Yeast biosensors have also been designed for the detection of water pollutants
[37]. A luminescence-based biosensor was developed for the detection of EDCs,
which employed yeast cells immobilized in calcium alginate or polyvinyl
alcohol-based hydrogels. Saccharomyces cerevisiae was genetically engineered by
incorporating luciferase reporter gene. The expression of this reporter gene was
mediated by estrogen receptor alpha. Thus, the detection of estrogen disrupting
chemicals such as 17-b-estradiol was possible. The system was stable as the
luminescence-based detection was maintained after storage of the biosensor at −80
°C for one month [38].
3.2 Different Types of Transducers
Based on transducers used in the fabrication of biosensors, the biosensors may be
classified into the following four categories:
(1) Electrochemical
(2) Thermal
(3) Optical
(4) Piezoelectric.
3.2.1 Electrochemical Biosensor
An electrochemical biosensor typically consists of a transducer, which functions
electrochemically. A typical electrochemical measurement incorporates the use of a
working electrode and a counter electrode through which a current flows due to the
difference in the respective electrode potential. A reference electrode is also
included, which is maintained at a stable potential and helps in the transduction of
the electrochemical reaction [39, 40]. The electrical circuit of the transducer consists mainly of an analyte medium, present in liquid form, which is a key distinguishing feature as compared to an electrical transducer. The analyte takes part in
the electrochemical reaction and works as a detector. Depending upon the response
from the analyte, the sensor relays the measurement to an electronic system in terms
of voltage, current or impedance.
The electrochemical transducers depending on the type of measurement are
discussed below:
Potentiometric type transducer: This type of transducer involves the measurement
of the voltage between the electrodes at the indicator and reference or between two
reference electrodes parted by a membrane. The measurement of the ion activity or
the gas concentration in the logarithmic scale is proportional to the difference of
potentials at the indicator and the reference electrode.
Materials in Bio-Sensing of Water Pollutants
195
[37]. A luminescence-based biosensor was developed for the detection of EDCs,
which employed yeast cells immobilized in calcium alginate or polyvinyl
alcohol-based hydrogels. Saccharomyces cerevisiae was genetically engineered by
incorporating luciferase reporter gene. The expression of this reporter gene was
mediated by estrogen receptor alpha. Thus, the detection of estrogen disrupting
chemicals such as 17-b-estradiol was possible. The system was stable as the
luminescence-based detection was maintained after storage of the biosensor at −80
°C for one month [38].
3.2 Different Types of Transducers
Based on transducers used in the fabrication of biosensors, the biosensors may be
classified into the following four categories:
(1) Electrochemical
(2) Thermal
(3) Optical
(4) Piezoelectric.
3.2.1 Electrochemical Biosensor
An electrochemical biosensor typically consists of a transducer, which functions
electrochemically. A typical electrochemical measurement incorporates the use of a
working electrode and a counter electrode through which a current flows due to the
difference in the respective electrode potential. A reference electrode is also
included, which is maintained at a stable potential and helps in the transduction of
the electrochemical reaction [39, 40]. The electrical circuit of the transducer consists mainly of an analyte medium, present in liquid form, which is a key distinguishing feature as compared to an electrical transducer. The analyte takes part in
the electrochemical reaction and works as a detector. Depending upon the response
from the analyte, the sensor relays the measurement to an electronic system in terms
of voltage, current or impedance.
The electrochemical transducers depending on the type of measurement are
discussed below:
Potentiometric type transducer: This type of transducer involves the measurement
of the voltage between the electrodes at the indicator and reference or between two
reference electrodes parted by a membrane. The measurement of the ion activity or
the gas concentration in the logarithmic scale is proportional to the difference of
potentials at the indicator and the reference electrode.
Materials in Bio-Sensing of Water Pollutants
195