and hence the pathogenic bacterial detection in a short period of 7–8 hours. This
method has been employed for detecting and quantifying Gram-positive bacteria
including Staphylococcus aureus (Dale et al. 2004; Zawadzka et al. 2009) and
Gram-negative bacteria such as Proteus species and Mycobacterium tuberculosis
(Wells et al. 2013; Himpsl et al. 2010; Adler et al. 2014).
Specific biological recognition elements such as antibodies are used in conjugation fluorescent labels for pathogen detection (Yang and Li 2006). Hu et al. have
employed specific antibodies labeled with fluorescein isothiocyanate to detect surface antigens of Escherichia coli O157:H7 with (Hu et al. 2016). The sensor surfacebound antibodies capture specific bacterial cells followed by the detachment of
fluorescein. This enhances the fluorescence intensity which is then utilized to
quantify bacterial cells. The detection limit using this method was found to be
3 cfu/ml. Quantum dots are yet another optical probe that can be tuned for fluorescence emission energy by modifying their sizes and chemical constituents. Simultaneous multiple-pathogen detection, of pathogens like E. coli O157:H7 and
Salmonella detection, is also reported (Yang and Li 2006), using semiconductor
quantum dots with multiple wavelengths: 525 nm and 705 nm as labels for their
respective specific antibodies attached by means of streptavidin and biotin conjugation. Quantum dots are known to be twentyfold more intense and hundredfold
relatively resistant to photobleaching as compared to other fluorescent labels/probes
such as organic dyes (Vinayaka and Thakur 2010). It also has its limitations like
toxicity, solubility issues, and low quantum yields (Shen et al. 2012). Like quantum
dots, carbon-based nanomaterials also possess photoluminescence features (Davis
et al. 1998; April et al. 2018) that are exploited for enrichment of pathogens for
detection (Deng et al. 2008; Srivastava et al. 2004; Upadhyayula et al. 2009; Elkin
et al. 2005). Yang et al. used anti-S. aureus antibody conjugated with carbon dots
trapped within organosilica nanocapsules for sensitive detection of S. aureus (Yang
et al. 2018). By using carbon dots, the fluorescence signals were enhanced 2 times as
compared with other fluorescence-based immunoassays. This method resulted in the
detection of S. aureus in the range of 1–200 cfu/ml and can be extended to other
pathogens also.
10.3.1.1 Fiber Optic-Based Biosensors
Biosensors equipped with fiber optics are found to work with fluorescence-based
labels using an optical transmitter for target detection and transmitting the fluorescent signals to a photodetector where it gets converted into electrical signals. Based
on the waveguide patterns (Banica 2012), they can be classified as planar and
cylindrical waveguides (Fig. 10.4).
Simultaneous multiple detection of Listeria monocytogenes, E. coli O157:H7,
and S. enterica (Ohk and Bhunia 2013) was made possible with a multiplex fiber
optic biosensor using waveguides coated with streptavidin and specific antibodies
tagged with Alexa Fluor 647. A lower limit of detection of 10
3 cfu/ml was reported
for all the above mentioned pathogens displaying negligible cross-reactivity. The
detection of cell number differences of E. coli present in the sample (Maas et al.
2018) was determined by Maas et al. employing an optical fiber-based biosensor
276
J. Brindha et al.
method has been employed for detecting and quantifying Gram-positive bacteria
including Staphylococcus aureus (Dale et al. 2004; Zawadzka et al. 2009) and
Gram-negative bacteria such as Proteus species and Mycobacterium tuberculosis
(Wells et al. 2013; Himpsl et al. 2010; Adler et al. 2014).
Specific biological recognition elements such as antibodies are used in conjugation fluorescent labels for pathogen detection (Yang and Li 2006). Hu et al. have
employed specific antibodies labeled with fluorescein isothiocyanate to detect surface antigens of Escherichia coli O157:H7 with (Hu et al. 2016). The sensor surfacebound antibodies capture specific bacterial cells followed by the detachment of
fluorescein. This enhances the fluorescence intensity which is then utilized to
quantify bacterial cells. The detection limit using this method was found to be
3 cfu/ml. Quantum dots are yet another optical probe that can be tuned for fluorescence emission energy by modifying their sizes and chemical constituents. Simultaneous multiple-pathogen detection, of pathogens like E. coli O157:H7 and
Salmonella detection, is also reported (Yang and Li 2006), using semiconductor
quantum dots with multiple wavelengths: 525 nm and 705 nm as labels for their
respective specific antibodies attached by means of streptavidin and biotin conjugation. Quantum dots are known to be twentyfold more intense and hundredfold
relatively resistant to photobleaching as compared to other fluorescent labels/probes
such as organic dyes (Vinayaka and Thakur 2010). It also has its limitations like
toxicity, solubility issues, and low quantum yields (Shen et al. 2012). Like quantum
dots, carbon-based nanomaterials also possess photoluminescence features (Davis
et al. 1998; April et al. 2018) that are exploited for enrichment of pathogens for
detection (Deng et al. 2008; Srivastava et al. 2004; Upadhyayula et al. 2009; Elkin
et al. 2005). Yang et al. used anti-S. aureus antibody conjugated with carbon dots
trapped within organosilica nanocapsules for sensitive detection of S. aureus (Yang
et al. 2018). By using carbon dots, the fluorescence signals were enhanced 2 times as
compared with other fluorescence-based immunoassays. This method resulted in the
detection of S. aureus in the range of 1–200 cfu/ml and can be extended to other
pathogens also.
10.3.1.1 Fiber Optic-Based Biosensors
Biosensors equipped with fiber optics are found to work with fluorescence-based
labels using an optical transmitter for target detection and transmitting the fluorescent signals to a photodetector where it gets converted into electrical signals. Based
on the waveguide patterns (Banica 2012), they can be classified as planar and
cylindrical waveguides (Fig. 10.4).
Simultaneous multiple detection of Listeria monocytogenes, E. coli O157:H7,
and S. enterica (Ohk and Bhunia 2013) was made possible with a multiplex fiber
optic biosensor using waveguides coated with streptavidin and specific antibodies
tagged with Alexa Fluor 647. A lower limit of detection of 10
3 cfu/ml was reported
for all the above mentioned pathogens displaying negligible cross-reactivity. The
detection of cell number differences of E. coli present in the sample (Maas et al.
2018) was determined by Maas et al. employing an optical fiber-based biosensor
276
J. Brindha et al.