Mikhail Artemyev

Highly Stable Fluorescent Nanocrystals as a Novel Class of Labels for Immunohistochemical Analysis of Paraffin-Embedded Tissue Sections

Highly Stable Fluorescent Nanocrystals as a Novel Class of Labels for Immunohistochemical Analysis of Paraffin-Embedded Tissue Sections

Electronic structure and exciton-phonon interaction in two-dimensional colloidal CdSe nanosheets.

We study the electronic structure of ultrathin zinc-blende two-dimensional (2D)-CdSe nanosheets both theoretically, by Hartree-renormalized k·p calculations including Coulomb interaction, and experimentally, by temperature-dependent and time-resolved photoluminescence measurements. The observed 2D-heavy hole exciton states show a strong influence of vertical confinement and dielectric screening. A very weak coupling to phonons results in a low phonon-contribution to the homogeneous line-broadening. The 2D-nanosheets exhibit much narrower ensemble absorption and emission linewidths as compared to the best colloidal CdSe nanocrystallites ensembles. Since those nanoplatelets can be easily stacked and tend to roll up as they are large, we see a way to form new types of multiple quantum wells and II-VI nanotubes, for example, for fluorescence markers.

Oriented conjugates of single-domain antibodies and quantum dots: toward a new generation of ultrasmall diagnostic nanoprobes

UNLABELLED Common strategy for diagnostics with quantum dots (QDs) utilizes the specificity of monoclonal antibodies (mAbs) for targeting. However QD-mAbs conjugates are not always well-suited for this purpose because of their large size. Here, we engineered ultrasmall nanoprobes through oriented conjugation of QDs with 13-kDa single-domain antibodies (sdAbs) derived from llama IgG. Monomeric sdAbs are 12 times smaller than mAbs and demonstrate excellent capacity for refolding. sdAbs were tagged with QDs through an additional cysteine residue integrated within the C terminal of the sdAb. This approach allowed us to develop sdAbs-QD nanoprobes comprising four copies of sdAbs coupled with a QD in a highly oriented manner. sdAbs-QD conjugates specific to carcinoembryonic antigen (CEA) demonstrated excellent specificity of flow cytometry quantitative discrimination of CEA-positive and CEA-negative tumor cells. Moreover, the immunohistochemical labeling of biopsy samples was found to be comparable or even superior to the quality obtained with gold standard protocols of anatomopathology practice. sdAbs-QD-oriented conjugates as developed represent a new generation of ultrasmall diagnostic probes for applications in high-throughput diagnostic platforms. FROM THE CLINICAL EDITOR The authors report the development of sdAbs-QD-oriented conjugates, comprised of single domain antibodies that are 12 times smaller than regular mAb-s and quantum dots. These ultrasmall diagnostic probes represent a new generation of functionalized ODs for applications in high-throughput diagnostic platforms.

ELECTROLUMINESCENCE IN THIN SOLID FILMS OF CLOSELY PACKED CDS NANOCRYSTALS

Thin solid films of closely packed CdS nanocrystals with sizes between 1.5 and 1.8 nm have been prepared and sandwiched between indium–tin–oxide (ITO) and silver contacts. At room temperature, these CdS nanocrystals start to emit light visible to the unaided eye at a bias above 15 V. The spectral characteristics are voltage controlled and tunable between 1.8 eV and 2.8 eV with increasing bias from 20 to 40 V. The current–voltage dependence indicates hopping conductivity of the carriers injected. At high voltage the electroluminescence and photoluminescence spectra are similar showing a strong red shift of the luminescence maximum with respect to the absorption peak at 3.75 eV which we explain by an effective radiative recombination through deep traps in the interface region. Consequently, the tunability of electroluminescence is attributed to excitation of different deep traps by electron transport across neighbouring CdS nanocrystals.

Quantum dots in photonic dots

A micrometer-sized spherical microcavity, the photonic dot, is made from semiconductor nanocrystals, the quantum dots. The coupling of electronic and photonic states is demonstrated for a single photonic dot by the observation of whispering gallery modes in the spectrum of spontaneous emission of the embedded CdSe quantum dots.

Basic Principles and Current Trends in Colloidal Synthesis of Highly Luminescent Semiconductor Nanocrystals

The principal methods for the synthesis of highly luminescent core-shell colloidal quantum dots (QDs) of the most widely used CdSe, CdS, ZnSe, and other A(II) B(VI) nanocrystals are reviewed. One-pot versus multistage core synthesis approaches are discussed. The noninjection one-pot method ensures slow, controllable growth of core nanocrystals starting from magic-size seed recrystallization, which yields defect-free cores with strictly specified sizes and shapes and a high monodispersity. Subsequent injection of shell precursors allows the formation of gradient core-shell QDs with a smooth potential barrier for electrons and holes, without strains or interfacial defects, and, as a consequence, a luminescence quantum yield (QY) approaching 100%. These general approaches can also be applied to semiconductor core-shell QDs other than A(II) B(VI) ones to cover the broad spectral range from the near-UV to IR regions of the optical spectrum, thus displacing fluorescent organic dyes from their application areas.

DNA-assisted formation of quasi-nanowires from fluorescent CdSe/ZnS nanocrystals

Highly ordered quasi-nanowires from fluorescent semiconductor CdSe/ZnS spherical (quantum dots) or rod-like (quantum rods) nanoparticles were produced using DNA as a template. Positively charged nanoparticles were fixed along the negatively charged DNA backbone by electrostatic interaction. After incubation of the solution of DNA and nanoparticles at different stoichiometric ratios the complexes were applied to the hydrophobic surface and stretched using the molecular combing technique. Here, we demonstrate that fluorescent patterns with desirable morphology and properties can be formed by varying the nanoparticle charge and shape and their stoichiometry in the complex with DNA.

Coupled-resonator optical waveguides doped with nanocrystals.

Microsphere resonators doped with semiconductor nanocrystals are explored as building blocks for coupled-resonator optical waveguides (CROWs). The evolution of individual cavity modes into coherently coupled waveguide modes is studied using polarization-sensitive microphotoluminescence spectroscopy. To demonstrate the formation of multisphere photon states, we use a bent linear array of microresonators and probe the properties of the cavity photon field by the spatially and spectrally resolved measurement of the nanocrystal emission. Photon mode coupling is evidenced by the observed mode splitting and emission intensity distributions along the CROW structure.

Photons confined in hollow microspheres

Incorporation of CdSe quantum dots into a thin (<1 μm) surface shell of polymer microspheres (R∼2–4 μm) is achieved. The room-temperature emission spectra of single, hollow microcavities show several, spectrally well-separated cavity modes in the red-orange spectral range which have been assigned to high-Q whispering gallery modes (WGM) with radial quantum number n=1 and high angular quantum number l. An enhancement of the cavity finesse Q by a factor of about 10 with respect to CdSe-doped bulk polymer microspheres is found.

CdSe-CdS nanoheteroplatelets with efficient photoexcitation of central CdSe region through epitaxially grown CdS wings.

We synthesized a new type of optically active semiconductor nanoheterostructure based on CdSe nanoplatelets with epitaxially grown CdS flat branches or wings. CdS branches work as efficient photonic antenna in the blue spectral region, enhancing the excitation of CdSe band edge emission. The formation of CdSe-CdS nanoheteroplatelets instead of CdSe/CdS core-shell nanoplatelets was achieved using short-chain Cd ethylhexanoate and sulfur in octadecene as precursors for CdS overgrowth in the presence of acetate salt.