Synthesis and Internal Structure of Finite-Size DNA–Gold Nanoparticle Assemblies

Spatially defined networks of 15 nm-sized DNA-functionalized gold nanoparticles (DNA–AuNPs) were studied using dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), as well as optical extinction spectroscopy (OES). We use a combination of these techniques with Monte Carlo simulations of pair-distance distribution function (PDDF) curves and generalized Mie theory simulations as well as in situ-transmission electron microscopy (in situ-TEM) to analyze the internal structure of the finite-size assemblies. The DLS data show that monodisperse, spherical networks with hydrodynamic radii of ca. 30 nm are found for reaction mixtures of complementarily functionalized DNA–AuNPs between 1:15 and 1:20. Different interparticle distances within these assemblies are identified and quantified. By controlling the network morphology through selection of the reaction mixture, center-shell geometries are obtained. The number of shell-AuNPs surrounding each center-AuNP is determined from the SAXS data and Monte Carlo simulations. This number is quantified to be ca. 10, with the exact number depending on the linking DNA double strand. The optical spectra of the networks are found to be consistent with the structural properties. The structural information gained here enables a quantitative description of optical and other physical properties, which is expected to prove useful for the construction and application of such systems, for example, in drug release, gene regulation, or external-stimuli-responsive materials