Search

Special attention is given to the development of rapid and sensitive detection of nitroaromatic explosives for homeland security and environmental concerns. As part of our contribution to the detection of nitroaromatic explosives, fluorescent materials (A), (B) and (C) were synthesized from the reaction of 1,2-diaminocyclohexane with pyrene-1-carbaldehyde, anthracene-9-carbaldehyde and 2-hydroxy-1-naphthaldehyde, respectively. The structures of the prepared fluorescent azomethine probes were confirmed using FTIR, 1H-NMR and 13C-NMR spectroscopies. The basis of the study is the use of the synthesized materials as fluorescent probes in the photophysical and fluorescence detection of some nitroaromatic explosives. Emission increases occurred due to aggregation caused by π-π stacking in synthesized azomethines. To measure the nitroaromatic detection capabilities of fluorescence probes, fluorescence titration experiments were performed using the photoluminescence spectroscopy. It was observed that compound A containing pyrene ring provided the best emission intensity-increasing effect due to aggregation with the lowest LOD value (14.96 μM) for the sensing of 4-nitrophenol. In compounds B and C, nitrobenzene with the lowest LOD (16.15 μM and 23.49 μM respectively) caused the most regular emission increase, followed by picric acid. [ABSTRACT FROM AUTHOR]

Herein, dual-emission carbon dots (DE-CDs) were synthesized using a one-pot hydrothermal method. DE-CDs exhibited two well-separated peaks at 433 and 513 nm under ultraviolet excitation. The prepared DE-CDs offer selective detection of Fe3+ ions via inner filter effect (IFE) and Pb2+ ions via aggregation-induced enhancement (AIE). The obtained DE-CDs showed a good affinity for both Fe3+ and Pb2+ ions in the presence of various interfering ions. The limits of detection were 0.797 ppm and 4.739 ppm for Pb2+ and Fe3+, respectively. The finding reveals the huge potential of DE-CDs for the selective detection of multiple targets in one solution. [ABSTRACT FROM AUTHOR]

For quantitation of amlodipine (AML) and perindopril (PER) in their authentic, pharmaceutical formulations and spiked human plasma, a simple, sensitive, validated and inexpensive spectrofluorimetric method has been developed. The proposed method is developed to be based on quantitative quenching effect of two antihypertensive drugs on Eosin Y's native fluorescence which was achieved by developing binary complexes between each of the cited drugs in an acidic environment using acetate buffer (pH 4.4) with Eosin Y. Fluorescence quenching was recorded at 544 nm after excitation at 425 nm. For AML and PER, calibration curves were obtained over the range of 0.3–3.0 µg/mL and 0.2–2.0 µg/mL, respectively, with correlation coefficients of 0.9993 and 0.9995, respectively. The developed method was validated according to ICH guidelines. The proposed spectrofluorimetric method is regarded new and sensitive. As a result, the proposed method might be used to estimate the quality of the cited drugs in their pharmaceutical formulations and biological fluid. [ABSTRACT FROM AUTHOR]

Rapid and selective detection of nitroaromatic explosives is very important for public safety, life, and environmental health. Current instrumental techniques suffer from high cost and poor site used. In order to investigate fluorescence sensing of nitroaromatics, we prepare a new small fluorescence probe derived from pamoic acid. This study covers the synthesis of Pamoic acid based [diisopropyl 4,4'-methylenebis(3-methoxy-2-naphthoate)] (2) material and characterization of its structure. The methylation of Pamoic acid ester, which we have successfully synthesized in our previous studies, was carried out in this study. Determination of the photophysical and fluorescent nitroaromatic detection properties of the compound forms the basis of the study. Structural characterization of the synthesized compound [diisopropyl 4,4'-methylenebis(3-methoxy-2-naphthoate)] (2) was characterized using spectroscopic methods. In addition, Molecular structure of the synthesized compound was determined by single crystal X-ray diffraction studies. In the final step, compounds [diisopropyl 4,4'-methylenebis(3-hydroxy-2-naphthoate)] (1) and [diisopropyl 4,4'-methylenebis(3-methoxy-2-naphthoate)] (2) were tested as fluorescent probes for the detection of some nitroaromatic explosives. It is seen that Nitrobenzene provides the best quenching effect on the compound [diisopropyl 4,4'-methylenebis(3-hydroxy-2-naphthoate)] (1) containing the -OH group, with lowest the limit of detection (LOD) value. It was observed that Picric acid provided the best quenching effect with lowest the limit of detection (LOD) value in the compound [diisopropyl 4,4'-methylenebis(3-methoxy-2-naphthoate)] (2) obtained by methylation of the -OH group in the compound [diisopropyl 4,4'-methylenebis(3-hydroxy-2-naphthoate)] (1). [ABSTRACT FROM AUTHOR]

We investigate the fluorescence from submonolayer rhodamine 6G molecules near gold nanoparticles (NPs) at a well-controlled poly (methyl methacrylate) (PMMA) interval thickness from 1.5 to 21 nm. The plasmonic resonance peaks of gold NPs are tuned from 530 to 580 nm by the PMMA spacer of different thicknesses. Then, due to the plasmonic resonant excitation enhancement, the emission intensity of rhodamine 6G molecules at 562 nm is found to be enhanced and shows a decline as the PMMA spacer thickness increases. The variation of spectral intensity simulated by finite-difference time-domain method is consistent with the experimental results. Moreover, the lifetime results show the combined effects to rhodamine 6G fluorescence, which include the quenching effect, the barrier effect of PMMA as spacer layer and the attenuation effect of PMMA films. [ABSTRACT FROM AUTHOR]

A novel hyperbranched mono-component intumescent flame retardant poly(piperazine methylphosphonic acid pentaerythritol ester) defined as PPMPPE was synthesized, and its chemical structure was characterized. The individual PPMPPE was incorporated into polyethylene (PE), and the fire resistance, thermal properties and flame retardant mechanism of PE composites were investigated in detail. The 1.6-mm PE/PPMPPE sheets fulfilled UL-94 V-0 level during vertical burning tests, and the limiting oxygen index was 25.3% when the loading amount of PPMPPE was 22 wt%. PPMPPE was completely melted, and the expanded char layer was generated on heating. The addition of PPMPPE stimulated the degradation and charring of PE composites in advance and improved the residual mass and thermal stability of FR-PE at high temperature. The cone calorimeter tests verified that the heat release rate and total heat release of PE/PPMPPE composites were obviously declined. PPMPPE exerted shielding effect in condensed phased and quenching active free radicals in the gas phase. The flame was constrained and even extinguished. Thus, PE composites fulfilled superior flame retardant properties. [ABSTRACT FROM AUTHOR]

Graphdiyne (GDY) as an emerging carbon nanomaterial has attracted increasing attention because of its uniformly distributed pores, highly π-conjugated, and tunable electronic properties. These excellent characteristics have been widely explored in the fields of energy storage and catalysts, yet there is no report on the development of sensors based on the outstanding optical property of GDY. In this paper, a new sensing mechanism is reported built upon the synergistic effect between inner filter effect and photoinduced electron transfer. We constructed a novel nanosensor based upon the newly-synthesized nanomaterial and demonstrated a sensitive and selective detection for both Fe3+ ion and ascorbic acid, enabling the measurements in real clinical samples. For the first time fluorescent graphdiyne oxide quantum dots (GDYO-QDs) were prepared using a facile ultrasonic protocol and they were characterized with a range of techniques, showing a strong blue-green emission with 14.6% quantum yield. The emission is quenched efficiently by Fe3+ and recovered by ascorbic acid (AA). We have fabricated an off/on fluorescent nanosensors based on this unique property. The nanosensors are able to detect Fe3+ as low as 95 nmol L−1 with a promising dynamic range from 0.25 to 200 μmol L−1. The LOD of AA was 2.5 μmol L−1, with range of 10–500 μmol L−1. It showed a promising capability to detect Fe3+ and AA in serum samples. [ABSTRACT FROM AUTHOR]

A polymer imprinted with acrylamide (AM-MIP) was synthesized on the surface of graphene oxide by surface polymerization of propionamide (serving as a dummy template), methacrylic acid (as the functional monomer) and ethylene glycol dimethacrylate (the cross-linker). ZnS quantumdots (QDs) doped with Mn(II) ions were added to theAM-MIP to act as fluorescence source. The AM-MIP was characterized by infrared spectroscopy, scanning electron microscopy and X-ray powder diffraction, suggesting that the imprinted layer was successfully grafted onto graphene oxide. The fluorescence of the doped QDs is quenched when loading the AM-MIP with acrylamide (AM), and the quenching effect is much stronger than the non-imprinted polymer (AMNIP). Quenching follows Stern-Volmer kinetics. The combination of imprinting and fluorometric detection offer AM-IIP capability to accumulate trace AM before direct determination, omitting desorption and separation or other methods. The excitation and emission spectra of AM-MIP peak at 325 nm and 601 nm, respectively. Under optimal conditions, fluorescence drops linearly in the 0.5-60 µmol⋅L-1 acrylamide concentration range, and the detection limit is 0.17 µmol⋅L-1. The method has been applied to the determination ofAMin spiked water samples and gave recoveries in the range from 100.2 to 104.5%, with relative standard deviations in the 1.9 to 3.9% range. In our perception, the AM-MIP presented here is a promising fluorescent probe for the detection of trace acrylamide in food. [ABSTRACT FROM AUTHOR]

The characterization of quantum dots (QDs) and their conjugates with bovine serum albumin was done using on-a-chip electrophoresis. Under optimal conditions, bioconjugated QDs were successfully separated from free QDs within ≈10 min. Influence of coupling agent on a quenching of QD fluorescence intensity caused by conjugation to a protein was studied. When using two-step procedure combining 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide with N-hydroxysulfosuccinimide, the highest quenching effect was notable. We showed that QDs and capillary electrophoresis on a chip can be applied as a sensitive technique for the detection of biological molecules. The characteristics of this method are simplicity, small sample and reagent requirements, and high efficiency of separation. Graphical abstract: [ABSTRACT FROM AUTHOR]

The series of Bi co-doped YPO : Eu nanophosphors were successfully synthesized by the slow evaporation method. Bi-doped and un-doped YPO : Eu phosphors were characterized by using powder X-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. Photoluminescence (PL) properties and decay time of phosphors were studied at room temperature. The YPO : Eu and Bi exhibit enhancement in PL intensity and quenched at 0.5 mol% of Bi ions. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) in wastewater can be characterized using fluorescence excitation-emission matrix and parallel factor (EEM-PARAFAC) analysis. Wastewater from animal farms or pharmaceutical plants usually contains high concentration of antibiotics. In this study, the quenching effect of antibiotics on the typical components of DOM was explored using fluorescence EEM-PARAFAC analysis. Four antibiotics (roxarsone, sulfaquinoxaline sodium, oxytetracycline, and erythromycin) at the concentration of 0.5∼4.0 mg/L and three typical components of DOM (tyrosine, tryptophan, and humic acid) were selected. Fluorescence quenching effects were observed with the addition of antibiotics. Among these four antibiotics, roxarsone (2.9∼20.2 %), sulfaquinoxaline sodium (0∼32.0 %), and oxytetracycline (0∼41.8 %) led to a stronger quenching effect than erythromycin (0∼8.0 %). From the side of DOM, tyrosine and tryptophan (0.5∼41.8 %) exhibited a similar quenching effect, but they were higher than humic acids (0∼20.2 %) at the same concentration of antibiotics. For humic acid, a significant quenching effect was observed only with the addition of roxarsone. This might be the first report about the fluorescence quenching effect caused by antibiotics. The results from this study confirmed the interference of antibiotics on the fluorescence intensity of the main components of DOM and highlighted the importance of correcting fluorescence data in the wastewater containing antibiotics. [ABSTRACT FROM AUTHOR]

In this paper, we report the production of C[C] with the highest specific radioactivity to date by improving of previously reported method. To avoid the loss of C, the porous carbon after adsorbing C labeled furan resin was sintered by 'Baking' method instead of heating at 1,000 °C in the electric furnace. As a result of this improvement, the specific radioactivity of the produced C[C] was found to be 0.958 MBq/mg (18.7 mCi/mmol). This is the highest specific radioactivity among those reported to date. [ABSTRACT FROM AUTHOR]

Single-event transient pulse quenching (Quenching effect) is employed to effectively mitigate W (SET pulse width). It enhanced along with the increased charge sharing which is norm for future advanced technologies. As technology scales, parameter variation is another serious issue that significantly affects circuit's performance and single-event response. Monte Carlo simulations combined with TCAD (Technology Computer-Aided Design) simulations are conducted on a six-stage inverter chain to identify and quantify the impact of charge sharing and parameter variation on pulse quenching. Studies show that charge sharing induce a wider W spread range. The difference of W range between no quenching and quenching is smaller in NMOS (N-Channel Metal-Oxide-Semiconductor Field-Effect Transistor) simulation than that in PMOS' (P-Channel Metal-Oxide-Semiconductor Field-Effect Transistor), so that from parameter variation view, quenching is beneficial in PMOS SET mitigation. The individual parameter analysis indicates that gate oxide thickness (TOXE) and channel length variation (XL) mostly affect SET response of combinational circuits. They bring 14.58% and 19.73% average W difference probabilities for no-quenching cases, and 105.56% and 123.32% for quenching cases. [ABSTRACT FROM AUTHOR]

Transition metal ions (Pb, Zn, Cd, Co, Mn, Cu, Ni, Hg, Ag, Fe) in water are used to quench emission of 2-(6-oxido-6H-dibenz 〈c,e〉 〈1,2〉 oxaphosphorin-6-yl)-1,4-phenylene-bis(p-pentyloxylbenzoate)s (MD5) with aggregation-induced emission enhancement (AIEE) in water-acetonitrile (AN) mixture (80:20 by volume). Among all metal ions, Fe exhibits the highest quenching efficiency on AIEE of MD5 even when the concentration of Fe is lower than 1×10 mol/L. The quenching efficiency of Hg is lower than that of Fe at the same concentration, though MD5 is used to detect Hg efficiently, too. To other metal ions, low quenching efficiency has few relations with a wider concentration range. The UV absorbance spectra show only red shift of absorbance wavelength in the presence of Hg and Fe, which indicates a salt-induced Jaggregation. SEM photos reveal larger aggregation and morphological change of nanoparticles of MD5 in water containing Hg and Fe, which reduce the surface area of MD5 emission for further aggregation. The selective quenching effect of transition metal ions to emission of MD5 has a potential application in chemical sensors of some metal ions. [ABSTRACT FROM AUTHOR]