Photoinduced electron transfer in nanostructures of ultrathin polyimide films containing porphyrin moieties

Photoinduced electron transfer between porphyrin moieties and pyromellitimide fragments has been investigated in multi-layered structures of ultrathin polyimide films prepared by the Langmuir-Blodgett (LB) technique. The LB films were composed of three kinds of polyimides, which contained zinc tetraphenylporphyrin (ZnTPP) unit as an electron donor (D-layer), no chromophoric groups (S-layer), and pyromellitimide fragments as an electron acceptor (A-layer). The layered structure and orientational distribution of porphyrin moieties in the LB films were evaluated by surface plasmon measurement and absorption dichroism measurement, respectively. The thickness of monolayer was estimated to be 0.9 nm for the polyamic acid films and 0.4 nm for the polyimide films. The molecular plane of porphyrin moieties was oriented in the direction parallel to the substrate plane. In the multi-layered structures of polyimide LB films, the efficiencies of photoinduced electron transfer from porphyrin moieties to pyromellitimide fragments varied sharply with the number of spacing layers, indicating that the short-range interactions such as electron transfer could be controlled by the fabric of ultrathin films. The rate of electron transfer observed by the fluorescence quenching measurements was numerically simulated for the nanostructure using the Monte Carlo method.     

Protein Modification with Ribose Generates Nδ-(5-hydro-5-methyl-4-imidazolone-2-yl)-ornithine

Advanced glycation end products (AGEs) are associated with diabetes and its complications. AGEs are formed by the non-enzymatic reactions of proteins and reducing sugars, such as glucose and ribose. Ribose is widely used in glycation research as it generates AGEs more rapidly than glucose. This study analyzed the AGE structures generated from ribose-modified protein by liquid chromatography–quadrupole time-of-flight mass spectrometry. Among these AGEs, N^δ-(5-hydro-5-methyl-4-imidazolone-2-yl)-ornithine (MG-H1) was the most abundant in ribose-glycated bovine serum albumin (ribated-BSA) among others, such as N^ε-(carboxymethyl) lysine, N^ε-(carboxyethyl) lysine, and N^ω-(carboxymethyl) arginine. Surprisingly, MG-H1 was produced by ribated-BSA in a time-dependent manner, whereas methylglyoxal levels (MG) were under the detectable level. In addition, Trapa bispinosa Roxb. hot water extract (TBE) possesses several anti-oxidative compounds, such as ellagic acid, and has been reported to inhibit the formation of MG-H1 in vivo. Thus, we evaluated the inhibitory effects of TBE on MG-H1 formation using ribose- or MG-modified proteins. TBE inhibited MG-H1 formation in gelatin incubated with ribose and ribated-BSA, but not in MG-modified gelatin. Furthermore, MG-H1 formation was inhibited by diethylenetriaminepentaacetic acid. These results demonstrated that ribose reacts with proteins to generate Amadori compounds and form MG-H1 via oxidation.     

Development of a mass-producible on-chip plasmonic nanohole array biosensor

We have developed a polymer film based plasmonic device whose optical properties are tuned for measuring biological samples. The device has a circular nanohole array structure fabricated with a nanoimprint technique using a UV curable polymer, and then gold thin film is deposited by electron beam deposition. Therefore, the device is mass-producible, which is also very important for bioaffinity sensors. First the gold film thickness and hole depth were optimized to obtain the maximum dip shift for the reflection spectra. The dip shift is equivalent to the sensitivity to refractive index changes at the plasmonic device surface. We also calculated the variation in reflection spectra by changing the above conditions using the finite-difference time domain method, and we obtained agreement between the theoretical and experimental curves. The nanohole periodicity was adjusted from 400 to 900 nm to make it possible to perform measurements in the visible wavelength region to measure the aqueous samples with less optical absorption. The tuned bottom filled gold nanohole array was incorporated in a microfluidic device covered with a PDMS based microchannel that was 2 mm wide and 20 μm deep. As a proof of concept, the device was used to detect TNF-α by employing a direct immunochemical reaction on the plasmonic array, and a detection limit of 21 ng mL(-1) was obtained by amplification with colloidal gold labeling instead of enzymatic amplification.     

Fabrication and Application of an Oxide Thermoelectric System

A plate-shaped thermoelectric module was prepared using 140 pairs of p -type Ca₃Co₄O₉ (Co-349) and n -type LaNiO₃ (Ni-113) bulks. The hot-pressed thermoelectric oxide bulks were connected with an Ag paste, incorporating oxide powder, and Ag sheets. The module's open-circuit voltage increases with increasing hot-side temperature ( T _H) and reaches 4.5 V at a T _H of 1072 K in air. No deterioration in output power was seen when power generation was carried out 10 times at a T _H of 723 K with intermediate cooling to room temperature. The module was successfully used to charge a lithium-ion battery in a mobile phone. Thermoelectric modules composed of p -type Co-349 and n -type CaMnO₃ (Mn-113) bulks, which have a pipe shape, were constructed using Ag electrodes and stainless-steel tubes. The devices were connected with the stainless-steel tube coated with ZrO₂ by thermal spray using a dielectric paste composed of silica glass and iron oxide. Power generation was carried out in flame by combustion of natural gas. Water flowed inside the stainless-steel tube for cooling. One module consisting of 54 pairs of legs can generate 1.5 V, 0.28 W, and steam simultaneously by installing in an instantaneous water heater. Power generation was carried out four times with intermediate cooling. Deterioration in the open-circuit voltage of the module was not observed after the fourth combustion.     

Effect of Mixed Grain Sizes on the Thermoelectric Propertiesof Ca0.9Yb0.1MnO3

Ca_0.9Yb_0.1MnO₃ has been identified as a material that might be suitable for thermoelectric applications. We fabricated micro/nanograined Ca_0.9Yb_0.1MnO₃ composites, with the aim of controlling the passage of electrons and phonons simultaneously. Micro/nanograined Ca_0.9Yb_0.1MnO₃ composites containing various fractions of nanosized powder were prepared by sintering mixtures of microparticulate and nanoparticulate Ca_0.9Yb_0.1MnO₃, obtained by solid-state reaction and by gas-phase reaction, respectively. The electrical resistivity increased markedly when the weight fraction of nanosized powder exceeded 50%, probably as a result of a percolation phenomenon. However, the thermal conductivity was considerably reduced when the weight fraction of nanosized powder exceeded 25%, but then remained almost constant. The absolute values of the Seebeck coefficient of micro/nanograined Ca_0.9Yb_0.1MnO₃ composites were larger than those of monolithic micro- or nanograin Ca_0.9Yb_0.1MnO₃, probably as a result of the effects of potential-barrier scattering. The highest dimensionless figure of merit ZT value of 0.09 at 973 K was achieved with a sample containing 50% nanosized powder, and this value is 10% larger than that of monolithic micrograined Ca_0.9Yb_0.1MnO₃.     

Determination of DNA methylation using electrochemiluminescence with surface accumulable coreactant

Cytosine methylation in DNA was determined by an enzyme linked immunosorbent assay (ELISA) with electrochemiluminescence (ECL) detection and employed for the DNA methylation assay of a long and real genomic sample for the first time. The developed method employed an antimethyl cytosine antibody labeled with acetylcholinesterase, which was added to recognize single methylated cytosine in a DNA oligomer. The acetylcholinesterase converted acetylthiocholine (substrate) to thiocholine (product), which was accumulated on a gold electrode surface via gold-thiol binding. This surface accumulated preconcentration made it possible to observe bright and distinctive ECL by applying a potential to the gold electrode in the presence of a tris(2,2-bipyridyl)ruthenium complex luminophore when the analyte DNA contained a methylation region. Methyl-cytosine was measured quantitatively in the 1-100 pmol range, which exhibits sufficiently high sensitivity to achieve real DNA measurements without amplification by a polymerase chain reaction (PCR). The proposed ECL method also exhibited high selectivity for methyl-cytosine against nonmethylated cytosine, guanine, thymine, and adenine nucleotides. Finally, original and methylated DNA samples were clearly distinguished with our method using a real DNA bacteriophage sample (48,502 base pairs).     

DNA methylation analysis triggered by bulge specific immuno-recognition

We report the sequence-selective discrimination of the cytosine methylation status in DNA with anti methylcytosine antibody for the first time. This was realized by employing an affinity measurement involving the target methylcytosine in a bulge region and anti methylcytosine antibody, following hybridization with a bulge-inducing DNA to ensure that only the target methylcytosine is located in the bulge. The affinity of the antibody for methylcytosine in the bulge was 79% of that in a single strand of DNA; however, the affinity for nontarget methylcytosine in a double strand of DNA decreased greatly. This is because the antibody cannot bind with an inwardly turned methylcytosine in the duplex region owing to the large antibody size. In contrast, the methylcytosine in the bulge is recognized by the antibody because it is available to rotate freely owing to the single bond between deoxyribose and phosphate in a DNA chain. By employing the difference between the affinity in the bulge and that in the duplex, we could determine selectively whether or not the target cytosine was methylated in an O(6)-methylguanine DNA methyltransferase (MGMT) promoter sequence with a single base level. The proposed bulge-specific assay technique can be combined with a widely used absorbance measurement method that employs the color change in tetramethyl benzidine induced by horseradish peroxidase-labeled secondary antibody. The sequence-selective discrimination of the methylation status could also be obtained with various types of interfering genomic DNA contamination without any conventional bisulfite treatment, polymerase chain reaction, (PCR) or electrophoresis.     

Electrochemical surface plasmon resonance measurement based on gold nanohole array fabricated by nanoimprinting technique

In this paper, we describe our development of an electrochemical surface plasmon resonance (EC-SPR) measurement device based on a bottom-filled gold nanohole array. The polymer based gold nanohole array was fabricated with a UV nanoimprint technique and electron beam gold deposition. Direct reflection mode measurement was used to monitor the SPR dip in the reflection spectra. A cyclic voltammogram was also operated by using the standard three electrodes containing working electrode having a gold nanohole array and counter and reference electrodes. The gold nanohole array was modified with an osmium-poly(vinylpyridine)-wired horseradish peroxidase (Os-gel-HRP) film, and its redox state induced by the change in potential was monitored simultaneously. The redox state of the local film was obtained simply by scanning the sample substrate stage. The substrate modified with Os-gel-HRP film was incorporated in a microfluidic chip, and then the hydrogen peroxide was determined in terms of the redox change in the Os complex mediator from the slope of the SPR dip shift. The linear relation of hydrogen peroxide from 10 to 250 μM was successfully monitored, and a high conversion efficiency was realized.