OBJECTIVE: To investigate the sensing volume of open-ended coaxial probe technique for measurement of dielectric characteristics. METHODS: A measurement model combining macro- measurement device with a layer model of dielectric properties parameters was established for evaluating the sensing volume of open-ended coaxial probe technique. We defined sensing depth and sensing diameter to describe the distance that could be detected in vertical and horizontal direction. Using a variety of materials with different dielectric properties (Teflon, deionized water, ethanol, and gradient concentration sodium chloride solution), a layered model of dielectric properties differentiation was established. The total combined uncertainties (TCU) were calculated for different output power, and the output power was controlled to increase from -50 dBm to 15 dBm to calibrate the error range of the dielectric properties measurement system. The optimal output power range was determined based on the results of TCU test. In sensing volume measurement experiment, we set the control groups based on measurement parameters that potentially affect the sensing volume including output power (-10, -5, 0, 3, 6, and 9 dBm), frequency (1-500 MHz), Teflon, deionized water, and ethanol to form a dielectric constant difference between high and low contrast groups. Different concentrations of sodium chloride solution and Teflon were used to generate a conductivity difference between high and low contrast groups. These groups were tested in the sensing depth and sensing diameter measurement experiments. RESULTS: The result of TCU test indicated that accurate and stable measurement results could be obtained when the output power was greater or equal to-10 dBm (TCU < 2%). Sensing volume measurement experiment revealed a positive correlation between the sensing depth and output power ( < 0.05). As the measured power increased, the sensing depth gradually increased in deionized water and ethanol, and the difference reached 70 μm. The sensing depth was negatively correlated frequency ( < 0.05). As the concentration of sodium chloride solution increased, the corresponding sensing depth gradually decreased, with a difference reaching 270 μm. The sensing depth of high dielectric materials was greater than that pf low dielectric materials. The results of sensing diameter measurement were not obviously affected by the measurement parameters, and the sensing diameter was stable in a fixed range (1.0 to 1.8 mm) between the diameter of the inner conductor and the diameter of the insulation layer, and was less than the diameter of the probe. CONCLUSIONS The sensing volume of open-ended coaxial probe technique is affected by measurement parameters and dielectric properties of materials, which significantly affect the sensing depth.
Algorithms ; Electric Conductivity ; Electrochemistry ; instrumentation

Chromatography, High Pressure Liquid ; methods ; Electrochemistry ; Homocysteine ; blood ; Humans

Three-electrode testing method was used to investigate the effect of temperature on electrode impedance, and the pH shifts in saline solution resulting from the electrical stimulation were also determined. Experiments in PBS (phosphate buffered solution) solution showed that the electrode impedance was almost invariable at the human body temperature range (35 degrees C-40 degrees C). And the experiments in unbuffered saline solution showed that pH shifts decreased from 0.03 to 0.005 when the frequency of biphasic charged-balanced pulses increased from 1 Hz to 100 Hz. Even stimulated by monophasic pulses (frequency is 15 Hz, amplitude is 50 microA), the stimulus-induced pH shift of electrode only varies 0.15 (anodic pulse current increased 0.15 and cathodic pulse current decreased 0.15).
Electrochemistry ; Eye, Artificial ; Materials Testing ; Microelectrodes ; Prostheses and Implants

The dielectric spectroscopy of human blood cells was measured within the frequency range of 0.01-100 MHz, and the dielectric numerical characters were determined as response to AC electric field. we measured the AC impedance of normal human blood cells with the impedance technique in the frequency domain, then the experimental data were drawn a relationship curve between the frequency of electric field and conductivity. The dielectric spectrum and the Cole-Cole plots of human blood cells were established. The characteristics of dielectric response of human blood cells were also established. The permittivity and the conductivity of human blood cells were frequency dependent, and dielectric dispersion of human blood cells had two characteristic frequencies: i.e. fc1, is 1.42 MHz, and fc2 is 3. 32 MHz.
Blood Cells ; physiology ; Electric Conductivity ; Electrochemistry ; Humans ; Spectrum Analysis ; methods

OBJECTIVETo study the effect on the corrosion resistance of Cr alloy in the artificial saliva with different pH value in vitro.

METHODSCompared to Ti alloy, electrochemical technique was used to measure the electric potential of corrosion (E(corr)), current density of corrosion (I(corr)) Cr alloy in the artificial saliva with different pH value. The corrosion and corrosion resistance mechanism on Cr alloy in the artificial saliva with different pH value had been investigated by the EIS curves.

RESULTSThe corrosion resistance of Co-Cr alloy was better than Ti alloy. The value of I(corr) was lower and the value of R(p) was larger than Ti alloy. The corrosion resistance of Ni-Cr alloy was worse than Ti alloy. The value of I(corr) was larger and the value of R(p) was lower than Ti alloy. The pH value in the artificial saliva was decreased, the I(corr) value of three types of alloy increased, the R(p) value of three types of alloy decreased. But the changes of Co-Cr alloy was smaller than that of Ti alloy or Ni-Cr alloy.

CONCLUSIONThe corrosion resistance of Co-Cr alloy was superior to that of Ni-Cr alloy and Ti alloy. In the acid artificial saliva, the corrosion resistance of three types of alloy descended evidently.

OBJECTIVEThe aim of this study was to investigate the korrosionsneigung of three metal specimens for casing removable denture by means of electrochemical method.

METHODSThree kinds of test specimens were prepared, including cobalt-chromium alloy, nickel-chrome alloy with titanium and pure titanium. Then they were analyzed via linear polarization in artificial saliva simulating oral environment. From this electrochemical test the polarization curves of these kinds of specimens were recorded. Then the scanning electron microscope (SEM) and X-ray diffractometer (XRD) were applied to assess the morphology and phase changes before and after electrochemical corrosion.

RESULTSNo typical Tafel curve had been recorded for pure titanium, other than cobalt-chromium alloy and nickel-chrome alloy with titanium. Nickel-chrome alloy with titanium got more negative corrosion potential and higher corrosion current than cobalt-chromium alloy. Via SEM, the obvious changes were observed on the morphology and phase before and after corrosion on cobalt-chromium and nickel-chrome alloy with titanium specimens while pure titanium having no change. The XRD provided us little changes on these all three materials.

CONCLUSIONThe results confirm that the korrosionsneigung of the studied cobalt-chromium alloy in artificial saliva is lower than that nickel-chrome alloy with titanium. Pure titanium is the most stable one of the three materials and is extreme hard to be etched.

OBJECTIVETo investigate the variation of the corrosion resistance of micro-arc oxidation film on titanium by electrochemical methods in simulated body fluid.

METHODSMicro-arc oxidation film was formed on the titanium surface using micro-arc oxidation. The morphology was observed with scanning electron microscopy (SEM) and the phase composition was analyzed using X-ray diffraction (XRD). Polarization curves and electrochemical impedance spectroscopy (EIS) in simulated body fluid were examined with electrochemical methods.

RESULTSOn the titanium surface with micro-arc oxidation, the film consisted of many volcanic micropores. The film formed was a titanium dioxide (TiO(2)) with peaks for both anatase and rutile phases. In addition, hydroxylapatite was also observed. The self-corrosion potential and self-corrosion current density of titanium with micro-arc oxidation film were -0.255 V and 0.80 microA/cm(2) respectively, while those of untreated titanium were -0.358 V and 0.55 microA/cm(2). Electrochemical impedance spectroscopy confirmed the model of equivalent circuits reasonable.

CONCLUSIONSThe results of electrochemical examinations indicate that micro-arc oxidation film increases the corrosion resistance of titanium.

Sterigmatocystin (ST), the secondary metabolite of many kinds of filamentous fungi, is a potent carcinogen structurally related to the aflatoxins (AFT). With similar chemical structure, sterigmatocystion behaves much the homogeneous properties to aflatoxins, both of these mycotoxins exhibit similar biological properties due to their bisfuranoid structure. Since the common, and even heavier pollution, found in foods and feeds-stuff, sterigmatocystion is more harmful than aflatoxins. The reported detection methods of sterigmatocystion included the Thin-layer Chromatography, the High-Performance-Liquid Chromatography, the Enzyme-Linked Immunosorbant Assay and the PCR detection to the toxic gene, however studies about both easy and inexpensive electro-chemical methods have not been found. Our previous studies had discovered that Sterigmatocystin (ST) exist similar sensitivity towards aflatoxin-detoxifizyme (ADTZ), which we had isolated from a fungus, as aflatoxin does. In this work, the preliminary study on electrochemical analysis and determination of ST with triplet electrode enzyme-biosensor system (Ag/AgCl as the reference electrode, Pt and Au as the pair and work electrode, respectively) was carried out. Multiwall-carbon-nanotube (MWNT) had been used to increase the electron transportation on electrode. In the research, the Au electrode was modified by MWNT-immobilized ADTZ, and then the voltammertric behavior of ST was studied by means of cyclic voltammogram analysis and different pulse analysis. Autoprobe CP Research Atomic Force Microscope and TECNAI 10 Transmission Electron Microscope, had been used to detect the MWNT as well as the surface of MWNT-modified ADTZ. The voltammertric behavior of ST was studied by means of cyclic voltammogram analysis and different pulse analysis. The results show that the red-ox peak potential of ST is at the point of -600 mV, the linear detection range is from 8.32 x 10(-5) to 66.56 x 10(-5) mg/mL, the detection limit is at 8.32 x 10(-5) mg/mL, and the response time is 10 seconds. This study provided a good basic work for further research.
Biosensing Techniques ; methods ; Electrochemistry ; Microscopy, Atomic Force ; Microscopy, Electron, Transmission ; Nanotubes, Carbon ; chemistry ; Sterigmatocystin ; analysis

OBJECTIVEThe aim of this study is to determine the electrochemical corrosion characteristics of Ni-Cr alloys in vitro.

METHODSThe electrochemical corrosion behavior of Ni-Cr alloys was studied by polarization curves in artificial saliva at 36.5 degrees C (pH = 7.0) to measure the corrosion potential and self-corrosion current density. With X-ray photoelectron spectroscopy, the element content was analyzed.

RESULTSIt was found that the dot corrosion voltage of Ni-Cr was -390 mv, and passivation voltage -160 mv. The area of active dissolvation was from -160 mv to -270 mv. The self-corrosion current density is 0.262 micro Acm(-2). From XPS, the content of Ni, Cr, Mo, Fe was increasing gradually, and the content of O, C was decreasing gradually. The content of Ca decreased because Ca existed in the artificial saliva.

CONCLUSIONAfter polarization curve test, Ni-Cr alloy would occur corrosive reaction, and the corrosion product would attach to the surface of the material.

AIMTo study the determination of dopamine (DA) in the presence of ascorbic acid (AA) using poly (isonicotinic acid) film modified electrode.

METHODSThe cyclic voltammetry and differential pulse voltammetry were used to study the electrochemical behavior of DA at the poly (isonicotinic acid) film modified electrode.

RESULTSThe poly (isonicotinic acid) film modified electrode showed an electrocatalytic effect on DA, and shifted the oxidation of AA to negative potential. The difference between the oxidation potentials of DA and AA was 204 mV, thus, AA did not interfere with the determination of DA. The linear range between the anodic currents and DA concentration was: 1.0 x 10(-7)-2.0 x 10(-5) and 2.0 x 10(-5)-1.0 x 10(-4) mol.L-1. The detection limit was 8.0 x 10(-9) mol.L-1.

CONCLUSIONThe useful life period of the modified electrode is three weeks at least. The modified electrode can be used to the determination of DA in the sample.