S. Kishwar

White Electroluminescence Using ZnO Nanotubes/GaN Heterostructure Light-Emitting Diode

We report the fabrication of heterostructure white light–emitting diode (LED) comprised of n-ZnO nanotubes (NTs) aqueous chemically synthesized on p-GaN substrate. Room temperature electroluminescence (EL) of the LED demonstrates strong broadband white emission spectrum consisting of predominating peak centred at 560 nm and relatively weak violet–blue emission peak at 450 nm under forward bias. The broadband EL emission covering the whole visible spectrum has been attributed to the large surface area and high surface states of ZnO NTs produced during the etching process. In addition, comparison of the EL emission colour quality shows that ZnO nanotubes have much better quality than that of the ZnO nanorods. The colour-rendering index of the white light obtained from the nanotubes was 87, while the nanorods-based LED emit yellowish colour.

Forward- and reverse-biased electroluminescence behavior of chemically fabricated ZnO nanotubes/GaN interface

Electroluminescence characteristics of an n-ZnO nanotubes/p-GaN heterostructure light-emitting diode (LED) have been investigated at forward and reverse bias. Distinctly different emission spectra have been observed and the location of the recombination of electron–hole is analyzed under both configurations. The forward-biased emission spectrum shows two peaks centered at around 450 and 560 nm, while the reverse-biased spectrum exhibits a single emission peak at 650 nm. By comparing the current transport mechanisms, it is suggested that the violet-blue emission peak (450 nm) observed only under forward bias is originating from the heterojunction of the ZnO nanotubes/p-GaN LED. The influence on the emission intensity of the device with the increase in temperature at constant current is studied in the range from 25 to 65 °C, to check its compatibility for practical applications and under harsh conditions.

Role of ALA sensitivity in HepG2 cell in the presence of diode laser

Abstract5-aminolevulinic acid (ALA) being an amazing second generation photosensitizer was studied as photodamaging drug on hepatocellular carcinoma (HepG2) cells. The mentioned photosensitizer is converted to PpIX in HepG2 cells in vitro, inducing haem in the cell causing generation of singlet oxygen leading to cell apoptosis. Cell uptake of 5-ALA was evaluated with different concentrations (ranging from 0–800 μg/ml) for 0–49 h incubation period. ALA administered in HepG2 cells is converted into Protoporphyrin IX (PpIX) which has a short half life and constitute a good hematoporphyrin derivative (HPD). Cytotoxicity of ALA in dark and cellular viability without ALA in the presence of light was studied, showing minimal toxic effects in dark with no photodamaging effect on mentioned cells in absence of ALA were observed. The optimal uptake of photosensitizer (5-ALA) in HepG2 cells was investigated by means of spectrophotometeric measurements, cellular viability was determined by means of neutral red assay (NRA). It was observed that with different concentrations (0–800 μg/ml) of ALA or light doses (0–160 J/cm2), there were no significant effect on cellular viability when studied independently. The novel of photocytotoxic study indicates that light dose of 120 J/cm2 produces convincing Photodynamic therapy (PDT) results for HepG2 cells incubated with 262 μg/ml of 5-ALA deducting that HepG2 cell line is sensitive to ALA mediated PDT. Finally morphological changes in HePG2 cells were determined before and after ALA-mediated PDT by confocal microscopy.

Tumoricidal effects of nanomaterials in HeLa cell line

The current study exhibits the cellular response of HeLa (cervical cancer) cells to metal oxides ultrafine nanomaterials e.g. manganese dioxide nanowires (MnO2 NRs), iron oxide nanoparticles (Fe2O3 NPs) and zinc oxide nanorods (ZnO NRs) as bare and as conjugated with photosensitizers. For cytotoxic evaluations, the cellular morphology, (MTT) assay, reactive oxygen species (ROS) production were used for cases with and without photo sensitizer as well illuminated with UV-visible laser exposed conditions. Three different photosensitizers were tested. These are 5-aminolevulinic acid (5-ALA), Photofrin® and protopor phyrin dimethyl ester (PPDME). Significant loss in cell viability was noted with 100–500 μg/ml in bare and conjugated forms of the metal oxides used. The effect was insignificant with lower concentrations (0.05–50 μg/ml). While notable anticancer effect of 5-ALA under 30 J/cm2 of diode laser irradiation was noted as compared to other photo sensitizer. By increasing the UV irradiation time of labeled cells, generation of ROS was observed, indicating the possibility of achieving efficient photodynamic therapy (PDT).

Investigation of the phototoxic effect of ZnO nanorods on fibroblasts and melanoma human cells

Photocytotoxic effects of as-grown and zinc oxide (ZnO) nanorods coated with 5-aminolevulinic acid (ALA) have been studied on human cells, i.e. melanoma and foreskin fibroblast, under dark and ultraviolet light exposures. Zinc oxide nanorods have been grown on the very sharp tip (diameter = 700 nm) of borosilicate glass pipettes and then were coated by the photosensitizer for targeted investigations inside human cells. The coated glass pipettes tip with photosensitizer has been inserted inside the cells with the help of a micro-manipulator and irradiated through ultraviolet light (UVA), which reduces the membrane potential of the mitochondria leading to cell death. Cell viability loss has been detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay when exposed to the dissolved ZnO nanorods and the production of the reactive oxygen species (ROS) has been detected along with the enhanced cytotoxic effect under UVA irradiation. Additionally, the influence of the lipid soluble antioxidant vitamin E and water-soluble N-acetyl-cysteine toward the enhancement or reduction of the toxicity has been investigated. A comparative analysis of the toxic nature of ZnO nanorods has been drawn between normal human fibroblast and melanoma cells, which can be favorable for understanding the clinical setting for killing tumor cells.