Impact of DNA Density on the Aggregation Kinetics of DNA/PEG-Modified Gold Nanoparticles Induced by DNA Hybridization: Implications for Colorimetric Nucleic Acid Detection

The aggregation of DNA-modified gold nanoparticles (DNA-GNPs) induced by three-dimensional (3D) DNA hybridization has attracted attention in the field of DNA nanotechnology. However, kinetic studies on the 3D DNA hybridization-induced aggregation of DNA-GNPs have been limited to a few studies. Among the numerous factors influencing aggregation rate, these studies strongly suggest that the aggregation rate relies on two opposing interactions dependent on DNA density: an interparticle attraction force based on DNA hybridization at the junctions between particles and an interparticle repulsion force due to the steric and electric charge of DNA strands. Moreover, existing literature has not clarified which of the opposing forces, which vary with DNA density, controls the kinetics of the 3D DNA hybridization-induced aggregation of DNA-GNPs. Herein, we systematically studied the impact of DNA density on the kinetics of the 3D DNA hybridization-induced aggregation of DNA and poly(ethylene glycol) (PEG)-co-modified GNPs (DNA/PEG-GNPs). A unique finding, which we would like to report here, is that there is the optimal DNA density for the 3D DNA hybridization-induced aggregation rate of DNA/PEG-GNPs. In particular, the rate of the 3D DNA hybridization-induced aggregation of DNA/PEG-GNPs increased with increasing DNA density because of the increase in attractive forces caused by the increase in the number of DNA strands hybridized at the junctions between particles. However, the rate decreased with increasing DNA density above a certain level because the electrostatic and steric repulsions between DNA strands on the GNPs increased. These results indicate that the predominant interaction (attraction or repulsion) in the rate of the 3D DNA hybridization-induced aggregation of DNA/PEG-GNPs depends on the DNA density of the GNPs. These new findings will be useful for the surface design of DNA-modified nanoparticles and practical applications of DNA nanotechnology through 3D DNA hybridization, especially, development of colorimetric nucleic acid detection systems.