Toward efficient modification of large gold nanoparticles with DNA

DNA-coated gold nanoparticles are one of the most researched nano-bio hybrid systems. Traditionally their synthesis has been a long and tedious process, involving slow salt addition and long incubation steps. This stems from the fact that both DNA and gold particles are negatively charged, therefore efficient interaction is possible only at high salt concentration. However, unmodified particles are susceptible to aggregation at high salt concentrations. Most of the recent modification methods involve the use of surfactants or other small molecules to stabilize the nanoparticles against aggregation, enabling faster modification. Here we present our result on an alternative route to reach fast modification in low salt conditions, namely, reduction of the charge of DNA. We will discuss both the use of natural DNA under acidic pH conditions, and the use of DNA with a cationic, spermine-based "tail" which is commercially available under the name ZNA. Additionally we introduce a characterization method based on ensemble localized surface plasmon resonance measurement (LSPR) which enabled us to extract the kinetics of DNA absorbance without the need for fluorescent tags. Lastly we show that the same ZNA-based modification protocol can be effectively used for silver nanoparticle modification.