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over a millisecond timescale. Here a more advanced light microscope (often called an

imaging system) is required.

Some microscopes are more suited to specific applications than others. There may

be constraints imposed by the specimen. Images may be required from specimens of

vastly different sizes and magnifications (Fig. 4.2). For example, for imaging whole

animals (metres), through tissues and embryos (micrometres), and down to cells,

proteins and DNA (nm). The study of living cells may require time resolution from

days, for example, when imaging neuronal development or disease processes to

milliseconds, for example, when imaging cell signalling events.

The field of microscopy has undergone a renaissance over the past 20 years with

many technological improvements to the instruments. Most images produced by

microscopes are now recorded electronically using digital imaging techniques –

digital cameras, digital image acquisition software, digital printing and digital display

methods. In addition, vast improvements have been made in the biological aspects of

specimen preparation. These advancements on both fronts have fostered many more

applications of the microscope in biomedical research.

Viruses Yeast elegansC.

Small

molecules

Globular

protein

Bacteria

Embryos

Ribosomes Plant cells

Organelles Animal cells

Electron microscope

Light microscope

MRI

Human eye

0.1 nm 1 nm 10 nm 100 nm 1.0 m 10 m 100 m 1 mm

Fig. 4.2The relative sizes of a selection of biological specimens and some of the devices used to image

them. The range of resolution for each instrument is included in the dark bars at the base of the figure.

MRI, magnetic resonance imaging.

102 Microscopy