Base dependent adsorption of single-stranded homo-oligonucleotides to gold nanoparticles

Many bioanalytical devices now feature DNA immobilised on optically or electrically addressed gold surfaces, either via covalent (thiol) tethers, or non-specifically adsorbed via the DNA nucleobases. To guide the development of colorimetric biosensors that depend on the dissociation of adsorbed DNA aptamers, the interaction of homo-30-mers composed of each of the bases with gold nanoparticles was investigated. Through colorimetric measurements of the stability of DNA-coated gold nanoparticle dispersions, stability was found to decrease in the order A > T > C ≥ G, counter to expectations based on intrinsic affinities. These observations were reconciled using electrochemical measurements of DNA surface densities on gold nanoparticle electrodes; while the measured surface densities correlated with the dispersion stabilities, it was apparent that many bases of a long DNA strand were dangling from the surface, rather than directly adsorbed. Thus, even (dT)30, whose bases have the weakest affinity to gold, can cover a gold surface with high total density since many of the bases will simply be tethered, and still contributing to the stability of a nanoparticle dispersion.