3.4 Biosensors
The biosensor can be defined as “a sensing device or a measurement system
designed specifically for the estimation of a material using the biological interactions
and then assessing these interactions into a readable form with the help of a
transduction and electro-mechanical interpretation” (Malik et al. 2013). In general,
three different assay formats are used in biosensors – the direct and the indirect
(competitive or noncompetitive) assay. In the case of the direct assay, the analyte is
bound by its biorecognition element, which is detected directly (Vasilescu et al.
2016). This can be an antigen binding to its antibody, a hormone binding to a
receptor, or a substrate reacting with its enzyme and producing a product
(Eijkelkamp et al. 2009). The detection of these binding events is limited to the
event itself and can be changed in mass, refractive index, impedance, pH, etc.
(Griffin et al. 2014). In contrast, in indirect format, an additional reaction has to
occur in order to detect the binding of analyte and biorecognition element. This
additional reaction can either be competitive or noncompetitive. In both cases, a
label is typically used for subsequent detection and quantification (Ramírez et al.
2009). The detection scheme is much less limited than in the case of the direct
approach and depends on the nature of the label. This label can be optical, electrochemical, or mass related and thus permits the use of any transduction principle with
indirect assay formats in contrast to the constraints given by the direct assay, which
is limited by the nature of the analyte itself (Baeumner 2003). Based on the
publication in reputed science journals, different methods which are applied in
detection of many foodborne bacterial pathogens were compared by Lazcka et al.
(2007) as shown in Fig. 3.1. The most popular methods are, by far, those based on
culture and colony counting methods (Leoni and Legnani 2001) and the polymerase
chain reaction, PCR (Bej et al. 1991). This can be explained on the grounds of
selectivity and reliability of both techniques. Culture and colony counting methods
are much more time-consuming than PCR methods, but both provide conclusive and
unambiguous results. On the other hand, recent advances in PCR technology,
namely, real-time PCR (Levi et al. 2003), now enable obtaining results in a few
hours.
Biosensor technology comes with promises of equally reliable results in much
smaller times, which is perhaps why they are currently drawing a lot of interest.
However, there is still much work to do before biosensors become a real alternative.
Figure 3.1 suggests that biosensor technology may soon move ahead of traditional
ELISA-based methods and their potential market (Alocilja and Stephen 2003) is
very encouraging too. Many biosensors rely on either specific antibodies or DNA as
biomolecules to provide specificity.
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101
The biosensor can be defined as “a sensing device or a measurement system
designed specifically for the estimation of a material using the biological interactions
and then assessing these interactions into a readable form with the help of a
transduction and electro-mechanical interpretation” (Malik et al. 2013). In general,
three different assay formats are used in biosensors – the direct and the indirect
(competitive or noncompetitive) assay. In the case of the direct assay, the analyte is
bound by its biorecognition element, which is detected directly (Vasilescu et al.
2016). This can be an antigen binding to its antibody, a hormone binding to a
receptor, or a substrate reacting with its enzyme and producing a product
(Eijkelkamp et al. 2009). The detection of these binding events is limited to the
event itself and can be changed in mass, refractive index, impedance, pH, etc.
(Griffin et al. 2014). In contrast, in indirect format, an additional reaction has to
occur in order to detect the binding of analyte and biorecognition element. This
additional reaction can either be competitive or noncompetitive. In both cases, a
label is typically used for subsequent detection and quantification (Ramírez et al.
2009). The detection scheme is much less limited than in the case of the direct
approach and depends on the nature of the label. This label can be optical, electrochemical, or mass related and thus permits the use of any transduction principle with
indirect assay formats in contrast to the constraints given by the direct assay, which
is limited by the nature of the analyte itself (Baeumner 2003). Based on the
publication in reputed science journals, different methods which are applied in
detection of many foodborne bacterial pathogens were compared by Lazcka et al.
(2007) as shown in Fig. 3.1. The most popular methods are, by far, those based on
culture and colony counting methods (Leoni and Legnani 2001) and the polymerase
chain reaction, PCR (Bej et al. 1991). This can be explained on the grounds of
selectivity and reliability of both techniques. Culture and colony counting methods
are much more time-consuming than PCR methods, but both provide conclusive and
unambiguous results. On the other hand, recent advances in PCR technology,
namely, real-time PCR (Levi et al. 2003), now enable obtaining results in a few
hours.
Biosensor technology comes with promises of equally reliable results in much
smaller times, which is perhaps why they are currently drawing a lot of interest.
However, there is still much work to do before biosensors become a real alternative.
Figure 3.1 suggests that biosensor technology may soon move ahead of traditional
ELISA-based methods and their potential market (Alocilja and Stephen 2003) is
very encouraging too. Many biosensors rely on either specific antibodies or DNA as
biomolecules to provide specificity.
3 Application of Nanobiosensors for Food Safety Monitoring
101