Investigation of Nonlinear Optical Properties of Quantum Dots Deposited onto a Sample Glass Using Time-Resolved Inline Digital Holography.

We report on the application of time-resolved inline digital holography in the study of the nonlinear optical properties of quantum dots deposited onto sample glass. The Fresnel diffraction patterns of the probe pulse due to noncollinear degenerate phase modulation induced by a femtosecond pump pulse were extracted from the set of inline digital holograms and analyzed. The absolute values of the nonlinear refractive index of both the sample glass substrate and the deposited layer of quantum dots were evaluated using the proposed technique. To characterize the inhomogeneous distribution of the samples' nonlinear optical properties, we proposed plotting an optical nonlinearity map calculated as a local standard deviation of the diffraction pattern intensities induced by noncollinear degenerate phase modulation.

Circular dichroism of surface complexes based on quantum dots and azo dye.

Chiral properties of surface complexes based on CdSe/ZnS quantum dots (QDs) and 1-(2-pyridylazo)-2-naphthol (PAN) azo dye were investigated by circular dichroism spectroscopy. The use of L-, D-cysteine (Lcys, Dcys) capping ligands allowed us to obtain water-soluble chiral QD-PAN complexes. The characterization of the complexes was performed by UV-vis, FTIR, and CD spectroscopy. Quantum chemical TDDFT calculated CD spectra reproduced the experimentally observed sign patterns, which originate from binding Lcys or Dcys and PAN molecules to the same Zn atom on the QD surface. The resulting complex is characterized by a large circular dichroism in comparison with an ordinary QD chirality induced by cysteine molecules. The pattern of CD signal is the same for Lcys and Dcys ligands in chiral QD-PAN complex.

Impact of Shell Thickness on Photoluminescence and Optical Activity in Chiral CdSe/CdS Core/Shell Quantum Dots.

Core/shell quantum dots (QDs) are of high scientific and technological importance as these nanomaterials have found a number of valuable applications. In this paper, we have investigated the dependence of optical activity and photoluminescence upon CdS shell thickness in a range of core-shell structured CdSe/CdS QDs capped with chiral ligands. For our study, five samples of CdSe/CdS were synthesized utilizing successive ion layer adsorption and reaction to vary the thickness of the CdS shell from 0.5 to 2 nm, upon a 2.8 nm diameter CdSe core. Following this, a ligand exchange of the original aliphatic ligands with l- and d-cysteine was carried out, inducing a chiroptical response in these nanostructures. The samples were then characterized using circular dichroism, photoluminescent spectroscopy, and fluorescence lifetime spectroscopy. It has been found that the induced chiroptical response was inversely proportional to the CdS shell thickness and showed a distinct evolution in signal, whereas the photoluminescence of our samples showed a direct relationship to shell thickness. In addition, a detailed study of the influence of annealing time on the optical activity and photoluminescence quantum yield was performed. From our work, we have been able to clearly illustrate the approach and strategies that must be used when designing optimal photoluminescent optically active CdSe/CdS core-shell QDs.

The influence of phthalocyanine aggregation in complexes with CdSe/ZnS quantum dots on the photophysical properties of the complexes.

The formation of nonluminescent aggregates of aluminium sulfonated phthalocyanine in complexes with CdSe/ZnS quantum dots causes a decrease of the intracomplex energy transfer efficiency with increasing phthalocyanine concentration. This was confirmed by steady-state absorption and photoluminescent spectroscopy. A corresponding physical model was developed that describes well the experimental data. The results can be used at designing of QD/molecule systems with the desired spatial arrangement for photodynamic therapy.

Intrinsic Chirality of CdSe/ZnS Quantum Dots and Quantum Rods.

A new class of chiral nanoparticles is of great interest not only for nanotechnology, but also for many other fields of scientific endeavor. Normally the chirality in semiconductor nanocrystals is induced by the initial presence of chiral ligands/stabilizer molecules. Here we report intrinsic chirality of ZnS coated CdSe quantum dots (QDs) and quantum rods (QRs) stabilized by achiral ligands. As-prepared ensembles of these nanocrystals have been found to be a racemic mixture of d- and l-nanocrystals which also includes a portion of nonchiral nanocrystals and so in total the solution does not show a circular dichroism (CD) signal. We have developed a new enantioselective phase transfer technique to separate chiral nanocrystals using an appropriate chiral ligand and obtain optically active ensembles of CdSe/ZnS QDs and QRs. After enantioselective phase transfer, the nanocrystals isolated in organic phase, still capped with achiral ligands, now display circular dichroism (CD). We propose that the intrinsic chirality of CdSe/ZnS nanocrystals is caused by the presence of naturally occurring chiral defects.

Energy transfer in complexes of water-soluble quantum dots and chlorin e6 molecules in different environments.

The photoexcitation energy transfer is found and investigated in complexes of CdSe/ZnS cationic quantum dots and chlorin e6 molecules formed by covalent bonding and electrostatic interaction in aqueous solution and in porous track membranes. The quantum dots and chlorin e6 molecules form stable complexes that exhibit Förster resonance energy transfer (FRET) from quantum dots to chlorin e6 regardless of complex formation conditions. Competitive channels of photoexcitation energy dissipation in the complexes, which hamper the FRET process, were found and discussed.

Fluorescence energy transfer in quantum dot/azo dye complexes in polymer track membranes.

Fluorescence resonance energy transfer in complexes of semiconductor CdSe/ZnS quantum dots with molecules of heterocyclic azo dyes, 1-(2-pyridylazo)-2-naphthol and 4-(2-pyridylazo) resorcinol, formed at high quantum dot concentration in the polymer pore track membranes were studied by steady-state and transient PL spectroscopy. The effect of interaction between the complexes and free quantum dots on the efficiency of the fluorescence energy transfer and quantum dot luminescence quenching was found and discussed.

Anisotropy of optical transitions in ordered ensemble of CdSe quantum rods.

We report on the observation of spectral dependence of absorption anisotropy in a CdSe quantum rod (QR) ensemble, which is aligned in a polymer film with a nanocrystal concentration of 2×10(-5) M. The experimental data on the polarization direction and anisotropy factor were obtained for the lowest excitonic transition and the second group of transitions in the QR. The nonzero constant value of anisotropy was investigated for the high-energy transitions, and is evidence of the one-dimensional confinement in the QR.

A study of urban housing demolition as a source of lead in ambient dust on sidewalks, streets, and alleys.

We examined changes in ambient dust lead (Pb) levels associated with the demolition of older row houses containing lead paint in Baltimore, MD, USA. Our previous paper describes the three study sites, the demolition processes, and increases in the Pb dustfall rate during demolition (>40-fold) and debris removal (>6-fold) within 10 m of sites where wetting was of limited effectiveness. This paper presents the analysis of settled dust collected using a cyclone device from streets, sidewalks, and alleys within 100 m of study sites before, immediately after, and 1 month after demolition. We found acute increases in Pb loadings and dust loadings after demolition and debris removal that are of public health concern. Streets and alleys had the greatest increases in Pb loadings and the highest levels overall. At one site, geometric mean (GM) Pb loadings immediately after demolition increased 200% for streets to 8080 microg/ft(2), 138% for alleys to 6020 microg/ft(2), and 26% for sidewalks to 2170 microg/ft(2). One month after demolition, the GM Pb loadings for streets, alleys, and sidewalks were reduced on average by 41-67% from post-demolition levels and were below baseline levels for alleys and sidewalks. The other main site had smaller increases in GM Pb loadings immediately after demolition-18% for alleys to 1740 microg/ft(2) and 18% for sidewalks to 2050 microg/ft(2)-and a decrease of 29% for streets to 2730 microg/ft(2). Exterior dust is a public health concern because it is a pathway of ambient Pb exposure and a potential source of residential exposure via tracking and re-aerosolization and re-deposition. Our findings highlight the need to control demolition-related Pb deposition and to educate planners, contractors, and health and housing agencies. This is particularly important given the large numbers of aging US dwellings that will be razed as part of future urban redevelopment efforts.

Biosolids compost amendment for reducing soil lead hazards: a pilot study of Orgro amendment and grass seeding in urban yards.

In situ inactivation of soil Pb is an alternative to soil removal and replacement that has been demonstrated in recent years at industrial sites with hazardous soil Pb concentrations. Most children exposed to elevated soil Pb, however, reside in urban areas, and no government programs exist to remediate such soils unless an industrial source caused the contamination. Modern regulated biosolids composts have low Pb concentrations and low bioaccessible Pb fractions and can improve grass growth on urban soils. High Fe and P biosolids composts can reduce the bioavailability and bioaccessibility of soil Pb and can aid in establishing vegetation that would reduce soil transfer into homes. For these reasons, we conducted a field test of their use to reduce Pb bioaccessibility in urban soils in Baltimore, MD USA. We chose biosolids compost for its expected reduction in the bioaccessible Pb fraction of urban soils, ease of use by urban residents, and ability to beautify urban areas. Nine urban yards with mean soil Pb concentrations >800 mg Pb kg(-1) were selected and sampled at several distances from the house foundation before soil treatment. The soils were rototilled to 20 cm depth to prepare the sites, and resampled. The yards were then amended with 6-8 cm depth of Orgro biosolids compost (110-180 dry t/ha) rich in Fe and P, mixed well by rototilling, and resampled. Kentucky bluegrass (Poa pratensis) was seeded and became well established. Soils were resampled 1 year later. At each sampling time, total soil Pb was measured using a modified U.S. EPA nitric acid hotplate digestion method (SW 846 Method 3050) and bioaccessible Pb fraction was measured using the Solubility/Bioaccesibility Research Consortium standard operating procedure with modifications, including the use of glycine-buffered HCl at pH 2.2. Samples of untreated soils were collected from each yard and mixed well to serve as controls for the Pb bioaccessibility of field treated soils over time independent of positional variance within yards. At 1-year post-treatment, grass cover was healthy and reductions in bioaccessible Pb concentrations compared to pre-tillage were 64% (from 1655 to 595 mg kg(-1)) and 67% (from 1381 to 453 mg kg(-1)) at the sampling lines closest to the houses. Little or no reduction in bioaccessible Pb concentration was observed at sampling lines more remote from the house that also had the lowest bioaccessible Pb concentrations at pre-tillage (620 and 436 mg kg(-1), respectively). For the control soils, changes over time in total Pb and bioaccessible Pb concentrations and the bioaccessible Pb fraction were insignificant. This study confirms the viability of in situ remediation of soils in urban areas where children are at risk of high Pb exposure from lead in paint, dust and soil.

Electronic health record - public health (EHR-PH) system prototype for interoperability in 21st century healthcare systems.

Information exchange, enabled by computable interoperability, is the key to many of the initiatives underway including the development of Regional Health Information Exchanges, Regional Health Information Organizations, and the National Health Information Network. These initiatives must include public health as a full partner in the emerging transformation of our nation's healthcare system through the adoption and use of information technology. An electronic health record - public health (EHR-PH)system prototype was developed to demonstrate the feasibility of electronic data transfer from a health care provider, i.e. hospital or ambulatory care settings, to multiple customized public health systems which include a Newborn Metabolic Screening Registry, a Newborn Hearing Screening Registry, an Immunization Registry and a Communicable Disease Registry, using HL7 messaging standards. Our EHR-PH system prototype can be considered a distributed EHR-based RHIE/RHIO model - a principal element for a potential technical architecture for a NHIN.

A study of urban housing demolitions as sources of lead in ambient dust: demolition practices and exterior dust fall.

Demolition of older housing for urban redevelopment purposes benefits communities by removing housing with lead paint and dust hazards and by creating spaces for lead paint-free housing and other community resources. This study was conducted to assess changes, if any, in ambient dust lead levels associated with demolition of blocks of older lead-containing row houses in Baltimore, Maryland (USA). In this article we present results based on dust-fall samples collected from fixed locations within 10 m of three demolition sites. In subsequent reports we will describe dust lead changes on streets, sidewalks, and residential floors within 100 m of the demolition sites. Geometric mean (GM) lead dust-fall rate increased by > 40-fold during demolition to 410 micro g Pb/m2/hr (2,700 micro g Pb/m2 per typical work day) and by > 6-fold during debris removal to 61 micro g Pb/m2/hr (440 micro g Pb/m2 per typical work day). Lead concentrations in dust fall also increased during demolition (GM, 2,600 mg/kg) and debris removal (GM, 1,500 mg/kg) compared with baseline (GM, 950 mg/kg). In the absence of dust-fall standards, the results were compared with the U.S. Environmental Protection Agency's (U.S. EPA's) dust-lead surface loading standard for interior residential floors (40 micro g/ft2, equivalent to 431 micro g/m2); daily lead dust fall during demolition exceeded the U.S. EPA floor standard by 6-fold on average and as much as 81-fold on an individual sample basis. Dust fall is of public health concern because it settles on surfaces and becomes a pathway of ambient lead exposure and a potential pathway of residential exposure via tracking and blowing of exterior dust. The findings highlight the need to minimize demolition lead deposition and to educate urban planners, contractors, health agencies, and the public about lead and other community concerns so that society can maximize the benefits of future demolition activities nationwide.

A UML-based meta-framework for system design in public health informatics.

UNLABELLED: The National Agenda for Public Health Informatics calls for standards in data and knowledge representation within public health, which requires a multi-level framework that links all aspects of public health. METHOD: The literature of public health informatics and public health informatics application were reviewed. A UML-based systems analysis was performed. Face validity of results was evaluated in analyzing the public health domain of lead poisoning. RESULTS: The core class of the UML-based system of public health is the Public Health Domain, which is associated with multiple Problems, for which Actors provide Perspectives. Actors take Actions that define, generate, utilize and/or evaluate Data Sources. The life cycle of the domain is a sequence of activities attributed to its problems that spirals through multiple iterations and realizations within a domain. CONCLUSION: The proposed Public Health Informatics Meta-Framework broadens efforts in applying informatics principles to the field of public health