Trace detection of hormones and sulfonamides in viscous cosmetic products by neutral desorption extractive electrospray ionization tandem mass spectrometry

A sensitive method based on a geometry-independent neutral desorption (GIND) in combination with extractive electrospray ionization mass spectrometry (EESI-MS) has been developed for fast detection of illicit additives such as sulfonamides and hormones in highly viscous cosmetic products. The method gave a low limit of detection (LOD) (in the range of 0.001-1 ng/g), acceptable relative standard deviation (RSD=6.8-11.4%) and reasonable recovery (87-116%) for direct measuring of nine types of hormones and sulfonamides in the cosmetic products. The average measurement time for two types of samples was less than 1 min. Trace amounts of analytes in commercial cosmetic products have been quantitatively detected, without any sample pretreatment. The experimental results showed that non-volatile illicit additives such as sulfonamides and hormones could be sensitively liberated using the GIND device for quantitative detection from the highly viscous cosmetic products, demonstrating that GIND-EESI-MS is a promising tool for high throughput, sensitive and quantitative analysis of highly complex viscous samples.     

Highly-photoluminescent ZnSe nanocrystals via a non-injection-based approach with precursor reactivity elevated by a secondary phosphine

Highly-photoluminescent ZnSe quantum dots with 72% quantum yield and 22 nm full width at half maximum were synthesized with more reactive precursors via a non-injection approach with high synthetic reproducibility; (31)P NMR provided insight into the formation mechanisms of ZnSe monomers.     

Preconcentration and detection of the phosphorylated forms of cardiac troponin I in a cascade microchip by cationic isotachophoresis

This paper describes the detection of a cardiac biomarker, cardiac troponin I (cTnI), spiked into depleted human serum using cationic isotachophoresis (ITP) in a 3.9 cm long poly(methyl methacrylate) (PMMA) microfluidic channel. The microfluidic chip incorporates a 100× cross-sectional area reduction, including a 10× depth reduction and a 10× width reduction, to increase sensitivity during ITP. The cross-sectional area reductions in combination with ITP allowed visualization of lower concentrations of fluorescently labeled cTnI. ITP was performed in both "peak mode" and "plateau mode" and the final concentrations obtained were linear with initial cTnI concentration. We were able to detect and quantify cTnI at initial concentrations as low as 46 ng mL(-1) in the presence of human serum proteins and obtain cTnI concentrations factors as high as ~ 9000. In addition, preliminary ITP experiments including both labeled cTnI and labeled protein kinase A (PKA) phosphorylated cTnI were performed to visualize ITP migration of different phosphorylated forms of cTnI. The different phosphorylated states of cTnI formed distinct ITP zones between the leading and terminating electrolytes. To our knowledge, this is the first attempt at using ITP in a cascade microchip to quantify cTnI in human serum and detect different phosphorylated forms.     

In situ analysis of agrochemical residues on fruit using ambient ionization on a handheld mass spectrometer

We describe a rapid in situ method for detecting agrochemicals on the surface or in the tissue of fruit using a portable mass spectrometer equipped with an ambient ionization source. Two such ionization methods, low temperature plasma (LTP) and paper spray (PS), were employed in experiments performed at a local grocery store. LTP was used to detect diphenylamine (DPA) directly from the skin of apples in the store and those treated after harvest with DPA were recognized by MS and MS/MS. These data therefore allowed ready distinction between organic and non-organic apples. DPA was also found within the internal tissue of purchased apples and its distribution was mapped using LTP. Similarly, thiabendazole residues were detected on the skin of treated oranges in a grocery store experiment in which paper spray was performed by wiping the orange surface with a moist commercial lens wipe and then applying a high voltage to ionize the chemicals directly from the wipe. The handheld mass spectrometer used in these measurements is capable of performing several stages of tandem mass spectrometry (up to MS(5)); the compounds on the fruit were identified by their MS/MS fragmentation patterns. Protonated DPA (m/z 170) produced a characteristic MS(2) fragment ion at m/z 92, while thiabendazole was identified by MS(3) using precursor to fragment ion transitions m/z 202 →m/z 175 →m/z 131. These particular examples exemplify the power of in situ analysis of complex samples using ambient ionization and handheld mass spectrometers.     

Resonance scattering spectral detection of trace ATP based on label-free aptamer reaction and nanogold catalysis

Double-stranded DNA (dsDNA) cannot protect gold nanoparticles (AuNPs) in the presence of NaCl, and dsDNA interacted with adenosine triphosphate (ATP) to form stable G-quartet and a single-stranded DNA (DNA 2) that can protect AuNPs. The unprotected AuNPs were aggregated to AuNP aggregations (AuNPA) that exhibited a resonance scattering (RS) peak at 590 nm. The RS intensity at 590 nm decreased linearly when the ATP concentration increased in the range of 6.6-110 nM. The catalysis of AuNP-DNA 2 was stronger than that of the AuNPA on the glucose-Cu(II) particle reaction, and the product appeared as an RS peak at 620 nm. When the ATP concentration was increased, the AuNP-DNA 2 increased, and the RS intensity at 620 nm increased linearly. The increased RS intensity (ΔI(620 nm)) was linear to ATP concentration in the range of 2.2-220 nM, with a regression equation of ΔI(620 nm) = 0.709C + 7.7, and a detection limit of 0.5 nM. Hereby, a new RS method of ATP detection was set up with high sensitivity and selectivity.     

Gas-liquid phase coexistence in quasi-two-dimensional Stockmayer fluids: A molecular dynamics study

The Maxwell construction together with molecular dynamics simulation is used to study the gas-liquid phase coexistence of quasi-two-dimensional Stockmayer fluids. The phase coexistence curves and corresponding critical points under different dipole strength are obtained, and the critical properties are calculated. We investigate the dependence of the critical point and critical properties on the dipole strength. When the dipole strength is increased, the abrupt disappearance of the gas-liquid phase coexistence in quasi-two-dimensional Stockmayer fluids is not found. However, if the dipole strength is large enough, it does lead to the formation of very long reversible chains which makes the relaxation of the system very slow and the observation of phase coexistence rather difficult or even impossible.     

UV-ablation nanochannels in micro/nanofluidics devices for biochemical analysis

This paper presents a simple and cost-effective UV-ablation technique for fabrication of size-tunable nanofluidics devices via photochemical decomposition reaction. UV-irradiation through a PET photomask results in continuous decomposition of poly(carbonate) (PC), forming nanochannel and carboxyl groups on the surface of the etched PC. This photochemical decomposition process occurs at molecular scale, therefore, the depth of nanochannels can be controlled at nanometer level. The etching rate is estimated to be ca. 0.015 nm s⁻¹. To demonstrate the potential application of the present UV-ablation technique, a nanochannel was fabricated and integrated with microchannels to form a micro/nanofluidics chip for protein concentration. Using this device, about 10³-10⁵ fold protein concentration can be achieved within 10 min. The present approach offers a simple and practical solution to fabricate nanofluidics devices at low-cost, and the resulting device could provide ideal platforms for μTAS towards various applications in biology and chemistry.     

Six new monoterpenoid indole alkaloids from the aerial part of Gelsemium elegans

Six new monoterpenoid indole alkaloids along with four known analogues were isolated from the aerial part of Gelsemium elegans. Their structures with absolute configurations were elucidated by NMR, HRESIMS, X-ray diffraction, CD spectra, and molecular modeling calculation. Among them, gelselenidine (1) is a new gelsedine-type alkaloid with a 2,3-epoxybutane unit. Gelseziridine (2) is the first example of monoterpenoid indole alkaloids with an oxaziridine residue. Compounds 6 and 7 are a pair of N₄ epimers of humantenine N₄-oxide. A plausible biogenetic pathway for compounds 1-4 was also proposed.     

Constructing a blue light photodetector on inorganic/organic p-n heterojunction nanowire arrays

We described a new structure photodetector, which is constructed by p-n heterojunction nanowire arrays of PANI (polyaniline)/CdS. The nanowire arrays exhibit excellent rectifying features and a diode nature and show a sensitive spectral response to blue light under 420 nm. The rectification ratio plots of different illumination intensities show straight line behavior, implying that the quantitative detection of illumination intensity can be achieved. The p-n heterojunction nanowire array is a great candidate for applications in high-sensitivity and high-speed blue light photodetectors.     

A Novel Glutamate Transport System in Poly(γ-Glutamic Acid)-Producing Strain <Emphasis Type="Italic">Bacillus subtilis</Emphasis> CGMCC 0833

Bacillus subtilis CGMCC 0833 is a poly(γ-glutamic acid) (γ-PGA)-producing strain. It has the capacity to tolerate high concentration of extracellular glutamate and to utilize glutamate actively. Such a high uptake capacity was owing to an active transport system for glutamate. Therefore, a specific transport system for l-glutamate has been observed in this strain. It was a novel transport process in which glutamate was symported with at least two protons, and an inward-directed sodium gradient had no stimulatory effect on it. K _m and V _m for glutamate transport were estimated to be 67 μM and 152 nmol⁻¹ min⁻¹ mg⁻¹ of protein, respectively. The transport system showed structural specificity and stereospecificity and was strongly dependent on extracellular pH. Moreover, it could be stimulated by Mg²⁺, NH₄⁺, and Ca²⁺. In addition, the glutamate transporter in this strain was studied at the molecular level. As there was no important mutation of the transporter protein, it appeared that the differences of glutamate transporter properties between this strain and other B. subtilis strains were not due to the differences of the amino acid sequence and the structure of transporter protein. This is the first extensive report on the properties of glutamate transport system in γ-PGA-producing strain.