Zhanxia Zhang

A sensitive impedimetric thrombin aptasensor based on polyamidoamine dendrimer

A label-free and highly sensitive impedimetric aptasensor based on a polyamidoamine dendrimer modified gold electrode was developed for the determination of thrombin. Amino-terminated polyamidoamine dendrimer was firstly covalently attached to the cysteine functionalized gold electrode through glutaraldehyde coupling. Subsequently, the dendrimer was activated with glutaraldehyde, and amino-modified thrombin aptamer probe was immobilized onto the activated dendrimer monolayer film. The layer-by-layer assembly process was traced by surface plasmon resonance and electrochemical impedance spectroscopy. After electrode preparation, the detection of thrombin was investigated in the presence of the reversible [Fe(CN)6](3-/4-) redox couple using impedance technique. The results showed that the charge-transfer resistance (Rct) value had a linear relationship with the concentrations of thrombin in the range of 1-50 nM, and the detection limit (S/N=3) as low as 0.01 nM was obtained. The covalent immobilization of dendrimer on the electrode surface not only improved the immobilization capacity of probe molecules but also magnified the response signal. The aptasensor exhibited favorable regeneration ability, selectivity and stability. It also showed the detectability in biological fluid.

Green synthesis of nanowire-like Pt nanostructures and their catalytic properties.

We reported a simple and effective green chemistry route for facile synthesis of nanowire-like Pt nanostructures at one step. In the reaction, dextran acted as a reductive agent as well as a protective agent for the synthesis of Pt nanostructures. Simple mixing of precursor aqueous solutions of dextran and K(2)PtCl(4) at 80 degrees C could result in spontaneous formation of the Pt nanostructures. Optimization of the experiment condition could yield nanowire-like Pt nanostructures at 23:1 molar ratio of the dextran repeat unit to K(2)PtCl(4). Transmission electron microscopy results revealed that as-prepared nanowire-like Pt nanostructures consisted of individual Pt nanoparticles with the size range from 1.7 to 2.5 nm. Dynamic light scattering analysis indicated that as-prepared nanowire-like nanostructures have already formed in solution. The as-prepared nanowire-like Pt nanostructures were further characterized by UV-vis spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. In addition, the ratio dependence and temperature dependence of this reaction have also been investigated. The as-prepared nanowire-like Pt nanostructures can be immobilized on glassy carbon electrodes using an electrochemical coupling strategy, and the resulting nanowire-like Pt nanostructures modified film exhibited an excellent electrocatalytic activity for the reduction of oxygen and the oxidation of NADH.

Real-Time Study of Genomic DNA Structural Changes upon Interaction with Small Molecules Using Dual-Polarization Interferometry

The structural changes of genomic DNA upon interaction with small molecules have been studied in real time using dual-polarization interferometry (DPI). Native or thermally denatured DNA was immobilized on the silicon oxynitride surface via a preadsorbed poly(ethylenimine) (PEI) layer. The mass loading was similar for both types of DNA; however, native DNA formed a looser and thicker layer due to its rigidity, unlike the more flexible denatured DNA, which mixed with PEI to form a denser and thinner layer. Ethidium bromide (EtBr), a classical intercalator, induced the large thickness decrease and density increase of native DNA (double-stranded), but a slight increase in both the thickness and density of denatured DNA (partial single-stranded). Spermine that electrostatically binds DNA induced the increase in layer thickness and decrease in the density of both native and denatured DNA. However, the looser structure of native DNA made it more accessible to spermine, leading to a higher binding amount and larger thickness increase. For native DNA, EtBr induced a slow and less reversible contraction of DNA owing to intercalation, while spermine induced a fast and reversible expansion of DNA owing to electrostatic interaction. DPI offers an effective means for real-time study of DNA structural changes during the interactions.

A sensitive choline biosensor with supramolecular architecture

A sensitive biosensor with supramolecular architecture was designed and implemented here to detect choline. Choline oxidase and horseradish peroxidase were assembled onto the polymer of thiolated beta-cyclodextrin and platinum nanoparticles modified gold electrode through 1-adamantane carboxylic acid coupling. Square wave voltammetry showed that the reduction currents at 0.38 mV had a linear relationship with the logarithms of choline concentrations in the range of 10(-9)-10(-2) M, and the detection limit was down to 0.1 nM. Such biosensor also exhibited excellent selectivity, reproducibility and stability.

The network monitoring system based on Cacti for EAST

During the smooth running of EAST (Experimental Advanced Superconducting Tokamak), a perfect network management system guaranteeing a robust network is important. In the present complex network infrastructure, it is a daunting task to manage all the devices manually in a network and make sure they are not only up and running but also performing optimally. Therefore, a web-based software system is developed to implement the real-time monitoring of the EAST experimental network in this paper. Written by the language of PHP, the system based on Cacti uses the RRDTool (Round-robin database tool) engine to store data, stores the systems configuration information by MySQL, and collects periodical data through Net-SNMP. It has realized data acquisition, network weathermap, fault alarm, user management and other modules. Compared with the previous management way, our system can dynamically monitor the network link state, bandwidth usage, the information of network devices load in real time, and give the real monitoring effect; it can also find the various faults and give alarm by sending text messages and emails respectively, so that we can take appropriate measures to resolve them in time. Compared to Email alarm, SMS (Short Message Service) based on the hardware of GSM Modem has the advantages of faster speed and more reliable communication signal. So far, the monitoring system has been successfully applied in the network of EAST and greatly improved the efficiency of network management.