Abdithiesen9708

Combining electrospray ionization mass spectrometry (ESI-MS) with circular dichroism (CD) spectroscopy, a G-rich sequence from miR-92a promoter region was discovered to form a parallel G-quadruplex structures in KCl or NH4OAc solution. In case of high concentration of NH4OAc, the ESI mass spectra showed peaks of a dimeric G-quadruplex structure with 4 ammonium ions. Meanwhile, palmatine, a natural alkaloid, was screened by ESI-MS to bind with the miR-92a G-quadruplex affinitively. The variable temperature experiment of CD also proved that high concentration of NH4OAc or palmatine could promote the stability of the dimeric G-quadruplex structure. To get the specific characteristics of the miR-92a G-quadruplex structure, systematic mutations of guanine were tested. Based on the number of NH4+ or ligands, the important guanines involved in the G-quadruplex could be determined. Considering the importance of involved guanines and the number of G-quartets, we speculated an interlocked dimeric parallel G-quadruplex as a possible conformation of the miR-92a promoter G-quadruplex. All results obtained from ESI-MS and CD illustrate structure characteristics of the miR-92a G-quadruplex, which is a promising method for preliminary structural analysis of G-quadruplexes. Besides, this study also provides a strategy for regulating the functions of microRNA by exploring and targeting higher-order structures of miRNAs. A semi-automated and sensitive method was developed for simultaneous determination of the six most consumed artificial sweeteners (AS) in surface waters using thin-film solid-phase microextraction (TF-SPME) and high-performance liquid chromatography (HPLC). A triple quadrupole mass spectrometer and an electrospray ionization source (ESI-MS) run in negative ionization and multiple reaction monitoring modes were employed for instrumental analysis. The TF-SPME method was optimized for the extraction phase, sample pH, desorption solvent, extraction time, and desorption time. In-house-synthetized-hydrophilic-lipophilic balance weak anion exchange (HLB-WAX) particles imbedded within a polyacrylonitrile (PAN) binder were selected as the extraction phase for the thin-film coating due to their cost-effectiveness and enhanced sensitivity for artificial sweeteners. Suitable analytical parameters that include linearity (R2 > 0.9914), recovery > 80%, inter, and intra-reproducibility less than 18% were obtained for the AS compounds studied. The developed method estimated limits of detection (LODs) ranging from 0.004 to 0.038 ng mL-1 The SPME method was successfully applied for the determination of ultra-trace levels of AS in water samples collected from Grand River (Ontario, Canada), downstream of three municipal wastewater treatment plants (WWTPs). Concentrations ranging from 0.03 to 20.3 ng mL-1 were found for the AS compounds studied. The ability to discover minute differences between samples or sample classes for gas chromatography coupled to mass spectrometry (GC-MS) can be a challenging endeavor, especially when those differences are not a priori. Fisher ratio (F-ratio) analysis is an apt technique to probe the differences between GC-MS chromatograms. F-ratio analysis is a supervised, non-targeted, discovery-based method that compares two different samples (or sample classes) to reduce the GC-MS dataset into a hit list composed of class distinguishing compounds. Three different F-ratio techniques, peak table, tile, and pixel-based were used to "discover" nine non-native analytes that were spiked into gasoline at four different nominal concentrations of 250, 85, 25, 5 parts-per-million (ppm). For the tile and pixel-based F-ratio calculations, a novel methodology is introduced to improve the sensitivity of the F-ratio calculations while reducing false positives. Furthermore, we use a combinatorial technique using null class comparisons, termed null distribution analysis, to determine a statistical F-ratio cutoff for analysis of the hit lists. The pixel-based algorithm was the most sensitive method and was able to "discover" all nine spiked analytes at a nominal concentration of 250 ppm albeit with one false positive interspersed towards the bottom of the hit list. selleck chemicals The pixel-based software was also able to "discover" more of the spiked analytes at the lower concentrations with seven of the spiked analytes "discovered" at 85 ppm, four of the spiked analytes "discovered" at 25 ppm, and one analyte "discovered" at 5 ppm. Rapid detection of foodborne pathogens is crucial to prevent the outbreaks of foodborne illnesses. In this study, a sensitive electrochemical aptasensor was developed using aptamer coated gold interdigitated microelectrode for target capture and impedance measurement, and antibody modified nickel nanowires (NiNWs) for target separation and impedance amplification. First, the interdigitated microelectrode was modified with the biotinylated aptamers against Salmonella typhimurium through electrostatic absorption of streptavidin onto the microelectrode and streptavidin-biotin binding. Then, the target Salmonella cells were magnetically separated and concentrated using the NiNWs modified with the anti-Salmonella typhimurium antibodies to form the bacteria-NiNW complexes, and incubated on the microelectrode to form the aptamer-bacteria-NiNW complexes. After an external arc magnetic field was developed and applied to control the NiNWs to form conductive NiNW bridges across the microelectrode, the enhanced impedance change of the microelectrode was measured and used to determine the amount of target bacteria. This electrochemical aptasensor was able to quantitatively detect Salmonella ranging from 102 to 106 CFU/mL in 2 h with the detection limit of 80 CFU/mL. The mean recovery for the spiked chicken samples was 103.2%. Controlled printing of biodegradable and bioresorbable polymers at desired 3D scaffold is of great importance for cell growth and tissue regeneration. In this work, a novel electrohydrodynamic jet 3D printing technology with the resultant effect of electrohydrodynamic force and thermal convection was developed, and its feasibility to fabricate controllable filament composite scaffolds was verified. This method introduces an effective thermal field under the needle to simultaneously enhance the ink viscosity, jetting morphology controllability and printing structure solidify. The fabrication mechanisms of thermal convection on jetting morphology and printed structures feature were investigated through theoretical analysis and experimental characterization. Under optimized conditions, a stable and finer jet was formed; then with the use of this jet, various 3D structures were directly printed at a high aspect ratio ~30. Furthermore, the PCL/PVP composite scaffolds with the controllable filament diameter (~10 μm) which is closed to living cells were printed.