Effects of growth temperature and thermal annealing on optical quality of GaNAs nanowires emitting in the near-infrared spectral range.

We report on optimization of growth conditions of GaAs/GaNAs/GaAs core/shell/shell nanowire (NW) structures emitting at ∼1 µm, aiming to increase their light emitting efficiency. A slight change in growth temperature is found to critically affect optical quality of the active GaNAs shell and is shown to result from suppressed formation of non-radiative recombination (NRR) centers under the optimum growth temperature. By employing the optically detected magnetic resonance spectroscopy, we identify gallium vacancies and gallium interstitials as being among the dominant NRR defects. The radiative efficiency of the NWs can be further improved by post-growth annealing at 680 °C, which removes the gallium interstitials.

Strongly polarized quantum-dot-like light emitters embedded in GaAs/GaNAs core/shell nanowires.

Recent developments in fabrication techniques and extensive investigations of the physical properties of III-V semiconductor nanowires (NWs), such as GaAs NWs, have demonstrated their potential for a multitude of advanced electronic and photonics applications. Alloying of GaAs with nitrogen can further enhance the performance and extend the device functionality via intentional defects and heterostructure engineering in GaNAs and GaAs/GaNAs coaxial NWs. In this work, it is shown that incorporation of nitrogen in GaAs NWs leads to formation of three-dimensional confining potentials caused by short-range fluctuations in the nitrogen composition, which are superimposed on long-range alloy disorder. The resulting localized states exhibit a quantum-dot like electronic structure, forming optically active states in the GaNAs shell. By directly correlating the structural and optical properties of individual NWs, it is also shown that formation of the localized states is efficient in pure zinc-blende wires and is further facilitated by structural polymorphism. The light emission from these localized states is found to be spectrally narrow (∼50-130 µeV) and is highly polarized (up to 100%) with the preferable polarization direction orthogonal to the NW axis, suggesting a preferential orientation of the localization potential. These properties of self-assembled nano-emitters embedded in the GaNAs-based nanowire structures may be attractive for potential optoelectronic applications.

Defect properties of ZnO nanowires revealed from an optically detected magnetic resonance study.

Optically detected magnetic resonance (ODMR) complemented by photoluminescence measurements is used to evaluate optical and defect properties of ZnO nanowires (NWs) grown by rapid thermal chemical vapor deposition. By monitoring visible emissions, several grown-in defects are revealed and attributed to Zn vacancies, shallow (but not effective mass) donor and exchange-coupled pairs of Zn vacancies and Zn interstitials. It is also found that the intensity of the donor-related ODMR signals is substantially lower in the NWs compared with that in bulk ZnO. This may indicate that formation of native donors is suppressed in NWs, which is beneficial for achieving p-type conductivity.

Moving nanoparticles with Raman scattering.

We show how to change optically the distance between two protein-linked gold nanoparticles by Raman-induced motion of the linker protein. Rayleigh scattering spectroscopy of the coupled-particle plasmon allows us to compare the inter-nanoparticle distance of individual protein-linked gold nanoparticle dimers before and after surface-enhanced Raman scattering (SERS). We find that low-intensity (50 microW/microm2) laser light in resonance with the nanoparticle-dimer plasmon provokes a change of the inter-nanoparticle distance on the order of 0.5 nm whenever SERS from the proteins connecting the nanoparticles can be observed.

Virus isolation for diagnosing dengue virus infections in returning travelers.

Dengue fever is recognized as one of the most frequent imported acute febrile illnesses affecting European tourists returning from the tropics. In order to assess the value of virus isolation for the diagnosis of dengue fever, 70 cases of dengue fever confirmed in German travelers during the period 1993-2001 were analyzed retrospectively. In 26 patients who had developed acute febrile illness within 2 weeks following their return from a trip to a dengue-endemic area, 9 of 13 attempts to isolate the virus were successful in sera drawn 1-5 days and 2 of 13 sera drawn 6-10 days after the onset of illness. DEN-1 was the most frequent serotype isolated. If performed early, virus isolation is a reliable tool for detecting dengue virus in returning travelers.

Basic examinations on chemical pre-oxidation by ozone for enhancing bioremediation of phenanthrene contaminated soils.

Biological treatment of polycyclic aromatic hydrocarbons (PAH) has been demonstrated to be a feasible and common remediation technology which has been successfully applied to the clean-up of contaminated soils. Because bioavailability of the contaminants is of great importance for a successful bioremediation, a chemical pre-oxidation step by ozone was tested to enhance the subsequent biodegradation steps. Oxidation of PAH by ozone should result in reaction products that have a better solubility in water and thus a better bioavailability. A major part of this work was done by examinations of the model substance phenanthrene as a typical compound of PAH. After initial ozonation of phenanthrene, analysis by GC-MS showed at least seven identified conversion-products of phenanthrene. In comparison with phenanthrene these conversion products were more efficiently biodegraded by Sphingomonas yanoikuyae or mixed cultures when the ozonation process resulted in monoaromatic compounds. Primary ozonation products with biphenylic structures were found not to be biodegradable. Investigations into the toxicity of contaminated and ozonated soils were carried out by well-established toxicity assays using Bacillus subtilis and garden cress. The ozonated soils surprisingly showed higher toxic or inhibitory effects towards different organisms than the phenanthrene or PAH itself. The microbial degradation of phenanthrene in slurry reactors by S. yanoikuyae was not enhanced significantly by preozonation of the contaminated soil.

Development of viremia and humoral and cellular parameters of immune activation after vaccination with yellow fever virus strain 17D: a model of human flavivirus infection.

To monitor early and late events of immune system activation after primary and secondary flavivirus infection, 17 healthy persons were vaccinated with the standard 17D vaccine virus strain of yellow fever (YF). Twelve of these persons had not received YF vaccine previously and 5 had been vaccinated once at least 10 years before. Viremia and various parameters of humoral and cellular immune activation were followed daily for 7 days and weekly thereafter. Viremia was detected by reverse transcriptase-polymerase chain reaction in all 12 first-time vaccinees beginning from the second to the sixth day after vaccination; most tested positive between the fourth and sixth day. Infectious 17D virus was detected using a plaque forming assay in the serum of 7 of the 12 first-time vaccinees. As first parameters of immune activation, neopterin and beta2-microglobulin markedly increased between day 2 and day 6 postvaccination. In parallel to the viremia, circulating CD8+ T-cells significantly increased, with peak levels at day 5 after primary vaccination, indicating an activation of the cellular immune system. Neither viremia nor significant changes of these activation markers were observed in the five revaccinated persons. Neutralizing antibodies directed against the 17D vaccine strain developed in all persons within 2 weeks after vaccination. No correlation was found between the extent of viremia and the titer of neutralizing antibodies. Revaccination was followed by a minor and transient increase of neutralizing antibodies. High titers of neutralizing antibodies persisted for at least 10 years after primary vaccination.

Laboratory scale production of monoclonal antibodies in a tumbling chamber.

A simple device for laboratory scale production of monoclonal antibodies has been developed. Hybridomas were cultured in four individual dialysis tubes containing 40-50 ml medium with 10% foetal calf serum, surrounded by 1.5-2 litres supply medium without any serum supplement. Once placed on a roller the special design of the apparatus leads to an eccentric rotation, thus keeping the cells in a stable homogeneous suspension. The system is automatically gassed, and this makes long term cultivation possible. Several hybridomas were tested over a culture period of at least 3 weeks, with supply medium changes every 3-4 days. Cell densities of up to 2.5 x 10(7)/ml and antibody concentrations of 0.3-1.9 mg/ml after purification were obtained. Results with this in vitro system allow a complete renunciation of the established in vivo method. The so called 'tumbling chamber' apparatus is easy to handle and to sterilize, is economic and universally adaptable in any research laboratory.

Antigen presentation, loss of immunological memory and AIDS.

A key factor causing immunodeficiency in HIV infection seems to be defective antigen presentation. Consequently, CD4+ T-cell populations, initially those expressing CD45RO, decrease in number not because of their destruction, but because they fail to expand in response to antigenic stimulation. This view implies that it would be mistaken to aim therapies only at correcting T-cell function or preventing infection of T cells.

CR1 (CD35) and CR3 (CD11b/CD18) mediate infection of human monocytes and monocytic cell lines with complement-opsonized HIV independently of CD4.

Peripheral blood and tissue mononuclear phagocytes serve as major viral reservoirs in HIV-infected individuals. We investigated the role of complement receptors CR1 (CD35) and CR3 (CD11b/CD18) in mediating productive infection with complement-opsonized HIV-1 and HIV-2 of cultured normal human peripheral blood monocytes, the promonocytic cell line THP-1, the monocytic cell line Mono Mac 6 and the glial cell line U251-MG. Cells were infected with the HTLV-IIIB strain of HIV-1 or the LAV-2 strain of HIV-2 that had been preopsonized with fresh human normal HIV seronegative serum. Productive infection was assessed by syncytia formation, the MTT cytotoxicity assay and/or release of p24 antigen in culture supernatants. Using suboptimal amounts of virus to infect the cells, we observed a higher and earlier productive infection of the cells with complement-opsonized HIV than with unopsonized virus. The enhancing effect of complement was totally suppressed by blocking CR1 or CR3 function with F(ab)'2 fragments of anti-receptor MoAbs; while blocking of the LFA-1 antigen had no effect. The infection of monocytic cells with complement-opsonized virus occurred independently of CD4 since it was not inhibited by F(ab)'2 fragments of a MoAb against the gp120 binding site of CD4 and since infection also occurred with Mono Mac 6 and U251-MG cells, which lack expression of the CD4 antigen and of CD4 mRNA. These observations suggest that complement may mediate productive infection of cells of the monocytic lineage with 'lymphocytotropic' HIV strains independently of CD4.

The effect of cyclosporine on the progression of human immunodeficiency virus type 1 infection transmitted by transplantation--data on four cases and review of the literature.

Two women and two men were infected with the human immunodeficiency virus type 1 (HIV-1) transmitted by renal transplantation from i.v. drug-addicted donors in 1984. The four recipients were treated with cyclosporine and methylprednisolone (one patient only for three months because of early graft failure). Two patients died 66 and 74 months after transplantation, one of endocarditis and one of cerebral hemorrhage. Despite several infections including urinary tract infection (n = 8), peritonitis (n = 1), shunt infection (n = 1), bronchitis (n = 1), salmonellosis (n = 1), herpes stomatitis (n = 2), herpes zoster (n = 1), and cytomegalovirus (n = 1), and despite treatment of several rejection episodes (n = 8), none of them had or has infections typical of the acquired immunodeficiency syndrome (AIDS). However, two patients developed cervical lymphadenopathy and one autoimmune thrombocytopenia 15-20 months after HIV-1 infection. Their T helper cell counts (355/microliters to 75/microliters) and helper/suppressor T cell ratios (1.0-0.2) are distinctly lowered. One patient has membranous glomerulopathy with virus-like particles within and on the outside of the basement membrane and tubuloreticular inclusions in glomerular endothelial cells. We evaluated the case reports of 53 patients with HIV-infection caused by an infected transplant or by blood transfusions during or shortly after transplantation. The cumulative incidence of AIDS was significantly lower in 40 transplant patients with an immunosuppressive regimen including cyclosporine than in 13 transplant patients receiving immunosuppressive treatment without cyclosporine (5-year cumulative risk of AIDS: 31% versus 90%, P = 0.001).

Infection of the human monocytic cell line Mono Mac6 with human immunodeficiency virus types 1 and 2 results in long-term production of virus variants with increased cytopathogenicity for CD4+ T cells.

The recently established human monocytic cell line Mono Mac6 expressing distinct characteristics of mature monocytes/macrophages was tested for its susceptibility to infection with human immunodeficiency virus. Inoculation of the cells with the T-cell-tropic human immunodeficiency virus strains human T-lymphotropic virus type IIIB and lymphadenopathy-associated virus type 2 led to a noncytopathic productive infection becoming apparent only after a latency period of up to 56 days. The infectibility of the Mono Mac6 cells was dependent on low levels of CD4 expression, as demonstrated by blocking experiments with various CD4-specific antibodies. Increasing with time after infection (greater than 200 days), the cultured Mono Mac6 cells released virus variants which showed shortened latency periods when passaged onto uninfected Mono Mac6 cells. Also, cytopathogenicity for several CD4+ T cells of the Mono Mac6-derived virus was drastically increased; thus, the infection of the H9 cell line with low doses of virus (less than 0.1 50% tissue culture infective dose per cell) led to giant syncytium formation within 1 day and subsequent death of all fused cells. We propose Mono Mac6 cells as a new model for the study of human immunodeficiency virus infecting the monocyte/macrophage lineage, particularly with regard to virus-host cell interaction and the influence of cell differentiation and activation on latency and development of virulence. The human immunodeficiency virus-infected Mono Mac6 cell may also serve as a valuable tool for in vitro testing of antiviral therapies.

Epitope mapping of monoclonal antibodies against human immunodeficiency virus type 1 structural proteins by using peptides.

Murine monoclonal antibodies directed against the structural proteins p17 and p24 of human immunodeficiency virus type 1 were investigated in an epitope mapping system. Overlapping peptides consisting of 15 amino acids of the p17 and p24 protein, respectively, were used as competitors in an enzyme-linked immunosorbent assay. Three different immunogenic regions (A, B, and C) could be defined, one on p17 and two on p24. Twenty monoclonal antibodies reacted with the human immunodeficiency virus type 1 peptides of region B, although differences in the reactivity of these antibodies with human immunodeficiency virus type 2 and simian immunodeficiency virus strain mac were detectable. Recognized epitopes were characterized by computer analysis as described by T.P. Hopp and K.R. Woods (Proc. Natl. Acad. Sci. USA 78:3824-3828, 1981) and P.Y. Chou and G.D. Fasman (Biochemistry 13:222-245, 1974).

Monoclonal antibodies directed against human immunodeficiency virus (HIV) gag proteins with specificity for conserved epitopes in HIV-1, HIV-2 and simian immunodeficiency virus.

Monoclonal antibodies (MAbs) were raised against gag proteins of human immunodeficiency virus type 1 (HIV-1), strain HTLV-IIIB. One of 29 antibodies was specific for p17 of HIV-1. Twenty of 28 MAbs reactive with the major core protein p24 of HIV-1 showed cross-reactivity with HIV-2, and five of these also detected the corresponding antigens of simian immunodeficiency virus (SIVmac). The MAbs were reactive in several tests, i.e. ELISA, immunostaining of Western blots, immunofluorescence, alkaline phosphatase-anti-alkaline phosphatase immunocytochemistry and immunoelectron microscopy. The submembrane protein p17 was clearly localized within the virion.

Human immunodeficiency virus transmission by organ donation. Outcome in cornea and kidney recipients.

The human immunodeficiency virus (HIV) is reportedly transmitted by sexual contact, sharing of infected needles among intravenous drug abusers, blood and blood products, artificial insemination, and kidney transplantation. This study reports on cornea and kidney recipients of two HIV-infected donors. HIV was transmitted to two kidney recipients who developed symptoms of acute HIV infection (i.e., fever, leukopenia, mild thrombopenia, splenomegaly) starting 12 days after transplantation. These signs of acute infection ended with seroconversion of HIV antibodies on approximately the 56th day after transplantation. The three cornea recipients showed no signs of acute infection and no HIV antibodies were detected up to three years after transplantation. The nontransmission observed in our cases, however, may not be representative of cornea transplantations in general. HIV is neurotropic in the later stages of the disease, and transmission of other neurotropic viruses like rabies and Creutzfeldt-Jakob disease by cornea transplantation has been reported. All tissue and organ donors should be tested for anti-HIV prior to donation.