9780521516358book.pdf

specialised applications, for example using total internal reflection microscopy

(TIRF) (Section 4.3.5).

Applications of the microscope in biomedical research may be relatively simple and

routine; for example, a quick check of the status of a preparation or of the health of

cells growing in a plastic dish in tissue culture. Here, a simple bench-top light

microscope is perfectly adequate. On the other hand, the application may be more

involved, for example, measuring the concentration of calcium in a living embryo

Electron

gun

Projector

lens

Specimen

(EM grid)

Light

source

Eyepiece

Slide

Specimen

Coverslip

Condenser

lens

Objective

lens

Light microscope electron microscopeTransmission

Eye or digital camera Viewing screen ordigital camera

(Resolution limit 0.2 m)

Live and dead cells

(Resolution limit 1 nm)

Dead cells only

Fig. 4.1Light and electron microscopy. Schematic that compares the path of light through a compound light

microscope (LM) with the path of electrons through a transmission electron microscope (TEM). Light from a

lamp (LM) or a beam of electrons from an electron gun (TEM) is focussed at the specimen by a glass condenser

lens (LM) or electromagnetic lenses (TEM). For the LM the specimen is mounted on a glass slide with a coverslip

placed on top, and for the TEM the specimen is placed on a copper or gold electron microscope grid. The image

is magnified with an objective lens, glass in the LM and electromagnetic lens in the TEM, and projected onto

a detector with the eyepiece lens in the LM or the projector lens in the TEM. The detector can be the eye or

a digital camera in the LM or a phosphorescent viewing screen or digital camera in the TEM. (Light and EM

images courtesy of Tatyana Svitkina, University of Pennsylvania, USA.)

101 4.1 Introduction