The ability of thin materials to shape-shift is a common occurrence that leads to dynamic pattern formation and function in natural and man-made structures. However, harnessing this concept to design inorganic structures at the nanoscale rationally has remained far from reach due to a lack of fundamental understanding of the essential physical components. Here, we show that the interaction between organic ligands and the nanocrystal surface is responsible for the full range of chiral shapes seen in colloidal nanoplatelets. The adsorption of ligands results in incompatible curvatures on the top and bottom surfaces of NPL, causing them to deform into helico\"ids, helical ribbons, or tubes depending on the lateral dimensions and crystallographic orientation of the NPL. We demonstrate that nanoplatelets belong to the broad class of geometrically frustrated assemblies and exhibit one of their hallmark features: a transition between helico\"ids and helical ribbons at a critical width. The effective curvature $\bar{\kappa}$ is the single aggregate parameter that encodes the details of the ligand/surface interaction, determining the nanoplatelets' geometry for a given width and crystallographic orientation. The conceptual framework described here will aid the rational design of dynamic, chiral nanostructures with high fundamental and practical relevance.

The difference between in-plane and out-of-plane bonding energy of transition metal dichalcogenides has provided the possibility of isolating single layers. A one step synthesis protocol to produce size-controlled single layers has always been challenging. Here we developed a new colloidal synthesis to produce monodisperse size-controlled 1T'-WS2 nano-monolayers with outstanding colloidal stability by using 1-octadecanethiol as the coordinating agent. Changes in the reaction time and amount of coordinating agent regulate the mean size of the nanosheets. We investigated the effect of octadecanethiol and injection rate on the dispersion and mean-size, using UV-Vis spectroscopy, X-ray diffraction techniques, and transmission electron microscopy. Furthermore, thermogravimetric analysis and Fourier transform infrared spectroscopy allow for ligands detection and analysis at the surface of the nanosheets. These results open a new pathway to synthesize, control and explore the properties of nanoscale transition metal dichalcogenides.

A new modular, easy-to-synthesize photocatalyst was prepared by assembling colloidal CdSe/ZnS quantum dots (QD) and gold nanoparticles (AuNP) via their ligands thanks to copper-catalyzed azide to alkyne cycloaddition (CuAAC) click chemistry. The resulting composite (QD-AuNP) photocatalyst was tested with a benchmark photoredox system previously reported by our group, for which QD alone acted as a photocatalyst but with a modest quantum yield (QY = 0.06%) and turnover number (TON = 350 in 3 h) due to poor charge separation. After optimization, the QD-AuNP composites exhibited much improved photocatalytic performances: up to five times higher TON (2600 in 3 h) and up to 24 times faster reaction in the first 10 min of visible irradiation. Such an improvement is attributed to an efficient electron transfer from QD to AuNP in the photoexcited QD-AuNP composites, which ensures a much better charge separation than that in QD alone. This was confirmed by studying both (i) the quenching of the QD photoluminescence during the synthesis of the QD-AuNP composites and (ii) the blue shift of the AuNP plasmon absorption band due to the accumulation of up to 7400 electrons per AuNP in QD-AuNP composites under visible light irradiation in the presence of electron donors.

Complex architectures like 3D gold dendritic nanostructures were synthesized by an in situ templated growth method using a thin film of a block copolymer [polystyrene-b-poly(4-vinylpyridine)] deposited onto silicon substrates. The overall study has demonstrated the strong link between the morphology, size, and distribution of the structures and the synthetic physicochemical parameters, such as pH, reaction temperature, concentration, and nature of reactants. A nonequilibirum state of the medium has been required to create a fractal growth of the gold structures onto a prepatterned gold-seeded surface and has led to a better control of the structures' surface coverage rate. Those as-prepared nanodendrites have also exhibited high electrocatalytic activity toward a significant enhancement factor, as well as important sensitivity, thanks to tip effects. The electrochemical experiment results have demonstrated efficient adsorption and quantification of very low traces of specific molecules like glutathione or hexadecanethiol.

We measured mechanical properties and dynamic assembly of actin networks with a new method based on magnetic microscopic cylinders. Dense actin networks are grown from the cylinders' surfaces using the biochemical Arp2/3-machinery at play in the lamellipodium extension and other force-generating processes in the cell. Under a homogenous magnetic field the magnetic cylinders self-assemble into chains in which forces are attractive and depend on the intensity of the magnetic field. We show that these forces, from piconewtons to nanonewtons, are large enough to slow down the assembly of dense actin networks and controlled enough to access to their non linear mechanical responses. Deformations are measured with nanometer-resolution, well below the optical resolution. Self-assembly of the magnetic particles into chains simplifies experiments and allows for parallel measurements. The combination of accuracy and good throughput of measurements results in a method with high potential for cell and cytoskeleton mechanics. Using this method, we observed in particular a strong non linear mechanical behavior of dense branched actin networks at low forces that has not been reported previously.

Superparamagnetic microscopic rings organised into an array of dimers on application of a homogenous magnetic field, B. The rings form via a wetting and de-wetting transition that takes place in circular cavities set within PDMS molds. The scale bar is 20 microns.

A novel approach for a controlled growth of pattern-directed organization of Au flower shape crystals (NFS) onto rigid substrate has been proposed to achieve large-scale functional materials. This process is based on the combination of soft nanoporous template and a multistage aqueous chemical method. First, a hexagonal array of gold nanoparticles was prepared using a nanoporous thin membrane by a seed-mediated growth colloidal process. The size and morphology of the Au NFs were then controlled by a site selective heterogeneous nucleation and growth onto the Au precursors. The growth mechanism of the template-directed synthesis of Au crystals arrays was investigated. The optical and electrochemical properties of Au NFs were discussed in relation with their morphology and organization. Results show that the nature, the size, the interparticle distance and their density strongly affect the intensity of the optical and electrochemical signals. Finally, this easy and multistep approach is particularly attractive due to its environmentally gentle processing conditions and represents an open pathway to several large-scale nanomaterials fabrication.

We developed a new method of mechanical measurement, based on the dipolar attraction between magnetic colloids. A spherical gel formed around magnetic colloids is progressively deformed between two surfaces as the dipolar attraction between the colloids increase. Applied force is controlled by the external magnetic field, while the gel deformation is monitored by video-microscopy. Elastic modulus of the gel material is extracted by the fit of the force-deformation curve. This method was used on in vitro dense branched networks formed by the Arp2/3-complex nucleator, which are crucial for cell migration. The high throughput of this method allowed the probing of thousands of gels, orders of magnitude more than previous experiments done with demanding techniques such as atomic force microscopy. By changing the concentration of proteins used during the growth of the gel, we changed the proportion of branches and the length of the filaments, and conducted the first systematic study linking the architecture of the actin networks to their architecture. A limitation of this technique is the requirement of sphericity to extract the elastic modulus from force-deformation curves. We solved this issue by developing new magnetic colloids of arbitrary shapes (cubes, cylinders, disks, etc.). This allows the deformation of objects between two flat surfaces while retaining the high throughput of this method. The technique now permits the measurement of non-linear elasticity, viscous modulus and speed of polymerization versus applied force for dense branched actin gels. Micro-objects of different shapes can be probed, and development is underway to use this technique for the measurement of adherent cells' mechanical properties. This technique could then be used as a diagnosis tool by probing metastatic cancer cells with a great throughput.

We outline a simple technique to engineer monodisperse, superparamagnetic, micron-sized prisms of arbitrary cross-section and large magnetic susceptibility. The fabrication process allows pre-positioning of the particles that introduces another lever to guide self-assembly. In this method, a dispersion of magnetic colloids in a UV-curable monomer is molded in PDMS wells and subsequently reticulated. High homogeneous magnetic content is achieved by preventing colloidal aggregation through careful choice of the colloid and monomer. Additionally, on their removal from the PDMS molds, the relative position of the magnetic particles is conserved: they are extracted as arrays whose patterns are set by the PDMS mold. This novel method therefore offers unique control of the self-assembly of specific 'higher order' structures mediated by dipolar interactions and directed by the geometry and initial positioning of the particles. This is also a promising approach to develop devices with complex responses to external fields.