Post-synthesis phase and shape evolution of CsPbBr3 colloidal nanocrystals: The role of ligands

The surface chemistry of colloidal cesium lead bromide (CsPbBr3) nanocrystals is decisive in determining the stability and the final morphology of this class of materials,characterized by ionic structure and a high defect tolerance factor.Here,the high sensitivity of purified colloidal nanocubes of CsPbBr3 to diverse environmental condition (solvent dilution,ageing,ligands post synthetic treatment) in ambient atmosphere is investigated by means of a comprehensive morphological (electron microscopy),structural (θ/2θ X-ray diffraction (XRD) and grazing incidence wide angle scattering (GIWAXS)),and spectroscopic chemical (1H nuclear magnetic resonance (NMR),nuclear Overhauser effect spectroscopy (NOESY),absorption and emission spectroscopy) characterization.The aging and solvent dilution contribute to modify the nanocrystal morphology,due to a modification of the ligand dynamic.Moreover,we establish the ability of aliphatic carboxylic acids and aikyl amines ligands to induce,even in a post preparative process at room temperature,structural,morphological and spectroscopic variations.Upon post synthesis alkyl amine addition,in particular of oleyl amine and octyl amine,the highly green emitting CsPbBr3 nanocubes effectively tum into one-dimensional (1 D) thin tetragonal nanowires or lead halide deficient rhombohedral zero-dimensional (0D) Cs4PbBr6 structures with a complete loss of fluorescence.The addition of an alkyl carboxylic acid,as oleic and nonanoic acid,produces the transformation of nanocubes into still emitting orthorombic two-dimensional (2D) nanoplates.The acid/base equilibrium between the native and added ligands,the edsorbed/free ligands dynamic in solution and the ligand solubility in non-polar solvent contribute to render CsPbBr3 particularly sensitive to environmental and processing conditions and,therefore prone to undergo to structural,morphological and,hence spectroscopic,transformations.

Integrin-targeting with peptide-bioconjugated semiconductor-magnetic nanocrystalline heterostructures

Binary asymmetric nanocrystals （BNCs）, composed of a photoactive TiO2 nanorod joined with a superparamagnetic γ-Fe203 spherical domain, were embedded in polyethylene glycol modified phospholipid micelle and successfully bioconjugated to a suitably designed peptide containing an RGD motif. BNCs represent a relevant multifunctional nanomaterial, owing to the coexistence of two distinct domains in one particle, characterized by high photoactivity and magnetic properties, that is particularly suited for use as a phototherapy and hyperthermia agent as well as a magnetic probe in biological imaging. We selected the RGD motif in order to target integrin expressed on activated endothelial cells and several types of cancer cells. The prepared RGD-peptide/BNC conjugates, comprehensively monitored by using complementary optical and structural techniques, demon- strated a high stability and uniform dispersibility in biological media. The cytotoxicity of the RGD-peptide/BNC conjugates was studied in vitro. The cellular uptake of RGD-peptide conjugates in the cells, assessed by means of two distinct approaches, namely confocal microscopy analysis and emission spectroscopy determination in cell lysates, displayed selectivity of the RGD-peptide-BNC conjugate for the cw]33 integrin. These RGD-peptide-BNC conjugates have a high potential for theranostic treatment of cancer.

Coupling effects in QD dimers at sub-nanometer interparticle distance

Currently,intensive research efforts focus on the fabrication of meso-structures of assembled colloidal quantum dots(QDs)with original optical and electronic properties.Such collective features originate from the QDs coupling,depending on the number of connected units and their distance.However,the development of general methodologies to assemble colloidal QD with precise stoichiometry and particle-particle spacing remains a key challenge.Here,we demonstrate that dimers of CdSe QDs,stable in solution,can be obtained by engineering QD surface chemistry,reducing the surface steric hindrance and favoring the link between two QDs.The connection is made by using alkyl dithiols as bifunctional linkers and different chain lengths are used to tune the interparticle distance from few nm down to 0.5 nm.The spectroscopic investigation highlights that coupling phenomena between the QDs in dimers are strongly dependent on the interparticle distance and QD size,ultimately affecting the exciton dissociation efficiency.