Toward Fast and Quantitative Modification of Large Gold Nanoparticles by Thiolated DNA: Scaling of Nanoscale Forces, Kinetics, and the Need for Thiol Reduction

We have recently reported on the fast and quantitative adsorption of DNA to 13 nm gold nanoparticles (AuNPs) at pH 3. This is in contrast to most traditional methods at neutral pH, where the adsorption is both slow and requires high excess of DNA. Direct application of our protocol to large particles in many cases did not result in particles that are stable at high (0.3 M) salt, and high excess of DNA was still required for the formation of stable particles. In this work, we investigate the reasons for this limitation on the basis of kinetics and colloidal stability. On the basis of our investigation, fast and quantitative modification of large AuNPs is still possible, either by working at high particle concentration, or by using sonication. As we have shown that fast quantitative modification of large particles is possible, the preparation step of reduction and purification of the thiolated DNA becomes the rate limiting step in the whole AuNP-DNA conjugate protocol. However, we show that this step is unnecessary when using our current protocol.