Po Wang

Fabrication of layer-by-layer modified multilayer films containing choline and gold nanoparticles and its sensing application for electrochemical determination of dopamine and uric acid

A novel electrochemical sensor has been constructed by use of a glassy carbon electrode (GCE) coated with a gold nanoparticle/choline (GNP/Ch). Electrochemical impedance spectroscopy (EIS), field emission scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the properties of this modified electrode. It was demonstrated that choline was covalently bounded on the surface of glassy carbon electrode, and deposited gold nanoparticles with average size of about 100nm uniformly distributed on the surface of Ch. Moreover, the modified electrode exhibits strong electrochemical catalytic activity toward the oxidation of dopamine (DA), ascorbic acid (AA) and uric acid (UA) with obviously reduction of overpotentials. For the ternary mixture containing DA, AA and UA, these three compounds can be well separated from each other, allowing simultaneously determination of DA and UA under coexistence of AA. The proposed method can be applied to detect DA and UA in real samples with satisfactory results.

Construction of Au nanoparticles on choline chloride modified glassy carbon electrode for sensitive detection of nitrite

A promising electrochemical sensor for sensitive determination of nitrite was fabricated by construction of Au nanoparticles on the surface of choline chloride (Ch) modified glassy carbon electrode (GCE). Field emission scanning electron microscope, powder X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical techniques were used for the surface characterization of the modified electrode. It was demonstrated that Ch was covalently immobilized onto the GCE surface forming a planted Ch monolayer, which could provide a suitable supporting material for the construction of Au nanoparticles. As a result, the Au nanoparticles with average size of about 110 nm were assembled to form a flowerlike structure on the surface of Ch monolayer. Moreover, the uniform nano-Au/Ch film exhibited remarkable electrocatalytic activity towards the oxidation of nitrite with obvious reduction of overpotential. Under the optimum conditions, the linear range for the detection of nitrite was 4.0 x 10(-7) to 7.5 x 10(-4)M with a high sensitivity of 0.354 microA microM(-1), and a low detection limit of 1.0 x 10(-7)M. The proposed method was successfully applied in the detection of nitrite in water samples and sausage samples, and the results were consistent with those obtained by ion chromatography and UV-visible spectrophotometric methods.

Simultaneous detection of guanine, adenine, thymine and cytosine at choline monolayer supported multiwalled carbon nanotubes film

A rapid, convenient and accurate method for the simultaneous detection of guanine (G), adenine (A), thymine (T) and cytosine (C) was developed at a multiwalled carbon nanotube (MWCNT)/choline (Ch) monolayer-modified glassy carbon electrode (GCE). X-ray photoelectron spectroscopy data demonstrated that Ch was covalently immobilised on the surface of GCE through oxygen atom. The Ch monolayer provides a positively charged surface with -N(+)(CH(3))(3) polar groups, so that it can attract negatively charged MWCNTs to the surface. Consequently, the MWCNT/Ch film exhibited remarkable electrocatalytic activities towards the oxidation of G, A, T and C due to the advantages of high electrode activity, large surface area, prominent antifouling property, and high electron transfer kinetics. All purine and pyrimidine bases showed well-defined catalytic oxidation peaks at MWCNT/Ch/GCE. The peak separations between G and A, A and T, and T and C are 270, 200, and 190 mV, respectively, which are sufficiently large for their potential recognition and simultaneous detection in mixture. Under the optimum conditions, the designed MWCNT/Ch/GCE exhibited low detection limit, high sensitivity and wide linear range for simultaneous detection of G, A, T and C. Moreover, the proposed method was successfully applied to the assessment of G, A, T and C contents in a herring sperm DNA sample with satisfactory results.

CdS nanocrystal induced chemiluminescence: reaction mechanism and applications

Water-soluble CdS nanocrystals (NCs) capped with mercaptoacetic acid (MA) were synthesized in aqueous solution. Hydrogen peroxide directly oxidized the MA-capped CdS NCs and produced strong chemiluminescence (CL) emission in basic conditions. It was found that the CL of CdS NCs was size-dependent, and the CL intensity increased with increasing CdS NCs size. UV–visible spectra, CL spectra, photoluminescence (PL) spectra, and transmission electron microscopy (TEM) were used to investigate the CL reaction mechanism. Moreover, the effects of reactant concentrations, surfactants, and some biological molecules and metal ions were carefully investigated. Some biological molecules and metal ions were observed to inhibit the CL signal of the H2O2–CdS NCs system, which makes it applicable for the detection of such species.

Site-selective probe for investigating the asynchronous unfolding of domains in bovine serum albumin.

A convenient method is proposed for precise investigation of the asynchronous structural transition of the domains in bovine serum albumin (BSA) during unfolding process. The method is based on a site-selective probe, alizarin red S (ARS), which has a high affinity to the subdomain IIA of BSA. BSA-ARS complex was formed and gradually unfolded by urea from 0 to 8.0M. The unfolding occurred in different domains of BSA resulted in distinct alterations of the microenvironment of the bound ARS. The spectral response of BSA-ARS complex, including the color, the UV absorption at 530 and 432 nm, and the intrinsic fluorescence at 342 and 310 nm with the excitation wavelength of 280 nm, showed slight changes in the urea concentration from 0 to 4.5M, drastic changes from 4.5 to 6.0M, and almost no changes from 6.0 to 8.0M. The redox behavior of bound ARS between 0.3 and 0.8 V also showed the same trend. Consequently, a two-step, three-state transition process was monitored by naked eyes, UV-vis spectroscopy and electrochemistry. It is the first report to realize the indicator of the intermediate state during the unfolding process of BSA through convenient methods instead of expensive approaches. The work provides a facile method for the investigation of the unfolding process of multidomain proteins.