dna, which is negatively charged, can adsorb onto the surface of citrate-capped au nanoparticles. explain why such a system would exhibit a langmuir adsorption isotherm.

Single-stranded DNA is adsorbed onto citrate-capped gold nanoparticles (AuNPs), which improves the stability of AuNPs and is the basis for many biochemical and analytical applications, but the basics of this adsorption reaction are interactions remain unknown.

In this study, we measured the kinetics, capacity and isotherms of DNA adsorption and showed that the adsorption process is governed by electrostatic forces. Charge repulsion between DNA strands and between DNA and AuNPs can be reduced by adding salt, lowering the pH, or using uncharged peptide nucleic acids (PNAs). A Langmuir adsorption isotherm is obtained, showing that there is both adsorption and desorption of DNA from the AuNPs. Higher salt concentrations promote DNA adsorption, but higher salt concentrations also increase the rate of desorption due to DNA compaction. DNA adsorption capacity is determined by the length of DNA oligomers, DNA concentration, and salinity. Previous studies have shown faster adsorption of short DNA oligomers by AuNPs. We find that AuNPs are more effectively protected from aggregation when longer DNA is adsorbed. DNA adsorption is also facilitated by the use of low pH buffers and high alcohol concentrations. A model based on electrostatic repulsion of AuNPs has been proposed to explain the adsorption/desorption behavior of DNA.

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