10.3.4.1 Amperometric/Voltammetric Biosensors
Biosensors detecting pathogens with respect to variations in current or potential
(Monzo et al. 2015), due to processes like oxidation or reduction of the targeted
biological species, where the electrode is at constant potential or current with respect
to a standard reference electrode (Bard and Faulkner 2001). Cyclic sweep
voltammetry is a common method to acquire data like oxidation/reduction
potentials, reaction kinetics, and mechanisms (Bard and Faulkner 2001; Compton
and Banks 2011). Using carbon electrodes infused with magnetic nanoparticles, the
specific genomic DNA of pathogens and gold nanoparticles in a sandwich assay like
format detection of Salmonella and E. coli could be performed (Blow 2015).
Electroanalysis using differential pulse voltammetry and square wave voltammetry
are known for better time resolution and high-frequency operation (Chen and Shah
2013). Labeled antibody-based electrochemical biosensor having an immunoelectrode made up of graphene oxide–silver nanoparticles fixed over anti-Salmonella
typhimurium antibody, along with the help of cyclic voltammetry was proved to be
used for Salmonella detection (Sign and Sumana 2016). Likewise, detection of other
pathogens can be carried out using specific antibodies.
Amperometric sensors are known to be fast and cost-effective (Barlett 2008; Wei
et al. 2009), while they also pose limitations such as poor selectivity due to other
interfering constituents in the sample mixture varying the faradaic current (Monzo
et al. 2015). Sensitivity in microbial/biomolecule detection enhances using semiconductor devices and field-effect transistors due to enrichment of sensor signals
(Grieshaber et al. 2008; Lin et al. 2008). Recently, a DNA chip-based sensor was
developed, for S. pyogenes detection, which works by hybridization of genomic
DNA of pathogens from the sample, with the selective probe bound to the screenprinted electrode resulting in an amperometric change in current recorded using
differential pulse voltammetry. It was reported to be a sensitive biosensor with a
limit of detection of 130 fg DNA per 6 μl of the sample.
10.3.4.2 Impedimetric/Conductometric Biosensors
Biosensors based on impedance measurements rely on the impedance variations
occurring due to voltage signal changes on the binding of targeted biomolecule/
pathogen to the electrode (Bard and Faulkner 2001; Barlett 2008). The targeted
pathogens interacting with the electrode are evaluated in accordance with variations
in the capacitance/impedance at the electrode interface. Impedance spectroscopy
offers high sensitivity and selectivity for the detection of biological analytes including pathogens (Felice et al. 1999). A carbon electrode modified with reduced
graphene oxide was reported to use impedance spectroscopy (Wang et al. 2011)
for the detection of methicillin-resistant S. aureus. Similarly, Salmonella detection
was also successful using a label-free technique employing a combination of
polypyrrole-based polymer, poly [pyrrole-co-3-carboxyl-pyrrole] copolymer, and a
selective aptamer (Sheikhzadeh et al. 2016). Also, researchers have developed
similar biosensors as above with geneÀ/immune-based (instead of aptamers) synthetically designed specific pathogenic peptides along with a record of impedance
variations (Liu et al. 2016b).
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J. Brindha et al.
Biosensors detecting pathogens with respect to variations in current or potential
(Monzo et al. 2015), due to processes like oxidation or reduction of the targeted
biological species, where the electrode is at constant potential or current with respect
to a standard reference electrode (Bard and Faulkner 2001). Cyclic sweep
voltammetry is a common method to acquire data like oxidation/reduction
potentials, reaction kinetics, and mechanisms (Bard and Faulkner 2001; Compton
and Banks 2011). Using carbon electrodes infused with magnetic nanoparticles, the
specific genomic DNA of pathogens and gold nanoparticles in a sandwich assay like
format detection of Salmonella and E. coli could be performed (Blow 2015).
Electroanalysis using differential pulse voltammetry and square wave voltammetry
are known for better time resolution and high-frequency operation (Chen and Shah
2013). Labeled antibody-based electrochemical biosensor having an immunoelectrode made up of graphene oxide–silver nanoparticles fixed over anti-Salmonella
typhimurium antibody, along with the help of cyclic voltammetry was proved to be
used for Salmonella detection (Sign and Sumana 2016). Likewise, detection of other
pathogens can be carried out using specific antibodies.
Amperometric sensors are known to be fast and cost-effective (Barlett 2008; Wei
et al. 2009), while they also pose limitations such as poor selectivity due to other
interfering constituents in the sample mixture varying the faradaic current (Monzo
et al. 2015). Sensitivity in microbial/biomolecule detection enhances using semiconductor devices and field-effect transistors due to enrichment of sensor signals
(Grieshaber et al. 2008; Lin et al. 2008). Recently, a DNA chip-based sensor was
developed, for S. pyogenes detection, which works by hybridization of genomic
DNA of pathogens from the sample, with the selective probe bound to the screenprinted electrode resulting in an amperometric change in current recorded using
differential pulse voltammetry. It was reported to be a sensitive biosensor with a
limit of detection of 130 fg DNA per 6 μl of the sample.
10.3.4.2 Impedimetric/Conductometric Biosensors
Biosensors based on impedance measurements rely on the impedance variations
occurring due to voltage signal changes on the binding of targeted biomolecule/
pathogen to the electrode (Bard and Faulkner 2001; Barlett 2008). The targeted
pathogens interacting with the electrode are evaluated in accordance with variations
in the capacitance/impedance at the electrode interface. Impedance spectroscopy
offers high sensitivity and selectivity for the detection of biological analytes including pathogens (Felice et al. 1999). A carbon electrode modified with reduced
graphene oxide was reported to use impedance spectroscopy (Wang et al. 2011)
for the detection of methicillin-resistant S. aureus. Similarly, Salmonella detection
was also successful using a label-free technique employing a combination of
polypyrrole-based polymer, poly [pyrrole-co-3-carboxyl-pyrrole] copolymer, and a
selective aptamer (Sheikhzadeh et al. 2016). Also, researchers have developed
similar biosensors as above with geneÀ/immune-based (instead of aptamers) synthetically designed specific pathogenic peptides along with a record of impedance
variations (Liu et al. 2016b).
282
J. Brindha et al.