Interaction of Gold Nanoparticles with Cyanine Dyes in Cholesteric DNA Submicroparticles

Structural changes in particles of cholesteric liquid crystal dispersion (CLCD) of DNA during the formation of complexes of the cyanine dyes SYBR Green I (SG) and PicoGreen (PG) with negatively charged gold nanoparticles (NPs) have been studied using circular dichroism spectroscopy. It has been shown that in the presence of the dyes, the degradation of the cholesteric DNA packing by the action of gold NPs increases by a factor of ~1.6 (SG) or ~2.7 (PG). Gold NPs have been found to prevent the formation of the reentrant cholesteric DNA phase during the quenching of DNA CLCD—its heating to 80°C and cooling to 20°C. Pretreatment of the DNA dispersion with SG or PG in this case facilitates the restoration of the circular dichroism signal. A greater effect is noted for PG, which can be explained by stronger electrostatic interaction of this dye with Au NPs, since its charge is +3, whereas the charge of SG is +2.