Biosensors for pesticides - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 31

2.1 INTRODUCTION

2.1.1 Need for pesticide biosensors
In agriculture, farmers randomly use several organic toxic compounds, i.e. pesticides,
herbicides, insecticides, to control diseases for obtaining high yields. Pesticide is a term
used in a broad sense for chemicals, synthetic or natural, that are used for the control
of insects, fungi, bacteria, weeds, nematodes, rodents and other pests [1, 2]. The unde-
graded pesticide residues may enter into the food chains through air, water and soil
and cause several health problems to ecosystems, birds, animals and human beings.
Pesticides can be carcinogenic or citogenic. They can produce bone marrow diseases,
infertility, nerve disorders and immunological and respiratory diseases. To circumvent
these problems the USA and European governments have imposed new legislation.
Enforcement of this legislation necessitates reliable monitoring of the environment for
the presence of compounds, which may adversely affect human health and local eco-
systems. The highest permissible levels of different pesticides in water for human use
go from 0.3 to 400

g l 1 [3]. In the last two decades organochlorine insecticides (e.g.
DDT, aldrin and lindane) have been progressively replaced by organophosphorus (e.g.
parathion and malathion) and derivatives of carbamic acid (e.g. carbaryl and aldicarb)
insecticides that show low persistence in the environment but represent a serious risk
due to their high acute toxicity.
The commonly used analytical methods for pesticide analysis include high pres-
sure liquid chromatography, gas chromatography or coupled techniques of GC-MS and
ELISA [4-6]. These conventional methods are sensitive, reliable and precise. In spite
of their advantages, these techniques need expensive instrumentation, require skilled
technicians, and are time consuming, laborious and not easily adoptable for fi eld analy-
sis. The simple and advantageous alternative is the use of biosensors. A biosensor is a
probe that integrates a biological component (e.g. an enzyme, whole cell, antibody, etc.)
with an electronic component to yield a measurable signal. Even though biosensors do
not compete with the above potent chromatographic techniques, they do provide fast
and reliable analysis. These devices are highly useful for preliminary screening before
applying more costly techniques. In the last three decades several quick and low cost
pesticide biosensors have also been developed using enzymes, antibodies, and whole
cells. This chapter comprehensively discusses various aspects of the pesticide biosen-
sors and tries to incorporate all-important aspects; however, addressing all reports in
one chapter is very diffi cult considering the size of the available literature.

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2.1.2 Developments in pesticide biosensors
Acetylcholinesterase (AChE) isolated from various organisms has been used in the
majority of pesticide biosensors. In the early 1950s potentiometric detection was
adopted for pesticide detection. In the middle of the 1980s it was used for the construc-
tion of the fi rst integrated biosensors for detection of pesticides based on inhibition
of AChE. Later rapid changes in science and technology introduced novel genetically