Surface Science of DNA\nAdsorption onto\nCitrate-Capped Gold Nanoparticles

Abstract

Single-stranded DNA can be adsorbed by citrate capped\ngold nanoparticles\n(AuNPs), resulting in increased AuNP stability, which forms the basis\nof a number of biochemical and analytical applications, but the fundamental\ninteraction of this adsorption reaction remains unclear. In this study,\nwe measured DNA adsorption kinetics, capacity, and isotherms, demonstrating\nthat the adsorption process is governed by electrostatic forces. The\ncharge repulsion among DNA strands and between DNA and AuNPs can be\nreduced by adding salt, reducing pH or by using noncharged peptide\nnucleic acid (PNA). Langmuir adsorption isotherms are obtained, indicating\nthe presence of both adsorption and desorption of DNA from AuNPs.\nWhile increasing salt concentration facilitates DNA adsorption, the\ndesorption rate is also enhanced in higher salt due to DNA compaction.\nDNA adsorption capacity is determined by DNA oligomer length, DNA\nconcentration, and salt. Previous studies indicated faster adsorption\nof short DNA oligomers by AuNPs, we find that once adsorbed, longer\nDNAs are much more effective in protecting AuNPs from aggregation.\nDNA adsorption is also facilitated by using low pH buffers and high\nalcohol concentrations. A model based on electrostatic repulsion on\nAuNPs is proposed to rationalize the DNA adsorption/desorption\nbehavior.