Marek Grzelczak

Directed Self-Assembly of Nanoparticles

Within the field of nanotechnology, nanoparticles are one of the most prominent and promising candidates for technological applications. Self-assembly of nanoparticles has been identified as an important process where the building blocks spontaneously organize into ordered structures by thermodynamic and other constraints. However, in order to successfully exploit nanoparticle self-assembly in technological applications and to ensure efficient scale-up, a high level of direction and control is required. The present review critically investigates to what extent self-assembly can be directed, enhanced, or controlled by either changing the energy or entropy landscapes, using templates or applying external fields.

Functionalization of Graphene via 1,3-Dipolar Cycloaddition

Few-layer graphenes (FLG) produced by dispersion and exfoliation of graphite in N-methylpyrrolidone were successfully functionalized using the 1,3-dipolar cycloaddition of azomethine ylides. The amino functional groups attached to graphene sheets were quantified by the Kaiser test. These amino groups selectively bind to gold nanorods, which were introduced as contrast markers for the identification of the graphene reactive sites. The interaction between gold nanorods and functionalized graphene was followed by UV-vis spectroscopy. The presence of the organic groups was confirmed by X-ray photoelectron spectroscopy and thermogravimetric analysis. The sheets were characterized by transmission electron microscopy, demonstrating the presence of gold nanorods distributed uniformly all over the graphene surface. This observation indicates that reaction has taken place not just at the edges but also at the internal C horizontal lineC bonds of graphene. Our results identify exfoliated graphene as a considerably more reactive structure than graphite and hence open the possibility to control the functionalization for use as a scaffold in the construction of organized composite nanomaterials.

Hydrophobic interactions modulate self-assembly of nanoparticles.

Hydrophobic interactions constitute one of the most important types of nonspecific interactions in biological systems, which emerge when water molecules rearrange as two hydrophobic species come close to each other. The prediction of hydrophobic interactions at the level of nanoparticles (Brownian objects) remains challenging because of uncontrolled diffusive motion of the particles. We describe here a general methodology for solvent-induced, reversible self-assembly of gold nanoparticles into 3D clusters with well-controlled sizes. A theoretical description of the process confirmed that hydrophobic interactions are the main driving force behind nanoparticle aggregation.

Influence of silver ions on the growth mode of platinum on gold nanorods

Gold nanorods were used as seeds for platinum growth, using a mild reducing agent, ascorbic acid, in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Highly preferential growth on the tips or complete overcoating can be achieved by manipulation of the reduction conditions, among which the presence of silver ions was found to be highly dominant. In either case, the growth was found to be epitaxial, as demonstrated by high resolution electron microscopy and Fourier transform analysis. Additionally, the deposition mode leads to very different effects on the optical properties of the nanoparticles, with tip growth inducing huge surface plasmon red shifts.

Molecular Thinking for Nanoplasmonic Design

The development of nanoplasmonics has been tremendous during the past two decades, driven in part by the improvements in colloidal synthesis of nanocrystals and manipulation of nanoparticle surface functionalities. This has granted access not only to exquisite control over the morphology of nanoparticles but also to novel multiparticle nanostructures with a variety of organizational motifs. Driven by such new possibilities, completely unforeseen plasmonic effects have been found, which let us think about applications in a variety of fields. In this Perspective, we discuss the evolution of plasmonic nanomaterials and their corresponding properties and correlations with molecular concepts that have been around for a long time. Additional thinking along these lines may lead to further expansion of nanoplasmonics and to multiple surprising discoveries in this field.

Multiwalled Carbon Nanotubes Drive the Activity of Metal@oxide Core–Shell Catalysts in Modular Nanocomposites

Rational nanostructure manipulation has been used to prepare nanocomposites in which multiwalled carbon nanotubes (MWCNTs) were embedded inside mesoporous layers of oxides (TiO(2), ZrO(2), or CeO(2)), which in turn contained dispersed metal nanoparticles (Pd or Pt). We show that the MWCNTs induce the crystallization of the oxide layer at room temperature and that the mesoporous oxide shell allows the particles to be accessible for catalytic reactions. In contrast to samples prepared in the absence of MWCNTs, both the activity and the stability of core-shell catalysts is largely enhanced, resulting in nanocomposites with remarkable performance for the water-gas-shift reaction, photocatalytic reforming of methanol, and Suzuki coupling. The modular approach shown here demonstrates that high-performance catalytic materials can be obtained through the precise organization of nanoscale building blocks.

Highly transparent and conductive films of densely aligned ultrathin Au nanowire monolayers.

The combination of low electrical resistance and high optical transparency in a single material is very uncommon. Developing these systems is a scientific challenge and a technological need, to replace ITO in flexible electronic components and other highly demanding applications. Here we report a facile method to prepare single layers of densely aligned ultrathin Au-nanowires, homogeneous over cm(2) areas. The as-deposited films show an electrical/optical performance competitive with ITO and graphene-based electrodes. Moreover, the Au-films show a good stability under ambient conditions, and the large aspect ratio of the ultrathin nanowires makes them perfect for deposition in flexible substrates.

Synthesis of Multifunctional Composite Microgels via In Situ Ni Growth on pNIPAM-Coated Au Nanoparticles

Novel colloidal composites have been designed to incorporate multiple functionalities that allow optical detection, magnetic manipulation, molecular trapping, and thermal response. Such particles are made of gold nanoparticle cores covered by a thin layer of metallic nickel and a poly(N-isopropylacrylamide) (pNIPAM) shell. While the gold cores provide efficient optical response through localized surface plasmon resonances, nickel allows external magnetic manipulation and the pNIPAM shell can be swollen or collapsed as a function of temperature, thus allowing capture and release of various types of molecules.

Colloidal Nanoplasmonics: From Building Blocks to Sensing Devices

Nanoplasmonics is a rapidly developing field of research and technology that is based on the ability of small metal particles to interact strongly with light of wavelength significantly larger than their size. The development of nanoplasmonics has been closely associated with the application of colloid science to the controlled growth of metal nanocrystals in solution and to directing the self-assembly of such nanocrystals into organized arrays with enhanced collective properties. Engineering the morphology and the assembly of metal nanoparticles is a key step toward the fabrication of devices with great potential in detection and diagnosis as well as in a wide variety of other fields. In this Feature Article, we provide an overview of the recent work in our laboratory, which in our view somehow reflects the evolution of the field itself and provides guidelines for future research.

Glycans as Biofunctional Ligands for Gold Nanorods: Stability and Targeting in Protein-Rich Media

Poly(ethylene glycol) (PEG) has become the gold standard for stabilization of plasmonic nanoparticles (NPs) in biofluids, because it prevents aggregation while minimizing unspecific interactions with proteins. Application of Au NPs in biological environments requires the use of ligands that can target selected receptors, even in the presence of protein-rich media. We demonstrate here the stabilizing effect of low-molecular-weight glycans on both spherical and rod-like plasmonic NPs under physiological conditions, as bench-marked against the well-established PEG ligands. Glycan-coated NPs are resistant to adsorption of proteins from serum-containing media and avoid phagocytosis by macrophage-like cells, but retain selectivity toward carbohydrate-binding proteins in protein-rich biological media. These results open the way toward the design of efficient therapeutic/diagnostic glycan-decorated plasmonic nanotools for specific biological applications.