3.1.1 Biocatalytic Biosensors
The enzymes used as recognition element by immobilization on the surface of the
electrode. When more than one enzyme is immobilized in the same layer, there are
many advantages which can be achieved. These may include conversion of an
analyte into the final product through several steps of enzymatic conversions. Thus,
the range of biosensor analyte is increased. Wollenberger et al. described this
functionality of the multi-enzyme system [12]. Another advantage associated with
multiple enzyme systems is an enhancement of biosensor selectivity by reducing
the local interference of electrochemical substances. Another approach for
enhancing the efficiency of the enzyme-based biosensor is the use of an organic
solvent, which provides a hydrophilic microenvironment for the partition between
the enzyme active site and the matrix. Andreescu et al. studied the detection of
endocrine—disrupting chemicals (EDCs) by developing a tyrosinase based
biosensor. Different polyphenol estrogens were studied such as resveratrol, quercetin and genistein and their structures were compared to the synthetic EDCs. Thus,
a tyrosinase based biosensor was developed for the detection of many phyto and
xenoestrogens having a polyphenolic structure in wastewater [13].
3.1.2 Bioaffinity Based Biosensors
The biosensor can also be fabricated by the use of bio-affinity agents. These are the
macromolecules which are isolated from the biological sources and may or may not
be engineered. When these components react with the analytes, equilibrium is
reached after this, there is no further interaction with the analyte. The
analyte-macromolecule complex so formed is measured by the integrated detector.
A modification to this type of biosensor could be the measurement of the
bio-complex reaction using another complementary biochemical reaction. The
signals of these secondary reactions are then measured using a detector [5]. The
bio-affinity reactions could be either an antigen-antibody reaction or receptor—
ligand reaction.
Antigen-antibody reaction: The immunochemical reactions between the antigen and
the antibody are utilized for the development of these types of biosensors.
Antibodies (also known as immunoglobulins) are Y-shaped proteins produced by
white blood cells and recognize a complementary macromolecule known as an
antigen. This type of bio-complexing has been widely employed in the detection of
pollutants in wastewater. Blake et al., in 1996, showed that 2A81G5 monoclonal
antibodies could recognize 16 different types of metal—EDTA complexes. This
study showed that equilibrium binding constants for cadmium and mercury were
higher than other metal—EDTA complexes. It was suggested that histidine amino
acid in the heavy chain of the antibody might assist in the binding of the
cadmium-EDTA complex [14].
Materials in Bio-Sensing of Water Pollutants
191
The enzymes used as recognition element by immobilization on the surface of the
electrode. When more than one enzyme is immobilized in the same layer, there are
many advantages which can be achieved. These may include conversion of an
analyte into the final product through several steps of enzymatic conversions. Thus,
the range of biosensor analyte is increased. Wollenberger et al. described this
functionality of the multi-enzyme system [12]. Another advantage associated with
multiple enzyme systems is an enhancement of biosensor selectivity by reducing
the local interference of electrochemical substances. Another approach for
enhancing the efficiency of the enzyme-based biosensor is the use of an organic
solvent, which provides a hydrophilic microenvironment for the partition between
the enzyme active site and the matrix. Andreescu et al. studied the detection of
endocrine—disrupting chemicals (EDCs) by developing a tyrosinase based
biosensor. Different polyphenol estrogens were studied such as resveratrol, quercetin and genistein and their structures were compared to the synthetic EDCs. Thus,
a tyrosinase based biosensor was developed for the detection of many phyto and
xenoestrogens having a polyphenolic structure in wastewater [13].
3.1.2 Bioaffinity Based Biosensors
The biosensor can also be fabricated by the use of bio-affinity agents. These are the
macromolecules which are isolated from the biological sources and may or may not
be engineered. When these components react with the analytes, equilibrium is
reached after this, there is no further interaction with the analyte. The
analyte-macromolecule complex so formed is measured by the integrated detector.
A modification to this type of biosensor could be the measurement of the
bio-complex reaction using another complementary biochemical reaction. The
signals of these secondary reactions are then measured using a detector [5]. The
bio-affinity reactions could be either an antigen-antibody reaction or receptor—
ligand reaction.
Antigen-antibody reaction: The immunochemical reactions between the antigen and
the antibody are utilized for the development of these types of biosensors.
Antibodies (also known as immunoglobulins) are Y-shaped proteins produced by
white blood cells and recognize a complementary macromolecule known as an
antigen. This type of bio-complexing has been widely employed in the detection of
pollutants in wastewater. Blake et al., in 1996, showed that 2A81G5 monoclonal
antibodies could recognize 16 different types of metal—EDTA complexes. This
study showed that equilibrium binding constants for cadmium and mercury were
higher than other metal—EDTA complexes. It was suggested that histidine amino
acid in the heavy chain of the antibody might assist in the binding of the
cadmium-EDTA complex [14].
Materials in Bio-Sensing of Water Pollutants
191