein the first and second waveforms are square pulses. 
   
   
       36 . The apparatus of  claim 35  wherein one of the square pulses is of higher amplitude than the other. 
   
   
       37 . The apparatus of  claim 35  wherein one of the square pulses is of longer duration than the other. 
   
   
       38 . The apparatus of  claim 27  wherein the asymmetrically alternating electric fields comprise:
 electric fields whose amplitudes are constant in time;   the field orientation varying with time in such a manner that ∫[θ(t)] n+1 dt are not zero for every n, where θ(t) is field orientation with respect to the time-average field orientation, and n is any even integer larger than zero.   
   
   
       39 . The apparatus of  claim 38  wherein the fields alternate between two fixed orientations. 
   
   
       40 . The apparatus of  claim 27  wherein the charged molecules are deoxyribonucleic acid (a.k.a. DNA). 
   
   
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       42 . The apparatus of  claim 27  further comprising extraction structures for extracting fractionated molecules from the array of obstacles. 
   
   
       43 . The apparatus of  claim 27  further comprising one or more loading channels for loading molecules. 
   
   
       44 . The apparatus of  claim 27  wherein the molecules are extracted from the array of obstacles using electric fields. 
   
   
       45 . The apparatus of  claim 27  wherein the molecules are loaded into the array of obstacles using electric fields. 
   
   
       46 . The apparatus of  claim 27  wherein the molecules are routed to the next processing step after fractionation. 
   
   
       47 . The apparatus of  claim 27 , wherein the asymmetrically alternating electric fields comprise alternating first and second electric pulses of first and second waveforms, an integral over time of one of the first or second pulses' amplitudes being maintained larger than that of the other pulse.