Time-resolved chloroquine-induced relaxation of supercoiled plasmid DNA.

Herein, we report on the in vitro change of DNA conformation of plasmids bound to a 3-aminopropyl-modified mica surface and monitoring the events by atomic force microscopy (AFM) imaging under near physiological conditions. In our study, we used an intercalating drug, chloroquine, which is known to decrease the twist of the double helix and thus altered the conformation of the whole DNA. During our experiments, a chloroquine solution was added while imaging a few highly condensed plasmid nanoparticles in solution. AFM images recorded after the drug addition clearly show a time-resolved relaxation of these bionanoparticles into a mixture of loose DNA strands.