AVS 52nd International Symposium
    DNA Topical Conference Monday Sessions
       Session DN+BI-MoM

Paper DN+BI-MoM1
Design Rules for the Assembly of DNA Modified Nanoparticles: Influence of Surface Chemistry, Ionic Strength, and a Polycation

Monday, October 31, 2005, 8:20 am, Room 311

Session: DNA Structures and Surfaces
Presenter: K.J. Jeong, Purdue University
Authors: K.J. Jeong, Purdue University
S. Bhattacharya, Purdue University
D.B. Janes, Purdue University
G.U. Lee, Purdue University
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DNA-modified gold nanoparticles are promising materials for the efficient assembly of hierarchical nanostructures because of their ability to self-assemble specifically. In this study, the affect of the DNA surface immobilization chemistry, ionic strength of the solution, and a polycation on the efficiency of assembly of DNA-modified gold nanoparticles on DNA-modified gold surfaces was quantitatively studied. The hybridization efficiency was studied for DNA gold nanoparticles on DNA surfaces treating with 6-mercapto-1-hexanol (MCH) and it was found to significantly enhance the density of nanoparticles found on the surface. Ionic strength played a complex role on the observed assembly of the particles. In pure water, no assembly was possible because the diffusion of the nanoparticles was prevented by strong electrostatic repulsion. In ionic strengths greater than 0.1M NaCl, electrostatic repulsion was effective only at short ranges so that the nanoparticles can assemble through DNA hybridization. However, at ionic concentrations greater than 0.4M NaCl, a slight decrease in assembly was observed, which is attributed to the partial loss of particles in solution through aggregation. Theoretical analysis of these results based on the surface forces that govern the interactions between DNA-modified gold surfaces - electrostatic, van der Waals, and steric forces - confirms the interpretation above. One important conclusion drawn from the theoretical analysis is that the forces that govern the stability of DNA-gold colloids are not DLVO forces but a mixture of electrostatic and steric interactions. Spermidine, a polycation, was used to irreversibly lock-in the nanoparticles assembled on the surface so that the samples could be rinsed with water and dried. The results found in this article provide new insight into design rules for controlling the efficient assembly of DNA-modified nanoparticles.