Yanjie Zheng

Simultaneous determination of dopamine, ascorbic acid and uric acid at poly (Evans Blue) modified glassy carbon electrode

A sensitive and selective electrochemical method for the determination of dopamine using an Evans Blue polymer film modified on glassy carbon electrode was developed. The Evans blue polymer film modified electrode shows excellent electrocatalytic activity toward the oxidation of dopamine in phosphate buffer solution (pH 4.5). The linear range of 1.0 x 10(-6)-3.0 x 10(-5) M and detection limit of 2.5 x 10(-7) M were observed in pH 4.5 phosphate buffer solutions. The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of ascorbic acid and uric acid. The separation of the oxidation peak potentials for dopamine-ascorbic acid and dopamine-uric acid were about 182 mV and 180 mV, respectively. The differences are large enough to determine AA, DA and UA individually and simultaneously. This work provides a simple and easy approach to selectively detect dopamine in the presence of ascorbic acid and uric acid in physiological samples.

Signal-on fluorescent sensor based on GQDs–MnO2 composite for glutathione

Graphene quantum dots (GQDs) exhibit strong photoluminescence, biocompatibility, and low toxicity and can easily functionalize surfaces to improve the detection of biomolecules. As-prepared MnO2 nanosheets were applied in the fabrication of GQDs–MnO2 composite to develop a signal-on fluorescent platform for sensing glutathione (GSH). The fluorescence of the GQDs was quenched by MnO2 in the GQDs–MnO2 composite as a result of fluorescence resonance energy transfer within the composite. The fluorescence of GQDs was restored when GSH was introduced because GSH reduced the MnO2 nanosheets into Mn2+ and released GQDs. Under the optimized conditions, the concentration of GSH can be accurately detected with high sensitivity and specificity in Tris–HCl buffer and simulated serum. The proposed sensing strategy was successfully used to measure GSH in the range of 1–1000 μM with a detection limit of 0.45 μM. In addition, GSH in reduced glutathione injection and reduced glutathione tablets can be determined accurately using the proposed method. GQDs–MnO2 composite is thus a promising GSH fluorescence sensor for the analysis of complex systems and for quality control in the pharmaceutical industry.

A robust and versatile signal-on fluorescence sensing strategy based on SYBR Green I dye and graphene oxide.

A robust and versatile signal-on fluorescence sensing strategy was developed to provide label-free detection of various target analytes. The strategy used SYBR Green I dye and graphene oxide as signal reporter and signal-to-background ratio enhancer, respectively. Multidrug resistance protein 1 (MDR1) gene and mercury ion (Hg2+) were selected as target analytes to investigate the generality of the method. The linear relationship and specificity of the detections showed that the sensitive and selective analyses of target analytes could be achieved by the proposed strategy with low detection limits of 0.5 and 2.2 nM for MDR1 gene and Hg2+, respectively. Moreover, the strategy was used to detect real samples. Analytical results of MDR1 gene in the serum indicated that the developed method is a promising alternative approach for real applications in complex systems. Furthermore, the recovery of the proposed method for Hg2+ detection was acceptable. Thus, the developed label-free signal-on fluorescence sensing strategy exhibited excellent universality, sensitivity, and handling convenience.

Electrochemical method for monitoring the progress of polymerase chain reactions using Methylene blue as an indicator

AbstractWe report on the proof-of-principle of an amperometric method to monitor the progress of a polymerase chain reaction (PCR) in real-time. It is based on the finding that the intercalating redox probe Methylene Blue (MB) becomes less easily electrochemically detectable once intercalated into double-stranded DNA (ds-DNA) compared to its free form. This was studied by cyclic voltammetry before and after addition of salmon sperm ds-DNA. Under optimized conditions, the products of the PCR of mitochondrial DNA fragments were quantitatively detected at different stages of amplification cycles. This strategy is potentially cheaper and easier to integrate into a hand-held miniaturized device than fluorescence-based real-time PCR. FigureWe report on the proof-of-principle of an amperometric method based on methylene blue which becomes less electrochemically detectable once intercalated into double-stranded DNA compared to its free form to monitor the progress of PCR in real-time. This strategy is potentially cheap and easy to integrate into a hand-held miniaturized device.

Halloysite clay nanotubes as effective nanocarriers for the adsorption and loading of vancomycin for sustained release

Ensuring the adequate delivery of local antibiotic concentrations to infected bone is crucial. Accordingly, we developed a new and simple controlled release system with halloysite clay nanotubes (HNTs) as nanocarriers of vancomycin (Van), a potent antibiotic drug, for the simple preparation of a local drug delivery system. Noncytotoxic HNTs served as barriers against cell ingrowth for the delivery system. The preparation conditions of HNTs–Van were optimized. With the mass ratio of Van and HNTs controlled at 2 : 1, HNTs–Van obtained the highest Van loading content under suitable preparation conditions. HNTs–Van allowed the effective and extended release of the drug over a period of 33 days, compared with only 1 day with the direct release of pristine Van. The feasibility of the highly effective local antibacterial activity of HNTs–Van in treating infections was confirmed through the Kirby–Bauer assay. This work suggests that HNTs are efficient for the local delivery of antibiotics in bacterial infection treatment.

Electrochemical DNA biosensor based on grafting-to mode of terminal deoxynucleoside transferase-mediated extension

Previously reported electrochemical DNA biosensors based on in-situ polymerization approach reveal that terminal deoxynucleoside transferase (TdTase) has good amplifying performance and promising application in the design of electrochemical DNA biosensor. However, this method, in which the background is significantly affected by the amount of TdTase, suffers from being easy to produce false positive result and poor stability. Herein, we firstly present a novel electrochemical DNA biosensor based on grafting-to mode of TdTase-mediated extension, in which DNA targets are polymerized in homogeneous solution and then hybridized with DNA probes on BSA-based DNA carrier platform. It is surprising to find that the background in the grafting-to mode of TdTase-based electrochemical DNA biosensor have little interference from the employed TdTase. Most importantly, the proposed electrochemical DNA biosensor shows greatly improved detection performance over the in-situ polymerization approach-based electrochemical DNA biosensor.

Anticancer effect of petroleum ether extract from Bidens pilosa L and its constituent's analysis by GC-MS

ETHNOPHARMACOLOGICAL RELEVANCE Bidens pilosa L, belonging to the family of Acanthaceae, has been used as an anticancer medicine in folk in China. In our preliminary experiments, the petroleum ether extract from B. pilosa showed good cytotoxic activity to human lung cancer A549 cell. However, to date, its lack of the further study on antitumor effect, mechanism and active substances composition of the petroleum ether extract of B. pilosa. AIM OF THE STUDY The study aimed to evaluate the anti-lung cancer efficacy of the petroleum ether extract from B. pilosa (PEEBP) in vitro and in vivo, explore the possible anticancer mechanisms, and further disclose the chemical composition of the extract. MATERIALS AND METHODS B. pilosa was extracted with 75% ethanol (v/v), followed by extracted with petroleum ether to obtain the objective fraction. Antiproliferation effect of the petroleum ether extract in HepG2, A549, CNE and B16 cells was evaluated by MTT assay. The in vivo anticancer effect was examined by A549 cells nude mice xenograft tumor model. The possible effect mechanism was studied by western blot assay. The chemical constituents of the extract was analyzed by GC-MS. RESULTS The petroleum ether extract showed favorable antiproliferation activity against the four human cancer cell lines, especially for A549 cells with an IC50 of 49.11 ± 2.72 μg/mL. The extract inhibited the growth of A549 cell in mice with the inhibitory rates of 24.76%, 35.85% and 53.07% for 90, 180 and 360 mg/kg oral dosages, respectively. The B. pilosa extract could significantly down-regulate the expression of apoptosis-related protein Bcl-2 and up-regulate the protein expression of Bax and Caspase-3. 138 compounds were identified by GC-MS in the extract and the main chemical components were triterpenes, including 4,22-cholestadien-3-one (4.82%), stigmasterol (4.56%), friedelan-3-one (3.28%), etc. CONCLUSION The PEEBP is abundant of triterpenes and has significant anti-tumor activities against human A549 cells in vitro and in vivo, indicating it a potential anticancer agent.