Reversible and Irreversible HAuCl4 Binding to DNA for Seeded Gold Nanoparticle Growth and Opposite DNA and Aptamers Colorimetric Sensing Outcomes

Abstract

DNA-directed seeded growth of gold nanoparticles has been used for the development of aptamer-based biosensors with the assumption that target analytes can modulate the adsorption of aptamers to the gold seeds and thus affect the growth reaction. To understand the reaction, the effect of single- and double-stranded DNA is first examined, and it is found that they have a similar promotion effect of anisotropic growth, suggesting that DNA cannot be detected using this method. By studying the interaction between HAuCl4 and DNA, both weak reversible binding and strong irreversible binding are identified, with the latter becoming dominating with a longer incubation time. Single- and double-stranded DNA have similar weak binding to HAuCl4, and this weak binding is more important for the growth reaction. Then three aptamers are tested, where only cortisol appeared to modulate its aptamer adsorption and the growth reaction reflected aptamer binding. Hg2+ shows no advantage for its aptamer, and quinine induced aggregation of AuNPs cannot be detected by this reaction either. Therefore, each aptamer target needs to be individually studied to test if this method is applicable. It is also noted that DNA and aptamers have opposite outcomes for the target-dependent growth reactions.