In this study, a new, simple, and sensitive method for voltammetric detection of silver nanoparticles was developed. This method was successfully used for fabricating a highly sensitive voltammetric immunosensor on the basis of a silver-nanoparticle-labelled sandwich-type immunoassay for human chorionic gonadotropin (hCG) used as a model protein. This immunosensor comprises a primary antibody immobilized on the surface of a screen-printed carbon strip and a silver-nanoparticle-labelled secondary antibody. After an immunoreaction, silver nanoparticles were captured on the electrode surface, and their quantity was immediately measured electrically, as follows. First, the silver nanoparticles were electrically oxidized to silver ions, and then, silver ions were electrodeposited on the electrode surface. Finally, the amount of deposited silver was determined using differential pulse voltammetry. These detection processes of silver nanoparticles were carried out on the same surface as that used for the immunoassay. Under optimized conditions, a linear relation between logarithmic current peak and logarithmic concentration of hCG was obtained in the range 10–1000 pg mL−1 in a 3 µL analyte sample. The detection limit for hCG was evaluated to be 7.2 pg mL−1 (122 fM, 7.2×10−5 IU cm−1, S/N=3). The proposed detection method has a wide variety of promising applications in electrochemical analysis.
Li4+xTi4.95−xNb0.05O12−δ (x=0.11∼0.13) materials were synthesized by using a spray-drying method followed by heat treating at 600∼900°C in air. Chemical and structural studies of the final products were done by X-ray diffraction (XRD) and inductively coupled plasma mass spectrometry (ICP-MS) etc. The optimum synthesis condition of the materials was examined in relation to the electrochemical characteristics including charge-discharge cycling tests. The charge-discharge cycling results of several the Nb-substituted samples indicated that the samples prepared at heat treatment temperature of 700°C for 12 h showed best cycling performance with the discharge capacity of 175∼140 mAh g−1 at the discharge rate of 0.5∼3C.
The changes in the anode and cathode potentials in the horizontal plane of a polymer electrolyte fuel cell (PEFC) under starving conditions for either air or fuel were studied using a single cell furnished with four reference electrodes which were located around the anode and the cathode. The distance between a reference electrode and the anode (or the cathode) was only 2 mm. When air starvation occurred, the cathode potentials approached 0 V against RHE, but the distribution of potentials in the horizontal plane of the cell was little changed. When fuel starvation occurred, the difference between the cathode potential in the fuel outlet area and that in the fuel inlet area increased. Immediately after the termination of fuel starvation, the cathode potential in the fuel outlet area shifted quickly and remarkably toward the positive, and it exceeded 1 V against RHE in a few seconds. When fuel supplied to the anode where air had been occupied, the cathode potential in the fuel outlet area reached to 1.5 V vs. RHE, and high possibility of corrosion was suggested at that area. These results are similar to the case of phosphoric acid fuel cell (PAFC).