DNA-based programming of quantum dot valency, self-assembly and luminescence.

The electronic and optical properties of colloidal quantum dots, including the wavelengths of light that they can absorb and emit, depend on the size of the quantum dots. These properties have been exploited in a number of applications including optical detection, solar energy harvesting and biological research. Here, we report the self-assembly of quantum dot complexes using cadmium telluride nanocrystals capped with specific sequences of DNA.

The Ia.2 epitope defines a subset of lipid raft-resident MHC class II molecules crucial to effective antigen presentation.

Previous work established that binding of the 11-5.2 anti-I-A(k) mAb, which recognizes the Ia.2 epitope on I-A(k) class II molecules, elicits MHC class II signaling, whereas binding of two other anti-I-A(k) mAbs that recognize the Ia.

Hierarchical nanotextured microelectrodes overcome the molecular transport barrier to achieve rapid, direct bacterial detection.

Detection of biomolecules at low abundances is crucial to the rapid diagnosis of disease. Impressive sensitivities, typically measured with small model analytes, have been obtained with a variety of nano- and microscale sensors. A remaining challenge, however, is the rapid detection of large native biomolecules in real biological samples.

Optimization of band structure and quantum-size-effect tuning for two-photon absorption enhancement in quantum dots.

The two-photon absorption, 2PA, cross sections of PbS quantum dots, QDs, are theoretically and experimentally investigated and are shown to be enhanced with increasing quantum confinement. This is in contrast to our previous results for CdSe and CdTe QDs where the reduced density of states dominated and resulted in a decrease in 2PA with a decrease in QD size. Qualitatively this trend can be understood by the highly symmetric distribution of conduction and valence band states in PbS that results in an accumulation of allowed 2PA transitions in certain spectral regions.

Patterns of recombination activity on mouse chromosome 11 revealed by high resolution mapping.

The success of high resolution genetic mapping of disease predisposition and quantitative trait loci in humans and experimental animals depends on the positions of key crossover events around the gene of interest. In mammals, the majority of recombination occurs at highly delimited 1-2 kb long sites known as recombination hotspots, whose locations and activities are distributed unevenly along the chromosomes and are tightly regulated in a sex specific manner. The factors determining the location of hotspots started to emerge with the finding of PRDM9 as a major hotspot regulator in mammals, however, additional factors modulating hotspot activity and sex specificity are yet to be defined.

Dead zones in colloidal quantum dot photovoltaics: evidence and implications.

In order to fabricate photovoltaic (PV) cells incorporating light-trapping electrodes, flexible foil substrates, or more than one junction, illumination through the top-contact (i.e.: non-substrate) side of a photovoltaic device is desirable.

Infrared colloidal quantum dots for photovoltaics: fundamentals and recent progress.

Colloidal quantum dots (CQDs) are solution-processed semiconductors of interest in low-cost photovoltaics. Tuning of the bandgap of CQD films via the quantum size effect enables customization of solar cells' absorption profile to match the sun's broad visible- and infrared-containing spectrum reaching the earth. Here we review recent progress in the realization of low-cost, efficient solar cells based on CQDs.

Role of symmetry breaking on the optical transitions in lead-salt quantum dots.

The influence of quantum confinement on the one- and two-photon absorption spectra (1PA and 2PA) of PbS and PbSe semiconductor quantum dots (QDs) is investigated. The results show 2PA peaks at energies where only 1PA transitions are predicted and 1PA peaks where only 2PA transitions are predicted by the often used isotropic k x p four-band envelope function formalism. The first experimentally identified two-photon absorption peak coincides with the energy of the first one photon allowed transition.

Nanostructuring of sensors determines the efficiency of biomolecular capture.

The detection of biologically important molecules such as proteins and nucleic acids is of high and growing interest in the diagnosis of diseases from cancer to infectious and cardiovascular disease. The use of nanostructures to enhance sensitivity in biomolecular detection has now been reported in a broad range of assays. Here we provide direct evidence that the display of nucleic acid probe molecules on a nanostructured surface dramatically enhances hybridization efficiency compared to the case of the same probe molecules tethered on a smoother surface.

Depleted-heterojunction colloidal quantum dot solar cells.

Colloidal quantum dot (CQD) photovoltaics combine low-cost solution processability with quantum size-effect tunability to match absorption with the solar spectrum. Rapid recent advances in CQD photovoltaics have led to impressive 3.6% AM1.

Nanostructured materials for photon detection.

The detection of photons underpins imaging, spectroscopy, fibre-optic communications and time-gated distance measurements. Nanostructured materials are attractive for detection applications because they can be integrated with conventional silicon electronics and flexible, large-area substrates, and can be processed from the solution phase using established techniques such as spin casting, spray coating and layer-by-layer deposition. In addition, their performance has improved rapidly in recent years.

Ambient-processed colloidal quantum dot solar cells via individual pre-encapsulation of nanoparticles.

We report colloidal quantum dot solar cells fabricated under ambient atmosphere with an active area of 2.9 mm(2) that exhibit 3.6% solar power conversion efficiency.

Quantum dot photovoltaics in the extreme quantum confinement regime: the surface-chemical origins of exceptional air- and light-stability.

We report colloidal quantum dot (CQDs) photovoltaics having a approximately 930 nm bandgap. The devices exhibit AM1.5G power conversion efficiencies in excess of 2%.

Programming the detection limits of biosensors through controlled nanostructuring.

Advances in materials chemistry offer a range of nanostructured shapes and textures for building new biosensors. Previous reports have implied that controlling the properties of sensor substrates can improve detection sensitivities, but the evidence remains indirect. Here we show that by nanostructuring the sensing electrodes, it is possible to create nucleic acid sensors that have a broad range of sensitivities and that are capable of rapid analysis.

Direct profiling of cancer biomarkers in tumor tissue using a multiplexed nanostructured microelectrode integrated circuit.

The analysis of panels of nucleic acid biomarkers offers valuable diagnostic and prognostic information for cancer management. A cost-effective, highly sensitive electronic chip would offer an ideal platform for clinical biomarker readout and would have maximal utility if it was (i) multiplexed, enabling on-chip assays of multiple biomarkers, and (ii) able to perform direct (PCR-free) readout of disease-related genes. Here we report a chip onto which we integrate novel nanostructured microelectrodes and with which we directly detect cancer biomarkers in heterogeneous biological samples-both cell extracts and tumor tissues.

Investigations of the use of bioavailability data to adjust occupational exposure limits for active pharmaceutical ingredients.

Occupational exposure limits (OELs) for active pharmaceutical ingredients have traditionally been established using no-observed-adverse-effect levels derived from clinical studies employing po and iv routes of administration and by applying default uncertainty factors or chemical-specific adjustment factors. However, exposure by the inhalation or dermal route is more relevant in terms of occupational safety. In this investigation, to explore new methods for route-to-route extrapolation, the bioavailability of MK-0679, a leukotriene D(4) receptor antagonist, was compared following iv, po, intranasal (in), or intratracheal (it) administration.

A general phase-transfer protocol for metal ions and its application in nanocrystal synthesis.

Nanocrystals prepared in organic media can be easily self-assembled into close-packed hexagonal monolayers on solvent evaporation for various applications. However, they usually rely on the use of organometallic precursors that are soluble in organic solvents. Herein we report a general protocol to transfer metal ions from an aqueous solution to an organic medium, which involves mixing the aqueous solution of metal ions with an ethanolic solution of dodecylamine (DDA), and extracting the coordinating compounds formed between the metal ions and DDA into toluene.

Colloidal quantum-dot photodetectors exploiting multiexciton generation.

Multiexciton generation (MEG) has been indirectly observed in colloidal quantum dots, both in solution and the solid state, but has not yet been shown to enhance photocurrent in an optoelectronic device. Here, we report a class of solution-processed photoconductive detectors, sensitive in the ultraviolet, visible, and the infrared, in which the internal gain is dramatically enhanced for photon energies Ephoton greater than 2.7 times the quantum-confined bandgap Ebandgap.

Heavy-metal-free solution-processed nanoparticle-based photodetectors: doping of intrinsic vacancies enables engineering of sensitivity and speed.

Photodetection in semiconductors enables digital imaging, spectroscopy, and optical communications. Integration of solution-processed light-sensing materials with a range of substrates offers access to new spectral regimes, the prospect of enhanced sensitivity, and compatibility with flexible electronics. Photoconductive photodetectors based on solution-cast nanocrystals have shown tremendous progress in recent years; however, high-performance reports to date have employed Pb- and Cd-containing materials.

Efficient, stable infrared photovoltaics based on solution-cast colloidal quantum dots.

Half of the sun's power lies in the infrared. As a result, the optimal bandgaps for solar cells in both the single-junction and even the tandem architectures lie beyond 850 nm. However, progress in low-cost, large-area, physically flexible solar cells has instead been made in organic and polymer materials possessing absorption onsets in the visible.