Zkoumání tkání pomocí STEM detektoru
Rastrovací elektronový mikroskop MIRA3 LMU se Schottkyho autoemisní katodou je určený pro snímání vodivých i nevodivých preparátů ve vysokém...
Observation of surface morphology as well as internal structure of different types of biological samples repre-sents an important part of Biology. Ultrathin sections of various cells and tissues are usually studied in transmis-sion electron microscopes (TEM). TESCAN’s STEM detector (scanning transmission electron microscope detector) with excellent resolution allows high quality investigation of the ultrastructure of samples prepared by the techniques ordinarily used for the TEM. Combination of field emission SEM MIRA3 with the STEM detector and the ability to acquire large panoramic images up to 42k × 42k represents very efficient tool for imaging large areas with excellent resolution.
Ultrathin sections of various biological samples are usually studied using the TEM where accelerating voltage up to hundreds of kilovolts can be used. If such high accelerating voltage is applied the value of resolution is higher but the electron scattering and the contrast is significantly lower. Lowering the accelerating voltage enhance electron scattering and thus more contrasting images can be achieved.
Standard sample preparation techniques for TEM observation can be used to prepare ultrathin sections of biological materials for investigation by the STEM detector.
Chemical fixation, dehydration, embedding and polymerization of a resin followed by ultrathin sectioning (from 50 to 100 nm) was performed to obtain delicate ultrathin sections which are placed on the standard TEM grids (3.05 mm). Biological samples consist mainly of chemical elements with smaller atomic mass that insufficiently scattered primary electrons. Therefore, the contrast of the ultrathin sections was enhanced directly on the grids using heavy metal salts, e. g. lead citrate and uranyl acetate.
Resolution 0.8 nm at 30 kV of STEM detector allows investigation of the cell and tissue nanostructure. Further-more, its unique feature simultaneous bright field and dark field imaging for observation is available.
Ultrathin sections are very delicate samples. Therefore, the usage of the electrostatic beam blanker is strong-ly recommended to avoid destruction of fine samples (e. g. ultrathin sections) during acquisition. Electrostatic beam blanker blanks the beam when it is not scanning the sample. As a result the specimen is minimally exposed to the electron beam and is protected from the destruction by radiation.