A microtiter plate or microplate or microwell plate or multiwell, is a flat
plate with multiple "wells" used as small test tubes. The microplate has
become a standard tool in analytical research and clinical diagnostic testing
laboratories. A very common usage is in the enzyme-linked immunosorbent assay,
the basis of most modern medical diagnostic testing in humans and
animals. A microplate typically has 6, 24, 96,
384 or even 1536 sample wells arranged in a 2:3 rectangular matrix. Some
microplates have even been manufactured with 3456 or even 9600 wells, and an
"array tape" product has been developed that provides a continuous strip of
microplates embossed on a flexible plastic tape.
Each well of a microplate typically holds somewhere between tens of
nanolitres to several millilitres of liquid. They can also be used to store
dry powder or as racks to support glass tube inserts. Wells can be either
circular or square. For compound storage applications, square wells with close
fitting silicone cap-mats are preferred. Microplates can be stored at low
temperatures for long periods, may be heated to increase the rate of solvent
evaporation from their wells and can even be heat-sealed with foil or clear
film. Microplates with an embedded layer of filter material were developed in the
early 1980s by several companies, and today, there are microplates for just
about every application in life science research which involves filtration,
separation, optical detection, storage, reaction mixing, cell culture and
detection of antimicrobial activity. The enormous growth in studies of whole
live cells has led to an entirely new range of microplate products which are
"tissue culture treated" especially for this work. The surfaces of these
products are modified using an oxygen plasma discharge to make their surfaces
more hydrophilic so that it becomes easier for adherent cells to grow on the
surface which would otherwise be strongly hydrophobic.
A number of companies have developed robots to specifically handle
microplates. These robots may be liquid handlers which aspirate or dispense
liquid samples from and to these plates, or "plate movers" which transport them
between instruments, plate stackers which store microplates during these
processes, plate hotels for longer term storage, plate washers for processing
plates, plate thermal sealers for applying heat seals, de-sealers for
removing heat seals, or microplate incubators to ensure constant
temperature during testing. Instrument companies have designed plate readers
which can detect specific biological, chemical or physical events in samples
stored in these plates. Manufacture and composition
Microplates are manufactured in a variety of materials. The most common is
polystyrene, used for most optical detection microplates. It can be
coloured white by the addition of titanium dioxide for optical absorbance
or luminescence detection or black by the addition of carbon for fluorescent
biological assays. Polypropylene is used for the construction of plates subject
to wide changes in temperature, such as storage at -80 °C and thermal cycling.
It has excellent properties for the long-term storage of novel chemical
compounds. Polycarbonate is cheap and easy to mould and has been used for
disposable microplates for the polymerase chain reaction method of DNA
amplification. Cyclo-olefins are now being used to provide microplates which
transmit ultraviolet light for use in newly developed assays. There are also
microplates constructed from solid pieces of glass and quartz for special
applications. The most common manufacturing process is
injection molding, used for polystyrene, polypropylene and cyclo-olefin ( no such
Material, however microplates are made from a variety of Polymers to resist a
wide temperature and chemical resistance. There are also plates made
from Glass, a combination of Plastic and with a glass bottom. Vacuum forming can
be used with many other plastics such as polycarbonate. Composite microplates, In
addition filter bottom platesSPE plates and even some advanced PCR plate designs
use multiple components which are moulded separately and later assembled
into a finished product. ELISA plates may now be assembled from twelve
separate strips of eight wells, making it easier to only partially use a plate.
This saves cost for the scientist. History
The earliest microplate was created in 1951 by a Hungarian, Dr. Gyula Takátsy,
who machined 6 rows of 12 "wells" in Lucite. However, common usage of the
microplate began in the late 1950s when John Liner in USA had introduced a
molded version. By 1990 there were more than 15 companies producing a wide range
of microplates with different features. It was estimated that 125 million
microplates were used in 2000 alone. The word "Microtiter" is a registered
trademark of Cooke Engineering Company, and Thermo Electron OY is the last
listed owner of the trademark It is now more usual to use the generic term
"microplate". Other tradenames for Microplates include
Viewplate, Unifilter introduced in the early 1990s by Polyfiltronics and sold
by Packard Instrument which is now part of Perkin Elmer
In 1996, the Society for Biomolecular Screening, later known as Society for
Biomolecular Sciences, began an initiative to create a standard
definition of a microtiter plate. A series of standards was proposed in 2003
and published by the American National Standards Institute on behalf of the
SBS. The standards govern various characteristics of a microplate
including well dimensions as well as plate properties, which allows
interoperability between microplates, instrumentation and equipment from
different suppliers, and is particularly important in laboratory automation. In
2010, the Society for Biomolecular Sciences merged with the Association for
Laboratory Automation to form a new organisation, the Society for Laboratory
Automation and Screening. Henceforth, the microplate standards are known as
ANSI/SLAS standards. References
External links [1] An article about the invention of
the microplate, published in G.I.T. Laboratory Journal
[2] Dr. Gyula Takátsy, at the Hungarian National Center of Epidemiology website
[3] Official website publishing Microplate Standards