Synthesis of tetrapod-shaped ZnO whiskers and microrods in one crucible by thermal evaporation of Zn/C mixtures

Tetrapod-shaped ZnO whiskers and microrods were synthesized in one crucible by thermal evaporation of Zn/C mixtures at 930 ℃ in air without any catalyst.The digital camera,optical microscopy,scanning electron microscopy,energy dispersive X-ray spectroscopy,and X-ray diffraction techniques were used to study the morphologies and crystal structures of these tetrapod-shaped ZnO microcrystals.The results show that these two types of ZnO tetrapods are grown at different heights within the same crucible.The legs of these tetrapod-shaped ZnO crystals are hexagonally faceted.Some tetrapod-shaped ZnO whiskers show hierarchical structures.A short button-like hexagonal ZnO microcrystal is observed at the triple junctions of some tetrapod-shaped ZnO whiskers.The tetrapod-shaped ZnO microrods are capped by two sets of hexagonal pyramids with two different groups of crystal planes for the surfaces.These two types of tetrapod-shaped ZnO microcrystals have different side faces and aspect ratio,which are believed to be the result of their different growth behaviors.The octa-twin model was used to discuss the different growth behaviors of these two types of ZnO tetrapods.The crystal planes of the legs and the pyramids were determined.

Extreme Light Concentration and High Absorption of the Double Cylindrical Microcavities

We numerically study the enhancement factor of energy density and absorption efficiency inside the double cylindrical microcavities based on a triple-band metamaterial absorber. The compact single unit cell consists of concentric gold rings with a gold disk in the center and a metallic ground plane separated by a dielectric layer. We demonstrate that the multilayer structure with subwavelength electromagnetic confinement allows 104-105-fold enhancement of the electromagnetic energy density inside the double cavities and contains the most energy of the incoming light. Particularly, the enhancement factor of energy density G shows strong ability of localizing light and some regularity as the change of the thickness of the dielectric slab and dielectric constant. At the normal incidence of electromagnetic radiation, the obtained reflection spectra show that the resonance frequencies of the double microcavities operate in the range of 10-30μm. We also calculate the absorption efficiency C, which can reach 95%, 97% and 95% at corresponding frequency by optimizing the structure＇s geometry parameters. Moreover, the proposed structure will be insensitive to the polarization of the incident wave due to the symmetry of the double cylindrical microcavities. The proposed optical metamaterial is a promising candidate as absorbing elements in scientific and technical applications due to its extreme confinement, multiband absorption and polarization insensitivity.

Near field enhancement and absorption properties of the double cylindrical microcavities based on triple-band metamaterial absorber

We numerically study the near field enhancement and absorption properties inside the double cylindrical microcavities based on triple-band metamaterial absorber. The compact single unit cell consists of concentric gold rings each with a gold disk in the center, and a metallic ground plane separated by a dielectric layer. At the normal incidence of electromagnetic radiation, the obtained reflection spectra show that the resonance frequencies of the double microcavities are 16.65 THz, 20.65 THz, and 25.65THz, respectively. We also calculate the values of contrast C （C = 1 - Rmin）, which can reach 95%, 97%, and 95% at the corresponding frequencies by optimizing the geometry parameters of structure. Moreover, we demon- strate that the multilayer structure with subwavelength electromagnetic confinement allows 104 -105-fold enhancement of the electromagnetic energy density inside the double cavities, which contains the most energy of the incoming electro- magnetic radiation. Moreover, the proposed structure will be insensitive to the polarization of the incident wave due to the symmetry of the double cylindrical microcavities. The proposed optical metamaterial is a promising candidate as an absorbing element in scientific and technical applications because of its extreme confinement, multiband absorptions, and polarization insensitivity.

Multi-Band Absorption Properties and Near-Field Enhancement in Mid-Infrared Based on the Interference Theory

We numerically study the multi-band absorption properties and near-field enhancement inside the microcavity based on the interference theory. The compact single unit cell consists of a gold square patch placed on the top of a metallic ground plane, separated by a dielectric layer. At the normal incidence of electromagnetic radiation, four bands of a maximum absorption of 98% are accomplished by appropriate sizes of the square patch. Furthermore, we demonstrate that the four bands, which are corresponding to the fundamental mode and higher modes of the standing wave, can be readily tuned in the mid-infrared region and associated with the near-field enhancement in the cuboid mierocavity. Since chemical and biological fingerprints of the common functional groups can be found in the mid-infrared region, we may readily tune the multi-bands of interest in the mid-infrared range and identify the molecular stretches of groups. Moreover, the proposed structure is insensitive to the polarization of the incident wave due to the complete rotational symmetry （C4 symmetry）. The unique properties of the optical metamaterial indicate that this approach is a promising strategy for surface-enhanced infrared absorption spectroscopy and for the tracking of characteristic molecular vibrational modes

Near-Field Enhancement and Absorption Properties of Metal-Dielectric-Metal Microcavities in the Mid-Infrared Range

An important property of optical metamaterials is the ability to concentrate light into extremely tiny volumes, so as to enhance their interaction with quantum objects. In this work, we numerically study the near-field en- hancement and absorption properties inside the cylindrical microcavities formed by a Au-GaAs-Au sandwiched structure. At normal incidence, the obtained reflection spectra show that the resonance wavelength of microcav- ities operates in the range of 5-5.S μm. We also calculate the contrast C （C = 1 - Rmln）, which can be increased to 97% by optimizing the structure＇s geometry parameters. Moreover, we demonstrate that the multilayer struc- ture with sub-wavelength electromagnetic confinement allows 10^3-10^4-fold enhancement of the electromagnetic energy density inside the cavities, which contains the most energy of the incident electromagnetic radiation and has a higher quality factor Q, indicating a narrower linewidth for surface enhanced molecular absorption spec- troscopy and the tracking of characteristic molecular vibrational modes in the mid-infrared region. The structure is insensitive to the polarization of the incident wave due to the symmetry of the cylindrical microcavities. The unique properties of the metal-dielectric-metal metamaterials will have potential applications in new plasmonic detectors, bio-sensing and solar cells, etc.

Synthesis of Crystallized BaWO₄Nanorods in a Microemulsion System

BaWO4 nanorods have been successfully synthesized in w/o microemulsion system containing barium ions via a simple reaction between Ba2+ and . The BaWO4 Nanorods were characterized by XRD, TEM, and SEM, respectively. Results showed that the solvents composition—volume ratio of 4-dioxane and distilled water—played the key role in the formation of BaWO4 Nanorods. Furthermore, the strong vibration at 925 cm﹣1 on its Raman spectrum indicated that the BaWO4 nanorods is good at stimulating Raman scattering in transient and steady-state, making it as a promising candidate material for laser with self-raman conversion of radiation inside the active medium.

Raman imaging analysis of intracellular biothiols independent of the aggregation of sensing substrates

The content of biothiols in cells is highly associated with the occurrence and development of several diseases.However,due to their active chemical properties,thiol-contained molecules are normally volatile during the detection process,rendering precise analysis of intracellular biothiols challenging.In this study,5,5’-dithiobis-(2-nitrobenzoic acid)(DTNB)is covalently modified on the surface of gold nanorods(AuNRs),constructing sensing substrates for in situ Raman imaging analysis of biothiols in cells.Au NRs are able to serve as ideal surface-enhanced Raman scattering substrates,and thus Raman signals of DTNB are greatly amplified by AuNRs.Meanwhile,the disulfide bond of DTNB can be broken by thiols,thereby releasing part of DTNB from the surface of AuNRs.As a result,three kinds of main biothiols are sensitively quantified with DTNB-modified AuNRs according to the variation of Raman signals,and DTNB-modified Au NRs exhibit far better analytical performance than a commercial probe.In addition,the sensing substrates can be readily delivered to cytoplasm with the transmembrane of Au NRs,and are capable of responding to biothiols in cells.Notably,the Raman approach is established by the breaking of chemical bonds rather than the aggregation of substrates,which is more inclined to analyze intracellular biothiols with a desirable spatial resolution.Therefore,fluctuation of biothiols in glioma cells is evidently observed via Raman imaging.Overall,this work provides an alternative strategy for designing Raman sensors to visualize active molecules in cells.

Chemical profiles and anticancer effects of saponin fractions of different polarity from the leaves of Panax notoginseng

AIM： To evaluate the chemical profiles and cytotoxic effects among the total saponin fraction （TSF）, 25% ethanol fraction （25EF）, 50% ethanol fraction （50EF）, and 85% ethanol fraction （85EF） prepared by macroporous resin from the leaves of Panax notoginseng. METHOD： The simultaneous determination of thirteen main saponins, as well as the chemical profiles of saponin fractions of different polarity, was made by HPLC-DAD and LC-ESI-MSn analysis. The cytotoxic effects were determined against KP4 cells （human pancreatic cancer）, NCI-H727 ceils （human lung cancer）, HepG2 cells （human hepatocellular cancer）, and SGC-7901 cells （human gastric adenocarcinoma）. RESULTS： Chemical analysis indicated that 85EF possessed the most abundant cytotoxic protopanaxadiol saponins, including the marker saponins F2, 20（R）-Rg3, 20（S）-Rg3, and Rh2. The MTT assay showed that 85EF also had the strongest cytotoxic effects among the four fractions. 25EF showed no anti-proliferative effects, while 50EF and TSF exhibited weak anti-proliferative activity. CONCLUSION： From the aspect of comprehensive utilization of resources, 85EF, enriched with low polarity PPD group saponins, is a new alternative source of anticancer saponins, and a promising botanical preparation for further anticancer studies.

Ultrasensitive determination of intracellular hydrogen peroxide by equipping quantum dots with a sensing layer via self-passivation

Abnormal expression of hydrogen peroxide(H_(2)O_(2))indicates the disorder of cell functions and is able to induce the occurrence and deterioration of numerous diseases.However,limited by its low concentration under pathophysiological conditions,intracellular H_(2)O_(2) is still difficult to be determined to date.Herein,to achieve sensitive quantification of H_(2)O_(2) in cells,CIS/ZnS/ZnS quantum dots(CIS/d-ZnS QDs)are retrofitted with ZnO shells via self-passivation.Different from the traditional self-passivation of QDs,self-passivation of CIS/d-ZnS QDs is realized facilely without the assistance of additional cation ions,which improves optical properties of QDs and equips the QDs with a sensing layer.As a result,the CIS/d-ZnS/ZnO QDs exhibit enhanced fluorescence emission and stability.Relying on the decomposition of ZnO and ZnS shells in the presence of H_(2)O_(2),aggregated QDs reveal exciton energy transfer effect,resulting in fluorescence quenching.On a basis of this principle,a fluorescence H_(2)O_(2) sensor is further established with the CIS/d-ZnS/ZnO QDs.To be noted,since the equipped ZnO shells are more susceptible to H2O2 than original ZnS shells,analytical performance of the fluorescence sensor is remarkably promoted by the self-passivation of QDs.Accordingly,H_(2)O_(2) can be measured in 5 orders of magnitude with a limit of detection(LOD)of 0.46 nM.Furthermore,because the ZnO shells improve H2O2-responsive selectivity and sensitivity,variation of H_(2)O_(2) in cells can also be quantified with the CIS/d-ZnS/ZnO QDs.In this work,sensitive detection of intracellular H_(2)O_(2) is enabled by equipping QDs with a sensing layer,which provides an alternative perspective of functionalizing nanomaterials for analytical applications.

Electromagnetic Resonant Properties of Metal-Dielectric-Metal （MDM） Cylindrical Microcavities

Optical metamaterials can concentrate light interaction with quantum objects. In this paper, into extremely tiny volumes to enhance their a cylindrical microcavity based on the Au-dielectric-Au sandwiched structure is proposed. Numerical study shows that the cylindrical microcavity has the strong ability of localizing light and confining 10^3- - 10^4-fold enhancement of the electromagnetic energy density, which contains the most energy of the incoming light. The enhancement factor of energy density G inside the cavity shows the regularities as the change in the thickness of the dielectric slab, dielectric constant, and the radius of gold disk. At the normal incidence of electromagnetic radiation, the obtained reflection spectra operate in the range from 4.8 μm to 6μm and with the absorption efficiency C （C=1-Rmin）, which can reach 99% by optimizing the structure＇s geometry parameters, and the dielectric constant. Due to the symmetry of the cylindrical microcavities, this structure is insensitive to the polarization of the incident wave. The proposed optical metamaterials will have potential applications in the surface enhanced spectroscopy, new plasmonic detectors, bio-sensing, solar cells, etc.