Student Recruitment Transmission electron microscopes Centre for Advanced Microscopy and Outreach Office • A static beam of electrons passes through the The Centre for Advanced Microscopy provides sample, so only very thin specimens can be imaged. state-of-the-art microscopy facilities for research, • This images the interior of the sample. diagnostics, and analysis in life and physical sciences. • A typical TEM has a resolving power of about 0.2nm. These advanced microscopes enable scientists, engineers and technologists to see details of • For TEM the typical maximum magnifications is Microscopy structures at the atomic level through the nanoscale about 1,000,000x. up to the macroscopic level. The facilities here at the • Biological material must be stained with heavy University of Reading have been used in projects as metals to generate contrast in the image. reference card diverse as nematode identification, ballpoint pen design and the analysis of volcanic ash! A student guide Scanning electron microscopes • A beam of electrons is scanned over the surface of the specimen. For more information about our • This generates secondary electrons from the surface Science Outreach Programme please contact: of the specimen. Dr Rachel South • Only the surface is imaged, so specimen thickness Student Recruitment and Outreach Office is not important. University of Reading , Agriculture Building Earley Gate, PO Box 236 • A typical SEM may have a resolving power of about 2nm. Reading RG6 6AR [email protected] • For SEM the typical maximum magnification is Tel (0118) 378 6127 about 100,000x. www.reading.ac.uk/student_recruitment See also: • Biological materials are usually dried and coated with www.reading.ac.uk/cfam metal before they can be imaged in the microscope. www.reading.ac.uk/biologicalsciences Definitions Units of measurement Resolution limit Magnification The ratio of an object’s image size to its 1mm = 1000 micrometres (µm) Resolution is inversely related to the wavelength of the radiation real size. a microscope uses for imaging. 1µm = 1000 nanometres (nm) Resolution The ability to distinguish two adjacent objects The resolution limit of light microscopes is about 200nm, as separate entities. or the maximum useful magnification a light microscope can provide is about 1,000x. Resolution limit The minimum distance between two adjacent 1mm = 10-3 m objects at which they can still be distinguished The resolution limit of electron microscopes is about 0.2nm, as separate entities. 1 µm = 10-3 mm = 10-6 m the maximum useful magnification an electron microscope can provide is about 1,000,000x. 1 nm = 10-3 µm = 10-9 m Some typical sizes of biological objects Width of human hair 20–200 µm (0.02–0.2 mm) Eukaryotic cell 10–100 µm Nucleus 3–10 µm Chloroplast 5–8 µm Mitochondrion 1–3 µm Bacterial cell 1–3 µm (1000–3000 nm) Ribosome 10–20 nm.