Transducer - a device that converts energy from one form into another
e.g., telephone companies use transducers to convert
sound energy into electrical energy to be carried long-
distance through telephone lines and then another
transducer at the receiving end to convert the electrical
energy back into sound
A biosensor is a sensing device that consists of a biological
component coupled to a transducer that converts biochemical
activity into, most commonly, electrical energy.
USE FOR BIOSENSORS: monitoring processes for better control in
the biotechnology industry in both R&D product development and
quality control in the plant.
At the present time monitoring of a bioprocess is limited to the
measurement of pH, temperature, and dissolved oxygen. A biosensor
can be used to monitor the presence of product, either biomass, enzyme,
or antibody, or of a by-product of the process as an indirect measure
of process conditions. Biosensors could make monitoring and control
in the biotech industry accurate and reproducible.
Specific fields of interest:
- the bioprocess industry
- the medical field
- environmental detection of pollutants or toxins
All biosensors must perform two tasks: molecular recognition and
The biological component could be an enzyme, antibody, cell
membrane receptors, tissue slices, or microbial cells that interact
with a specific analyte. The use of enzymes and antibodies is the
most popular because they are simpler. Tissue slices and microbial
cells are more complicated to use because they must be kept alive;
nutrients must be supplied and wastes removed.
The transducer can measure electrical activity (by either
measuring voltage or current), light (optical), sound, mass (piezo-
electric), or temperature.
In this tutorial we will concentrate on electrical transducers for
application in the bioprocess industry. We will only consider
biosensors that use enzymes or antibodies as their biological
In the operation of a bioreactor it is always necessary to monitor
the properties of the media in which the cells are living.
Typically the situation involves an organism that will not survive
or will not produce a product if the media is not maintained at the
correct physical parameters.
Measuring media properties such as temperature and pH is relatively easy.
Measuring the concentrations of nutrients, metabolic wastes, and
products is not easy, but like the measuring of temperature and pH
they are of great importance to maintenance of the biological
environment that exists in a bioreactor.
One possibility for monitoring media properties such as concentration
is the use of biosensers.
A biosensor consists of an immobilized biological system such as
a cell colony, an enzyme,or an antibody; and a measuring device. In
the presence of a certain molecule the biological system changes the
The measuring device sensitive to this change sends a signal.
This signal can be converted into the measurement parameter.
Often the biological system is an actual cell.
The key thing to remember is that it is an actual organism that
detects the concentration change of the molecule in the media.
This organism could be the same one as the one in the media or
it could be different. In either case it must be kept separate from
This can be done with a membrane that is permeable to the molecule that
is being measured but impermeable to the cells and most other
macromolecules in the reactor media.
The change that biosensor organism produces is usually a result of
its use of the measured molecule in its metabolic processes.
The biosensor organism might metabolize molecule A and release
molecule B into the system. A B-electrode would be affected by this.
In another common variation the biosensor organism metabolizes
molecule A by using molecule B which is sensed. A
B-electrode would detect the change in the concentration of B.
What are the advantages of biosensors over other measurement schemes?
There are also disadvantages to be dealt with.
- They can measure nonpolar molecules that do not repond to most measurement devices.
- They are as specific as the immobilized system used in them.
- They allow rapid continuous control.