Selective nucleic acid fragment recovery

1. A method to selectively recover nucleic acid fragments with a desired size range comprising:

a) mixing target nucleic acids with a binding buffer having a selected pH and chaotropic salt concentration to allow the nucleic acid fragments with the desired size range to be bound to a solid surface, wherein said chaotropic salt comprises guanidinium thiocyanate (GITC) in a final concentration between 0.7-1M;

b) applying the mixture from step a) to the solid surface so that the nucleic acid fragments with the desired size range reversibly and non-specifically bind to the solid surface; and

c) selectively recovering the nucleic acid fragments with the desired size range by eluting the bound nucleic acid fragments from the solid surface with an eluting buffer.

2. The method of claim 1 , wherein said chaotropic salt concentration of said binding buffer is adjusted by water in an amount that allows said nucleic acid fragments with the desired size range being bound to and subsequently eluted from said solid surface.

3. The method of claim 2 , wherein said solid surface is silica membrane filter column or silica coated magnetic microparticles.

4. The method of claim 3 , wherein said nucleic acid fragments are DNA fragments, RNA fragments, or PNA fragments.

5. The method of claim 4 , wherein DNA fragments with the desired size range less or equal to 100 bp bind to and subsequently eluted from a silica membrane filter column, when the final concentration of GITC in the binding buffer is about 1.0M.

6. The method of claim 4 , wherein DNA fragments with the desired size range less or equal to 200 bp bind to and subsequently eluted from a silica membrane filter column when the final concentration of GITC in the binding buffer is about 0.8M.

7. The method of claim 4 , wherein DNA fragments with the desired size range less or equal to 300 bp bind to and subsequently eluted from a silica membrane filter column when the final concentration of GITC is about 0.7M.

8. A method to selectively recover nucleic acid fragments with a desired size range comprising:

a) providing a first sample mixture by mixing target nucleic acids with a first binding buffer, wherein a chaotropic salt concentration or pH of said first binding buffer is adjusted to allow nucleic acid fragments of more than 700 bps to bind to a solid surface;

b) applying said first sample mixture from step a) to a first solid surface;

c) collecting a flow-through solution from centrifuging the first solid surface with the first sample mixture;

d) providing a second sample mixture by mixing the flow-through solution with a second binding buffer, wherein a chaotropic salt concentration or pH of said second binding buffer is adjusted to allow nucleic acid fragments with a desired size range of 100 to 700 bps to bind to a solid surface, wherein said chaotropic salt comprises guanidinium thiocyanate (GITC) in a final concentration between 0.7-1M;

e) applying the second sample mixture from step d) to a second solid surface; and

f) selectively recovering the nucleic acid fragments with the desired size range of 100 to 700 bps by separately eluting the bound nucleic acid fragments from the second solid surfaces with an eluting buffer.

9. The method of claim 8 , wherein said first binding buffer comprises an acid or an acidic salt thereof, to reduce pH of the binding buffer so as to facilitate larger nucleic acid fragments to be bound to the solid surface.

10. The method of claim 8 , wherein said second binding buffer comprises a base, or basic salt thereof, to increase pH of the binding buffer so as to remove smaller nucleic acid fragments.

11. The method of claim 8 , wherein pH of said binding buffers ranges between 5.5 and 7.5.