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

Microanalytical Assays 685

TABLE I Historical Landmarks in the Development of Chemical Sensors and Biosensors
Date Event Investigators
1916 First report on the immobilization of proteins: Adsorption of invertase to activated charcoal J. M. Nelson and E. G. Griffin
1922 First glass pH electrode W. S. Hughes
1954 Invention of the oxygen electrode L. C. Clark, Jr.
Invention of the pCO 2 electrode R. W. Stow and B. F. Randall
1962 First amperometric biosensor: Glucose oxidase-based enzyme electrode for glucose L. C. Clark, Jr., and C. Lyons
1964 Coated piezoelectric quartz crystals as sensors for water, hydrocarbons, polar molecules, W. H. King, Jr.
and hydrogen sulfide
1969 First potentiometric biosensor: Acrylamide-immobilized urease on an ammonia electrode G. Guilbault and J. Montalvo
to detect urea
1972–1974 First commercial enzyme electrode (for glucose) and glucose analyzer using the electrode
(Yellow Springs Instruments)
1975 First binding-protein biosensor: Immobilized concanavalin A in a polyvinyl chloride J. Janata
membrane on a platinum wire electrode to measure yeast mannan
Invention of the pCO 2 /pO 2 optrode D. W. Lubbers and N. Opitz
1979 Surface acoustic wave sensors for gases J. Wohltjen and R. Dessey
1979 Fiber-optic-based biosensor for glucose J. S. Schultz and G. Sims
1980 Fiber-optic pH sensors for in vivo blood gases J. I. Peterson, S. R. Goldstein,
R. V. Fitzgerald, and
D. K. Buckhold
1983 Molecular-level fabrication techniques and theory for molecular-level electronic devices F. L. Carter
1986 First tissue-based biosensor: Antennules from blue crabs mounted in a chamber with S. L. Belli and G. A. Rechnitz
a platinum electrode to detect amino acids
1987 First receptor-based biosensor: Acetylcholine receptor on a capacitance transducer R. F. Taylor, I. G. Marenchic,
for cholinergics and E. J. Cook
1991 First array sensor on a chip S. Fodor

glucose oxidase, glucose is oxidized to gluconic acid and well because the platinum electrode is protected from the
hydrogen peroxide, which can further be decomposed to external environment by a polymer film; this film allows
produce water with the net utilization of one mole of oxy- gases to pass relatively freely into the electrochemical
gen. This chemical reaction produces a number of changes compartment but prevents organic materials such as glu-
such as pH, temperature, and H 2 O 2 that could be detected cose or other electroactive substances from passing into
for the purpose of creating a glucose sensor as discussed the detector compartment. This combination of detector
below. and enzyme biorecognition elements resulted in the first
documented biosensor that became the basis for a series of
Glucose + 2O 2 → Gluconic Acid + H 2 O 2 , commercial biosensors produced by the YSI Corporation,
discussed below.
2H 2 O 2 → 2H 2 O + O 2 .
This sensor works in the presence other sugars, amino
However, Dr. Clark utilized the fact that one result of this acids, or biochemicals in the sample fluid that might pro-
catalyzedreactionisthedepletionofthemolecularoxygen vide interference in other methods. The influence of these
in the vicinity of the enzyme, since the biological reaction potential interferences on the output of the sensor will be
utilizes one mole of oxygen for each mole of glucose that minor because glucose oxidase has a very high selectivity
is oxidized. He showed that the enzymatically produced for glucose and does not oxidize other compounds to any
change in oxygen content can be detected polarograph- measurable extent.
ically by the so-called oxygen electrode, also developed One of the requirements of a practical biosensor is that
by Dr. Clark. This particular device is a polarographic cell the various components have to be assembled into a de-
encapsulated by a gas-permeable polymer membrane such vice that preserves the configuration of the various ele-
as a silicon rubber. Oxygen that diffuses into the cell re- ments so that they maintain their functional capabilities
acts at a polarized electrode to form hydroxide, and the over time. Figure 8 shows the structure of sensor meeting
current is proportional to the oxygen concentration in the these requirements that is marketed by YSI; in this family
enzyme compartment. Clark’s electrochemical cell works ofdevicessamplesizeisontheorderof10–25µl.Byusing