Colloidal CdSe/CdS Dot-in-Plate Nanocrystals with 2D-Polarized Emission

We report the synthesis and properties of a novel class of nanocrystals with mixed dimensionality: a dot-in-plate core/shell nanostructure. This system was synthesized by growing a flat, disk-shaped, CdS shell on spherical CdSe cores. The anisotropic pressure induced by the shell drastically splits the first exciton fine structure in two: the “heavy hole” and “light hole” states become separated by up to 65 meV. As a result, these nanocrystals exhibit an emission strongly polarized in two dimensions, in the plane perpendicular to the wurtzite crystal <i>c</i> axis. We use polarization measurements on single nanocrystals and ensemble anisotropy studies to confirm the nature and position of the excitonic energy levels. These nanocrystals orient spontaneously when evaporated on a substrate, enabling a precise control of the orientation of their emission dipole

Fast, Efficient, and Stable Conjugation of Multiple DNA Strands on Colloidal Quantum Dots

A novel method for covalent conjugation of DNA to polymer coated quantum dots (QDs) is investigated in detail. This method is fast and efficient: up to 12 DNA strands can be covalently conjugated per QD in optimized reaction conditions. The QD-DNA conjugates can be purified using size exclusion chromatography and the QDs retain high quantum yield and excellent stability after DNA coupling. We explored single-stranded and double-stranded DNA coupling, as well as various lengths. We show that the DNA coupling is most efficient for short (15 mer) single-stranded DNA. The DNA coupling has been performed on QDs emitting at four different wavelengths, as well as on gold nanoparticles, suggesting that this technique can be generalized to a wide range of nanoparticles

Highly Enhanced Affinity of Multidentate versus Bidentate Zwitterionic Ligands for Long-Term Quantum Dot Bioimaging

High colloidal stability in aqueous conditions is a prerequisite for fluorescent nanocrystals, otherwise known as “quantum dots”, intended to be used in any long-term bioimaging experiment. This essential property implies a strong affinity between the nanoparticles themselves and the ligands they are coated with. To further improve the properties of the bidentate monozwitterionic ligand previously developed in our team, we synthesized a multidentate polyzwitterionic ligand, issued from the copolymerization of a bidentate monomer and a monozwitterionic one. The nanocrystals passivated by this polymeric ligand showed an exceptional colloidal stability, regardless of the medium conditions (pH, salinity, dilution, and biological environment), and we demonstrated the affinity of the polymer exceeded by 3 orders of magnitude that of the bidentate ligand (desorption rates assessed by a competition experiment). The synthesis of the multidentate polyzwitterionic ligand proved also to be easily tunable and allowed facile functionalization of the corresponding quantum dots, which led to successful specific biomolecules targeting

Sulfobetaine–Vinylimidazole Block Copolymers: A Robust Quantum Dot Surface Chemistry Expanding Bioimaging’s Horizons

Long-term inspection of biological phenomena requires probes of elevated intra- and extracellular stability and target biospecificity. The high fluorescence and photostability of quantum dot (QD) nanoparticles contributed to foster their promise as bioimaging tools that could overcome limitations associated with traditional fluorophores. However, QDs’ potential as a bioimaging platform relies upon a precise control over the surface chemistry modifications of these nano-objects. Here, a zwitterion–vinylimidazole block copolymer ligand was synthesized, which regroups all anchoring groups in one compact terminal block, while the rest of the chain is endowed with antifouling and bioconjugation moieties. By further application of an oriented bioconjugation approach with whole IgG antibodies, QD nanobioconjugates were obtained that display outstanding intra- and extracellular stability as well as biorecognition capacity. Imaging the internalization and intracellular dynamics of a transmembrane cell receptor, the CB1 brain cannabinoid receptor, both in HEK293 cells and in neurons, illustrates the breadth of potential applications of these nanoprobes

Cumulative indium content in excretions of mice after subcutaneous QDs administration.

<p>Mice were subcutaneously injected with 20 pmol of CuInS₂/ZnS QDs, urine (white) and faeces (gray) were collected daily and subjected to mass spectroscopy (ICP-MS). The indium contents were cumulated every day and were expressed as percentage of injected dose (% ID). Data are mean ± SD (n = 3 per group).</p

Biodistribution of QDs in selected organs and tissues in function of time after injection.

<p>Mice were subcutaneously injected with 20 pmol of CuInS₂/ZnS QDs in the right anterior paw. Blood samples were collected through cardiac puncture. Mice were then sacrificed at 1 h, 4 h, 8 h, 3 days, 7 days and 3 months after injection and organs were subjected to mass spectroscopy (ICP-MS). The indium concentrations in RALN, RLTLN, injection point, spleen, liver and blood were expressed as the quantity of indium (in µg) per gram of tissue or per milliliter of blood. Data are mean ± SD (n = 3 per group).</p

Mapping of sentinel lymph node (SLN) of tumour-bearing mice 15 min after sc. injection of 20 pmol of CuInS₂/ZnS QDs in the right anterior paw.

<p>Metastatic cells were detected in lymph node by CK19 expression using immunohistochemistry (IHC, n = 25) or molecular biology analysis (RT-qPCR, n = 28).</p><p>Data are mean ± SD.</p

Histology of sentinel lymph node sections of tumour-bearing mice.

<p>Sections were subjected to CK19 immunohistochemistry and hematoxylin staining. Black scale corresponds to 100 µm, the arrow indicates the metastatic invasion of the cortical sinus.</p

Cytotoxicity of CdTeSe/ZnS or CuInS₂/ZnS QDs on normal fibroblasts.

<p>MRC-5 cells viability was assessed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay.</p><p>Concentration of QDs causing 50% of cell death (IC₅₀) was measured 24 h or 48 h after exposure.</p><p>Data are mean ± SD (n = 6 per condition).</p

Sequence of primers used for real-time qPCR of cytokeratin 19 and â actin.

<p>Sequence of primers used for real-time qPCR of cytokeratin 19 and â actin.</p