We
present ensembles of surface-ordered nanoparticle arrangements, which
are formed by template-assisted self-assembly of monodisperse, protein-coated
gold nanoparticles in wrinkle templates. Centimeter-squared areas
of highly regular, linear assemblies with tunable line width are fabricated
and their extinction cross sections can be characterized by conventional
UV/vis/NIR spectroscopy. Modeling based on electrodynamic simulations
shows a clear signature of strong plasmonic coupling with an interparticle
spacing of 1–2 nm. We find evidence for well-defined plasmonic
modes of quasi-infinite chains, such as resonance splitting and multiple
radiant modes. Beyond elementary simulations on the individual chain
level, we introduce an advanced model, which considers the chain length
distribution as well as disorder. The step toward macroscopic sample
areas not only opens perspectives for a range of applications in sensing,
plasmonic light harvesting, surface enhanced spectroscopy, and information
technology but also eases the investigation of hybridization and metamaterial
effects fundamentally.
We
present a bottom-up assembly route for a large-scale organization
of plasmonic nanoparticles (NPs) into three-dimensional (3D) modular
assemblies with core/satellite structure. The protein-assisted assembly
of small spherical gold or silver NPs with a hydrophilic protein shell
(as satellites) onto larger metal NPs (as cores) offers high modularity
in sizes and composition at high satellite coverage (close to the
jamming limit). The resulting dispersions of metal/metal nanoclusters
exhibit high colloidal stability and therefore allow for high concentrations
and a precise characterization of the nanocluster architecture in
dispersion by small-angle X-ray scattering (SAXS). Strong near-field
coupling between the building blocks results in distinct regimes of
dominant satellite-to-satellite and core-to-satellite coupling. High
robustness against satellite disorder was proved by UV/vis diffuse
reflectance (integrating sphere) measurements. Generalized multiparticle
Mie theory (GMMT) simulations were employed to describe the electromagnetic
coupling within the nanoclusters. The close correlation of structure
and optical property allows for the rational design of core/satellite
nanoclusters with tailored plasmonics and well-defined near-field
enhancement, with perspectives for applications such as surface-enhanced
spectroscopies.
What's going on in there?! Little is known about the fate of nanoparticles (NPs) after their internalization by cells and organisms. Protein‐coated gold NPs were used to study the physicochemical properties of NPs in extra‐ and intracellular fluids. These potential vehicles for enzymatic drug delivery were highly stable at pH 7.4 in the presence of salts and free proteins, but agglomerated reversibly under acidic conditions (see picture).
This article presents the synthesis and physicochemical behavior of dual‐responsive plasmonic nanoparticles with reversible optical properties based on protein‐coated gold nanoparticles grafted with thermosensitive polymer brushes by means of surface‐initiated atom transfer radical polymerization (SI‐ATRP) that exhibit pH‐dependent thermo‐responsive behavior. Spherical gold NPs of two different sizes (15 nm and 60 nm) and with different stabilizing agents (citrate and cetyltrimethylammonium bromide (CTAB), respectively) were first capped with bovine serum albumin (BSA). The resulting BSA‐capped NPs (Au@BSA NPs) exhibited not only extremely high colloidal stability under physiological conditions, but also a reversible U‐shaped pH‐responsive behavior, similar to pure BSA. The ϵ‐amine of the L‐lysine in the protein coating was then used to covalently bind an ATRP‐initiator, allowing for the SI‐ATRP of thermosensitive polymer brushes of oligo(ethylene glycol) methacrylates with an LCST of 42 °C in pure water and around 37 °C under physiological conditions. Such protein coated nanoparticles grafted with thermosensitive polymers exhibit a smart pH‐dependent thermosensitive behavior.
In this work, we investigate the
ligand exchange of cetyltrimethylammonium bromide (CTAB) with bovine
serum albumin for gold nanorods. We demonstrate by surface-enhanced
Raman scattering measurements that CTAB, which is used as a shape-directing
agent in the particle synthesis, is completely removed from solution
and particle surface. Thus, the protein-coated nanorods are suitable
for bioapplications, where cationic surfactants must be avoided. At
the same time, the colloidal stability of the system is significantly
increased, as evidenced by spectroscopic investigation of the particle
longitudinal surface plasmon resonance, which is sensitive to aggregation.
Particles are stable at very high concentrations (cAu 20 mg/mL) in biological media such as phosphate buffer
saline or Dulbecco’s Modified Eagle’s Medium and over
a large pH range (2–12). Particles can even be freeze-dried
(lyophilized) and redispersed. The protocol was applied to gold nanoparticles
with a large range of aspect ratios and sizes with main absorption
frequencies covering the visible and the near-IR spectral range from
600 to 1100 nm. Thus, these colloidally stable and surfactant-free
protein-coated nanoparticles are of great interest for various plasmonic
and biomedical applications.
Since the layer-wise polyelectrolyte deposition offers the opportunity to modify surfaces for biomedical applications, interactions and toxicity between polyelectrolytes and living cells become interesting. The aim of the present work is to determine the different factors such as contact area, charge, and transplantation site that influence the cell reaction to a specific polymer. We found that toxicity is influenced by all these factors and cannot be tested easily in a model.
Sustainable societies require the development of engineered hybrid materials. Bio-inspired mineralization of the wood cell wall architecture with calcium carbonate offers a green alternative to conventional fire-retardant systems.
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