Positively charged nanogold label allows the observation of fine cell filopodia and flagella in solution by atmospheric scanning electron microscopy

Optical microscopy is generally the first choice to observe microbes and cells. However, its resolution is not always sufficient to reveal specific target structures, such as flagella and pili, which are only nanometers wide. ASEM is an attractive higher resolution alternative, as the sample is observed in aqueous solution at atmospheric pressure. Sample pretreatment for ASEM only comprises simple tasks including fixation, gold labeling, and reagent exchange, taking less than 1 h in total. The lengthy sample pretreatments often required for more classical electron microscopies, such as embedding and dehydration, are unnecessary, and native morphology is preserved. In this study, positively charged nanogold particles were used to label the surfaces of bacteria and cultured animal cells, exploiting their net negative surface charge. After gold enhancement to increase the size of the nanogold particles, ASEM imaging of the bacteria in aqueous solution revealed pili and delicate spiral flagella. This natural shape contrasts starkly with images of dried flagella recorded by standard SEM. Positively charged nanogold labeled the plasma membrane of cultured COS7 cells, and after enhancement allowed filopodia as thin as 100 nm in diameter to be clearly visualized. Based on these studies, ASEM combined with positively charged nanogold labeling promises to become an important tool for the study of cell morphology and dynamics in the near future. Microsc. Res. Tech. 77:153–160, 2014. © 2013 Wiley Periodicals, Inc.     

Identifying sources and mass balance of dioxin pollution in Lake Shinji Basin, Japan

On the basis of congener-specific analysis of dioxins in a dated sediment core, the sources and behavior of dioxins in Lake Shinji Basin, Japan, were estimated. The dioxins in the core showed that their deposition in the lake increased rapidly during the 1960s, peaked in the early 1970s, and then decreased gradually. Principal component analysis of the congener-specific data showed that three major sources existed: pentachlorophenol (PCP), chloronitrophen (CNP), and combustion. PCP and CNP are paddy field herbicides used extensively in the basin. The time trends of source contributions were estimated by multiple regression analysis using the source profiles. The results revealed that dioxin emission from PCP and CNP herbicides was high in the 1960s and the early 1970s, respectively. The contributions from PCP, CNP, and combustion in recent surface sediment were about 68, 16, and 16% in terms of total amount of dioxins. From the decreasing trend of dioxin deposition in the lake after extensive herbicide use, the amount of dioxins that accumulated in the agricultural soil in the basin was estimated to have decreased by about 2%/yr or a half-life of about 35 yr, indicating that dioxin runoff from agricultural fields would continue for a long time.     

Enhancement of the nitrogen fixation efficiency of genetically-engineered Rhizobium with high catalase activity

The vktA catalase gene, which had been cloned from Vibrio rumoiensis S-1^T having extraordinarily high catalase activity, was introduced into the root nodule bacterium, Rhizobium leguminosarum bv. phaseoli USDA 2676. The catalase activity of the vktA-transformed R. leguminosarum cells (free-living) was three orders in magnitude higher than that of the parent cells and this transformant could grow in a higher concentration of exogenous hydrogen peroxide (H₂O₂). The vktA-transformant was inoculated to the host plant (Phaseolus vulgaris L.) and the nodulation efficiency was evaluated. The results showed that the nitrogen-fixing activity of nodules was increased 1.7 to 2.3 times as compared to the parent. The levels of H₂O₂ in nodules formed by the vktA-transformant were decreased by around 73%, while those of leghemoglobins (Lba and Lbb) were increased by 1.2 (Lba) and 2.1 (Lbb) times compared with the parent. These results indicated that the increase of catalase activity in rhizobia could be useful to improve the nitrogen-fixing efficiency of nodules by the reduction of H₂O₂ content concomitantly with the enhancement of leghemoglobins contents.     

High‐Performance n‐Channel Organic Transistors Using High‐Molecular‐Weight Electron‐Deficient Copolymers and Amine‐Tailed Self‐Assembled Monolayers

While high‐performance p‐type semiconducting polymers are widely reported, their n‐type counterparts are still rare in terms of quantity and quality. Here, an improved Stille polymerization protocol using chlorobenzene as the solvent and palladium(0)/copper(I) as the catalyst is developed to synthesize high‐quality n‐type polymers with number‐average molecular weight up to 10⁵ g mol^?1. Furthermore, by sp²‐nitrogen atoms (sp²‐N) substitution, three new n‐type polymers, namely, pBTTz, pPPT, and pSNT, are synthesized, and the effect of different sp²‐N substitution positions on the device performances is studied for the first time. It is found that the incorporation of sp²‐N into the acceptor units rather than the donor units results in superior crystalline microstructures and higher electron mobilities. Furthermore, an amine‐tailed self‐assembled monolayer (SAM) is smoothly formed on a Si/SiO₂ substrate by a simple spin‐coating technique, which can facilitate the accumulation of electrons and lead to more perfect unipolar n‐type transistor performances. Therefore, a remarkably high unipolar electron mobility up to 5.35 cm² V^?1 s^?1 with a low threshold voltage (≈1 V) and high on/off current ratio of ≈10⁷ is demonstrated for the pSNT‐based devices, which are among the highest values for unipolar n‐type semiconducting polymers.     

Phospholipid-Coated Boronic Oxide Nanoparticles as Boron Agents for Boron Neutron Capture Therapy

Minimally invasive boron neutron capture therapy (BNCT) is an elegant approach for cancer treatment. The highly selective and efficient deliverability of boron agents to cancer cells is the key to maximizing the therapeutic benefits of BNCT. In addition, enhancement of the frequencies to achieve boron neutron capture reaction is also significant in improving therapeutic efficacy by providing a highly concentrated boron agent in each boron nanoparticle. As the density of the thermal neutron beam remains low, it is unable to induce high-efficiency cell destruction. Herein, we report phospholipid-coated boronic oxide nanoparticles as agents for BNCT that can provide a highly concentrated boron atom in each nanoparticle. The current system exhibited in vitro BNCT activity seven times higher than that of commercial boron agents. Furthermore, the system could penetrate cancer spheroids deeply, efficiently suppressing thermal neutron irradiation-induced growth.     

BAMO/NMMO Copolymer with Polyester Initiation

In order to improve of mechanical properties at low temperature region, 3,3-bis(azidomethyl)oxetan (BAMO), 3-nitratomethyl-3-methyloxetane (NMMO) and polyester (PE) copolymer were synthesized by using polyester initiator with boron trifluoride etherate. The molar ratio of each units in the BAMO/NMMO/PE copolymer was 7.4/2.6/0.39 according to the ¹H-NMR spectrum analysis and was almost exactly the same composition as the monomer fed (7/3/0.33). The relative composition of triad microstructures was same as theoretical value and they were randomly arranged. The PE, which was a replacement of 1,4-butanediol, acted as an excellent soft segment in the copolymer, and the glass transition point of the elastomer was 4.8 degrees lowered by the replacement. This effect was also verified in the mechanical properties of the composite propellant and the tensile elongation was increased from 15% to 40%percnt; at −40 °C.     

Designing of passive cooling silicon oxynitride composite cement

Si₂N₂O, which shows high radiative cooling ability, was mixed and hardened with ordinary Portland cement to prepare cement specimens having radiative cooling abilities. The bulk cement specimens were prepared with diameters of 50 mm and two different thicknesses of 3 and 10 mm, and Si₂N₂O powder were mixed with 2 and 10 wt%. The temperatures of the blank specimen (without radiative cooling Si₂N₂O powder) and the cement composite specimens were measured in a thermostatic chamber maintained at ambient temperature, and the radiative cooling abilities of the specimens were evaluated. The obtained specimens showed a radiative cooling ability in the range 0.077–0.92 W/m²; thus, the results of this study suggested the possibility of a cement composite with passive cooling property.