DNA Strand Elongation Induced by Small Gold Nanoparticles at High Ethanol Content

Small N-(2-mercaptopropionyl)glycine gold nanoparticles (AuNPs) of 1.6 nm core size were synthesized. The mode of binding and the effect of ethanol on DNA conformational changes induced by AuNPs nanoparticles were studied in detail by means of fluorescence and circular dichroism (CD) spectroscopy, zeta potential, dynamic light scattering (DLS), viscometric, and atomic force microscopy (AFM) methods. The measurements were done at different molar ratios R = C-AuNPs/C-DNA and at different ethanol content. Both spectroscopic and structural techniques revealed that the binding of AuNPs with DNA grooves largely prevailed up to 30% EtOH (v/v). For higher ethanol levels (from 40% to 65% EtOH (v/v)), all methods concurred by showing that AuNPs were able to induce DNA strand elongation, which preceded formation of the AuNPs/DNA groove complex. Moreover, under suitable R values and ethanol content, the CD spectra, DLS, and AFM experiments revealed that AuNPs nanoparticles induced the formation of a rather compact AuNPs/DNA complex. The results suggested that this form is a coiled DNA structure stabilized by AuNPs interconnections.