Ailanthus altissima leaf extract mediated green production of zinc oxide (ZnO) nanoparticles for antibacterial and antioxidant activity

BackgroundFabricating zinc oxide nanoparticles (ZnO-NPs) from plant extracts is a cost-effective, safe, and environmentally friendly alternative to established chemical procedures. This study was aimed at the environmentally friendly fabrication of ZnO-NPs from plant extract. An additional objective was to investigate the antibacterial and antioxidant activity of these biosynthesized ZnO-NPs.MethodsZnO-NPs were fabricated using the leaf extract of Ailanthus altissima, as an eco-friendly approach. The physicochemical properties of ZnO-NPs were explored using UV–visible spectroscopy, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectrometry. The bio-fabricated ZnO-NPs were examined for bactericidal activity against pathogenic bacteria (gram-negative and gram-positive) using the agar well diffusion technique. The antioxidant efficiency of ZnO-NPs was assessed using a DPPH assay.ResultsA surface Plasmon peak was recorded at 327 nm, showing the existence of ZnO-NPs in the reaction solution of plant extract and zinc sulfate hexahydrate salt. These nanoparticles were predominantly spherical and capped by different functional groups of biomolecules. Furthermore, ZnO-NPs showed a dose-dependent antibacterial and antioxidant activity. At 20 mg/mL ZnO-NPs, the maximum bactericidal potential of ZnO-NPs was reported against Staphylococcus aureus (201.2 mm). ZnO-NPs have an IC₅₀ value of 78.23 µg/mL, indicating that they are an effective antioxidant.ConclusionThis research presents an environmentally acceptable method for producing spherical ZnO-NPs with high antibacterial and antioxidant activities. These bio-fabricated ZnO-NPs could be a good option for applications in medicine and the healthcare industry.     

In‐vivo Tumor detection using diffusion reflection measurements of targeted gold nanorods – a quantitative study

The ability to quantitatively and non‐invasively detect nanoparticles has important implications on their development as an in‐vivo cancer diagnostic tool. The Diffusion Reflection (DR) method is a simple, non‐invasive imaging technique which has been proven useful for the investigation of tissue's optical parameters. In this study, Monte Carlo (MC) simulations, tissue‐like phantom experiments and in‐vivo measurements of the reflected light intensity from tumor bearing mice are presented. Following intravenous injection of antibody conjugated poly (ethylene glycol)‐coated (PEGylated) gold nanorods (GNR) to tumor‐bearing mice, accumulation of GNR in the tumor was clearly detected by the DR profile of the tumor. The ability of DR measurements to quantitate in‐vivo the concentration of the GNR in the tumor was demonstrated and validated with Flame Atomic Absorption spectroscopy results. With GNR as absorbing contrast agents, DR has important potential applications in the image guided therapy of superficial tumors such as head and neck cancer, breast cancer and melanoma. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interplay of Optical,Morphological, and Electronic Effects of ZnO Optical Spacers in Highly Efficient Polymer Solar Cells

Optical spacers based on metal oxide layers have been intensively studied in poly(3‐hexylthiophene) (P3HT) based polymer solar cells for optimizing light distribution inside the device, but to date, the potential of such a metal oxide spacer to improve the electronic performance of the polymer solar cells simultaneously has not yet be investigated. Here, a detailed study of performance improvement in high efficient polymer solar cells by insertion of solution‐processed ZnO optical spacer using ethanolamine surface modification is reported. Insertion of the modified ZnO optical spacer strongly improves the performance of polymer solar cells even in the absence of an increase in light absorption. The electric improvements of the device are related to improved electron extraction, reduced contact barrier, and reduced recombination at the cathode. Importantly, it is shown for the first time that the morphology of optical spacer layer is a crucial parameter to obtain highly efficient solar cells in normal device structures. By optimizing optical spacer effects, contact resistance, and morphology of ZnO optical spacers, poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6diyl] [3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl] thieno[3,4‐b]thiophenediyl]] (PTB7):[6,6]‐phenyl‐C71‐butyric acid (PC₇₀BM) bulk heterojunction solar cells with conversion efficiency of 7.6% are obtained in normal device structures with all‐solution‐processed interlayers.     

Second harmonic imaging of plants tissues and cell implosion using two‐photon process in ZnO nanoparticles

The optical properties of colloidal ZnO nanoparticle (NP) solutions, with size ranging from several nm to around 200 nm, have been tailored to have high optical nonlinearity for bioimaging with no auto‐fluorescence above 750 nm and minimal auto‐fluorescence below 750 nm. The high second harmonic conversion efficiency enables selective tissue imaging and cell tracking using tunable near‐infrared femtosecond laser source ranging from 750‐980 nm. For laser energies exceeding the two‐photon energy of the bandgap of ZnO (half of 3.34 eV), the SHG signal greatly decreases and the two‐photon emission becomes the dominant signal. The heat generated due to two‐photon absorption within the ZnO NPs enable selective cell or localized tissue destruction using excitation wavelength ranging from 710–750 nm. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Highly hydrophilic cationic gold nanorods stabilized by novel quaternary ammonium surfactant with negligible cytotoxicity

The photothermal cancer therapy using cationic gold nanorods (GNRs) stabilized by quaternary ammonium salts (QAS) have a great potential to enhance conventional cancer treatment as it promises the effective eradication of cancer cells including cells resistant to radio‐ and chemo‐therapy and the stimulation of anti‐tumor immune response. However, as the cytotoxicity of the conventional alkanethiol‐QAS compounds limits their utility in medicine, here we developed GNRs modified by novel highly hydrophilic cationic surfactant composed of the quaternary ammonium group and ethylene glycol chain N,N,N‐trimethyl‐3,6,9,12,15‐pentaoxaheptadecyl‐17‐sulfanyl‐1‐ammonium bromide (POSAB) showing insignificant cytotoxicity in the free state. Surface modification of GNRs by POSAB allowed to prepare nanoparticles with good stability in water, high cellular uptake and localization in lysosomes that are a promising alternative to alkanethiol‐stabilized GNRs especially for biomedical applications.     

Abundance of Escherichia coli F1-ATPase molecules observed to rotate via single-molecule microscopy with gold nanorod probes

The abundance of E. coli F₁-ATPase molecules observed to rotate using gold nanorods attached to the γ-subunit was quantitated. Individual F₁ molecules were determined to be rotating based upon time dependent fluctuations of red and green light scattered from the nanorods when viewed through a polarizing filter. The average number of F₁ molecules observed to rotate in the presence of GTP, ATP, and without nucleotide was ∼50, ∼25, and ∼4% respectively. In some experiments, the fraction of molecules observed to rotate in the presence of GTP was as high as 65%. These data indicate that rotational measurements made using gold nanorods provide information of the F₁-ATPase mechanism that is representative of the characteristics of the enzyme population as a whole. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. This work was supported by National Institutes of Health grant GM50202 to W.D.F.     

Multiplexed DNA detection using a gold nanorod‐based fluorescence resonance energy transfer technique

A fluorescence resonance energy transfer method for multiplex detection DNA based on gold nanorods had been successfully constructed. This method is simple, easy to operate, good selectivity, no requirement to label the probe molecule and can analyze simultaneously multiple targets of DNA in one sample. The limit of detection for the 18‐mer, 27‐mer and 30‐mer targets is 0.72, 1.0 and 0.43 nM at a signal‐to‐noise ratio of 3. The recoveries of three targets were 96.57–98.07%, 99.12–100.04% and 97.29–99.93%, respectively. The results show that the method can be used to analyze a clinical sample or a biological sample; it also can be used to develop new probes for rapid, sensitive and highly selective multiplex detection of analytes in real samples. Copyright © 2015 John Wiley & Sons, Ltd.     

Far-Field Raman Imaging of Short-Wavelength Particle Plasmons on Gold Nanorods

The surface plasmon fields of gold nanorods with a diameter of 100 nm and lengths of 1–5 m are imaged by using far-field Raman scattering of methylene blue adsorbed on the rods. When optically exciting the nanorods under total internal reflection with wave vector and electric field vector orientations along the rod axis, the plasmon field intensity along this axis is observed to be periodically modulated. This modulation is attributable to a beating of the exciting light wave and the nanorod plasmon mode. The plasmon wavelength deduced from the beat frequency is 379 nm, which is considerably smaller than the exciting laser wavelength of 647 nm. In general, Raman imaging is shown to be a powerful technique to probe local plasmon fields using far-field spectroscopy.     

Harvesting Solar Energy by Means of Charge-Separating Nanocrystals and Their Solids

Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials offering a superior control over the spatial distribution of charge carriers across material interfaces. As this study demonstrates, a combination of donor-acceptor nanocrystal (NC) domains in a single nanoparticle can lead to the realization of efficient photocatalytic^1-5 materials, while a layered assembly of donor- and acceptor-like nanocrystals films gives rise to photovoltaic materials.Initially the paper focuses on the synthesis of composite inorganic nanocrystals, comprising linearly stacked ZnSe, CdS, and Pt domains, which jointly promote photoinduced charge separation. These structures are used in aqueous solutions for the photocatalysis of water under solar radiation, resulting in the production of H₂ gas. To enhance the photoinduced separation of charges, a nanorod morphology with a linear gradient originating from an intrinsic electric field is used⁵. The inter-domain energetics are then optimized to drive photogenerated electrons toward the Pt catalytic site while expelling the holes to the surface of ZnSe domains for sacrificial regeneration (via methanol). Here we show that the only efficient way to produce hydrogen is to use electron-donating ligands to passivate the surface states by tuning the energy level alignment at the semiconductor-ligand interface. Stable and efficient reduction of water is allowed by these ligands due to the fact that they fill vacancies in the valence band of the semiconductor domain, preventing energetic holes from degrading it. Specifically, we show that the energy of the hole is transferred to the ligand moiety, leaving the semiconductor domain functional. This enables us to return the entire nanocrystal-ligand system to a functional state, when the ligands are degraded, by simply adding fresh ligands to the system⁴.To promote a photovoltaic charge separation, we use a composite two-layer solid of PbS and TiO₂ films. In this configuration, photoinduced electrons are injected into TiO₂ and are subsequently picked up by an FTO electrode, while holes are channeled to a Au electrode via PbS layer⁶. To develop the latter we introduce a Semiconductor Matrix Encapsulated Nanocrystal Arrays (SMENA) strategy, which allows bonding PbS NCs into the surrounding matrix of CdS semiconductor. As a result, fabricated solids exhibit excellent thermal stability, attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces, and show compelling light-harvesting performance in prototype solar cells⁷.