High-accuracy determination of trace elements by total reflection X-ray fluorescence spectrometry using freeze-dried specimens.

Total reflection X-ray fluorescence (TXRF) analysis is conducted to determine trace elements in a sample solution, which is dropped onto a substrate and dried. Therefore, the form of the residue affects the quantitative results. The absorption of X-ray fluorescence (XRF) follows the Lambert-Beer law; the absorption effect of XRF in a thick residue (dotted-type residue) is stronger than that in a thin residue (film-type residue). The absorption effect is particularly remarkable during the determination of low-Z elements in a high-elemental concentration solution. In this study, we propose a new film-like-residue preparation process based on the freeze-drying method to obtain accurate TXRF results. The sample solution is dropped onto the substrate and inserted into a chamber. The chamber is cooled using liquid nitrogen; resultantly, an aliquot of the sample is frozen. The chamber is depressurized using a vacuum pump, and the freeze-dried residue is prepared by maintaining the chamber at room temperature. To evaluate the efficiency of the freeze-drying-based method for sample preparation for TXRF analysis, we prepare a multi-element solution containing high-elemental concentration components. For the residue prepared using the freeze-drying method, the relative standard deviations of the quantitative values and the minimum detection limits are improved because the absorption effect is weakened. The sample preparation process based on the freeze-drying method facilitates accurate TXRF analysis of high-elemental concentration solutions and can be applied for the analysis of trace elements in different types of solutions such as environmental water and wastewater.

De Novo Synthesis of Basal Bacterial Cell Division Proteins FtsZ, FtsA, and ZipA Inside Giant Vesicles.

Cell division is the most dynamic event in the cell cycle. Recently, efforts have been made to reconstruct it using the individual component proteins to obtain a better understanding of the process of self-reproduction of cells. However, such reconstruction studies are frequently hampered by difficulties in preparing membrane-associated proteins. Here we demonstrate a de novo synthesis approach based on a cell-free translation system. Genes for fundamental cell division proteins, FtsZ, FtsA, and ZipA, were expressed inside the lipid compartment of giant vesicles (GVs). The synthesized proteins showed polymerization, membrane localization, and eventually membrane deformation. Notably, we found that this morphological change of the vesicle is forced by only FtsZ and ZipA, which form clusters on the membrane at the vesicle interior. Our cell-free approach provides a platform for studying protein dynamics associated with lipid membrane and paves the way to create a synthetic cell that undergoes self-reproduction.