Yalei Dong

Graphene oxide–Fe3O4 magnetic nanocomposites with peroxidase-like activity for colorimetric detection of glucose

In this report, graphene oxide-Fe(3)O(4) magnetic nanocomposites were demonstrated to possess intrinsic peroxidase-like activity and enhanced affinity toward H(2)O(2). The nanocomposites retain their magnetic properties and can be effectively separated by a magnet. Significantly, they were proved to be novel peroxidase mimetics which could quickly catalyze oxidation of the peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H(2)O(2), producing a blue-colored solution. Kinetic analysis indicates that the catalytic behavior is in accord with typical Michaelis-Menten kinetics and follows a ping-pong mechanism. On the basis of the high activity, the reaction provides a simple, sensitive and selective method for colorimetric detection of glucose in diabetic urine.

In situ loading of gold nanoparticles on Fe3O4@SiO2 magnetic nanocomposites and their high catalytic activity

In this work, a facile approach was successfully developed for in situ catalyzing Au nanoparticles loaded on Fe3O4@SiO2 magnetic nanospheres via Sn(2+) linkage and reduction. After the Fe3O4@SiO2 MNPs were first prepared via a sol-gel process, only one step was needed to synthesize the Fe3O4@SiO2-Au magnetic nanocomposites (Fe3O4@SiO2-Au MNCs), so that both the synthesis step and the reaction cost were remarkably decreased. Significantly, the as-synthesized Fe3O4@SiO2-Au MNCs showed high performance in the catalytic reduction of 4-nitrophenol to 4-aminophenol and could be reused for several cycles with convenient magnetic separability. This approach provided a useful platform based on Fe3O4@SiO2 MNPs for the fabrication of Au or other noble metal magnetic nanocatalysts, which would be very useful in various catalytic reductions.

In situ synthesis of MIL-100(Fe) in the capillary column for capillary electrochromatographic separation of small organic molecules.

Because of the unusual properties of the structure, the metal organic frameworks (MOFs) have received great interest in separation science. However, the most existing methods for the applications of MOFs in separation science require an off-line procedure to prepare the materials. Here, we report an in situ, layer-by-layer self-assembly approach to fabricate MIL-100(Fe) coated open tubular (OT) capillary columns for capillary electrochromatography. By a controllable manner, the OT capillary columns with a tailored MIL-100(Fe) coating have been successfully synthesized. The results of SEM, XRD, FT-IR, and ICP-AES indicated that MIL-100(Fe) was successfully grafted on the inner wall of the capillary. Some neutral, acidic and basic analytes were used to evaluate the performance of the MIL-100(Fe) coating OT capillary column. Because of the size selectivity of lattice aperture and hydrophobicity of the organic ligands, three types of analytes were well separated with this novel MIL-100(Fe) coating OT capillary column. For three consecutive runs, the intraday relative standard deviations (RSDs) of migration time and peak areas were 0.4-4.6% and 1.2-6.6%, respectively. The interday RSDs of migration time and peak areas were 0.6-8.0% and 2.2-9.5%, respectively. The column-to-column reproducibility of retention time was in range of 0.6-9.2%. Additionally, the 10 cycles OT capillary column (10-LC) could be used for more than 150 runs with no observable changes on the separation efficiency.

Preparation and characterization of open-tubular capillary column modified with graphene oxide nanosheets for the separation of small organic molecules

A novel coated capillary was prepared by immobilizing graphene oxide (GO) on the fused-silica capillary (75 μm i.d.) which was derivatized by 3-aminopropyl-trimethoxysilane (APTMS). The bare capillary, APTMS modified capillary (NH2-capillary) and GO coated capillary (GO-capillary) were characterized by streaming potentials (SPs), fluorescence microscope and scanning electron microscope (SEM). The results indicated that the capillary was successfully modified with GO sheets via covalent bonding and electrostatic effect. Compared with bare capillary, greater separation efficiency was achieved by GO-capillary column as a result of the increasing interactions between the small organic molecules and the inner wall of the GO-capillary column originated from the π-π electrostatic stacking. For three consecutive runs, the intra-day relative standard deviations (RSDs) of migration time and peak areas were 0.6-4.3% and 2.8-9.3%, respectively. The inter-day relative standard deviations of migration time and peak areas were 0.2-8.3% and 4.5-9.6%. Additionally, one GO-capillary column could be used for more than 100 runs with no observable changes on the separation efficiency.

A sensitive colorimetric method for the determination of nitrite in water supplies, meat and dairy products using ionic liquid-modified methyl red as a colour reagent

This paper describes a colorimetric approach to determine trace amounts of nitrite in water supplies, meat and dairy products using 1-butyl-3-methylimidazolium-modified methyl red ([BMIM]MR) as a colour reagent. The technique capitalises on the catalytic effect of nitrite on the oxidative degradation of [BMIM]MR by potassium bromate in acidic media. The absorbances were proportional to nitrite concentrations in the range of 8.70×10(-2) to 4.17 μM with a detection limit of 1.64×10(-2) μM. Compared with the method using methyl red as a colour reagent, 60 times improvement of sensitivity was obtained. Activation energy and the apparent rate constant for the catalytic reaction are 61.11 kJ mol(-1) and 1.18×10(4) s(-1), respectively. The proposed method was successfully applied for the analysis of nitrite in Yellow River water, chicken, and milk with recoveries ranging from 96% to 105%.

In-line preconcentration of oxidized and reduced glutathione in capillary zone electrophoresis using transient isotachophoresis under strong counter-electroosmotic flow.

Transient isotachophoresis (tITP) can improve the sensitivity of capillary electrophoresis (CE). In general, it was carried out under the condition of suppressed electroosmotic flow (EOF). However, some special conditions, such as extreme low pH background electrolyte and coating were needed to achieve the requirements of suppressed EOF. In this work, an approach of tITP under the strong counter-EOF in open system (counter-EOF-tITP) is presented for the rapid and sensitive preconcentrating the reduced glutathione (GSH) and the oxidized glutathione (GSSG) without modifying the capillary and the commercial CE instrument. The parameters of the experimental system, such as the concentration of leading electrolyte, the injected amount of terminating electrolyte and the injected pressure of sample were investigated in detail to understand the mechanism of counter-EOF-tITP. The sensitivity enhancement factors were of 320 for GSH and 280 for GSSG. In addition, the detection limit of 23.4 and 18.0 microg L(-1) for GSH and GSSG was achieved, respectively. The methods applicability was demonstrated by determining GSH and GSSG in tomato and human serum.

A new on-line concentration method of cationic molecules in capillary electrophoresis by a hyphenated micelle to solvent stacking coupling with large amount sample electrokinetic stacking injection.

In this paper, we established a new on-line method using micelle to solvent stacking (MSS) technique combining with large amount sample electrokinetic stacking injection (LASEKSI) for the analysis of cationic molecules. In this MSS-LASEKSI, by modulating the integral EOF across the capillary, a equilibrium state was formed and can be maintained for a long time, leading to the continuous stacking of the analytes on the basis of MSS. Thereby, an extremely large amount sample was permitted to be injected into the capillary and then an improved enrichment fold can be achieved comparing with the each case. The variables affecting the performance of MSS-LASEKSI were investigated and discussed. Under the optimized conditions, 6.3 × 10(3)- and 6.4 × 10(2)-fold enrichment in peak heights upon normal CZE method (injected at 0.5 psi for 3 s) and number of plates of 2.9 × 10(6) and 6.5 × 10(5) were attained for berberine and theophylline, respectively. The developed method described here may provide prospects for exploiting a new concentration technique to achieve higher enrichment factor.

Rapid and sensitive determination of hydroxyproline in dairy products using micellar electrokinetic chromatography with laser-induced fluorescence detection.

Many reports have focused on the determination of hydroxyproline (Hyp) in blood plasma, urine sample, meat and meat products, however, there are few concerned with the Hyp assay in dairy products for food quality assurance up to now. In this paper, we described a sensitive and automated approach for the determination of Hyp in milk powder, liquid milk, milk drink and soymilk powder samples by micellar electrokinetic chromatography (MEKC) based on in-capillary derivatization for the first time. Under the optimal conditions, derivatization and separation procedure could be completed within 7 min and the detection limit for Hyp was 1.6±0.5 ng mL(-1). Comparing with the existing alternatives, the present method exhibited some relevant advantages, including full automation, satisfactory sensitivity, and short analysis time for Hyp assay in dairy products.

Off-line hyphenation of molecularly imprinted magnetic nanoparticle-based extraction with large volume sample stacking capillary electrophoresis for high-sensitivity detection of trace chloro-phenols

The present work developed a sensitive and selective method for the determination of 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) in an environmental water sample by molecularly imprinted magnetic nanoparticle (Fe3O4@MIP) based extraction coupled with capillary electrophoresis (CE). The highly selective, fast and effective sample pretreatment method with Fe3O4@MIPs can overcome the low sensitivity of the highly efficient capillary electrophoresis-ultraviolet detection method (CE-UV). In order to further improve the detection sensitivity, the analytes eluted from the Fe3O4@MIPs were analyzed by the on-line sample preconcentration large volume sample stacking (LVSS) technique with MEKC. Under optimal concentration conditions, signal enhancements of 781, 3276 and 8916-fold were achieved for 4-CP, 2,4-DCP and 2,4,6-TCP, respectively. The average recoveries of the three analytes in spiked water samples were 99.33–104.5% with a relative standard deviation (RSD) below 6.8%. The detection limits for 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol were 1.1 × 10−3, 2.13 × 10−4 and 6.68 × 10−5 μg mL−1, respectively.

The binding affinity of amino acid-protein: hydroxyproline binding site I on human serum albumin

The binding affinity between hydroxyproline (Hyp) and human serum albumin (HSA) was investigated under simulated physiological conditions, using molecular modeling in combination with steady-state fluorescence, synchronous fluorescence, time-resolved fluorescence, UV-vis absorption, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectroscopy. Molecular modeling studies suggested that the Hyp molecule was situated within subdomain IIA of HSA. The fluorescence quenching analysis indicated that the fluorescence of HSA was quenched by Hyp with a dynamic quenching mechanism. The binding constants were calculated according to Scatchards equation and implied that Hyp can bind to different binding sites on HSA. The thermodynamic analysis implied that hydrophobic forces were the main interaction in the Hyp-HSA system, which was found to be in line with the results of molecular modeling. Furthermore, the conformational structure of HSA was changed with various amounts of Hyp, which was confirmed by synchronous fluorescence, UV-vis absorption, CD, and FT-IR spectra.