Directly correlated microscopy of trench defects in InGaN quantum wells

Directly correlated measurements of the surface morphology, light emission and subsurface structure and composition were carried out on the exact same nanoscale trench defects in InGaN quantum well (QW) structures. Multiple scanning probe, scanning electron and transmission electron microscopy techniques were used to explain the origin of their unusual emission behaviour and the relationship between surface morphology and cathodoluminescence (CL) redshift. Trench defects comprise of an open trench partially or fully enclosing material in InGaN QWs with different CL emission properties to their surroundings. The CL redshift was shown to typically vary with the width of the trench and the prominence of the material enclosed by the trench above its surroundings. Three defects, encompassing typical and atypical features, were prepared into lamellae for transmission electron microscopy (TEM). A cross marker technique was used in the focused ion beam-scanning electron microscope (FIB-SEM) to centre the previously characterised defects in each lamella for further analysis. The defects with wider trenches and strong redshifts in CL emission had their initiating basal-plane stacking fault (BSF) towards the bottom of the QW stack, while the BSF formed near the top of the QW stack for a defect with a narrow trench and minimal redshift. The raised-centre, prominent defect showed a slight increase in QW thickness moving up the QW stack while QW widths in the level-centred defect remained broadly constant. The indium content of the enclosed QWs increased above the BSF positions up to a maximum, with an increase of approximately 4% relative to the surroundings seen for one defect examined. Gross fluctuations in QW width (GWWFs) were present in the surrounding material in this sample but were not seen in QWs enclosed by the defect volumes. These GWWFs have been linked with indium loss from surface step edges two or more monolayers high, and many surface step edges appear pinned by the open trenches, suggesting another reason for the higher indium content seen in QWs enclosed by trench defects.

Cross-shaped markers for the preparation of site-specific transmission electron microscopy lamellae using focused ion beam techniques

We describe the use of a cross-shaped platinum marker deposited using electron-beam-induced deposition (EBID) in a focused ion beam - scanning electron microscope (FIB-SEM) system to facilitate site-specific preparation of a TEM foil containing a trench defect in an InGaN/GaN multiple quantum well structure. The defect feature is less than 100 nm wide at the surface. The marker is deposited prior to the deposition of a protective platinum strap (also by EBID) with the centre of the cross indicating the location of the feature of interest, while the arms of the square cross make an acute angle of 45° with the strap's long axis. During the ion-beam thinning process, the marker may be viewed in cross-section from both sides of the sample alternately, and the coming together of the features relating to the arms of the cross indicates increasing proximity to the feature of interest. Although this approach does allow increased precision in locating the region of interest during thinning, it also increases the time required to complete the sample preparation. Hence, this method is particularly well suited to directly correlated multi-microscopy investigations in previously characterised material where high yield and the precise location are more important than preparation time. In addition to TEM lamella preparation, this method could equally be useful for preparing site-specific atom probe tomography (APT) samples.

A cyclic voltammetry and PM6 semi-empirical molecular orbital method study of the capacity behaviour of an aluminum-8-hydroxyquinoline complex modified carbon paste electrode

A graphite powder surface was modified by aluminum-8-hydroxyquinoline complex, and functionalised as an electron storage and transfer surface for use as one of the electrodes in an electrochemical capacitor.

Postlumpectomy loco-regional breast cancer therapy with liposomal therapeutic agents: Retention and distribution in nude rats

e11562

Background: Post-lumpectomy loco-regional radiation therapy, such as brachytherapy, has been shown to decrease breast cancer recurrence and increase patient survival. Limitations of current brachytherapy are the relatively high radiation absorbed dose delivered to normal breast and the inability to treat potentially involved lymph nodes. Locally administered liposomes are being investigated for delivery of drugs and therapeutic radionuclides. We propose a new post-lumpectomy loco-regional therapy with liposome-carried therapeutic agents. To investigate, radiolabeled liposomes were injected into the surgical cavity of a nude rat model one day following surgical removal of the breast tumor, and in vivo retention and distribution were monitored with nuclear imaging and post- mortem dissection. Methods: Six liposome formulations containing 0.2% molar ratio Rhodamine B-lipid and cationic, neutral, or anionic surface charges were manufactured at diameters of 400 or 100 nm and characterized. Breast cancer xenograft model in female nude rats was set up by inoculating MDA-MB-231 cells into the fat pad of the left breast of each rat. When tumor volumes reached 1.9 cm3 on average, the majority of each tumor was surgically removed, leaving ∼0.05 cm3 tumor tissue in the cavity. Then, each rat (3–4 rats/group) was intracavitarily injected with 0.5 ml of 99mTc-liposomes (4 mCi., 30 mg total lipids/kg body weight). In vivo distribution of 99mTc-activity was measured with planar gamma camera and SPECT imaging at various times. Post-mortem stereo fluorescent images of surgical cavity and the surrounding lymph nodes at 44 h were acquired. Results: All 99mTc-liposome formulations had approximately ≥ 50% retention in the surgical cavity at 44 h after injection. 99mTc-anionic liposomes of 100 nm diameter had an optimal lymph node targeting with ∼6%/g tissue in the surrounding lymph nodes at 44 h. Fluorescence imaging of the liposomes clearly showed their clearance through surrounding lymphatics and retention in lymph nodes. Conclusions: Anionic liposomes of 100 nm diameter are promising carriers for the simultaneous treatment of the surgical cavity and its draining lymph nodes.

No significant financial relationships to disclose.

Overexpression of NQO1 protects human SK-N-MC neuroblastoma cells against dopamine-induced cell death

NAD(P)H quinone oxidoreductase 1 (NQO1) can metabolize dopamine-derived quinones (DAQ) and absence of NQO1 due to the NQO1*2 polymorphism has been suggested to be a risk factor for Parkinson's disease. In order to define whether NQO1 plays a protective role in dopamine toxicity, we have examined the potential role of NQO1 in the SK-N-MC human neuroblastoma cell line. SK-N-MC cells were stably transfected with NQO1 to generate stable clones with NQO1 enzymatic activity of 245 nmol/mgmin while vector control and parental cells had NQO1 activities of less than 12 nmol/mgmin. Incubation of dopamine for 24 h in both parental and vector control SK-N-MC cells resulted in 85% and 72% cell death as assessed by annexin-V/propidium iodide analysis. In agreement, 88% and 84% of parental and vector control cells, respectively underwent loss of mitochondrial membrane potential (MMP) assessed by tetramethylrhodamine ethyl ester. In contrast, NQO1-transfected cells were resistant to dopamine toxicity and both cell death and loss of MMP were markedly abrogated in NQO1-transfected SK-N-MC cells. When dopamine was added to medium, oxygen uptake could be detected indicating autoxidation with concomitant formation of oxygen radicals and quinones. However, dopamine-induced cell death was not affected by the inclusion of either superoxide dismutase or catalase suggesting that superoxide and hydrogen peroxide were not involved in toxicity. Quinones formed in medium may exert toxicity extracellularly or intracellularly but the protective role of NQO1 argues for an intracellular mechanism. In summary, transfection of SK-N-MC cells with NQO1 protects against dopamine-induced toxicity.

[Analysis of bone mineral density and relevant factors in 781 healthy people aged 15 to 50]

OBJECTIVE

To determine further the age to form peak bone mass (PBM) and the factor influencing it and bone mineral density (BMD) and to find an effective way to prevent from osteoporosis in the elderly.

METHODS

BMD was measured in 781 people aged 15 to 50 years and relevant factors in lifestyle were investigated. Multivariate regression was used to analyze the relationship between BMD and lifestyles and to identify both risk and benefit factors for osteoporosis.

RESULTS

For every ten-kilogram increase in body weight, BMD at varied sites increased by an amount of 0.028 - 0.056 g/cm(2) for males and 0.050 - 0.086 g/cm(2) for females, respectively. During their adolescence for males, for every increase of one grade in physical exercise, BMD at varied sites increased by an amount of 0.034 - 0.078 g/cm(2) in males and BMD at lumbar vertebra in males aged 15 - 24 correlated negatively with their total amount of alcohol drinking, and that at lumbar vertebra and of the whole body increased by about 0.035 g/cm(2) in females, which correlated negatively with their total amount of cigarette smoking. Female BMD at lumbar vertebra correlated reversely with their age of menarche and correlated positively with their average time of breast feeding.

CONCLUSION

Increase in physical exercise during puberty could increase PBM for the adolescents and keeping adequate body weight and reducing cigarette smoking and alcohol drinking would benefit for the prevention from age-related osteoporosis.

Preliminary study on the relationship between osteoporosis and trace elements with rat models

Thirty rats were divided randomly into five groups and fed with different feeds. They were killed after 2 mo. Right thighs of these rats were taken as samples. Bone mineral densities of these samples were measured by the double-energy x-ray bone mineral densitometer, and trace elements contents of the samples were analyzed by neutron activation analysis. Results of the experiments showed that some elements were well correlated with others, and there were obvious variances between some elements of the normal group and those of other four groups.