Chang Ji

Size-dependent cellular uptake efficiency, mechanism, and cytotoxicity of silica nanoparticles toward HeLa cells

In this study, we investigated and reported the cellular uptake efficiency, mechanism, and cytotoxicity of silica nanoparticles (SNPs) with different sizes. Using confocal laser scanning microscope (CLSM), flow cytometry (FCM), and graphite furnace atomic absorption spectrometry (GFAAS), the qualitative and quantitative experimental results showed that the cellular uptake of SNPs toward HeLa cells is size-dependent. To further examine the uptake process, three different inhibitors including sucrose, Filipin III, and Cytochalasin D (Cyt D) were introduced to pretreat the HeLa cells. It appeared that the largest SNPs (SNPs-307.6) take an energy-dependent uptake pathway (clathrin dependent and caveolin independent) while that for the medium size SNPs-167.8 involves clathrin and caveolin dependent endocytosis. In contrast, the smallest SNPs (SNPs-55.6) follow not only energy required clathrin and caveolin dependent endocytosis but also an energy independent pathway to efficiently enter the cells. Moreover, the cellular uptake efficiency of SNPs, which also show excellent biocompatibility, is size-dependent in the order of 55.6>167.8>307.6 nm. This knowledge is fundamentally important and will facilitate more development of size-defined SNPs as the transporters for various purposes.

Nanocomposites of palladium nanoparticle-loaded mesoporous carbon nanospheres for the electrochemical determination of hydrogen peroxide.

Palladium nanoparticles (Pd NPs) were loaded in situ on novel mesoporous carbon nanospheres (MCNs), which possess high specific surface area and large pore volume. The resulting Pd/MCNs hybrid nanocomposites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). By using Pd/MCNs as the catalyst matrices to modify the surface of glassy carbon electrode, a nonenzymatic sensor was developed for the determination of hydrogen peroxide (H(2)O(2)). Cyclic voltammetry (CV) and amperometry (at an applied potential of -0.30 V versus SCE) were used to study and optimize the performance of the electrochemical sensor. It was demonstrated that the sensor not only exhibits good electrocatalytic activity toward the reduction of H(2)O(2) but also has high sensitivity (307.5 μA mM(-1) cm(-2)), low detection limit of 1.0 μM, and wide linear response range from 7.5 μM to 10 mM. Moreover, the sensor shows excellent stability and anti-interference capability for the detection of H(2)O(2).

Nitrogen-Doped Mesoporous Graphene as a Synergistic Electrocatalyst Matrix for High-Performance Oxygen Reduction Reaction

To balance the anchoring sites and conductivity of the catalyst supports is a dilemma in electrocatalytic oxygen reduction reaction (ORR). Nitrogen-doped mesoporous graphene (N-MG) with large surface area, high porosity, and superior intrinsic conductivity has been developed to address this issue. Using N-MG as the backbone, a hybrid catalyst of Co3O4 nanocrystals embedded on N-MG (Co3O4/N-MG) was prepared for the electrocatalytic ORR in alkaline media. The Co3O4/N-MG showed high catalytic activity for the four-electron ORR, giving a more positive onset potential (0.93 V vs RHE) and a higher current density. The unique property of N-MG and the synergetic effect of Co3O4 and N-MG are prominent for ORR. With improved electrocatalytic activity and durability, the Co3O4/N-MG can be an efficient nonprecious metal catalyst and potentially used to substitute the platinum-based cathode catalysts in fuel cells and metal-air batteries.

Electro-Induced Covalent Cross-Linking of Chitosan and Formation of Chitosan Hydrogel Films: Its Application as an Enzyme Immobilization Matrix for Use in a Phenol Sensor

We report a novel electrochemical method for making covalently cross-linked chitosan films on the surface of a screen printed carbon electrode. In the presence of a freely diffusing ruthenium complex, Ru(bpy)(2)Cl(2), soluble chitosan becomes irreversibly cross-linked in response to a reducing potential and subsequently deposits on the electrode surface to form a hydrogel film which shows robustness in harsh acidic conditions. The cross-linked chitosan film presents excellent ability to facilitate the diffusion and electron transfer process of the negatively charged redox couple [Fe(CN)(6)](3-)/[Fe(CN)(6)](4-) at the electrode surface, while its impact on the positively charged redox couple [Ru(NH(3))(6)](2+)/[Ru(NH(3))(6)](3+) is minimal. By covalently immobilizing the enzyme tyrosinase in a preformed cross-linked chitosan film via a similar mechanism, a sensitive phenol sensor is constructed with a broad dynamic range. The potential advantages of this method are also discussed.

A three-dimensional silver nanoparticles decorated plasmonic paper strip for SERS detection of low-abundance molecules.

The fabrication of SERS substrates, which can offer the advantages of strong Raman signal enhancement with good reproducibility and low cost, is still a challenge for practical applications. In this work, a simple three-dimensional (3D) paper-based SERS substrate, which contains plasmonic silver-nanoparticles (AgNPs), has been developed by the silver mirror reaction. This paper strip was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), etc. Pretreatment of the paper as well as the reaction time, temperature, and reagent concentrations for the silver mirror reaction were varied for further studies. With the optimized experimental parameters, the AgNPs synthesized and distributed in-situ on the paper strip could give more favorable SERS performance. The limit of detection (LOD) as low as 10(-11)M for Rhodamine 6G (R6G) and 10(-9)M for p-aminothiophenol (p-ATP) plus wide linear range for the log-log plot of Raman intensity versus analyte concentration were achieved. The detection of R6G in rain water was also carried out successfully. The merits of this protocol include low cost, easy operation, high sensitivity and acceptable stability, which make it ideal for the detection of environmental samples in trace amounts.

Using an internal standard method to determine Henry's law constants

An internal standard method is developed for the measurement of thermodynamic Henrys law constants (H). In this method, a mixture of the analytes and an internal standard is prepared and used to make a standard solution (organic solvent) and a dilute aqueous solution. Both the standard solution and the headspace samples above the aqueous solution at partitioning equilibrium in closed containers are subject to gas chromatographic (GC) analysis. Subsequently, the values of H for the analytes can be calculated from the known H of the internal standard and the GC peak-area ratios. Only approximate values of the concentrations of the compounds, the GC injection volumes, and the vapor-phase to liquid-phase volume ratios in the closed containers are needed in this approach. The method works particularly well for compounds that are highly soluble in water or that have low vapor pressures. Experimentally determined values of H are reported for some low-molecular-weight aldehydes, ketones, and nitriles, and their temperature dependencies are examined. The results also are compared with literature values. The applicability of this new approach is limited to compounds that have dimensionless H on the order of 10(-3) or less.

Electrochemical Reduction of Cinnamyl Bromide at Carbon Cathodes in Acetonitrile: A Further Mechanistic Study

Cyclic voltammetry and controlled-potential electrolysis have been employed to examine the electrochemical reduction of cinnamyl bromide at glassy carbon cathodes in acetonitrile containing tetramethylammonium tetrafluoroborate. A cyclic voltammogram for the reduction of cinnamyl bromide exhibits one irreversible wave, which is due to the cleavage of the carbon-bromine bond. Bulk electrolyses of the substrates have been carried out at two different potentials (-1.35 and -1.85 V vs saturated calomel electrode) in the absence and in the presence of diethyl malonate as a proton donor. Coulometric n values and product distributions indicate that the reduction of cinnamyl bromide at -1.35 V mainly gives radical intermediates, whereas that at 1.85 V forms cinnamyl anions. A direct reduction of cinnamyl bromide in the presence of nitric oxide (NO) at -1.35 V reveals that the cinnamyl radical can couple with NO to generate cinnamaldehyde oxime and cinnamonitrile. More interestingly, both 5-phenylisoxazoline and 5-phenylisoxazole, arising from the cyclization of cinnamaldehyde oxime, have been found among the products. Detailed mechanisms for the reductions are proposed and discussed.

Mesoporous Silica for Triphase Nucleophilic Substitution Reactions

Mesoporous silica SBA-15 is shown to be a very efficient alternative to phase transfer catalyst salts for two-phase nucleophilic substitutions. The two-phase reaction can efficiently take place in the absence of PTCs. The high catalytic activity and reaction rates can be attributed to the amphiphilic and negatively charged surface of SBA-15 as well as the rapid ingress of the reactants and egress of the products.