Gold Sandwich Research Articles

MXene Quantum Dot/Polymer Hybrid Structures with Tunable Electrical Conductance and Resistive Switching for Nonvolatile Memory Devices

AbstractLow‐dimensional MXene materials including MXene quantum dots (MQDs) and nanosheets have attracted extensive attention owing to their unique structures and novel properties, but their most attractive features are still less explored than expected. A systematic study of the memory effects of MQD‐based electronics is reported. Monodisperse MQDs are prepared by using a one‐step facile hydrothermal synthetic method. By varying the MQD content in polyvinylpyrrolidone (PVP) hybrid composite films, the electrical conductance of an indium tin oxide (ITO)/MQD‐PVP/gold (Au) sandwich structure can be tuned precisely from insulator behavior to irreversible resistive switching, reversible resistive switching, and conductor behavior. These irreversible and reversible resistive switches are capable of exhibiting write‐once‐read‐many times (WORM) and flash memory effects, respectively. Both types of devices operate stably under retention testing, with a high on/off current ratio up to 100. The tunable memory and transient features of these hybrid films are likely due to MQD charge trapping due to their quantum confinement and dissolvability of memristive components. The results suggest that MXene nanomaterials are promising as resistive switching trigger for emerging nonvolatile memories for data storage, specially data storage security.

Novel polyclonal antibody-based rapid gold sandwich immunochromatographic strip for detecting the major royal jelly protein 1 (MRJP1) in honey.

Honey adulteration is becoming increasingly alarming incidents in food safety. Monitoring and detecting adulteration face greater challenges. Honey contains the major royal jelly proteins (MRJP) secreted by bee workers. To detect honey adulteration fast and accurately, a rapid gold sandwich immunochromatographic strip (GSIS) was developed based on two specific polyclonal antibodies (PoAbs) against the MRJP1, the most abundant protein of all MRJPs. We determined the best of pH value (pH 8.6) and PoAb SP-1 amount (5 μg/mL) in conjunction with colloidal. The cut-off value (sensitivity) of GSIS in detecting MRJP1 is 2.0 μg/mL in solution. Validation analysis with RJ, milk vetch honey, acacia honey and honey adulteration containing rice syrup and corn syrup with different ratios demonstrated that the GSIS could show consistent Test line (T line) when the test samples contain more than 30% pure honey or MRJP1 0.4 mg/g. The validation results by isotope ratio mass spectrometry on the same pure and all adulteration milk vetch honey samples showed the same information of GSIS test. The qualitative assay GSIS provided a valuable new way for honey authenticity and laid the foundation for the future application of GSIS with monoclonal antibodies in honey authentication.

Copper–gold sandwich structures on PE and PET and their SERS enhancement effect

In this paper we have investigated the SERS effect of gold–copper sandwich structures i.e. the coupling between surface plasmon polaritons supported by the gold grating and localized surface plasmons excited on the grafted copper nanoparticles.

A plasmon-tuned ‘gold sandwich’ for metal enhanced fluorescence in silica coated NaYF4:Yb,Er upconversion nanoparticles

The low quantum yield of luminescence from lanthanide-doped up-conversion nanoparticles (UCNPs) has been enhanced by using an optimized ‘gold sandwich’ with a transparent top layer and a reflecting bottom layer at 980 nm excitation. Erbium (Er)-doped UCNPs, with a NaYF4:Yb,Er core, were synthesized by a thermal decomposition process and coated with silica to assist in metal-enhanced fluorescence (MEF). A bottom layer of thick coalesced gold island film, acting as a mirror, increases the optical path length of the 980 nm radiation through the UCNP layer dispersed on it. This layer enhances the UCNPs' 540 nm green emission by a factor of 5–8 compared to that in the absence of the gold reflector. A thin nanoparticle-like gold layer on top of the UCNPs, with a surface plasmon absorption around ∼550 nm, completes the sandwich, which augments the luminescence enhancement by another factor of ∼2.5, thus taking the net enhancement factor to ∼13–19 when compared to the luminescence in the absence of the gold-sandwich. The surface plasmon absorption in the top gold layer enhances the local electric field at the UCNPs to promote their radiative decay. Compared to previous reports, mostly for the solution state, the current case study is a solid state measurement.

Quantitative, single-step dual measurement of hemoglobin A1c and total hemoglobin in human whole blood using a gold sandwich immunochromatographic assay for personalized medicine

We describe a gold nanoparticle-based sandwich immunoassay for the dual detection and measurement of hemoglobin A1c (HbA1c) and total hemoglobin in the whole blood (without pretreatment) in a single step for personalized medicine. The optimized antibody-functionalized gold nanoparticles immunoreact simultaneously with HbA1c and total hemoglobin to form a sandwich at distinctive test lines to transduce visible signals. The applicability of this method as a personal management tool was demonstrated by establishing a calibration curve to relate % HbA1c, a useful value for type 2 diabetes management, to the signal ratio of captured HbA1c to all other forms of hemoglobin. The platform showed excellent selectivity (100%) toward HbA1c at distinctive test lines when challenged with HbA0, glycated HbA0 and HbA2. The reproducibility of the measurement was good (6.02%) owing to the dual measurement of HbA1c and total hemoglobin. A blood sample stability test revealed that the quantitative measurement of % HbA1c was consistent and no false-positive results were detected. Also, this method distinguished the blood sample with elevated HbF from the normal samples and the variants. The findings of this study highlight the potential of a lateral flow immunosensor as a simple, inexpensive, consistent, and convenient strategy for the dual measurement of HbA1c and total Hb to provide useful % HbA1c values for better on-site diabetes care.

The measurement of electron number density in helium micro hollow gas discharge using asymmetric He I lines

The electron number density Ne in helium micro hollow gas discharge (MHGD) is measured by means of optical emission spectroscopy (OES) techniques. The structure of MHGD is a gold–alumina–gold sandwich with 250 μm alumina thickness and 100 μm diameter hole. The electron temperature Te and gas temperature Tg in the discharge is determined using the relative intensity of He I lines and R branch lines in the frame of BP technique, respectively. The simple procedure based on spectral line broadening theory was developed in MATLAB to generate synthetic neutral line asymmetric profiles. The synthetic profiles were compared with an experimental He I 447.1 nm and He I 492.2 nm line to obtain Ne from the centre of a micro hollow gas discharge (MHGD) source in helium. The Ne results were compared with Ne values obtained from the forbidden-to-allowed (F/A) intensity ratio technique. The comparison confirmed higher Ne determined using a F/A ratio due to large uncertainty of the method. Applying the fitting formula for a He I 492.2 nm line derived from computer simulation (CS) gives the same Ne values as the one determined using the MATLAB procedure in this study. The dependence of Ne on gas pressure and electric current is investigated as well.

New Nano Architecture for SERS Applications.

Silver silica gold sandwich nanoparticles were synthesized by a multistep seeded growth process and were characterized by UV-vis spectroscopy, transmission electron microscopy, and X-ray diffraction. Gold islands allow passage of light through the crevices into the silica layer, and the silver core-silica shell behaves like a mirror, thus reflecting the light incident on it. These structures facilitate light amplification due to mixing of light waves from the multiple reflections. Sandwich nanoparticles show SERS enhancement of ∼10(6). This enhancement factor is 6-fold larger in magnitude than that of similar nanoparticles without the silver core under identical experimental conditions.

The prevalence of HIV infection and the risk factors among MSM in 4 cities, China

To access the prevalence of HIV infection and the associated factors among urban MSM in China. Participants were recruited using respondent driven sampling and snowball sampling method in Beijing, Harbin, Zhengzhou and Chengdu city. A face-to-face questionnaire was administrated to collect relevant demographic and ethological data; 5 ml venous blood sample was taken from each subject to measure HIV antibody in serum (samples were first screened by colloidal gold, latex chromatographic and double-antigen sandwich ELISA method, positive samples were further confirmed by immunoblotting method). The characteristics of HIV infection was described and the risk factors were analyzed. A total of 1864 MSM were recruited and the prevalence of HIV was 6.7% (125/1864). It was 9.5% (24/252) among MSM older than 39 years and it was 1.9% (2/105) among those less than 20 years old. The prevalence was 8.4% (31/371) among MSM with junior level education and was 4.8% (41/858) among those with college level education. It was 10.3% (35/340) among MSM with sexual partner old than him for over 10 years while it was 5.0% (58/1168) among those having sexual partner within 10 years older. The prevalence of HIV infection was 8.9% (61/695) among MSM with unprotected receptive anal sex and it was 5.5% (64/1169) among those without unprotected receptive anal sex. The risk factors independently associated with HIV infection included being older than 39 years (OR = 6.5, 95%CI: 1.5 - 28.7), with junior or lower level education (OR = 1.8, 95%CI: 1.2 - 2.7), having sexual partner older than himself for over 10 years (OR = 2.1, 95%CI: 1.3 - 3.3) and having unprotected receptive anal intercourse (OR = 1.6, 95%CI: 1.1 - 2.4). MSM had a high rate of HIV infection. Older age, lower level education, having older sexual partner and unprotected receptive anal intercourse were related to HIV infection.

Two-Dimensional Combinatorial Investigation of Raman and Fluorescence Enhancement in Silver and Gold Sandwich Substrates

We present a two-dimensional combinatorial investigation of resonant Raman and fluorescence enhancement in silver and gold sandwich structures. Gold and silver, separated by a thin alumina spacer layer, were deposited in two orthogonal gradients, with a thickness from a few hundred to a few nanometers, covering the range from island films through percolation to continuous films. Resonant Raman spectra of Rhodamine 6G adsorbed on the substrate surface were recorded in a 13 × 13 matrix using an automated scanning stage. The most Raman-active substrates were composed of silver (8 nm)-on-alumina (7 nm)-on-gold (5 nm). They consist of both gold and silver discontinuous nanoparticle films separated by alumina, forming a labyrinthine network structure. Gold-on-alumina-on-silver substrates also displayed increased activity compared with that of gold-on-alumina substrates. Maximum fluorescence intensity was observed on silver films nominally 35 nm thick covered by 8 nm of alumina. The efficacy of the combinatorial method to correlate multiple aspects of the measurements and reduce uncertainties is demonstrated.

Synthesis and characterization of new monomeric and polymeric phthalocyanines

AbstractMonomeric (M = 2Li or 2H) and polymeric (M = 2H, Zn, Cu, Co, or Ni), where M is metal or hydrogen, phthalocyanines were prepared by the tetramerization reaction of bisphthalonitrile monomer with appropriate materials. The electrical conductivities of the polymeric phthalocyanines, which were measured as gold sandwiches, were found to be 10−10–10−7 S/cm in vacuo and in air. The binding property of a Co‐containing polymeric phthalocyanine (10) toward alkali, alkaline‐earth, and some heavy cations was studied in tetrahydrofuran. The extraction affinity of 10 for K+ was found to be the highest in the heterogeneous phase extraction experiments. The disaggregation property of a Ni‐containing polymeric phthalocyanine (11) was investigated with K+, Na+, and NH4+ cations. The intrinsic viscosities of all polymers were also measured by means of viscometry. All the novel compounds were characterized with elemental analysis, ultraviolet–visible, Fourier transform infrared, NMR, and mass spectrometry spectral data, and differential thermal analysis/thermogravimetry. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Gold nanoparticle aggregation-based highly sensitive DNA detection using atomic force microscopy

The potential ability of atomic force microscopy (AFM) as a quantitative bioanalysis tool is demonstrated by using gold nanoparticles as a size enhancer in a DNA hybridization reaction. Two sets of probe DNA were functionalized on gold nanoparticles and sandwich hybridization occurred between two probe DNAs and target DNA, resulting in aggregation of the nanoparticles. At high concentrations of target DNA in the range from 100 nM to 10 microM, the aggregation of gold nanoparticles was determined by monitoring the color change with UV-vis spectroscopy. The absorption spectra broadened after the exposure of DNA-gold nanoparticles to target DNA and a new absorption band at wavelengths >600 nm was observed. However, no differences were observed in the absorption spectra of the gold nanoparticles at low concentrations of target DNA (10 pM to 10 nM) due to insufficient aggregation. AFM was used as a biosensing tool over this range of target DNA concentrations in order to monitor the aggregation of gold nanoparticles and to quantify the concentration of target DNA. Based on the AFM images, we successfully evaluated particle number and size at low concentrations of target DNA. The calibration curve obtained when mean particle aggregate diameter was plotted against concentration of target DNA showed good linearity over the range 10 pM to 10 nM, the working range for quantitative target DNA analysis. This AFM-based DNA detection technique was three orders of magnitude more sensitive than a DNA detection method based on UV-vis spectroscopy.

Novel phthalocyanine polymers with very flexible pentathiatetraethylene units

A series of polymeric metal-free and metallophthalocyanine (M = 2H, Ni, Co, Fe, Pb, Cu and Zn) polymers were prepared by polymeric tetramerization reaction of bisphthalonitrile monomer with proper materials. The Co–phthalocyanine polymer was prepared by two different methods. The metal-free ( 3) and the Co-containing phthalocyanine polymer ( 5) were chemically doped with iodine (I 2) and nitrosyl tetrafluoroborate (NOBF 4), respectively. The electrical conductivities of the polymeric phthalocyanines measured as gold sandwiches were found to be 10 −8–10 −4 S cm −1 in vacuum and in argon. The electrical conductivities of I 2-doped metal-free phthalocyanine ( 3a) and NOBF 4-doped Co–phthalocyanine ( 5a) polymers were found to be approximately 110 and 89 times higher than those of undoped versions, respectively. The extraction ability of 3 was also evaluated in tetrahydrofuran using several transition metal picrates such as Ag +, Hg 2+, Pb 2+, Cd 2+, Cu 2+ and Zn 2+. The extraction affinity of 3 for Ag + was found to be highest in the heterogeneous phase extraction experiments. The aggregation and disaggregation properties of 3 were investigated with silver(I), mercury(II) and methanol as solvent. All the novel compounds were characterized by using elemental analysis, UV–vis, FT-IR, NMR and MS spectral data and DTA/TG.

Synthesis and characterization of new polymeric phthalocyanines substituted with diaza-18-crown-6 macrocycles through ethyleneoxy bridges

A tetranitrile monomer was synthesized by nucleophilic aromatic substitution of N, N′-bis(2-hydroxyethyl)-4,13-diaza-18-crown-6 onto 4-nitrophthalonitrile. A series of polymeric metal-free and metallophthalocyanine (M = 2H, Zn, Cu, Co and Ni) polymers was prepared by polymeric tetramerization reaction of the tetranitrile monomer with proper materials. The electrical conductivities of the polymeric phthalocyanines measured as gold sandwiches were found to be ∼10 −9–10 −4 S cm −1 in a vacuum and in argon. The extraction ability of the metal-free polymeric phthalocyanine was evaluated in tetrahydrofuran using several alkali metal picrates such as Li +, Na +, K + and Cs +. The extraction affinity of the metal-free polymeric phthalocyanine for K + was found to be highest in the heterogeneous solid–liquid phase extraction experiments. The disaggregation property of the metal-free polymeric phthalocyanine was investigated with sodium, potassium and ammonium ions and methanol. All the novel compounds were characterized by using elemental analysis, UV–Vis, FT-IR, NMR and MS spectral data and DTA/TG.

Novel Network Polymeric Phthalocyanines: Synthesis and Characterization

AbstractSummary: New p‐xylylenebis‐(oxa‐thia‐propan) bridged metal‐free and metallophthalocyanine polymers were synthesized. The metal‐free phthalocyanine polymer (3) was prepared by the reaction of a tetranitrile monomer with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) in pentanol. Ni‐ and Co‐phthalocyanine polymers were prepared by reaction of the tetranitrile compound with the chlorides of Ni(II) and Co(II) in quinoline. Cu‐ and Zn‐phthalocyanine polymers were prepared by the reaction of the tetranitrile compound with the acetates of Cu(II) and Zn(II) and DBU in amyl alcohol. Yellow PbO and Fe(CO)5 were used to prepare Pb‐ and Fe‐analog polymers, respectively. The Co‐phthalocyanine polymer was also prepared using ethylene glycol instead of quinoline in the presence of the catalyst ammonium molybdate. (3) was chemically doped with iodine. The electrical conductivities of the polymeric phthalocyanines measured as gold sandwiches were found to be 10−9–10−7 S · cm−1 in a vacuum and in argon. The electrical conductivity of iodine doped metal‐free phthalocyanine (3a) was found to be approximately 57 times higher than that of the undoped version. The extraction ability of (3) was also evaluated in THF using transition metal picrates, such as Ag1+, Hg2+, Pb2+, Cd2+, Cu2+ and Zn2+. The extraction affinity of (3) for Ag1+ was found to be highest in the heterogeneous phase extraction experiments. All the novel compounds were characterized using elemental analysis, UV‐Vis, FT‐IR, NMR and MS spectral data and DSC.Synthesis of new network polymeric phthalocyanines.magnified imageSynthesis of new network polymeric phthalocyanines.

DC conductivity in RF magnetron sputtered gold–silicon nitride–gold sandwich structures

Our recent work on RF magnetron sputtered silicon nitride films has been extended to include the effects of gold electrodes on the electrical conductivity. The sandwich structure films were RF sputtered from a silicon nitride target at a power of 100 W using N 2 as the sputtering gas. In agreement with the results for samples with Al electrodes, the capacitance was independent of the applied voltage, indicating that Schottky barriers were absent at the interfaces and that Au provided an ohmic contact to the silicon nitride films. Measurements of capacitance as a function of inverse thickness showed a geometric variation, with a relative permittivity value of 6.8, slightly higher than in the case of Al electrodes. When DC voltages exceeding approximately 2 V were applied, there was a decrease in the current and the establishment of differential negative resistance behaviour. This is typical of electroforming, a process which is known to appear in thin film insulators having certain noble metal electrodes. At low voltages, Ohm's law was obeyed, followed by a field lowering process, with coefficient β∼1.95×10 −5 eV m 1/2 V −1/2. This was identified with Poole–Frenkel emission rather than the Schottky effect, since the electrodes were ohmic contacts. Such behaviour was in contrast to that observed in sputtered silicon nitride films with Al electrodes, which showed space-charge limited conductivity but had similarities to results for ion beam synthesised silicon nitride films, where the measured field lowering coefficient was also smaller than the theoretical value.

Synthesis and characterization of new tetraaza-bridged polymeric phthalocyanines

New tetraaza-bridged metal-free and metal phthalocyanine polymers were prepared. The metal-free phthalocyanine polymer was obtained by the reaction of 4,4′-(octane-1,5,8,12-tetra-p-tolysulphonyl-1,5,8,12-tetraamine)-diphthalonitrile with hydroquinone. The chlorides of Cu(II), Ni(II) and Co(II) were employed in order to synthesize the corresponding metal-phthalocyanine polymer, Zn(CH 3CO 2) 2 was used for the preparation of the zinc phthalocyanine, and Fe(CO) 5 was used for the preparation of the Fe-analog. For the preparation of the Co-containing polymer, ammonium molybdate had to be added as catalyst. The new polymers have been characterized by elemental analyses, IR, NMR and UV-VIS spectroscopy. The electrical conductivities of the phthalocyanine polymers measured as gold sandwiches are about 10 −9 Sm −1 in vacuo and 10 −8 Sm −1 in air.

Synthesis and properties of 1,5-dithio-3-oxa-pentanediyl bridged polymeric phthalocyanines

Oxa-thio bridged metal-free and metal phthalocyanine polymers were prepared. Metal-free phthalocyanine polymer (H 2Pc) and metal phthalocyanine polymers (Ni, Cu, Co, Zn or Fe) carrying dithio-oxa bridged were synthesized from 3,3′-4,4′-tetracyanodiphenyl-1,5-dithiopenanyl-oxa-ether and hydroquinone or the corresponding anhydrous metal salts [NiCl 2, CuCl, CoCl 2, Zn(CH 3CO 2) 2 or Fe(CO) 5]. The model phthalocyanine compounds were characterized by IR, UV/VIS and DTA. The electrical conductivities of the phthalocyanines measured as gold sandwiches are about 10 −10 Sm −1 in vacuo and in air.

Cadmium telluride/doped poly( N-epoxypropylcarbazole) structure of a solid-state photovoltaic cell

A solid-state photovoltaic cell based on a polycrystalline cadmium telluride/doped poly( N-epoxypropylcarbazole)/gold sandwich structure has been proposed for converting luminous energy to electrical energy with an efficiency of up to 3.2% and a spectral sensitivity range spanning the UV, the visible and the near-infrared.

Synthesis, characterization and electrical properties of phthalocyanines substituted with 17-membered trioxadiaza macrocycles

New phthalocyanines (M = Cu, Zn, Ni, Co or 2H) substituted with four 17-membered trioxadiaza macrocycles have been prepared. Detosylation of aza groups with concentrated sulfuric acid simultaneously leads to sulfonated groups on the aromatic rings of the macrocyclic substituents. While the N-tosylated derivatives are soluble in organic solvents, the detosylated ones are extremely soluble in water. The electrical conductivities of the phthalocyanines measured as gold sandwiches are about 10–12 S m–1in vacuo and show some increase in the presence of dry air.

Islamic gold sandwich glass: some fragments in the David Collection, Copenhagen

Sandwich glass is the product of a technique practised from antiquity. Essentially, decoration is achieved by laying gold to a glass surface, patterning this gold in various ways, and then adding a second layer of glass to encapsulate the gold pattern. The technique seems to have been employed only rarely by craftsmen in Islamic areas; certainly surviving examples are rare.