More recently development of a microfluidic impedance-based biosensor is
shown to be successful for E. coli O157:H7 (Yao et al. 2018) detection with a
minimum limit of 12 cfu/ml within a period of 2 hours. Here, the impedance was
monitored using the microfluidic chip, and normalization of impedance helped in the
detection of E. coli O157:H7. Another recent patent involves the use of conductometric biosensors along with the use of nanotubes for pathogen detection (April et al.
2018). The conductometric component involving the electrodes measures the resistance variation that is proportional to target analyte concentrations specifically
interacting with the recognition elements on the electrodes.
10.3.5 Biochemical Biosensors
Biochemical biosensors help in the detection of specific biochemical reactions
occurring between a specific target analyte in the test sample and its specific
substrate/receptor molecule on these sensors. These substrates used can be any
compatible specific biomolecules such as antibodies/enzymes essential for the
immuno/biochemical reactions.
10.3.5.1 Immunosensors
Immunosensors detect a biomolecule/analyte using specific immunochemical or
biochemical reactions occurring between bio-recognition elements and specific
receptors along with the help of transducers to convert the binding interactions
into readable output signals. These immuno/biochemical reactions or the ligand–
receptor binding offers high sensitivity and selectivity to the immunosensors. These
sensors are equipped with signal amplification in the presence of either magnetic
particles or gold nanoparticles (Wang and Alocilja 2015) for high sensitivity of
pathogen detection. Developments are made in designing an integrated
immunosensor, with specific antibody conjugated to gold nanoparticles employed
in enzyme-linked immunosorbent assay along with enrichment of target analytes in
the sample mixture, using immunomagnetic separation (Cho and Irudayaraj 2013). It
was proven analytically with microtiter assay, for a highly sensitive pathogen
detection including E. coli O157:H7 and S. typhimurium detection up to 3 cells/ml
in buffer.
Continuous efforts are made to develop immunosensors with high sensitivity
employing signal amplification strategies (Guo et al. 2013). A visible indication
strategy is one of those techniques that employ color formation based on nanoparticle aggregation (Priyadarshini and Pradhan 2017). Here, the limitation is the requirement of the presence of a large number of analytes for the generation of visible
colorimetric detection signal that lowers the sensitivity of the biosensor (Yoo and
Lee 2016). The need for high sensitivity, real-time detection, and lower detection
time remains the significant areas under research in the biosensor field, due to
existing problems in the current methods. For example, the minimum limit of
detection reported to date is 10
2 cfu/ml, and detection time is greater than 6 hours
(Prasad and Vidyarthi 2011; Raj et al. 2015). This has encouraged researchers to
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283
shown to be successful for E. coli O157:H7 (Yao et al. 2018) detection with a
minimum limit of 12 cfu/ml within a period of 2 hours. Here, the impedance was
monitored using the microfluidic chip, and normalization of impedance helped in the
detection of E. coli O157:H7. Another recent patent involves the use of conductometric biosensors along with the use of nanotubes for pathogen detection (April et al.
2018). The conductometric component involving the electrodes measures the resistance variation that is proportional to target analyte concentrations specifically
interacting with the recognition elements on the electrodes.
10.3.5 Biochemical Biosensors
Biochemical biosensors help in the detection of specific biochemical reactions
occurring between a specific target analyte in the test sample and its specific
substrate/receptor molecule on these sensors. These substrates used can be any
compatible specific biomolecules such as antibodies/enzymes essential for the
immuno/biochemical reactions.
10.3.5.1 Immunosensors
Immunosensors detect a biomolecule/analyte using specific immunochemical or
biochemical reactions occurring between bio-recognition elements and specific
receptors along with the help of transducers to convert the binding interactions
into readable output signals. These immuno/biochemical reactions or the ligand–
receptor binding offers high sensitivity and selectivity to the immunosensors. These
sensors are equipped with signal amplification in the presence of either magnetic
particles or gold nanoparticles (Wang and Alocilja 2015) for high sensitivity of
pathogen detection. Developments are made in designing an integrated
immunosensor, with specific antibody conjugated to gold nanoparticles employed
in enzyme-linked immunosorbent assay along with enrichment of target analytes in
the sample mixture, using immunomagnetic separation (Cho and Irudayaraj 2013). It
was proven analytically with microtiter assay, for a highly sensitive pathogen
detection including E. coli O157:H7 and S. typhimurium detection up to 3 cells/ml
in buffer.
Continuous efforts are made to develop immunosensors with high sensitivity
employing signal amplification strategies (Guo et al. 2013). A visible indication
strategy is one of those techniques that employ color formation based on nanoparticle aggregation (Priyadarshini and Pradhan 2017). Here, the limitation is the requirement of the presence of a large number of analytes for the generation of visible
colorimetric detection signal that lowers the sensitivity of the biosensor (Yoo and
Lee 2016). The need for high sensitivity, real-time detection, and lower detection
time remains the significant areas under research in the biosensor field, due to
existing problems in the current methods. For example, the minimum limit of
detection reported to date is 10
2 cfu/ml, and detection time is greater than 6 hours
(Prasad and Vidyarthi 2011; Raj et al. 2015). This has encouraged researchers to
10 Environment Remediation Tools: Chemosensors and Biosensors
283