Biology Reference
In-Depth Information
6.8. MINIATURIZED DETECTION OF WATERBORNE
PATHOGENS
Classifying miniaturized electrochemical biosensors for waterborne
pathogen detection and analysis is a difficult task. One can define differ-
ent categories according to the type of bioreceptor, the type of electrical
probe, the fabrication processes, the type of electrochemical transduction
(see Section 6.2-6.6 ) or the type of pathogen (see Chapter 2 for an over-
view of waterborne pathogens).
6.8.1. Bioreceptors
Bioreceptors can be classified into six different categories including (1)
antibodies, (2) enzymes, (3) nucleic acids, (4) cells or specific cell proteins,
(5) biomimetic structures and (6) bacteriophages. The choice of one of
them will depend on the target analyte. It can be an antigen on the whole
pathogen surface, a protein produced by the pathogen, a nucleic acid of
the pathogen, and a specific cellular response of a living microorganism in
contact with the pathogen (i.e. antibody production, membrane deterio-
ration, etc. …). The two main factors important for every biorecognition
element are affinity and specificity. New techniques allow the selection of
more specific ligands. They are evolving rapidly and represent the future of
recognition elements. Antibodies are the most common bioreceptor. 69,70
They may be polyclonal, monoclonal or recombinant depending on the
way they are synthesized. They can bind with high affinity against a tar-
get protein, another antibody, or even a whole pathogen. Biosensors using
enzymes as the biorecognition elements have been reported. 71-73 Enzymes
are chosen based on their specific binding capability and their catalytic activ-
ity, which provide electron transfer to the working electrode and are the
key elements for highly sensitive analysis. However, in most cases, enzymes
are used to function as labels and not as bioreceptors. Recent advances in
nucleic acid recognition have expanded the use of deoxyribonucleic acid
as a bioreceptor. 74,75 For pathogen detection, the identification of a target
analyte's nucleic acid is achieved by hybridization of the complementary
base pairs. Since each organism has unique deoxyribonucleic acid sequences,
any self-replicating microorganism can be easily identified. With cell-based
bioreceptors, biorecognition is based on a whole cell that is capable to respond
to stimuli. 76,77 The transduction mechanism is a two-step process. First, the
cell converts the effect of the pathogen into a cellular response. Second, the
 
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