If you have the possibility of excitation with 480nm you'd better use SYBR Green I or PicoGreen or related DNA dye. They are 100- to 1000-fold more sensitive than EtBr.

Picogreen will be better option here if the DNA is double stranded

Pico Green

You may have to use any of the fluorescent dyes like Syber Green than EtBr for such low concn. of DNA

Dear dr I dont have sybr green dye except sybr green master mix for qPCR could I use it instead ????

Should work.

Try the Agilent Bioanalyzer 2100. It offers very sensitive measurement.