Simple and inexpensive apparatus, called "redox monitoring cell," rapidly detects presence of bacteria. Bacteria is detected by measuring drop in oxygen content in test solution. Apparatus consists of vial with two specially designed electrodes connected to sensitive voltmeter

Fealey, R. D.

Renner, W.

English

NASA Technical Reports Server

Solution	 Vial 
Reference 
Electrode 
Glac 
Columr 
Porou 
Plug
Slass 
Envelope 
Sensing 
Electrode
February 1973	 B73-10045 
NASA TECH BRIEF 
Goddard Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Rapid Detection of Bacteria in Foods

and Biological Fluids 
The problem: 
Detection of bacteria is one of the primary concerns 
in food processing and medicine. It is constantly applied 
in the food processing industry to avoid distribution of 
products that may threaten the health of consumers. In 
medicine, on the other hand, the presence of bacteria 
must be detected in human biological fluids such as 
blood, urine, cerebrospinal fluid, etc., to determine the 
presence and nature of infections. Techniques and equip-
ment used in bacterial detection are many and varied; 
however, they are all time consuming and costly. 
Connections To
Voltmeter By

Shielded Cables
The solution: 
A simple and inexpensive apparatus, called the 
"redox monitoring cell", has been developed which 
rapidly detects the presence of bacteria. 
How it's done: 
The apparatus detects bacteria by measuring a drop 
An oxygen content in a test solution. Basically the 
apparatus (see figure) consists of a vial with two specially 
designed electrodes connected to a sensitive voltmeter. 
Before the test is conducted, a fluid sample is poured 
into a vial and mixed with a suitable culture medium to 
permit bacterial growth. In general, foods do not require 
such media because they themselves are sufficient for 
bacterial growth. To maintain bacterial growth, the test 
solution temperature should be kept near that of the 
human body (37° Q. This can be done by placing the 
vial into any commercially available heating block de-
signed for this purpose. Bacteria are then detected by 
observing a voltage drop across the two electrodes 
immersed in the test solution. This drop occurs as a 
result of oxygen consumption by bacteria present in 
the solution. 
Construction of the apparatus is shown in the figure. 
A plain 5/8-inch (1.6-cm) test tube may be used as the 
vial. The two electrodes, connected by shielded cables 
to a voltmeter, are different in composition and struc-
ture. 
The sensing electrode uses a noble metal wire, such as 
platinum, gold, etc., to prevent chemical reaction with 
the test solution. This electrode provides a half-cell 
reaction whose potential is proportional to the oxygen 
content of the test solution. To prevent its exposure to 
oxygen outside the solution, part of this electrode is 
covered with a,glass envelope which is sealed at the top 
with a resilient plug. 
(continued overleaf) 
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	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000045 2020-03-17T06:41:12+00:00Z
The reference electrode, on the other hand, is designed 
to produce a constant half-cell potential using calomel 
or silver-silver chloride wire. The wire is enclosed in a 
glass column which is filled with a saturated solution of 
silver chloride and potassium chloride in ethylene glycol 
containing 5% water. Both ends of the column are 
plugged, with the bottom plug allowing ionic flow 
between the electrode and the test solution. The porosity 
of this plug is approximately 40 angstroms. 
Voltmeters for measuring the potential difference 
between the electrodes are commercially available but 
are carefully selected. Sensitivity should be 1 millivolt. 
Because the electrodes have impedances of approximately 
100 kilohms, while the typical impedance of a test solu-
tion is 500 kiohms, a suitable voltmeter input impedance 
should be at least 10 to 50 megohms to detect a 1-
millivolt change. Most voltmeters, however, may be 
interfaced with the "redox monitoring cell" by use of a 
suitable integrated-circuit operational amplifier of the 
field-effect transistor type.
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: TSP73-10045 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning non-
exclusive or exclusive license for its commercial develop-
ment should be addressed to: 
Patent Counsel 
Goddard Space Flight Center 
Code 204 
Greenbelt, Maryland 20771 
Source: Robert D. Fealey and William Renner

Goddard Space Flight Center

(GSC-1 1738)
. 
B73-10045	 Category 05, 02, 04


Rapid detection of bacteria in foods and biological fluids

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