Lipids are major components of biomembranes. Therefore, artificial lipid-based particles composed of amphipathic phospholipids are used as a model of biomembranes for life sciences. Furthermore, they are applied to a variety of fields, such as foods, cosmetics, and medical products. In order to produce functionalized lipid membrane vesicles based on the intended use, the control of lipid compositions and the physicochemical properties of the vesicles are important. We have developed an analytical method for the physicochemical properties of membrane vesicles, mainly used for medical applications. Concerning the size analysis of nano-sized membrane vesicles, we developed a size separation method using monolithic capillary columns. Furthermore, by using dynamic light scattering for detection, we used an on-line system that enables both the size separation and determination of analyzed nanoparticles. We have also developed the system for observing lipid membrane vesicles in an aqueous medium using atomic force microscopy. This system has enabled determining the stiffness of a lipid membrane. We elucidated the relationship between the stiffness of the lipid membrane of the nanovesicles and the product performance, such as in vitro release, cell uptake and cell spheroids penetration of the vesicles. These show that the analytical systems introduced here would contribute to the development of lipid membrane nanovesicles for medical applications.
Multiphoton ionization time-of-flight mass spectrometry (MPI-TOFMS) was applied to the measurement of toluene oil-in-water (O/W) emulsions prepared via shirasu porous glass (SPG) membrane emulsification. In the present study, the relationship between small oil droplets introduced into TOFMS and obtained signals was discussed. In the case of a toluene O/W emulsion prepared by a SPG membrane with a pore size of 1 μm, the flow of oil droplets could not be confirmed. Moreover, no spikes were observed on the time profile of the peak area for toluene obtained by MPI-TOFMS. In the case of an O/W emulsion prepared by a SPG membrane with a pore size of 3 μm, oil droplets with a diameter of ca. 12 μm, in addition to droplets of various sizes, were intermittently introduced. Moreover, a lot of spikes were detected on the time profile of the peak area obtained by MPI-TOFMS. In the case of an O/W emulsion prepared by a SPG membrane with a pore size of 5 μm, larger droplets and their aggregates were introduced. Intense spikes were detected on the time profile in the early stage of the measurement, but the number and the intensity of spikes decreased with time due to creaming of the sample. In addition, the minimum diameter of a droplet that produces a detectable spike was calculated to be 3.4 μm in the present study.
The determination of trace-level Rb was achieved by cool plasma ICP-OES, for which the optimum operating conditions for RF power and carrier gas were 750 W and 0.95 mL min−1. Such a highly sensitive analysis could be attributed to the effective suppression of spectral interference from Ar emission lines while measuring the Rb emission line, having improved the signal-to-background ratio by 20-fold. The present method provided an instrumental detection limit of 0.005 mg kg−1 for Rb. Apparent matrix effects of K and Ca were observed for the measurement of Rb by cool plasma ICP-OES, suggesting that approaches are required to cancel the matrix effect for the determination of Rb in real samples. Gravimetric standard addition incorporating an internal standard correction was applied to the determination of Rb in three certified reference materials (CRMs) for food analysis, i.e. NMIJ CRMs 7502-a (white rice flour), 7505-a (tea leaf powder), and 7512-a (milk powder). The observed values for these CRMs were (1.77±0.12) mg kg−1, (7.30±0.24) mg kg−1, and (8.91±0.29) mg kg−1, respectively. These observed values agreed with the certified values: (1.77±0.07) mg kg−1, (7.3±0.3) mg kg−1, and (8.93±0.31) mg kg−1, respectively. Both the observed values and the certified values were given as (mean±expanded uncertainty), while the expanded uncertainty was calculated using a coverage factor (k) of 2, giving a level of confidence of approximately 95 %.
A dissolved oxygen sensor consisting of a poly(acrylamide-co-methacrylic acid) microsphere gel and tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ([Ru(Ph2phen)3]2+) was developed. This sensor determines dissolved oxygen based on the quenching of the fluorescence (peak wavelength: 615 nm) of the Ru complex in microsphere gels that are immobilized on an ITO substrate in the presence of oxygen. The extinction ratio, defined as the ratio of the fluorescence intensity in a solution saturated with oxygen gas to that saturated with nitrogen gas, appeared to be independent of the film condition (62±7 %). A Stern-Volmer plot showed an excellent relationship between the fluorescent intensity and the oxygen concentration with R2 being higher than 0.95; the Ksv value was found to be 0.036 - 0.053. The determination of the dissolved oxygen concentration in a real sample (tap water) showed a relative error of at most 14 % to a commercially available sensor.
The prevention of lifestyle-related diseases is important for improving health and reducing medical costs in aged societies, like Japan. Our country is the most aged society in the world, with medical costs reaching 38 % of the national budget. Thus, the prevention of lifestyle-related diseases is critical for reducing medical costs and improving public health. We improved a fingertip blood sampling kit, to facilitate medical examinations at home. We have collaborated with Fujifilm, the manufacturer of the kit, and KDDI, a leading mobile communications company, that reports test results. Using this system, examinations of 60000 subjects who do not regularly have medical checkups (self-test group) have started throughout Japan. We developed the test kit for performing health checkups based on 65 μL fingertip blood samples. The examinees collect blood samples according to instructions and isolate diluted plasma by themselves. The samples are then mailed to a laboratory. We recently produced a test kit for performing health checkups based on 65 μL fingertip blood samples to measure biochemical parameters. The plasma sample dilution ratio was measured by assessing the sodium level of each diluted sample. The development of a way to measure the dilution of plasma sodium was achieved by using an enzymatic rate assay. Reliable examination data are provided, and thus facilitating exact diagnoses, early detection, and treatment. In the present study, tests were conducted on subjects, including self-employed individuals and housewives, using DEMECAL kits. As a result, the number of subjects who need further examinations was twice as large as those who had already undergone regular medical examinations. This examination system facilitates the early detection and treatment of diseases, while reducing national medical costs and improving public health.
The effects of residual silanol groups of a reversed-phase C18 silica column which was precoated with dodecylammonium chloride (DAC) were examined for the determination of six inorganic anions [iodate ion (IO3−), bromate ion (BrO3−), bromide ion (Br−), nitrite ion (NO2−), nitrate ion (NO3−), and iodide ion (I−)] in seawater by ion chromatography. We used 0.3 M sodium chloride + 0.5 mM DAC + 5 mM phosphate buffer solution (pH 4.5) as an eluent (flow rate, 1 mL min−1) and a UV detector (225 nm) for determination. It was possible to measure the analyte ions within 19 minutes. On the reversed-phase C18 silica column with residual silanol groups, separation between Br− and NO2− was better than those of end-capped columns, thus, retention mechanisms of anions were considered. The repeatability was within 1.55 % (n = 5) of the relative standard deviation (RSD (%)) of retention time, peak area, and peak height, and also was within 2.97 % (n = 48) in a continuous measurement for 24 hours. The calibration curves showed good linearity with a correlation coefficient of r2 > 0.999. The detection limit (S/N = 3) was IO3− (8.3 μg L−1), BrO3− (24 μg L−1), Br− (92 μg L−1), NO2− (0.8 μg L−1), NO3− (3.2 μg L−1), and I− (1.0 μg L−1). Similar results were obtained at a flow rate of 1.5 mL min−1 (measurement time, 13 min per sample). The present method was applied to water samples from Seto Inland Sea waters. The recovery rate by the standard addition was in the range of 93 to 108 %. Further, the method was applied to the depth profiles of anions during the summer season at five points in the Seto Inland Sea (Hiroshima Bay).