Mass spectrometric imaging of ginsenosides localization in Panax ginseng root.

We performed mass spectrometric imaging (MSI) to localize ginsenosides (Rb(1), Rb(2) or Rc, and Rf) in cross-sections of the Panax ginseng root at a resolution of 100 microm using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Tandem mass spectrometry (MS/MS) of alkali metal-adducted ginsenoside ions revealed structural information of the corresponding saccharides and aglycone. MALDI-MSI confirmed that ginsenosides were located more in the cortex and the periderm than that in the medulla of a lateral root. In addition, it revealed that localization of ginsenosides in a root tip (diameter, 2.7 mm) is higher than that in the center of the root (diameter, 7.3 mm). A quantitative difference was detected between localizations of protopanaxadiol-type ginsenoside (Rb(1), Rb(2), or Rc) and protopanaxatriol-type ginsenoside (Rf) in the root. This imaging approach is a promising technique for rapid evaluation and identification of medicinal saponins in plant tissues.

Maximum diameter of the rod-shaped specimen for transmission electron microtomography without the "missing wedge".

In our recent study, the complete rotation of a rod-shaped specimen during transmission electron microscopy (TEM) has been successfully carried out, yielding a truly quantitative three-dimensional (3D) structure of a ZrO(2)/polymer nano-composite. This result allows the further development of transmission electron microtomography (TEMT) for materials science. The diameter of the rod-shaped specimen was about 150 nm, which may not be statistically large enough to evaluate structural parameters, e.g., volume fraction of Zr nano-particles. Thus, it is preferable to image rods with larger diameters in 3D. In this study, several rod-shaped specimens whose diameters ranged from 150 to 530 nm were subjected to the "distortion-free TEMT". The maximum diameters, l, observable under 200 and 300 kV-TEMTs were, respectively, 460-470 and 600-670 nm (corresponding the maximum relative diameters, l/lambda (lambda: mean free path), were ca. 2.2 and 2.7-3.0).

Transmission electron microtomography without the "missing wedge" for quantitative structural analysis.

A three-dimensional (3D) visualization and structural analysis of a rod-shaped specimen of a zirconia/polymer nanocomposite material were carried out by transmission electron microtomography (TEMT) with particular emphasis on complete rotation of the specimen (tilt angular range: +/-90 degrees ). In order to achieve such an ideal experimental condition for the TEMT, improvements in the specimen as well as the sample holder were made. A rod-shaped specimen was necessary in order to obtain a high transmission of the specimen upon tilting to large angles. The image resolution of the reconstructed tomogram was isotropic, in sharp contrast to the anisotropic image resolution of the conventional TEMT with a limited angular range (the "missing wedge" problem). A volume fraction of zirconia, phi, evaluated from the 3D reconstruction was in quantitative agreement with the known composition of the nanocomposite. A series of 3D reconstructions was made from the tilt series with complete rotation by limiting the maximum tilt angle, alpha, from which a couple of structural parameters, the volume fraction and surface area per unit volume, Sigma, of the zirconia, were evaluated as a function of alpha. It was confirmed from actual experimental data that both phi and Sigma slightly decreased with the increasing alpha and reached constant values at around alpha=80 degrees , suggesting that the specimen may have to be tilted to +/-80 degrees for truly quantitative measurements.