with GO, resulted in the fast electron transfer kinetics. AlOOH-GO nanocomposite
could be used for multiple detection due to unique stripping peak of each metal.
Mercury
Mercury (Hg
2+ ) is extremely toxic and human exposure to Hg
2+ can cause dangerous
health effects including negative effects on the neurological system. The presence of
Hg
2+ results in the formation of metal base pair, which can stabilize the thiaminethiamine (T-T) mismatch in DNA. Based on this effect, DNA-based probes can be
potentially utilized for development of nanosensors for the detection of Hg
2+ . In the
literature, two major Hg
2+ oligonucleotides probes have been reported: (1) one
which unfolds i.e., G-quadruplexes, (2) which hybridizes i.e., nearly complimentary
single strands. Many nano-elements have been used for the construction of Hg
2+
nanosensors. In their work, Liu et al. (2014a) reported an assay designed by Au
shells encapsulated with magnetic silica spheres. They used complementary DNA
sequences with 5 mismatched thiamine site, for functionalization of the Au NPs.
Selection of the DNA sequences was done so that full hybridization was not
permitted due to insufficient binding energy between the strand’s complimentary
aspects. In the presence of Hg
2+ , plasmonic hotspot formation occurred due to
reduction in the inter-probe spacing, resulting from full hybridization with introduction of Hg
2+ . The recovery and recycling of the nanoprobes was easily possible due
to the magnetic nature of the particle cores. The fabrication and application of
DNA-MSS@Au NPs and DNA-Au NPs as SERS-based nanosensor for detection
of Hg
2+ is represented schematically in Fig. 5.8 (Liu et al. 2014a).
Nanoparticles like, Ag, Au, QDs have been reported in the literature for developing thiol-mediated assays for Hg
2+ detection. Colometric response is obtained on the
basis of aggregation and disaggregation principles. Huang and Chang (2006)
reported fluorescence-based nanosensor with Au NPs for Hg
2+ detection. The
fluorescence of Rhodamine B (RB) was quenched on getting adsorbed on the Au
NPs surface due to FRET and collision. The fluorescence signal was emitted by the
on-sensor with the introduction of Hg
2+ in the system, due to the displacement of RB
from the surface of nanoparticles. The authors explored three sensor designs, and
found an increase in the specificity of the assay for Hg
2+ , with the thiol coatings. The
sensor exhibited low LOD values of 2.0 ppb and fast time of analysis i.e., less than
10 min.
Cadmium
Nanosensors fabricated with SWCNTs, QDs, antimony (Sb) nanoparticles etc., have
been used for cadmium detection. Gui et al. (2012) reported on/off-fluorescence
sensor based on photoluminescent CdTe/CdS QDs for Cd
2+ detection. APDC was
used for quenching (turn off) the photoluminescence (PL) of CdTe/CdS QDs as a
result of surface passivation due to partial loss of the surface layer of Cd-S. In the
presence of Cd
2+ the ADPC were displaced from the QD surface resulting in
restoration of PL i.e., turning-on the sensor. The LOD was 6 nM and the sensor
showed selectively 3-folds increase in PL in the presence of Cd
2+ .
5 Development of Environmental Nanosensors for Detection Monitoring. . .
127
could be used for multiple detection due to unique stripping peak of each metal.
Mercury
Mercury (Hg
2+ ) is extremely toxic and human exposure to Hg
2+ can cause dangerous
health effects including negative effects on the neurological system. The presence of
Hg
2+ results in the formation of metal base pair, which can stabilize the thiaminethiamine (T-T) mismatch in DNA. Based on this effect, DNA-based probes can be
potentially utilized for development of nanosensors for the detection of Hg
2+ . In the
literature, two major Hg
2+ oligonucleotides probes have been reported: (1) one
which unfolds i.e., G-quadruplexes, (2) which hybridizes i.e., nearly complimentary
single strands. Many nano-elements have been used for the construction of Hg
2+
nanosensors. In their work, Liu et al. (2014a) reported an assay designed by Au
shells encapsulated with magnetic silica spheres. They used complementary DNA
sequences with 5 mismatched thiamine site, for functionalization of the Au NPs.
Selection of the DNA sequences was done so that full hybridization was not
permitted due to insufficient binding energy between the strand’s complimentary
aspects. In the presence of Hg
2+ , plasmonic hotspot formation occurred due to
reduction in the inter-probe spacing, resulting from full hybridization with introduction of Hg
2+ . The recovery and recycling of the nanoprobes was easily possible due
to the magnetic nature of the particle cores. The fabrication and application of
DNA-MSS@Au NPs and DNA-Au NPs as SERS-based nanosensor for detection
of Hg
2+ is represented schematically in Fig. 5.8 (Liu et al. 2014a).
Nanoparticles like, Ag, Au, QDs have been reported in the literature for developing thiol-mediated assays for Hg
2+ detection. Colometric response is obtained on the
basis of aggregation and disaggregation principles. Huang and Chang (2006)
reported fluorescence-based nanosensor with Au NPs for Hg
2+ detection. The
fluorescence of Rhodamine B (RB) was quenched on getting adsorbed on the Au
NPs surface due to FRET and collision. The fluorescence signal was emitted by the
on-sensor with the introduction of Hg
2+ in the system, due to the displacement of RB
from the surface of nanoparticles. The authors explored three sensor designs, and
found an increase in the specificity of the assay for Hg
2+ , with the thiol coatings. The
sensor exhibited low LOD values of 2.0 ppb and fast time of analysis i.e., less than
10 min.
Cadmium
Nanosensors fabricated with SWCNTs, QDs, antimony (Sb) nanoparticles etc., have
been used for cadmium detection. Gui et al. (2012) reported on/off-fluorescence
sensor based on photoluminescent CdTe/CdS QDs for Cd
2+ detection. APDC was
used for quenching (turn off) the photoluminescence (PL) of CdTe/CdS QDs as a
result of surface passivation due to partial loss of the surface layer of Cd-S. In the
presence of Cd
2+ the ADPC were displaced from the QD surface resulting in
restoration of PL i.e., turning-on the sensor. The LOD was 6 nM and the sensor
showed selectively 3-folds increase in PL in the presence of Cd
2+ .
5 Development of Environmental Nanosensors for Detection Monitoring. . .
127