An easy and cost-effective fabrication method of microfluidic cell culture devices is presented. A consumer laser cutter was employed to fabricate an acrylic mold possessing convex microchannel patterns. The mold was successfully fabricated by both laser engraving and laser cutting. A poly(dimethylsiloxane) substrate possessing recessed channel patterns was obtained after molding, and then bonded to the bottom part of a cell culture dish to complete the device. Human umbilical vein endothelial cells (HUVEC) were cultured in the microchannel and oriented along the direction of the fluid flow. Another device possessing a porous membrane sandwiched with a microchannel and a well was fabricated to co-culture HUVEC with HeLa cells. HUVEC reached confluence in the microchannel. However, the density of HUVEC decreased after co-culture with HeLa cells for 24 h. We expect that the present fabrication method can be utilized by researchers not familiar with microfabrication, and can accelerate the application of microfluidic devices to cell-based experiments.
Electrochemically active (charged and/or redox active) species are under the influence of the electric field at the electrode surface. Electrochemical reactions vary the concentration of the electrochemically active species at the electrode surface from the bulk solution. The reaction fields affected by the electric potential and the chemical potential gradients are known as the electrochemical double layer and the diffusion layer, respectively. Three characteristic situations, such as the electrical double layer at a microporous electrode, potential-dependent adsorption of redox active ion, and bioelectrocatalytic reaction at a micro electrode, are modeled and numerically simulated. In a micro pore, the electrical double layers will overlap with each other. This overlapping causes a decrement of the double layer capacitance of the electrode. The adsorption of the charged redox active species at the electrode surface depends on the electrode potential. The maximum adsorption occurs around its standard redox potential. The mediator-type bioelectrocatalytic reaction at the microelectrode is able to provides a steady-state current. When the enzymatic reaction is extremely fast, the current is controlled by the diffusion of the substrate. Understanding the concentration profiles of the components in the system will provide an understanding of electrochemical reactions.
The safety of tap water is kept by evaluating chemical species under the Water Supply Act in Japan. The total concentrations of five anionic surfactants, linear alkylbenzene sulfonate homologues having different lengths of alkyl chains are regulated by using standard solutions of sodium alkylbenzene sulfonate under the law. Each homologue is measured as the total amount of many kinds of isomers for tap-water analysis. These days, the metrological traceability is frequently required to ensure the reliability of analytical result. However, it is difficult to establish the traceability for determining the total amount of an isomeric mixture. In this research, the application of quantitative NMR for determining the total anionic surfactant concentrations in commercial standard solutions was studied, and they were successfully quantified with an uncertainty of 0.5 % or less. Moreover, we validated the approach through comparisons between our results and reference values of the standard solutions.
Due to the increase of industrial use of rare earth elements, their amounts in the environment should also increase in the future. To estimate the human intake of rare earth elements in the future, the soil-to-crop transfer factor (TF), which is defined as a concentration ratio between crop (mg kg−1-dry) and soil (mg kg−1-dry), is a useful tool. Unfortunately, however, only a limited number of TF data sets for rare earth elements was available for agricultural crops world widely (number of TF data ≤ 20). Because rice is a staple food in Japan, in this study, paddy soil-to-brown rice transfer of rare earth elements, i.e., La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy. Ho, Er, Tm, Yb, and Lu (hereafter REE) were determined by measuring the concentrations in brown rice and associated soil sample sets collected from 98 sites throughout Japan. The soil and rice samples were digested separately and we measured their REE concentrations by ICP-MS; the measured values were used to calculate TF values of REE (number of TF data = 57 - 91). The obtained TF values distributed log-normally, so that the geometric mean (GM) for each REE was calculated. The GM of TF ranged from 4.2 × 10−5 to 6.9 × 10−4, and no significant difference was observed among REE. The dataset size increments provided greater confidence in them compared with the previous values. In brown rice grain, by comparing the GM of REE concentrations in brown rice and rice bran, it was clear that the concentrations of light REE in the rice bran part were higher than those in the white rice part; however, heavy REE tended to show only a slight increase in the rice bran compared to those in the white rice part.
In Lake Biwa, an increase of refractory dissolved organic matter (DOM) has been a problem since 1985. The main origin of this material may be soil humic substances and algal DOM. The fractionation of hydrophobic acids (humic substances) with DAX-8 resin is time consuming and cannot be applied to water samples whose DOC concentrations are low. Thus, a simple analysis of humic substances in water samples using a three-dimensional excitation emission matrix (3-DEEM) and DOC was investigated. This was compared with fractionation analysis, and applied to the dynamics of humic substances in Lake Biwa and its surrounding rivers. The results of humic substances in Yodo rivers by simple analysis using soil fulvic acid (Dando FA) as a standard were in relatively good agreement with those by the fractionation analysis, except for Uji River, where the water of Lake Biwa have an affect through Seta River. This simple analysis was also applied to the dynamics of humic substances in the rivers flowing into Lake Biwa. In the case of a simple analysis of humic substances in Lake Biwa, Biwako FA was used as a standard instead of Dando FA.
In determining As and Se in soil samples by ICP-MS, doubly charged ions due to Nd, Sm, and Gd cause severe spectral interferences. In the present work, a separation method of Nd, Sm, and Gd by cation exchange was examined. As a result, it was found that Nd, Sm, and Gd could be removed by cation exchange when the concentration of HCl was smaller than 0.1 mol L−1, while As and Se could be recovered quantitatively. The recovery values of As and Se were 104.7 ± 2.1 % and 100.3 ± 0.4 %, respectively, and their detection limits were 0.006 mg kg−1 and 0.003 mg kg−1; in the case that 1 mol L−1 HCl extracted solution (6 g of soil sample was extracted with 200 mL of 1 mol L−1 HCl) was diluted 50-times and treated with 0.40 g of cation exchange resin. The feasibility of the present method was examined by analyzing soil certified reference material (JSAC 0402). The present method was applicable for the determination of As and Se in various soil samples.