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Silica-coated magnetic nanoparticles with greater ability to remain dispersed, and methods of making and using silica-coated magnetic nanoparticles. The magnetic nanoparticles comprise a core and a coating, where the core comprises Fe3O4 or other magnetic material and the coating has a thickness of

Silica-coated magnetic nanoparticles with greater ability to remain dispersed, and methods of making and using silica-coated magnetic nanoparticles. The magnetic nanoparticles comprise a core and a coating, where the core comprises Fe3O4 or other magnetic material and the coating has a thickness of from about 1.5 nm to about 2 nm. The magnetic nanoparticles are useful for preparing nucleic acids for analysis, by separating nucleic acids from other components and by normalizing nucleic acid concentrations.

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1. A composition comprising magnetic nanoparticles in a liquid medium, wherein each of the magnetic nanoparticles comprises a magnetic core and a coating on the core, wherein the coating has a thickness from about 1 nm to about 2 nm; and the magnetic nanoparticles in the composition have a Brunauer-

1. A composition comprising magnetic nanoparticles in a liquid medium, wherein each of the magnetic nanoparticles comprises a magnetic core and a coating on the core, wherein the coating has a thickness from about 1 nm to about 2 nm; and the magnetic nanoparticles in the composition have a Brunauer-Emmett-Teller (BET) surface area of from about 110 m2/g to about 130 m2/g. 2. The composition of claim 1, wherein the coating has a thickness of from about 1.5 nm to about 2.0 nm. 3. The composition of claim 1, wherein the magnetic nanoparticles have a BET surface area of from about 113 m2/g to about 127 m2/g. 4. The composition of claim 1, wherein the magnetic nanoparticles have an average total diameter of about 15 nm or less. 5. The composition of claim 1, wherein the magnetic nanoparticles have an average total diameter from about 10 to about 15 nm. 6. The composition of claim 1, wherein the cores of the magnetic nanoparticles have an average diameter of about 10 nm or less. 7. The composition of claim 1, wherein the cores are single domain magnetic nanoparticles of Fe3O4 which display paramagnetism. 8. The composition of claim 1, wherein the cores are single nanoscale crystals of magnetite. 9. The composition of claim 1, wherein the cores are substantially free of Fe2O3. 10. The composition of claim 1, wherein the coating comprises silica. 11. The composition of claim 1, wherein the coating further comprises a binding moiety that binds an analyte. 12. The composition of claim 11, wherein the analyte is nucleic acid. 13. The composition of claim 1, wherein the liquid medium is water. 14. The composition of claim 13, wherein the composition is a stable aqueous dispersion. 15. The composition of claim 13, wherein the composition comprises clusters of the magnetic nanoparticles dispersed in the water. 16. The composition of claim 15, wherein the clusters have an average cluster size in from about 50 nm to about 190 nm. 17. The composition of claim 1, wherein the composition is a stable suspension of the magnetic nanoparticles, and the magnetic nanoparticles are present in at a concentration of from about 3 to about 30 g/L. 18. The composition of claim 17, wherein the magnetic nanoparticles remain suspended for at least 6 months at a temperature of about 25° C. 19. A packaged stable suspension of magnetic nanoparticles in a sealed package, wherein: the magnetic nanoparticles comprise a core and a coating on the core, and the coating has a thickness of from about 1 nm to about 2 nm; andan interior volume of the sealed package is substantially free of oxygen. 20. A method of making silica-coated magnetic nanoparticles comprising: preparing an aqueous solution of Fe3+ and Fe2+ ions in deionized, de-oxygenated water in a Fe3+/Fe2+ molar ratio of about 2/1;sonicating the aqueous solution;precipitating Fe3O4 from the aqueous solution, thereby forming a mixture comprising Fe3O4 nanoparticles;adding a de-oxygenated alcohol and a silicate to the mixture;forming a silica coating on the Fe3O4 nanoparticles; andseparating the silica-coated Fe3O4 nanoparticles from the mixture.