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PubMed1995

A role for airborne particulates in high mercury levels of some cetaceans.

In a study of 25 Tursiops truncatus and two Globicephala macrorhynchus examined by necropsy, abundant HgSe was found in both the liver and in the respiratory system (lung and hilar lymph nodes). In the liver HgSe was consistently associated with the cell-breakdown pigment lipofuscin, whereas in lung and hilar lymph nodes it was consistently associated with particulates consisting of partially graphitic soot and silicates. This supports earlier suggestions that in the liver HgSe may be a storage end product of Hg metabolism, while adding the new suggestion that in the respiratory system HgSe may be inhaled, preformed in combustion emissions.

Air Pollutants↗
PubMed1987

Trimethylselenonium ion.

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Chromatography, High Pressure Liquid↗
PubMed2004

Analogues of tetramethylrosamine as transport molecules for and inhibitors of P-glycoprotein-mediated multidrug resistance.

Tetramethylrosamine and its thio- and seleno- analogues (TMR-O, TMR-S, and TMR-Se, respectively) were examined for their ability to be transported by Pgp into chemo-resistant CR1R12 cells. Verapamil (7 x 10(-6)M) enhanced the uptake of TMR-O and TMR-S into CR1R12 cells compared to those cultures not previously exposed to verapamil. The uptake of TMR-O and TMR-S in CR1R12 cells in the presence of 7 x 10(-6)M verapamil was equivalent to its uptake in the chemo-sensitive parent cell line AUXB1 in the absence or presence of verapamil. None of the TMR analogues were effective alone as photosensitizers of CR1R12 cells. However, when either TMR-S or TMR-Se was added to CR1R12 cells after 7 x 10(-6)M verapamil exposure for 2h, irradiation of cultures with 5.0J cm(-2) of 350-750 nm light caused significant phototoxicity. TMR-O showed no significant phototoxicity in the presence of verapamil. Chemo-sensitive AUXB1 cells are equally susceptible to phototoxicity using TMR-Se with or without previous exposure to verapamil. The Pgp modulators verapamil and CsA increased the uptake of CAM into CR1R12. Exposure of CR1R12 cells to TMR-S or TMR-Se for 2h in the dark resulted in no significant change in the intracellular accumulation of CAM. However, 1h of light exposure after incubation of cells with TMR-S or TMR-Se resulted in an up to 2-fold increase in CAM uptake.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

Enhancement of the photoluminescence of CdSe quantum dots during long-term UV-irradiation: privilege or fault in life science research?

The present study describes an impressive enhancement of the photoluminescence (PL) intensity of low-temperature synthesized CdSe nanocrystals (75 degrees C) during long-term UV-irradiation. The integrated PL-intensity of CdSe core and CdSe/ZnS core/shell nanocrystals, dispersed in chloroform, enhanced about 3 and 6 times, respectively, during 9 h exposure to UV-light, without any significant changes in the characteristic absorbance spectra and shifting of PL-spectra. After termination of the irradiation a comparatively slow photobleaching was detected with tau(1/2) = 6 h for CdSe core and tau(1/2) = 14 h for CdSe/ZnS core/shell nanocrystals. The most impressive was the effect of UV-irradiation on the photoluminescence of water-soluble CdSe nanocrystals. The integrated PL-intensity enhanced about 10 times during 11 h exposure to UV-light and the improved PL-intensity was preserved during 3 days after termination of the irradiation without any significant photobleaching. The results are discussed in the context of application of CdSe nanocrystals as novel fluorophores in life science experiments.

Biological Science Disciplines↗
PubMed2007

Luminescent quantum dots fluorescence resonance energy transfer-based probes for enzymatic activity and enzyme inhibitors.

The paper describes the development and characterization of analytical properties of quantum dot-based probes for enzymatic activity and for screening enzyme inhibitors. The luminescent probes are based on fluorescence resonance energy transfer (FRET) between luminescent quantum dots that serve as donors and rhodamine acceptors that are immobilized to the surface of the quantum dots through peptide linkers. Peptide-coated CdSe/ZnS quantum dots were prepared using a one-step ligand exchange process in which RGDC peptide molecules replace trioctylphosphine oxide (TOPO) molecules as the capping ligands of the quantum dots. The peptide molecules were bound to the surface of the CdSe/ZnS quantum dots through the thiol group of the peptide cysteine residue. The peptide-coated quantum dots were labeled with rhodamine to form the FRET probes. The emission quantum yield of the quantum dot FRET probes was 4-fold lower than the emission quantum yield of TOPO-capped quantum dots. However, the quantum dot FRET probes were sufficiently bright to enable quantitative enzyme and enzyme inhibition assays. The probes were used first to test the enzymatic activity of trypsin in solution based on FRET signal changes of the quantum dot-based enzymatic probes in the presence of proteolytic enzymes. For example, exposure of the quantum dot FRET probes to 500 microg/mL trypsin for 15 min resulted in 60% increase in the photoluminescence of the quantum dots and a corresponding decrease in the emission of the rhodamine molecules. These changes resulted from the release of rhodamine molecules from the surface of the quantum dots due to enzymatic cleavage of the peptide molecules. The quantum dot FRET-based probes were used to monitor the enzymatic activity of trypsin and to screen trypsin inhibitors for their inhibition efficiency.

Cadmium Compounds↗
PubMed2004

Near-complete suppression of quantum dot blinking in ambient conditions.

Colloidal semiconductor quantum dots are attractive fluorophores for multicolor imaging because of broad absorption and narrow emission spectra, and they are brighter and far more photostable than organic dyes. However, severe intermittence in emission (also known as blinking) has been universally observed from single dots and has been considered an intrinsic limitation difficult to overcome. This is unfortunate because growing applications in spectroscopy of single biological molecules and quantum information processing using single photon sources could greatly benefit from long-lasting and nonblinking single-molecule emitters. For instance, in a recent application of single-dot imaging, the tracking of membrane receptors was interrupted frequently due to the stroboscopic nature of recording. Blinking can also reduce the brightness in ensemble imaging via signal saturation. Here we show that the quantum dot blinking can be suppressed with the emission duty cycle approaching 100% while maintaining biocompatibility.

Biocompatible Materials↗
PubMed2005

Synthesis of compact multidentate ligands to prepare stable hydrophilic quantum dot fluorophores.

We describe a simple and versatile scheme to prepare an array of heterofunctional multidentate ligands that permit strong and stable interactions with colloidal semiconductor nanocrystals (quantum dots, QDs) and render them soluble in aqueous environments. These ligands were synthesized by reacting various chain length poly(ethylene glycols) with thioctic acid, followed by ring opening of the dithiolane moiety, creating a bidentate thiol motif with enhanced affinity for CdSe-ZnS core-shell QDs. Functionalization with these ligands permits processability of the nanocrystals not only in aqueous but also in many other polar solvents. These ligands provide a straightforward means of preparing QDs that exhibit greater resistance to environmental changes, making them more amenable for use in live cell imaging and other biotechnological applications.

Biotechnology↗
PubMed2005

Chemical aerosol flow synthesis of semiconductor nanoparticles.

Nanometer-sized semiconductor particles (quantum dots) have been the subject of intense research during the past decade owing to their novel electronic, catalytic, and optical properties. Fundamental properties of these nanoparticles (1-20 nm diameter) can be systematically changed simply by controlling the size of the crystals while holding their chemical composition constant. We describe here a new methodology for the continuous production of fluorescent CdS, CdSe, and CdTe nanoparticles using ultrasonically generated aerosols of high boiling point solvents. Each submicron droplet serves as a separate nanoscale chemical reactor, with reactions proceeding as the liquid droplets (which hold both reactants and surface stabilizers) are heated in a gas stream. The method is inexpensive, scalable, and allows for the synthesis of high quality nanocrystals. This chemical aerosol flow synthesis (CAFS) can be extended to the synthesis of nanostructured metals, oxides, and other materials.

Aerosols↗
PubMed2005

Internal field switching in CdSe quantum dot films on Si.

If a thin film (tens of nm) of CdSe quantum dots (4 nm diameter) is deposited by chemical bath deposition onto various substrates, the films, although essentially intrinsic, behave as if they were n-type with respect to charge separation. However, films deposited under certain deposition conditions on Si (both n(+)- and p(+)-type) behave as if they were p-type. In this case, we show that it is possible to switch this p-type photoresponse by either light illumination intensity or injection of electrons from an external filament. Using both surface photovoltage spectroscopy and a novel adaptation of X-ray photoelectron spectroscopy, we show how this behavior results from a Cd(OH)(2) layer adsorbed at the Si surface at the beginning of the deposition. This response is explained by a competition between a high concentration of relatively shallow hole traps in the CdSe and a lower concentration of deeper electron traps in the Cd(OH)(2). The relative occupancies of these traps determine the fields in the film and their response to external parameters.

Cadmium Compounds↗
PubMed2005

Subsecond luminescence intensity fluctuations of single CdSe quantum dots.

Photoluminescence (PL) intermittency characteristics are examined for single quantum dots (QDs) in a CdSe QD sample synthesized at a slow rate at 75 degrees C. Although the PL quantum efficiency was relatively low ( approximately 0.25), we noticed that the PL intensity of single CdSe QDs fluctuated on a subsecond time scale with short-lived "on" and "off" states. The subsecond PL intensity fluctuations of CdSe QDs are different from "on" and "off" PL blinking generally observed for QDs fluctuating on a millisecond to minute time scale. We characterized single QDs by identifying polarized excitations, topographic imaging using atomic force microscopy (AFM), and transmission electron microscopy (TEM). From analysis of the PL intensity trajectories from >100 single CdSe QDs, the average intermittency time was 213 ms. From the PL quantum efficiency, slow growth of QDs, intensity trajectory analyses, and previous reports relating surface trap states and PL properties of QDs, we attribute the subsecond PL intensity fluctuations of single CdSe QDs and short-lived "on" and "off" states to a high-density distribution of homogeneous surface trap states.

Cadmium Compounds↗
PubMed2006

Fluorescence blinking statistics from CdSe core and core/shell nanorods.

We report fluorescence blinking statistics measured from single CdSe nanorods (NRs) of seven different sizes with aspect ratios ranging from 3 to 11. This study also included core/shell CdSe/ZnSe NRs and core NRs with two different surface ligands producing different degrees of surface passivation. We compare the findings for NRs to our measurements of blinking statistics from spherical CdSe core and CdSe/ZnS core/shell nanocrystals (NCs). We find that, for both NRs and spherical NCs, the off-time probability distributions are well described by a power law, while the on-time probability distributions are best described by a truncated power law, P(tau(on)) approximately tau(on)(-alpha)e((-tau)(on)/(tau)(c)). The measured crossover time, tau(c), is indistinguishable within experimental uncertainty for core and core/shell NRs, as well as for core NRs with different ligands, for the same core size, indicating that surface passivation does not affect the blinking statistics significantly. We find that, at fixed excitation intensity, 1/tau(c) increases approximately linearly with increasing NR aspect ratio; for a given sample, 1/tau(c) increases very gradually with increasing excitation intensity. Examining 1/tau(c)versus the single-particle photon absorption rate for all samples indicates that the change in NR absorption cross section with sample size can account for some but not all of the differences in crossover time. This suggests that the degree of quantum confinement may be partially responsible for the aspect ratio dependence of the crossover time.

Absorption↗
PubMed1963

ENZYMATIC REDUCTION OF SELENITE.

Nickerson, Walter J. (Rutgers, The State University, New Brunswick, N.J.) and Giuseppe Falcone. Enzymatic reduction of selenite. J. Bacteriol. 85:763-771.-1963. Extraction of boiled yeast extract with n-hexane removed its ability to restore selenite-reducing capacity in dialyzed enzyme preparations obtained from baker's yeast or from Candida albicans. Menadione or thiodione substituted for the quinone(s) extracted by n-hexane. Active components of the water-soluble, dialyzable fraction of yeast extract included: glucose-6-phosphate, triphosphopyridine nucleotide, and glutathione. Selenite appears to be bound to protein through vicinal thiol groups, and to be released therefrom as metallic selenium after accepting four electrons.

Candida↗
PubMed2006

Synthesis and characterization of metal selenide (ZnSe, CdSe, HgSe) nanoparticles.

Thermolysis of [M(SeCH2CH2CH2NMe2)2] (M = Zn, Cd, Hg), prepared by the reactions of sodium salt of 3-(N,N-dimethylamino)propaneselenolate with metal acetates, afforded metal selenides (MSe). The metal selenides were characterized by XRD, EDAX, SEM, AFM, and TEM techniques. Nanoparticles of HgSe were prepared by pyrolysis in a quartz boat, solvothermal, and sonochemical methods. EDAX showed 1:1 Hg/Se ratio, while XRD and SAED patterns confirmed the formation of cubic HgSe. These particles are spherical in nature with an average diameter of 15 nm (from TEM).

Cadmium Compounds↗
PubMed1981

A randomized, controlled clinical trial of four anti-dandruff shampoos.

A total of 199 patients were selected for a comparison of the anti-dandruff efficacy of four shampoos. After a 2-week lead in (all patients used only Johnson's Baby Shampoo twice weekly) the patients were randomly assigned to Selsun Blue, Head & Shoulders, Flex, or Tegrin. The test preparation, which was unknown to the observer, was used twice weekly for 4 weeks. Loose and adherent dandruff were each rated on a scale of 0 to 20 (absent to severe) at the end of the lead-in (when a total score of 15 was required), and each week of study. The mean total pre-study score for all subjects was 19.5. At the end of the study the mean improvement scores were: 16.2 (Selsun Blue), 14.6 (head & Shoulders), 13.5 (Flex), and 13.1 (Tegrin). The improvement was significantly greater (p less than 0.05) on Selsun Blue than on any of the other shampoo. At the end of the study significantly (p less than 0.05) more patients had total scores of zero on Selsun Blue (15) than on Tegrin or Head & Shoulders. In addition, the rate of improvement was significantly (p less than 0.05) faster with Selsun Blue than with any of the other test preparations.

Adolescent↗