Lihua Nie

High dispersion and electrocatalytic properties of platinum nanoparticles on graphitic carbon nanofibers (GCNFs).

Highly dispersed platinum nanoparticles were electrodeposited on graphitic carbon nanofibers (GCNFs) by cyclic voltammetry (CV) in 7.7 mM H2PtCl6+0.5 M HCl aqueous solutions. The graphitic carbon nanofibers (GCNFs) used in this paper were grown directly on a graphite disk by chemical vapor deposition (CVD). The micrographs and element composition of Pt/GCNFs/graphite electrode were characterized by scanning electron microscopy (SEM) and electron diffraction spectroscopy (EDS). The electrocatalytic properties of Pt/GCNFs/graphite electrode for methanol oxidation have been investigated by CV and excellent electrocatalytic activity can be observed even at very low platinum loading (md=8.79 microg cm(-2)). The highest mass activity (MA) for methanol oxidation reaches 323 Ag(-1) when Pt/GCNFs/graphite electrode was cycled at a sweep rate of 50 mVs(-1) by CV in 2 M CH3OH+1 M H2SO4 aqueous solutions. This may be attributed to the small particle size and high dispersion of platinum particles coated on GCNFs and shows good potential application in direct methanol fuel cell (DMFC). Additionally, the long-term cycling stability of platinum catalysts was also investigated.

A study of a new TSM bio-mimetic sensor using a molecularly imprinted polymer coating and its application for the determination of nicotine in human serum and urine

A new bio-mimetic quartz crystal thickness-shear-mode (TSM) sensor, using an imprinted polymer coating as the sensitive material, has been fabricated and applied to the determination of nicotine (NIC) in human serum and urine. The molecularly imprinted polymer (MIP) was synthesized using NIC as the template molecule and methacrylic acid (MAA) as the functional monomer. The sensor showed high selectivity and a sensitive response to NIC in aqueous system. The linear response range of the sensor was between 5.0 x 10(-8) and 1.0 x 10(-4) M with a detection limit of 2.5 x 10(-8) M. The viscoelasticity of the coating in the air and in liquid has been studied by the impedance spectrum. The MIP sensor was stable and exhibited effective reproducibility. Satisfactory results were achieved in the detection of the real samples.

Determination of microorganisms with a quartz crystal microbalance sensor

A technique using a quartz crystal microbalance sensor coated with a thin culture medium film was developed and successfully applied to determine the number of Staphylococcus epidermidis (S. epidermidis) in the range of 1 × 102 −4.1 × 107 cells ml−1, based on a good linear relationship between the turning point time and the number of S. epidermidis. The technique is fast and accurate for detection of microorganisms due to the thin culture film and the sharp turning point of the response. The experimental conditions were discussed in detail.

Study of a molecular imprinting polymer coated BAW bio-mimic sensor and its application to the determination of caffeine in human serum and urine

A bio-mimic bulk acoustic wave (BAW) sensor was fabricated by coating the caffeine (CAF) template molecular imprinting polymer (MIP). This sensor exhibited high selectivity and a sensitive mass response to CAF. The response range of the sensor was between 5.0 x 10(-9) and 1.0 x 10(-4) M with a detection limit of 5.0 x 10(-9) M at pH 8.0. Recoveries were 96.1-105.6%. Influencing factors were investigated in detail and optimized. When employed to detect real samples, the proposed method proved to be a convenient method with the advantages of high sensitivity, good selectivity and ease of handling.

A novel dual-impedance-analysis EQCM system--investigation of bovine serum albumin adsorption on gold and platinum electrode surfaces.

Both quartz crystal micro-balance (QCM) impedance and electrochemical impedance spectroscopy (EIS) methods are widely used in interface studies. This paper presents details about a new strategy for simultaneous, mutual-interference-free and accurate measurements of QCM impedance and EI, through connecting a suitable capacitance in series with the piezoelectric quartz crystal (PQC) between QCM impedance and EIS measurement instruments. Combined and individual measurements of QCM impedance and EIS during silver deposition gave results comparable with each other, demonstrating the reliability of the proposed method. Bovine serum albumin (BSA) adsorption on gold and platinum electrodes in Britton-Robinson (B-R) buffers was investigated, and the Fe(CN)6(3-)/Fe(CN)6(4-) couple was used as an electrochemical probe to characterize BSA adsorption. While the reversibility of Fe(CN)6(3-)/Fe(CN)6(4-) couple on bare Au and Pt electrodes changed very slightly with decreasing solution pH from pH approximately 7 to pH approximately 2, the standard rate constant (ks) of this couple increased abruptly with solution pH below pH approximately 4.5 at a BSA-modified Au electrode, but decreased with solution pH at a BSA-modified Pt electrode. By analyzing the QCM impedance data with a modified BVD equivalent circuit and the EI data with a modified Randles equivalent circuit, inflexion changes at pH approximately 4.5 were all found at pH-dependent responses of the resonant frequency, the double-layer capacitance, the capacitance of the adsorbed BSA layer, the peak-absorbance values of BSA solutions at 277.5 and 224.5 nm, and so on. It was also found that a BSA adsorption layer can effectively inhibit gold corrosion during ferrocyanide oxidation in a ferrocyanide-containing BR solution. Some preliminary explanations of these findings have been given. The proposed method is highly recommended for wider applications in surface science.

A study of a bio-mimetic recognition material for the BAW sensor by molecular imprinting and its application for the determination of paracetamol in the human serum and urine

A new bio-mimetic bulk acoustic wave (BAW) sensor for paracetamol, with a high selectivity and sensitivity, was fabricated by using the molecularly imprinted polymer (MIP) as the sensing material. Non-covalent molecular imprinting polymers were synthesized simultaneously using two different functional monomers, namely the weakly basic 4-vinylpyridine (4-VP) and the acidic and hydrogen binding methacrylic acid (MAA). Such imprinted polymers improved recognition capability as compared with the polymers that were synthesized using only one of the functional monomers. Dynamic quartz crystal impedance analysis was employed to study the effect of the viscoelasticity of the polymer coating on the measurement. There was no variation in the viscoelasticity during the detection. The sensor was stable and exhibited good reproducibility. Satisfactory results were obtained in the determination of paracetamol in real samples.

An XPS and BAW sensor study of the structure and real-time growth behaviour of a complex surface film on copper in sodium chloride solutions (pH = 9), containing a low concentration of benzotriazole

The structures and growth kinetics of the complex surface films on copper in sodium chloride solutions (pH = 9) containing low concentrations of benzotriazole have been studied by X-ray photo-electron spectroscopy and a BAW sensor. It is shown that there are some differences in growth kinetics and structures for these surface complex films, even though the copper surfaces prior to the contact with BTA are of the same state and the treated solutions have a same pH value (pH = 9). When the BTA concentration (CBTA) in the treating solution is zero, low (<0.17mM) and high (⩾0.17mM), the film growth can be best represented by a linear, parabolic and logarithmic law, respectively; and the corresponding structures of the surface films of copper are the multilayer structure of Cu/CuCu2O, Cu/CuCu2O/CuOCu(I)BTA and Cu/CuCu2OCu(I)BTA, respectively. With CBTA increasing, the growth kinetics of the surface film changes from a parabolic law to a logarithmic law, the critical concentration of BTA is 0.17 mM, above which CuO cannot be detected in the surface film and a higher inhibition efficiency can be obtained.

Rapid detection of Escherichia coli using a separated electrode piezoelectric crystal sensor

Abstract A separated electrode piezoelectric crystal sensor was used to determine Escherichia coli bacteria. This method is based on the fact that the resonant frequency shifts with the culture time in a culture medium where E. coli is inoculated, and the frequency detection time (FDT) is linearly related to the initial number of E. coli in the range 10–10 6 cells ml −1 . Factors that affect the determination are discussed. E. coli determination in pure culture was tested by the FDT method and compared with the most probable number technique and standard plate counts method. A correlation coefficient of 0.96 was obtained between the FDT and the decadic logarithm of initial concentration of bacteria. The proposed piezoelectric method is much more rapid and sensitive for determining microorganisms than the traditional methods.

Behaviour of series piezoelectric sensor in electrolyte solution: Part II. Applications in titrimetry

Abstract The applications of a series piezoelectric sensor for end-point determination in frequencimetric titrations, including neutralization, precipitation, complexation and redox titrations, are reported. The method is based on the fact that a series piezoelectric sensor shows a sensitive and selective frequency response to changes in conductivity of solution and can be applied to sample solutions containing large amounts of unreacted foreign electrolytes.

Modification of VTMS hybrid monolith via thiol-ene click chemistry for capillary electrochromatography

An n-octadecanethiol (C(18))/3-mercapto-1-propane-sulfonate (MPS) modified organic-inorganic hybrid silica monolithic column possessing vinyl ligands through thiol-ene click chemistry for capillary electrochromatography (CEC) is described. The proposed column is prepared via the sol-gel process by in situ co-condensation using vinyltrimethoxysilane (VTMS) and tetra-methoxysilane (TMOS) as precursors. Examination by SEM shows that the capillary has homogenous macroporous morphology and is well attached to the inner wall of the capillary. The obtained C(18)-MPS-VTMS silica hybrid monolithic column demonstrated an enhanced hydrophilic property and could be applied as a reversed-phase stationary phase in CEC directly. Compared with unmodified VTMS silica hybrid monolithic column, stronger EOF was observed using this monolithic column. VTMS/TOMS ratios in the reaction mixture were varied and 1:3 was found to be optimum. Good separations of benzenes, aromatic amines, acids and peptides were achieved, the lowest plate height of ≈ 3μm was obtained, the peak symmetry range from 0.98 to 1.29. The resulting C(18)-MPS-VTMS silica hybrid monolithic column can be used in different separation modes, including reversed phase mode and ion exchange mode.