Bioluminescence-based biosensor Any biochemical reaction between the analyte
and the bio sensing material is followed by the phenomenon of bioluminescence,
which is transferred as a signal from the analyte to the optical fiber. The light output
is thus helpful in the detection of harmful toxins present in wastewater.
Interferometry based biosensor: In interferometry, the difference between two light
beams travelling along similar paths is compared. Planar waveguides are preferred
for the development of interferometry-based biosensor. The sensing beam interacts
with the bio-sensing element. The refractive index of the element comes into play
and induces a change in the speed of sensing beam or a change in its phase. In order
to measure this change, an interferogram is created with the help of a reference
beam propagated adjacent to the sensing beam. A shift in the interference pattern is
observed which is directly related to the chemical or physical changes associated
with the sensing beam.
Refractive index based biosensor: In this type of biosensor, the change in refractive
index is measured when the analyte comes in contact with the evanescent field
emerging out as a result of total internal reflection of light interacting with the
sensor surface. The change is refractive index is correlated with the chemical or
physical changes associated with the analyte.
Optical biosensors are as a strong contender for bio sensing purposes. Varieties
of elements were reported useful for the biosensor fabrication in terms of sensitivity
and detection time. Gold nanoparticle-based optical biosensor has been used
extensively for detection of lead [55] and mercury [56] in aqueous samples. The
detection time averaged from six to ten minutes. A detection time around tens of
seconds was reported in an optical biosensor with reduced graphene oxide as the
primary sensing element for detecting mercury [57]. Carbon nanotubes were also
found successful in detecting the concentration of cadmium in water-based samples
with a detection time of 30 min [58]. Graphene also served as a good candidate for
detecting Escherichia coli K12 bacteria found in water-based samples with a
detection time of 30 min [59].
3.2.4 Piezoelectric Biosensors
A piezoelectric biosensor is a composition of materials, which generate a potential
difference upon the application of mechanical stress. An analyte bound on the
surface of a piezoelectric crystal when excited by an alternating voltage through
electrodes attached to the surface, results in the change of oscillating frequency of
the crystal. This change in frequency is correlated to the mass of the analyte bound
on the surface of the crystal. Piezoelectric effect is found in organic, inorganic and
some group of biomolecules as well. Quartz crystal is a commonly found inorganic
material with piezoelectric effect. Other inorganic materials include zinc oxide,
aluminum nitride, quartz SiO 2 [60]. Organic materials possessing piezoelectric
effect include Rochelle salt, polyvinylidene fluoride, and polyamides [61, 62].
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and the bio sensing material is followed by the phenomenon of bioluminescence,
which is transferred as a signal from the analyte to the optical fiber. The light output
is thus helpful in the detection of harmful toxins present in wastewater.
Interferometry based biosensor: In interferometry, the difference between two light
beams travelling along similar paths is compared. Planar waveguides are preferred
for the development of interferometry-based biosensor. The sensing beam interacts
with the bio-sensing element. The refractive index of the element comes into play
and induces a change in the speed of sensing beam or a change in its phase. In order
to measure this change, an interferogram is created with the help of a reference
beam propagated adjacent to the sensing beam. A shift in the interference pattern is
observed which is directly related to the chemical or physical changes associated
with the sensing beam.
Refractive index based biosensor: In this type of biosensor, the change in refractive
index is measured when the analyte comes in contact with the evanescent field
emerging out as a result of total internal reflection of light interacting with the
sensor surface. The change is refractive index is correlated with the chemical or
physical changes associated with the analyte.
Optical biosensors are as a strong contender for bio sensing purposes. Varieties
of elements were reported useful for the biosensor fabrication in terms of sensitivity
and detection time. Gold nanoparticle-based optical biosensor has been used
extensively for detection of lead [55] and mercury [56] in aqueous samples. The
detection time averaged from six to ten minutes. A detection time around tens of
seconds was reported in an optical biosensor with reduced graphene oxide as the
primary sensing element for detecting mercury [57]. Carbon nanotubes were also
found successful in detecting the concentration of cadmium in water-based samples
with a detection time of 30 min [58]. Graphene also served as a good candidate for
detecting Escherichia coli K12 bacteria found in water-based samples with a
detection time of 30 min [59].
3.2.4 Piezoelectric Biosensors
A piezoelectric biosensor is a composition of materials, which generate a potential
difference upon the application of mechanical stress. An analyte bound on the
surface of a piezoelectric crystal when excited by an alternating voltage through
electrodes attached to the surface, results in the change of oscillating frequency of
the crystal. This change in frequency is correlated to the mass of the analyte bound
on the surface of the crystal. Piezoelectric effect is found in organic, inorganic and
some group of biomolecules as well. Quartz crystal is a commonly found inorganic
material with piezoelectric effect. Other inorganic materials include zinc oxide,
aluminum nitride, quartz SiO 2 [60]. Organic materials possessing piezoelectric
effect include Rochelle salt, polyvinylidene fluoride, and polyamides [61, 62].
198
R. Sinha et al.