An electrochemical oxidation of methanol in a strong acid solution was investigated at a polycrystalline platinum electrode in the presence of different concentrations of hypochlorite. The addition of a slight amount of hypochlorite brought about drastic increase in the oxidation current of methanol, because the presence of hypochlorite inhibited the formation of a platinum oxide film on platinum electrodes. However, the oxidation current of methanol decreased with increasing the concentration of coexisting hypochlorite. The result may be due to i) the enhancement of the methanol adsorption to the surface of platinum electrodes by the inhibition of the formation of oxide film, and ii) the inhibition of methanol adsorption on platinum electrodes by higher concentration of NaClO and chemical compounds generated by the chemical reaction between methanol and increased hypochlorite. Electrochemical oxidation of methanol on a polycrystalline platinum electrode in strong acidic solution was observed in the presence of different concentrations of NaClO. The results showed that the oxidation current of methanol increased rapidly with the addition of a small amount of NaClO. However, the oxidation current of methanol decreased with increasing the concentration of coexisted NaClO.
[Introduction] MicroRNA (miRNA), which is RNA molecule with approximately 22 nucleotides in length, has attracted attention as novel biomarkers for the diagnosis of cancer, hepatitis, and other conditions. The miRNA has been commonly detected by RT-qPCR, used for synthesizing and quantifying cDNA. We can detect minute quantities of miRNA by this method. However, it requires laborious procedures, complex reagents, and fluorescent probes for labeling DNA. Thus, simple and rapid detection methods of miRNA have been required for point-of-care testing. When microparticles are exposed to a rotating electric field, the electrostatic interaction between the induced polar charges on the particles and the rotating electric field generates the torque on the particles. This phenomenon is called electrorotation (ROT). The rotation rate depends on the electrical properties of the particle surface. We developed the miRNA detection system based on the decrease of ROT rate of rod-shaped glass microparticles (micro-rods) by binding miRNA. The surface of micro-rods was modified by peptide nucleic acid (PNA) with a complementary sequence of target miRNA. The recognition of miRNA charged negatively to the modified PNA gives rise to the increase of surface conductivity of micro-rods and thereby the decrease of the rotation rate. In addition, the surface conductivity of micro-rods was almost constant by introducing PNA without the charge. Thus, the system could provide the simple detection of miRNA required no labeling with fluorescence molecules. [Experimental Methods] ROT measurements of micro-rods were conducted by a three-dimensional interdigitated array electrode device (3D-IDA) (Fig. A). The device consisted of two glass substrates with micropatterns of IDA (35 µm in electrode width and 70 µm in gaps between electrodes) made of indium-tin-oxide (ITO). A substrate was mounted orthogonally to another substrate via double adhesive tape (60 µm in thickness), resulting in the formation of microgrids (70 µm in length) surrounded by four microband electrodes. Applying AC voltages with a phase difference of 90 degrees each to the four microband electrodes generates a rotational electric field in microgrids. Micro-rods were treated with 100 mM 3-aminopropyltriethoxysilane for 1 hour, 10 mM 3-Sulfo-N-succinimidyl 4-(N-Maleimide-methyl) cyclohexane-1-carboxylate sodium salt for 1 hour, and 5 µM thiolated single-stranded PNA for 4 hours to modify the surface by PNA. The PNA-modified micro-rods were then treated with miRNA for 1 hour. The temperature gradually decreased from 45 ºC to 20 ºC at 0.83 ºC min -1 and then kept at room temperature for 30 min. The treated micro-rods were injected into the 3D-IDA and subjected to the ROT measurement. [Results and Discussion] The application of voltage (10 Vpp, 100 kHz) to the 3D-IDA caused the micro-rods to rotate at the center of each grid (Fig. B). The rotation rate decreased with increasing the length of micro-rods. The micro-rods with the length of 40 µm that is the maximum frequency value of the length were selectively observed in this work. The PNA-modified micro-rods introduced in the device adsorbed on the IDA substrate. The adsorption could be due to the electrostatic interaction between the positive charge on micro-rods derived from unreacted amino group introduced for the PNA modification and the negative charge on the IDA substrate. Most of micro-rods treated with miRNA were rotated at the center of grids. For the micro-rods treated with 5 nM miRNA, the rotation rate slightly increased with increasing the applied frequency up to 50 kHz, followed by a decrease of the rate (Fig. C). Rotation rate decreased with increasing the miRNA concentration. Furthermore, the frequency with maximum rate shifted to higher-frequency region with increasing the concentration. These results were attributed to the increase of the surface conductivity by binding miRNA with the negative charge on the micro-rods. However, the micro-rods treated with non-complementary miRNA absorbed on the IDA substrate to observe no electrorotation. In addition, the rotation was inhibited by the shift of the rotation center of microrods to the edge of electrodes by applying AC voltage with over 200 kHz. The shift of the center is due to the force of the negative dielectrophoresis. These results indicate that the rotation rate of micro-rods in lower frequency region allows to the determination of miRNA with target sequence without fluorescence label. Figure 1
We applied a rapid and simple fabrication method of the island pattern of particles and cells to discriminating cells with specific surface antigen. The Upper interdigitated microband array (IDA) electrode was mounted on the lower substrate with the same design to fabricate a microfluidic-channel device for dielectrophoretic manipulation. Grid formation of electrodes was fabricated by rotating the upper template IDA by 90° relative to the lower IDA. A suspension of particles modified with anti-CD33 antibody or/and HL60 cells was introduced into the channel. AC electric signal (typically 20 V peak-to-peak, 100 kHz) was then applied to the bands on the upper and lower IDA, resulting in the formation of island patterns at the intersections with low electric fields. The accumulated particles and cells were fixed to produce the complexes through the immunoreactions between the antibody immobilized on the particle and CD33 on the cell surface. The complexes were only produced by the corresponded pair of antigen-antibody. It is noted that the time required for single sensing is as short as 6 min in the presented procedure. Furthermore, the present method for a novel cell binding assay does not require pretreatment such as target labeling or washing of unbound cells.
Scanning electrochemical microscopy (SECM) has been used to noninvasively characterize oxygen consumption rate of single mammalian embryos and oocytes under physiological condition in culture medium at 37degC. Local oxygen concentration profile near the embryo sample was monitored by scanning with a Pt microelectrode probe, and then mass transfer rate for oxygen has been estimated based on spherical diffusion theory. A bovine embryo at two-cell stage was located in either a conventional culture dish or a cone-shaped microwell and compared the differences in concentration profile and diffusion behavior. We found that the cone-shaped microwell functions to amplify the oxygen concentration difference between the sample surface and the bulk. Further more, a measuring plate equipped with the cone-shaped six-microwells was developed to easily handle many embryos in a short time. The respiration activities significantly increased with the embryo development for both bovine and mouse.
