Rapid synthesis of DNA-functionalized gold nanoparticles in salt solution using mononucleotide-mediated conjugation

DNA functionalized gold-nanoparticles (Au-nps) have been broadly used as labeling reagents in the development of molecular diagnostics as well as building blocks in nanotechnology. Conventional methods for the synthesis of DNA functionalized Au-nps require long incubation, typically overnight, and delicate control of the ionic strength to compensate for the charge repulsion between the nanoparticles surface and the DNA strands, which generally affect the stability of the nanoparticles and the DNA loading density. In this study, we present a novel mononucleotide-mediated conjugation approach to synthesize DNA-functionalized Au-nps within 4 h in a high ionic strength environment. Au-nps covered with a thermally tunable stabilization layer through mononucleotide adsorption were shown to readily conjugate with thiol-DNAs in 0.1 M NaCl solution upon heating. Monitoring this mononucleotide-mediated conjugation reaction through dynamic light scattering and UV-vis spectroscopy demonstrated the formation of stable DNA/Au-nps conjugates. The resulting conjugates, as characterized by fluorescence spectroscopy, are loaded by approximately 80 strands per particle, comparable to the DNA loading density of current approaches. The general applicability of this approach was further verified in a nanoparticle-bound DNA hybridization test. Our results show that mononucleotide-mediated thermal conjugation is an attractive alternative that allows temperature-controlled and salt-enhanced functionalization of gold nanoparticles with DNAs in just a few hours.