Method and kit for purifying nucleic acids

Abstract

Methods for automated extraction of nucleic acids are disclosed. Also disclosed are method and kits for isolating fetal nucleic acids from a plasma sample of a pregnant woman. The method includes flowing the plasma sample through a first filter under conditions that allow binding of the fetal and maternal nucleic acids to the first filter; eluting the fetal and maternal nucleic acids bound to the first filter to produce a concentrated nucleic acid sample; flowing the concentrated nucleic acid sample through a second filter under conditions that allow preferential binding of the maternal nucleic acids to the second filter; and recovering the fetal nucleic acid from the concentrated nucleic acid sample that flow through the second filter.

1 - 20 . (canceled) 
     
     
         21 . A method for separating and isolating low molecular weight (LMW) nucleic acids from high molecular weight (HMW) nucleic acids in a sample, comprising:
 (a) flowing a sample comprising LMW nucleic acids and HMW nucleic acids through a first filter, under conditions that allow specific binding of the LMW and HMW nucleic acids to the first filter;   (b) eluting bound LMW and HMW nucleic acids from the first filter to form a concentrated nucleic acid sample comprising LMW nucleic acids and HMW nucleic acids;   (c) flowing the concentrated nucleic acid sample through a second filter, under conditions that allow the HMW nucleic acids to bind to the second filter and the LMW nucleic acids to flow through the second filter; and   (d) collecting the flow-through fraction from the second filter, wherein the flow-through fraction from the second filter contains LMW nucleic acids,   wherein the conditions that allow specific binding of the LMW and HMW nucleic acids to the first filter in step (a) comprise forming a first binding mixture that comprises the sample, an aliphatic alcohol in a range between about 17-25% (v/v) and a chaotropic salt in a concentration range between about 0.5 M to about 4.0 M.   
     
     
         22 . The method of  claim 21 , wherein the conditions for binding the HMW nucleic acids to the second filter in step (c) comprise forming a second binding mixture that comprises the concentrated nucleic acid sample, an aliphatic alcohol in a range between about 0-100/(v/v) and a chaotropic salt in a concentration range between about 1 M to about 4.0 M. 
     
     
         23 . The method of  claim 21 , further comprising the steps of:
 (e1) eluting bound HMW nucleic acids from the second filter to produce a regenerated second filter;   (f1) flowing the flow-through fraction from the second filter through the regenerated second filter under conditions that allow binding of LMW nucleic acids to the second filter; and   (h1) eluting bound LMW nucleic acids from the second filter in step (f1).   
     
     
         24 . The method of  claim 23 , wherein the conditions for binding the LMW nucleic acids to the second filter in step (f1) comprise forming a third binding mixture that comprises the flow-through fraction from the second glass frit filter, an aliphatic alcohol in a range between about 10-25% (v/v) and a chaotropic salt in a concentration range between about 1 M to about 5.0 M. 
     
     
         25 . The method of  claim 21 , wherein the first and second filters are self-supporting glass frits. 
     
     
         26 . The method of  claim 25 , wherein the glass flits are sintered glass frits. 
     
     
         27 . The method of  claim 25 , wherein the first glass frit filter has a pore size of 16-40 micron and the second glass frit filter has a pore size of 4-5.5 micron. 
     
     
         28 . The method of  claim 21 , further comprising the steps of:
 (e2) flowing the flow-through fraction from the second filter through a third filter under conditions that allow binding of the LMW nucleic acids to the third filter; and   (f2) eluting bound LMW nucleic acids from the third filter.   
     
     
         29 . The method of  claim 21 , wherein one or both of the first and second filter comprises a glass frit comprising a first section having a first pore size and second section having a second pore size, wherein the first pore size is different from the second pore size. 
     
     
         30 . A kit for isolating LMW nucleic acids from HMW nucleic acids in a sample, comprising:
 a pipette tip comprising a self-supporting glass flit filter, wherein the glass frit filter specifically binds to nucleic acids, wherein the glass frit filter has a pore size of 2-220 microns and is not treated or coated with an agent that improves binding of nucleic acid to the glass frit filter,   a first binding buffer formulated to be mixed with a plasma sample and provide a first binding mixture having about 17-25% v/v of an aliphatic alcohol and a chaotropic salt at a concentration of between about 0.5 M to about 4.0 M; and   a second binding buffer formulated to be mixed with a plasma sample and provide a first binding mixture having about 0-10% v/v of an aliphatic alcohol and a chaotropic salt at a concentration of between about 1 M to about 4.0 M.   
     
     
         31 . The kit of  claim 30 , comprising:
 a first pipette tip comprising a first glass frit filter and having a tip volume of 10-50 ml; and   a second pipette tip comprising a second glass flit filter and having a tip volume of 0.5-2 ml.   
     
     
         32 . The kit of  claim 31 , wherein the first glass frit filter has a pore size of 16-40 microns and the second glass frit filter has a pore size of 4-5.5 microns. 
     
     
         33 . The kit of  claim 31 , further comprising a third pipette tip comprising a third glass frit filter and having a tip volume of 0.2-2 ml. 
     
     
         34 . The kit of  claim 33 , wherein the third glass frit filter has a pore size of 16-40 microns. 
     
     
         35 . The kit of  claim 33 , wherein the third glass frit filter has a pore size of 4-10 microns. 
     
     
         36 . The kit of  claim 30 , wherein the glass frit filter comprises a fused glass frit comprising a first section having a first pore size and second section having a second pore size. 
     
     
         37 . The kit of  claim 36 , wherein the first section has a pore size of 100-160 microns and the second section has a pore size of 16-40 microns, or wherein the first section has a pore size of 16-40 microns and the second section has a pore size of 4-5.5 microns. 
     
     
         38 . The kit of  claim 36 , wherein the glass frit filter has a pore size of 16-40 micron and the glass frit filter in the additional pipette tip has a pore size of 4-10 micron. 
     
     
         39 . The kit of  claim 36 , wherein the glass frit filter comprises a fused glass frit comprising a first section having a first pore size and second section having a second pore size. 
     
     
         40 . The kit of  claim 39 , wherein the first section has a pore size of 100-160 microns and the second section has a pore size of 16-40 microns, or wherein the first section has a pore size of 16-40 microns and the second section has a pore size of 4-10 microns.