Page 180 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioTechnology

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Encyclopedia of Physical Science and Technology EN009J-69 July 19, 2001 22:50

680 Microanalytical Assays

Electroosmotic The motion of a liquid through a mem- analyzed and the increasing voltage used to produce
brane under the influence of an applied electric field. the current.
Electrophoresis The motion of colloidal particles sus- Potentiometry A precision instrument for measuring an
pended in a fluid medium, due to the influence of an electric potential difference of constant polarity with-
electric field on the medium. Also called cataphoresis. out drawing current from the circuit being examined.
Enzyme Any of various complex organic substances, as Receptor Any cellular macromolecule that undergoes
pepsin, originating from living cells and capable of pro- combination with a hormone, neurotransmitter, drug,
ducing certain chemical changes in organic substances or intracellular messenger to initiate a change in cell
by catalytic action, as in digestion. function.
Dialysis A process in which solute molecules are ex- Spectrophotometer An apparatus to measure the pro-
changed between two liquids through a membrane in portion of the incident light (or other electromagnetic
response to differences in chemical potentials between radiation) absorbed (or transmitted) by a substance or
the liquids. solution at each wavelength of the specturm.
Fluorescence A type of luminescence that consists of the Transducer Anydevicethatconvertsaquantityofenergy
emission by a substance of electromagnetic radiation, from one form into another.
especially visible light, immediately (10–100 ns) after
the absorption of energy derived from exciting radi-
ation of another, usually shorter, wavelength or from ONE OF THE MAJOR technological advances that has
incident subatomic particles (especially electrons or α helped the field of microassays has been the translation
particles); the property of emitting such radiation. of fabrication methods from the chip industry into mi-
Hybridization The act or process of forming a macro- crofabrication of devices for chemical sensors. This type
molecular hybrid by the artificial recombination of of fabrication procedure allows the synthesis of systems
subunits. that can have various components. Each of these compo-
Immobilize To render any agent, whether a micro- or nents has some similarities to the components or stages
macrosolute, a particle, or an intact cell, nondispersible that are used in the traditional chemical analytical labo-
in an aqueous medium with retention of its specific ratory. These stages included sample preparation, sample
ligating, antigenic, catalytic, or other properties. purification followed by sample measurement, and then fi-
Immunoassays Any of a group of techniques for the nally output of an electronic signal. The microfabrication
measurement of specific biochemcial substances, com- methods allow the production of multiple array systems
monly at low concentrations and in complex mixtures thatcanbeassmallas500nmoneachsidesothathundreds
such as biological fluids, that depend upon the speci- of the sensors can be placed in one device. A number of
ficity and high affinity shown by suitably prepared and transducer technologies can be used as sensors for particu-
selected antibodies. lar analytes. These include electrodes, optical techniques,
Immunoglobulin Any member of a group of proteins oc- temperature measurement, charge measurement, capac-
curring in higher animals as major components of the ity measurement, and more recently magnetoresistance.
immune system. Also, atomic force microscopy has been used as a way of
Macromolecule Any molecule composed of a very measuring interactions between molecules at the almost
large number of atoms, operationally defined as any molecular level. The general structure of a biosensor is
molecule of mass greater than about 10 kDa that is in- shown in Fig. 1.
capable of passing through the pores of dialysis tubing Most of the efforts for the development of sensors and
as generally used. analytical methods has been for clinical diagnosis such as
Osmosis The spontaneous net flow of solvent by dif- for glucose, and many of the technologies described here
fusion through a semipermeable membrane from a utilize applications to the clinical field. It should be rec-
phase where the solvent has a higher chemcial po- ognized that there are many other areas and fields where
tential to one where the solvent has a lower chemical sensors can now be used very effectively. This includes
potential. environmental analysis, fertilizers, toxic substances, the
Piezoelectric The generation of electricity or of electric testing of foods, and also the testing of drugs, particu-
polarity in dielectric crystals subjected to mechanical larly hallucinogenic drugs. Further developments in sen-
stress and, conversely, voltage. sor technology has allowed innovative methods for the
Polarography An electrochemical method of quantita- measurement of DNA fragments. Recently discovered
tive analysis based on the relationship between an in- technologies of combinatorial chemistry allow the rapid
creasing current passing through the solution being selection of bioreceptors for specific analytes and also