This invention provides a method of isolating and purifying nucleic acid using a binding buffer comprising a sodium- or potassium-ion-containing solution with the final concentrations of either sodium- or potassium-ion concentration of at least about 500 mM, preferably greater than about 1 M to saturate, and the pH of such solution of being adjusted in the range of about 2.0 to 5.0, for reversible binding of the nucleic acid to a silicon-containing matrix. The invention further provides a method of increasing reversible binding of the nucleic acid to a silicon-containing matrix using the binding buffer of the invention in addition to 20% to 50% (v/v) of a water-soluble organic solvent, e.g., ethanol. Nucleic acid obtained thereof that is free of chaotropes and other toxic chemicals, and nucleic acid purification kits comprising the binding buffer of the invention are also provided.