Using a DNA-fluorescent dye like Hoechst 33258 can greatly increase the sensitivity at which DNA concentrations can be quantified.

Mix equal volumes of DNA in water with 2x Hoechst 33258 staining solution. Measure in a UV-fluorometer.

Make a standard curve with the following final DNA concentrations:

• 0 ng/ml, 200 ng/ml, 500 ng/ml, 1000 ng/ml, 1500 ng/ml
  

The Hoechst fluorescence has a reasonably linear response to DNA concentrations up to about 1000 ng/ml.

2x	Hoechst 33258 staining solution	final concentration
200 μl	1M Tris pH 8.0	20 mM
40 μl	500 mM EDTA pH 8.0	2 mM
4000 μl	1M NaCl	400 mM
4 μl	1 mg/ml Hoechst 33258	400 ng/ml
5756 μl	H2O	10 ml final total volume

Hoechst 33258 fluorescence is sensitive to salt concentration. A final concentration of 200 mM minimizes variability.