Biosensors for pesticides - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 47

(95%) of simazine immunocomplex within 5 min. However, at lower concentrations of
HCl dissociation was poor, and at higher concentrations antibody was destroyed dras-
tically, though the dissociation was fast. The enzyme pepsin has also been employed
in the regeneration of sensing surface. Pepsin acts on bound antibodies and breaks up
the peptide chains into less active and inactive fragments, which could be more easily
removed in acidic conditions (pH 1.9) [82]. Rodriguez-Mozaz et al. [87] employed
SDS solution (pH 1.9, 5 mg mL 1 ) for the regeneration of the immunosensor surface.

2.5 WHOLE CELL AND TISSUE-BASED PESTICIDE
BIOSENSORS

In whole cell biosensors the enzyme is stable, as it is present in natural biological
surroundings and can reduce the cost of enzyme purifi cation. Potato slices are rich
in polyphenol oxidase (PPO), and PPO activity can be inhibited by atrazine. Thus, a
PPO whole cell biosensor has been reported [119]. A thin slice of potato tissue was
clamped onto the surface of an O 2 selective Clark electrode and catechol was used as
substrate for PPO. The linear detection range and detection limit of this low cost whole
cell-based biosensor are 20-130 M, respectively. A cucumber tissue was

sandwiched between Tefl on and nylon membranes at the surface of an oxygen elec-
trode [14]. An amperometric biosensor has been designed for the detection of ethyl
paraoxon based on the inhibition activity of ascorbate oxidase. The detection limit is
1

µ M and 10 µ

g mL 1 and analysis time for one sample is 10 min. Other plant materials such as
tissues [120] and thylakoid membranes [121] were also employed in pesticide deter-
mination. A novel whole cell biosensing method has been reported for the determi-
nation of herbicide glyphosate by assessing electrophysiological interactions with cell
components ( Johnsongrass ) immobilized in an agarose gel matrix that preserves cell
“physiological” functions. In this biorecognition assay (BERA) cellular response to the
herbicide was evaluated by measuring the cellular electric potential. This preliminary
work showed linear response in potentiometric measurements from 0.1 to 1 mM of
glyphosate [122].
Like plant cells, microbial cells have also been used in whole cell biosensors.
Recombinant E. coli cells, which are capable of hydrolyzing a wide spectrum of OPs
and chemical warfare agents, were entrapped in PVA to prepare a packed column. The
packed column was interfaced with a pH electrode to construct a whole cell biosensor
[54]. The proton released through the hydrolysis of OP pesticides by organophosphate
hydrolase was correlated with the concentration of pesticide. The linear detection range
of paraoxon was from 0.25 to 250

µ

g mL 1 (0.001-1.00 mM) and the cryoimmobilized
organophosphate hydrolase exhibited stability over 2 months in phosphate buffer at
4ºC. Luciferease is another enzyme whose activity can be inhibited by the herbicides.
It presents in bioluminescent cyanobacteria Synechocystis sp. (rec. PCC6803) cells and
has been used in the detection of atrazine, propazine, simazine, paraquat, and glypho-
sate by measuring the luminescence after pesticide inhibition [123]. Interfacing of this
type of luminescent cells with optical transducers may be used to develop low cost

µ