We propose all‐dielectric metasurfaces that can be actively re‐configured using the phase‐change material Ge2Sb2Te5 (GST) alloy. With selectively controlled phase transitions on the composing GST elements, metasurfaces can be tailored to exhibit varied functionalities. Using phase‐change GST rod as the basic building block, we have modelled metamolecules with tunable optical response when phase change occurs on select constituent GST rods. Tunable gradient metasurfaces can be realized with variable supercell period consisting of different patterns of the GST rods in their amorphous and crystalline states. Simulation results indicate a range of functions can be delivered, including multilevel signal modulating, near‐field coupling of GST rods, and anomalous reflection angle controlling. This work opens up a new space in exploring active meta‐devices with broader applications that cannot be achieved in their passive counterparts with permanent properties once fabricated.
Two new polyhydroxylated sterols, named verumbsteroids A and B ( 1 and 2 , resp.), along with seven known analog, 3 – 9 , were isolated from the gorgonian Verrucella umbraculum collected from the South China Sea. The structures and relative configurations of the new compounds were elucidated by comprehensive spectroscopic investigations. The absolute configuration of 1 was determined by using modified Mosher method with the acetonide derivative of 1 . Compounds 1 and 3 – 5 were found to show cytotoxicities against five human tumor cell lines (HL‐60, K562, HeLa, A‐549, and HCT‐116) with the IC50 values ranging from 2.76 to 9.62 μM . 相似文献
We report on the detection of trace quantities of melamine (MA) by a colorimetric method that exploits the conformational change of hemin G-quadruplex-DNAzyme. The addition of MA to hemin G-quadruplex-DNAzyme structure containing thymine bases causes the thymine in the DNAzyme to interact with MA via a stable triple H-bond and leads to a conformational change. This, in turn, affects the peroxidase-like activity of hemin which is determined colorimetrically at 450 nm by adding 3,3’,5,5’-tetramethylbenzidine and hydrogen peroxide. The method was applied to the colorimetric determination of MA over a wide range of concentrations (0.2 to 24 μM) with a detection limit of 80 nM. The effect also can be detected with bare eyes. The method was successfully applied to the determination of MA in spiked milk powder.
Figure
A novel, simple and rapid, visual colorimetric method is applied for the detection of melamine with a wide range of 8?×?10?7 M to 1?×?10?3 M and low detection limit of 2.7?×?10?7 M. 相似文献
Electrochemical detection of p-nitrophenol (P-NP) using a highly sensitive and selective platform based on single-walled carbon nanotube/pyrenecyclodextrin (SWCNT/PyCD) nanohybrids is described for the first time. The electrochemical performance of the SWCNT/PyCD nanohybrid electrode was fully compared with bare glassy carbon, single-SWCNT, single-PyCD, and SWCNT/CD (without pyrene rings) electrodes. Besides the techniques of cyclic voltammetry and chronoamperometric transients, differential pulse voltammetry (DPV) has been used for the detection of P-NP without any interference from o-nitrophenol (O-NP) at the potentials of -0.80 and -0.67 V, respectively. The SWCNT/PyCD nanohybrid electrode is highly sensitive, and it shows an ultrahigh sensitivity of 18.7 μA/μM toward P-NP in contrast to the values reported previously. The detection limit (S/N = 3) of the SWCNT/PyCD nanohybrid electrode toward P-NP is 0.00086 μM (0.12 ppb), which is well below the allowed limit in drinking water, 0.43 μM, given by the U.S. Environmental Protection Agency (EPA). The analytical performance of the SWCNT/PyCD nanohybrid electrode toward P-NP is superior to the existing electrodes. 相似文献
A promising electrochemical sensor was fabricated by the self-assembling of Pt nanoparticles (nano-Pts) on a chitosan (CS) modified glassy carbon electrode (GCE). A field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM) and electrochemical techniques were used for characterization of these composites. It has been found that nano-Pts are inserted into the CS layer uniformly, and have a larger surface area compared to the chitosan modified glassy carbon electrode. Electrocatalytic experiments for the oxidation of nitrite and the reduction of iodate have shown that nano-Pts/CS/GCE can decrease the over-potential and increase the faradic current, which can be used for the sensitive determination of nitrite and iodate. Moreover, the prepared modified electrode exhibits good reproducibility and stability, and it is possible that this novel electrochemical sensor can be applied in the sensing and/or biosensing field. 相似文献
Rapid identification of unknown microorganisms of clinical and agricultural importance is not only critical for accurate diagnosis of infections but also essential for appropriate and prompt treatment. We describe here a rapid method for microorganisms typing based on quantitative analysis of fatty acids by iFAT approach (Isotope-coded Fatty Acid Transmethylation). In this work, lyophilized cell lysates were directly mixed with 0.5M NaOH solution in d3-methanol and n-hexane. After 1 min of ultrasonication, the top n-hexane layer was combined with a mixture of standard d0-methanol derived fatty acid methylesters with known concentration. Measurement of intensity ratios of d3/d0 labeled fragment ion and molecular ion pairs at the corresponding target fatty acids provides a quantitative basis for hierarchical clustering. In the resultant dendrogram, the Euclidean distance between unknown species and known species quantitatively reveals their differences or shared similarities in fatty acid related pathways. It is of particular interest to apply this method for typing fungal species because fungi has distinguished lipid biosynthetic pathways that have been targeted for lots of drugs or fungicides compared with bacteria and animals. The proposed method has no dependence on the availability of genome or proteome databases. Therefore, it is can be applicable for a broad range of unknown microorganisms or mutant species. 相似文献
We report on the layer-by-layer assembly and electrochemical properties of 4-aminothiophenol (P-ATP) and ytterbium(III) trifluoromethanesulfonate hydrate (Yb(OTf)(3)) film supported on a gold surface. The fabricated film was characterised electrochemically using redox couples Fe(CN)(6)(3-/4-), complemented with imaging using atomic force microscopy (AFM). The electrocatalytic activity of the prepared electrodes was studied using cyclic and differential pulse voltammetries. Electrochemical measurements show that the P-ATP/Yb(OTf)(3) modified electrode has superb activity towards hydroquinone (HQ) oxidation and that there is a significant improvement in the electrode stability and reproducibility due to the covalent and coordination reactions. 相似文献