Fluorescence superquenching of SYBR green I in crowded DNA by gold nanoparticles

Gold nanoparticles (GNPs) are known to efficiently quench fluorescence with high constants (107-1011 M−1). Quenching efficiency is determined by GNPs parameters, the properties of dye complex with biomolecular substrate may also affect this efficiency. In the present work quenching of SYBR Green I fluorescence by 2.5 nm GNPs was investigated in an isotropic DNA solution and on cholesteric (DNA CLCD) and hexagonal (DNA HLCD) liquid crystalline dispersion templates obtained with polymer and salt-induced condensation. Superquenching of SYBR Green I fluorescence was observed in all investigated models. The quenching efficiency increased as the DNA molecules were spatially ordered: the greatest quenching was observed for DNA HLCD where DNA molecules are packed most densely. In the condensed DNA systems, unlike DNA solution, the mechanism of quenching was not only the formation of a nonfluorescent complex, but also energy transfer between dye molecules and GNPs. The Stern-Volmer and Perrin models were insufficient for description of quenching processes. The Perrin equation was in an agreement with experiment only for DNA in solution. The model of microphase separation most adequately described the SYBR Green I fluorescence quenching by GNPs in DNA solution as well as in the molecularly organized DNA CLCD and DNA HLCD.