Yuqing Miao

Preparation and characterization of gold nanoparticles using ascorbic acid as reducing agent in reverse micelles

In this study, well-dispersed gold nanoparticles were prepared by the reduction of HAuCl4 in sodium bis(2-ethylhexyl)sulfosuccinate/isooctane reverse micelles system using ascorbic acid as reducing agent. The properties of the obtained nanoparticles were characterized with transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, and UV–vis absorption spectrophotometer. Due to its high water solubility, biodegradability, and low toxicity, ascorbic acid could be used as a benign naturally available reducing agent to synthesize gold nanoparticles.

Robust TiO2/BDD heterojunction photoanodes for determination of chemical oxygen demand in wastewaters

A TiO2/BDD heterojunction photoanode, utilizing the inherent properties of nanostructured titanium dioxide (TiO2) and boron-doped diamond (BDD), was prepared and used to determine chemical oxygen demand (COD) in wastewaters. The TiO2 nanoparticles were dip-coated on a BDD substrate and subject to calcination processes. A uniform, continuous and robust mixed-phase (anatase and rutile) TiO2/BDD heterojunction electrode was obtained. The TiO2/BDD heterojunction electrode was evaluated using a series of materials characterisation, electrical and electrochemical techniques. The preliminary results suggest the elevated photoelectrocatalytic activity over the oxidation of organic compounds stemmed from the formation of the p–n junction of the TiO2/BDD electrode. The TiO2/BDD electrode has an excellent resistance towards strong acid due to the use of BDD substrate, which is an added advantage for practical application. Under the optimized experimental conditions, the TiO2/BDD electrode is capable of indiscriminately oxidizing a wide spectrum of organic compounds in a photoelectrochemical thin-layer cell. This bestows the photoelectrochemical system with the ability to measure the COD of synthetic and real samples in a fast, sensitive, reproducible and accurate fashion. In particular, a typical analysis time of 5 minutes, a practical detection limit of 0.12 mg L−1COD, a RSD% value of 1.5% and a linear range of 0–300 mg L−1 were achieved. The TiO2/BDD electrode can be an ideal sensor for online and in situ monitoring of organic pollutants in wastewaters.

Determination of cadmium in water samples by graphite furnace atomic absorption spectrometry after cloud point extraction

The formation of a complex with 2-(5-brom-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP) and cloud point extraction have been applied to the preconcentration of cadmium followed by its determination by graphite furnace atomic absorption spectrometry (GFAAS) using octylphenoxypolyethoxyethanol (TritonX-114) as surfactant. The chemical variables affecting the separation were optimized. At pH 7.0, preconcentration of only 10 mL of sample in the presence of 0.05% TritonX-114 and 2.5 × 10−6 M 5-Br-PADAP enabled the detection of 0.04 μg/L cadmium. The enrichment factor was 21 for cadmium. The regression equation was A = 0.0439C(μg/L) + 7.2 × 10−3. The correlation coefficient was 0.9995. The precision for 10 replicate determinations at 10 μg/L Cd was 2.7% relative standard deviation (RSD). The proposed method has been applied to the determination of cadmium in water samples.

Immobilization of Prussian blue nanoparticles onto thiol SAM modified Au electrodes for analysis of DL-homocysteine

Prussian blue (PB) nanoparticles were immobilized onto gold electrodes using L-cysteine, 1,3-propanedithiol, and 1,8-octanedithiol as a bridge between the gold surface and the PB nanoparticles by the self-assembly method. The obtained PB/thiol/Au electrodes exhibit direct and indirect electrocatalytic activity toward DL-homocysteine (HCys) oxidation. It is possible for these PB nanoparticles modified electrodes to be used for the determination of HCys.

Preparation of Au/ polypyrrole composite nanoparticles and study of their electrocatalytical reduction to oxygen with (without) lacasse

The colloids of Au/polypyrrole (AuPPy) composite nanoparticles were prepared by oxidizing pyrrole monomer with HAuCl4 in a cetyltrimethylammonium bromide (CTAB) solution. Scanning electron microscopy (SEM) suggests the AuPPy nanoparticles in the form of regular spheres, approximately 200 nm in diameter. The resulting colloid of AuPPy composite nanoparticles strongly adheres to the surface of Au electrodes and exhibits better electrocatalytical reduction of oxygen than bare Au electrodes. It means that the complex procedures of centrifuge and wash are avoided. Also, no linker molecules are needed and the immobilization of nanoparticles is achieved easily in a single-step procedure. The experimental parameters were optimized with regard to the concentration of pyrrole and HAuCl4. The direct electron transfer of laccase is observed after it is immobilized on AuPPy modified electrodes by glutaraldehyde. With the help of mediator 2,2′-azino-bis-(3-ethylbenzothiazoline-sulfonic acid) (ABTS), laccase electrode gives an electrocatalytical reduction wave of oxygen at least at 0.8 V. This material is an excellent choice for the design of metal nanoparticle modified electrodes or biosensors

Development of square wave voltammetry method for the assessment of organophosphorus compound impact on the cholinesterase of Pheretima with 2,6-dichloroindophenol as a redox indicator.

A square wave voltammetry method was developed for the assessment of organophosphorus (OPs) compound impact on the cholinesterase of Pheretima with 2,6-dichloroindophenol (2,6-DCIP) as a redox indicator. The substrate of acetylthiocholine is hydrolysed by the cholinesterase (ChE) from soil animal pheretima, and the produced thiocholine reacts with the 2,6-DCIP to give obvious shift of electrochemical signal. The inhibition of ChE was assessed by measuring the enzyme activity before and after incubating with parathion-methyl. The reduction peak current of 2,6-DCIP decreases with the time of enzymatical reaction. The ChE loses almost 32.74% activity after 10 min incubation with 1ng mL(-1) paraoxon and 54.62% with 10 microg mL(-1) paraoxon, while the activity that corresponds to 100 microg mL(-1) paraoxon was nearly completely inhibited. This method can be employed to assess the inhibition of ChE and investigate OPs impact on environmental animals.

Electrochemical characterization of Prussian Blue nanoparticles

Mixing of FeCl3 solution with the excess of K4Fe(CN)6 solution results in well-dispersed Prussian Blue (PB) nanoparticles that are stable over at least one month. Polyaniline was deposited onto the PB-nanoparticle-modified electrode to provide its stability. Promising results of the enhanced detection of H2O2 with these PB nanoparticles are described.

ELECTROCHEMICAL BEHAVIORS OF MATRINE AT L-CYSTEINE-MODIFIED ELECTRODES

Matrine is an important natural occurring component in sophora roots. It has a wide range of pharmacological actions. In this work, electrochemical investigation of matrine and its interaction with L-cysteine (L-Cys) is reported. Via the electrochemical approach, we have proved that the distribution coefficients of protonated and deprotonated matrine affect its electrochemical response on Au or L-Cys modified Au electrodes. The study by ultraviolet spectroscopy also finds that the molecular interaction between matrine and L-Cys changes with the distribution coefficients of protonated and deprotonated matrine at different pH value. Compared with the response of matrine on the bare gold electrode, the L-Cys/Au self-assembled monolayers modified electrodes exhibit obviously higher current response toward matrine oxidation. The oxidation current of matrine at L-Cys assembled electrode has a good linear relation in the range of 0.2–5 mM, with the correlation coefficient of 0.989 by cyclic voltammagrams. Electrochemical combined with spectroscopic techniques would provide relatively easy way to better understand the underlying mechanism of matrine/L-Cys interaction and will be helpful for the development of electroanalytical techniques for the determination of matrine.

Electrochemical Assay of Methyl Parathion in Homogeneous Reaction Using Water Soluble Films with Immobilized Acetylcholinesterase

Water soluble poly (vinyl alcohol) (PVA) was used to prepare the enzyme membranes of acetylcholinesterase (AChE) for electrochemical assaying methyl parathion in water insoluble organic solvent. The immobilized enzyme was separated from electrode for the development of enzyme inhibition-based bioassays. This assay is simple and convenient where enzyme membrane is applicable for single use and the electrode for repeated use. The enzyme membranes can be used handily piece by piece and the released AChE performs catalytic reaction homogeneously. The inhibition percentage of AChE increases with the concentration of methyl parathion ranging from 0.1 to 1 mg/mL.

CHARACTERIZATION OF PRUSSIAN BLUE NANOPARTICLES PREPARED BY REVERSE MICELLE AND ELECTROCHEMICAL STUDY OF THEIR ASSEMBLY

Well-dispersed Prussian blue (PB) nanoparticles were successfully prepared by reverse micelle. This method is based on one-step rapid formation in different sizes of nano-pool with water/oil system, which leads to a homogeneous distribution of PB nanoparticles. Scanning electronic microscopy, UV–vis, and Fourier infrared spectra give supportive evidence of PB nanoparticles. Electrochemical study shows that PB nanoparticles are modified onto cysteine-assembled Au electrodes and exhibit high efficiency of electron transfer.