Electrocatalytic degradation of methyl orange and 4-nitrophenol on a Ti/TiO2-NTA/La-PbO2 electrode: electrode characterization and operating parameters.

The anode material plays a crucial role in the process of electrochemical oxidation. Herein, a TiO2 nanotube arrays (TiO2-NTA) intermediate layer and La-PbO2 catalytic layer were synthesized on a Ti surface by the electrochemical anodic oxidation and electrochemical deposition technology, respectively. The prepared Ti/TiO2-NTA/La-PbO2 electrode was used as an electrocatalytic oxidation anode for pollutant degradation. Scanning electron microscopy (SEM) analysis showed that the TiO2-NTA layer possessed a highly ordered and well-aligned nanotube array morphology, and the La-PbO2 layer with angular cone cluster was uniform and tightly bonded. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis indicated that the intermediate layer primarily consisted of the anatase crystal structure of TiO2 and the catalyst layer was made of La-PbO2. Electrochemical analysis revealed that Ti/TiO2-NTA/La-PbO2 electrode exhibited higher oxidation peak current, electrochemical active surface area, and oxygen evolution potential (OEP, 1.64 V). Using methyl orange and 4-nitrophenol as model pollutants, electrocatalytic properties of the prepared Ti/TiO2-NTA/La-PbO2 electrode were systematically investigated under different conditions, and the electrochemical degradation fitted well with the pseudo-first-order kinetics model. Efficient anodic oxidation of model pollutants was mainly attributed to the indirect oxidation mediated by hydroxyl radicals (•OH). The total organic carbon (TOC) removal efficiency of methyl orange and 4-nitrophenol was 70.2 and 72.8%, and low energy consumption (2.50 and 1.89 kWh g-1) was achieved after 240 min of electrolysis under the conditions of initial concentration of model pollutant, electrode spacing, and electrolyte concentration were 50 mg L-1, 2 cm, and 0.1 mol L-1, respectively. This work provided a new strategy to develop the high-efficiency electrode for refractory pollutants degradation.

Preparation of novel fluorescent DNA bio-dots and their application for biothiols and glutathione reductase activity detection.

A new class of fluorescent bio-dots have been successfully prepared by hydrothermal treatment of poly-cytosine DNA at low temperature down to 80 °C. The inter-molecule interaction of aromatic cytosine bases forms sp(2) carbon-like centers as the luminescence centers or chromophores. In the presence of Ag(+), the formation of C-Ag(+)-C base pairs results in the destroying of the luminescence centers and thus the fluorescence (FL) quenching of the bio-dots. However, with the addition of biothiols, Ag(+) prefers to react with biothiols to form the Ag(+)-S bond, hence a restoration of FL emission can be observed. Moreover, by employing the classic glutathione reductase (GR) catalyzed enzymatic reaction, this concept can be readily applied to the selective quantification of oxidized glutathione (GSSG) as well as the activity of GR with a very robust, simple, and rapid procedure. It is worth looking forward to design DNAs with a specific function to prepare fluorescent bio-dots for simple biological applications.

Amelioration of insulin resistance in rat cells by Astragalus polysaccharides and associated mechanisms.

The aim of this study was to investigate the function of Astragalus polysaccharides (APS) in ameliorating insulin resistance (IR) in rat cells and to elucidate the associated mechanisms. Fully differentiated, induced 3T3-L1 rat adipocytes were divided into a control group and three intervention groups. The intervention groups were incubated in media containing 0.001, 0.1 and 10 µg/µl APS, respectively, for 48 h. Following treatment, levels of interleukin (IL)-6 and adiponectin secreted by the cultured adipocytes were measured using enzyme-linked immunosorbent assay. Levels of adiponectin secreted by the 3T3-L1 adipocytes in the moderate-concentration intervention group were significantly increased compared with those in the control group (P<0.05), whereas levels of adiponectin secreted by the 3T3-L1 adipocytes in the low- and high-concentration intervention groups were decreased compared with those in the control group (P<0.05 and P>0.05, respectively). Levels of IL-6 secreted by the 3T3-L1 adipocytes in the three intervention groups were lower than those in the control group (P>0.05, P<0.05 and P<0.05 for the low- moderate- and high-concentration intervention groups, respectively), and demonstrated APS dose-dependence. The results indicate that APS are capable of increasing adiponectin secretion and reducing IL-6 secretion by 3T3-L1 rat adipocytes in a dose-dependent manner. These findings may identify a potential mechanism for ameliorating IR using APS.

DNA-templated Ag nanoclusters as fluorescent probes for sensing and intracellular imaging of hydroxyl radicals.

We have developed a simple, rapid and label-free sensor for the essential biological OH radicals based on the fluorescence quenching of DNA-templated Ag nanoclusters (DNA-Ag NCs). The OH radicals generated from the Fenton reagent attack and cleave the DNA template, which disturbs the microenvironments around Ag NCs, resulting in spontaneous aggregation due to the lack of stabilization and further the quenching of the Ag NCs fluorescence. These changes in fluorescence intensity allow sensing of OH radicals with good sensitivity and selectivity under optimal conditions. The sensor can be also applied for quantifying the radical scavenging action of antioxidants. Various characterizations including absorption spectra, fluorescence lifetimes, light scattering (LS) spectra, transmission electron microscopy (TEM), dark field light scattering imaging, and circular dichroism (CD) spectrometry have been employed to illustrate the proposed sensing mechanism. Further investigations demonstrate that the fluorescent probe could penetrate into intact cell membranes to selectively detect intracellular OH radicals induced by the phorbol myristate acetate (PMA) stimulation. These advantageous characteristics make the fluorescent DNA-Ag NCs potentially useful as a new candidate to monitor OH in broad biosystems.

Using graphene quantum dots as photoluminescent probes for protein kinase sensing.

A simple and sensitive photoluminescence (PL) assay for the activity of a protein kinase based on the selective aggregation of phosphorylated peptide-graphene quantum dot (GQD) conjugates triggered by Zr(4+) ion coordination has been established. With more sophisticated design of the peptide substrate sequences, detecting other enzymes could also be possible. Under optimal conditions, a linear relationship between the decreased PL intensity of peptide-GQD conjugates and the concentration of casein kinase II (CK2) in the range from 0.1 to 1.0 unit mL(-1) with a detection limit of 0.03 unit mL(-1) (3σ) was obtained. The EC50 value (i.e., the enzyme concentration producing 50% substrate conversion) for CK2 was evaluated to be 0.34 unit mL(-1). The proposed method showed potential applications in kinase inhibitor screening. To demonstrate the potential of this GQD-based platform for screening of kinase inhibitors in real biological systems, the inhibition of CK2 phosphorylation activity by four different inhibitors (ellagic acid, 5,6-dichlorobenzimidazole-l-ß-d-ribofuranoside, emodin, and quercetin) was tested in human serum by comparing signals from samples incubated with the inhibitors against that without any inhibitor. As expected, in the presence of inhibitors, the PL intensity increased with increasing inhibitor efficiency. The IC50 value (inhibitor concentration producing 50% inhibition) for ellagic acid was estimated to be 0.041 µM. The developed protocol provides a new and promising tool for the analysis of both the enzyme and its inhibitors with low cost and excellent performance.

Graphene quantum dots combined with europium ions as photoluminescent probes for phosphate sensing.

The sense of it: A new type of rapid, sensitive, and specific photoluminescence (PL)-based assay has been proposed for the detection of phosphate (Pi) based on the competition of oxygen-donor atoms from Pi with those from the carboxylate groups on a graphene-quantum-dot (GQD) surface for Eu(3+) ions. The graphene-like structures combined with QD-like optical properties suggest the promising nature of the GQDs as versatile tools in the fields of analytical science and biotechnology.