Hierarchical superaggregates consisting of DNA‐linked 14 nm AuNPs are synthesized and characterized by optical and scattering methods. Temperature changes, induced either thermally or photothermally, lead to a switching between specific sizes associated with superaggregates, primary networks, and individual nanoparticles. This could be of interest in the design of stimuli‐responsive materials.
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.
A one-step soft lithography based pathway to manufacture aligned gold nanorod@poly-(N-isopropylacrylamide) (GNR@pNIPAM) hybrid chains with hexagonal arrangement of the nanorods and with an anisotropic optical response is presented. After demonstration of an efficient synthesis protocol, yielding uniform composite microgels in high concentration, a micromolding procedure using wrinkled polydimethylsiloxane (PDMS) templates to fabricate aligned hybrid chains is introduced. It is found that the self-assembled GNR@pNIPAM microgels inside the PDMS wrinkle grooves can be transferred onto solid substrates, on which they exhibit a hexagonal order, as confirmed by small-angle X-ray scattering. Further, it is shown that the application of minimized PDMS wrinkle dimensions aligns GNRs inside the pNIPAM microgels, and that the optical response of such molded assemblies is anisotropic.
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