Page 118 - The Veterinary Laboratory and Field Manual 3rd Edition

The selection, use, maintenance and quality control of laboratory equipment and supplies 87

Figure 2.50 Working principle
of an oil immersion objective.
Photo: Idzi Potters, ITG, Antwerp,
Belgium.

2.5 Specialized technology range of diagnostic tests-kits for veterinary dis-
ease diagnosis at the district and regional level.
ELISa The ELISA plate reader is a rather expensive
but robust piece of equipment, which provides
The technology associated with the ELISA the opportunity to expand the technology sig-
(enzyme linked immunosorbent assay) has nificantly. It is basically a spectrophotometer
made diagnostic serology and antigen capture that is able to rapidly read and record colour or
tests much more accessible for smaller veteri- turbidity in 96 wells in a microtiter plate (Figure
nary laboratories. However, to perform a lot of 2.51 and Figure 2.52). The cheaper models of
tests it is necessary to use a semi-automated plate readers use filters to select a wavelength
ELISA system. This may include a multiplate (each wavelength needs a specific filter), the
system, a photoelectric reader, an automated more expensive readers use a monochromator
washer, shaker and specialist incubators. Many (can select a wavelength from 200 to 999 nm)
ELISA test-kits allow manual processing, but (Figure 2.53).
for multiple sampling, a reliable plate reader It is worth noting that dual-wavelength
which can be set to the wavelength required for measurements can compensate for optical
the test, is needed. The widespread availability interference. Dual wavelength is used in many
of enzyme-linked reagents and suitable colour- microplate-based applications to reduce optical
linked enzyme systems has resulted in a wide interference caused by scratches, fingerprints or

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