Genomic DNA was obtained from peripheral blood samples of healthy volunteers and interacted with two fluorescent dyes (i.e. Hoechst 33,258 and ethidium bromide) in aqueous media. These media containing DNA-dye complexes deposited on the gold coated mica surfaces. Then, STM images were obtained in which the STM was operated in air at atmospheric pressure with a tip-to-substrate bias voltage of 250-1000 mV (sample positive) and the tunneling currents in the range of 10-20 pA by using etched tips of Pt/Ir, in constant current mode. Both dyes from molecular clusters on DNA. While, the Hoechst molecules were observed on the DNA chains at regular distances, the ethidium bromide molecular clusters did not.