of these fluorescent nanoparticles compared to conventional chromophores make
them the ideal candidate for development of IFE based fluorescent chemosensors
[41].
Recently noble metal nanoparticles are adopted in fluorescence assays [42] to
enhance the sensitivity by means of interaction between the fluorophore and metal
nanoparticles. The interaction between the fluorophore and the metal nanoparticles
requires the linking through covalent bonding which requires the surface functionalization and modification of the fluorophore. However, surface modification of
the fluorophore without affecting the inherent properties of the fluorophore is a
tedious and time consuming procedure. In this context, IFE based sensing system
proves to be a better alternative to the conventional fluorescence sensing techniques
as it does not require any link between the fluorophore and the absorber. Thus,
noble metal nanoparticles (gold and silver) are chosen to be potential absorber in
IFE based sensing system. The spectral overlap of the fluorophore and absorber is
made possible by simply fine tuning the localized surface plasmon resonance peak
of metal nanoparticles which is dependent on the size and shape of the nanoparticles
and is highly sensitive to the local environment changes such as refractive index
and pH. The sensing mechanism involves the translation of the changes in the
absorbance of the metal nanoparticles into the fluorescence of the fluorophores
exponentially which eventually led to the improved detection limit compared to
conventional fluorescence methods. A turn on fluorescence chemosensor for
detection of cyanide in drinking water was proposed by combining gold
nanoparticles
with
a
model
fluorophore
(Poly
[2-methoxy-5(3,7-dimethyloctyloxy)-1,4-phenylenevinylene]MDMO-PPV) [43]. The sensing of
cyanide involves initially decrement in the fluorescence of the fluorophore for the
respective increase in the concentration of gold nanoparticles and the decreased
fluorescence was recovered upon addition of cyanide. Cyanide is known to dissolve
nanoparticles yielding gold cyanide complex and does not interfere with the
fluorophore which is revealed from the control experiments. The efficiency of
cyanide sensing due to inner filter effect is validated by conducting optical absorbance based sensing of cyanide by dissolution of gold nanoparticles with increasing
concentration of cyanide. The enhanced sensitivity was achieved using IFE which
is attributed to the intrinsic relation between the model fluorophore and the gold
nanoparticles.
A fluorescent nanoswitch employing polymer carbon dots (PCDs) for detection
of explosives in water samples was reported [44]. The polymer carbon dots exhibit
two characteristic absorption peaks at 234 and 410 nm which is completely overlapping with the absorption spectrum of 4-nitrophenol. This resulted in the
quenching of PCDs upon interaction with 4-nitrophenol. In addition, PCDs were
explored as fluorescent nanoswitch based on the changes in pH. 4-nitrophenol
exhibits peak absorbance at 400 nm in pH 8 whereas, the spectrum is blue shifted to
320 nm in acidic pH. Hence in acidic pH, the absorption spectrum is not overlapping with that of PCDs. Due to the failure in meeting the criteria for IFE, a
significant enhancement in fluorescence was observed, thus acting as a fluorescent
nanoswitch.
Fluorescent Chemosensor for Detection of Water Pollutants
153
them the ideal candidate for development of IFE based fluorescent chemosensors
[41].
Recently noble metal nanoparticles are adopted in fluorescence assays [42] to
enhance the sensitivity by means of interaction between the fluorophore and metal
nanoparticles. The interaction between the fluorophore and the metal nanoparticles
requires the linking through covalent bonding which requires the surface functionalization and modification of the fluorophore. However, surface modification of
the fluorophore without affecting the inherent properties of the fluorophore is a
tedious and time consuming procedure. In this context, IFE based sensing system
proves to be a better alternative to the conventional fluorescence sensing techniques
as it does not require any link between the fluorophore and the absorber. Thus,
noble metal nanoparticles (gold and silver) are chosen to be potential absorber in
IFE based sensing system. The spectral overlap of the fluorophore and absorber is
made possible by simply fine tuning the localized surface plasmon resonance peak
of metal nanoparticles which is dependent on the size and shape of the nanoparticles
and is highly sensitive to the local environment changes such as refractive index
and pH. The sensing mechanism involves the translation of the changes in the
absorbance of the metal nanoparticles into the fluorescence of the fluorophores
exponentially which eventually led to the improved detection limit compared to
conventional fluorescence methods. A turn on fluorescence chemosensor for
detection of cyanide in drinking water was proposed by combining gold
nanoparticles
with
a
model
fluorophore
(Poly
[2-methoxy-5(3,7-dimethyloctyloxy)-1,4-phenylenevinylene]MDMO-PPV) [43]. The sensing of
cyanide involves initially decrement in the fluorescence of the fluorophore for the
respective increase in the concentration of gold nanoparticles and the decreased
fluorescence was recovered upon addition of cyanide. Cyanide is known to dissolve
nanoparticles yielding gold cyanide complex and does not interfere with the
fluorophore which is revealed from the control experiments. The efficiency of
cyanide sensing due to inner filter effect is validated by conducting optical absorbance based sensing of cyanide by dissolution of gold nanoparticles with increasing
concentration of cyanide. The enhanced sensitivity was achieved using IFE which
is attributed to the intrinsic relation between the model fluorophore and the gold
nanoparticles.
A fluorescent nanoswitch employing polymer carbon dots (PCDs) for detection
of explosives in water samples was reported [44]. The polymer carbon dots exhibit
two characteristic absorption peaks at 234 and 410 nm which is completely overlapping with the absorption spectrum of 4-nitrophenol. This resulted in the
quenching of PCDs upon interaction with 4-nitrophenol. In addition, PCDs were
explored as fluorescent nanoswitch based on the changes in pH. 4-nitrophenol
exhibits peak absorbance at 400 nm in pH 8 whereas, the spectrum is blue shifted to
320 nm in acidic pH. Hence in acidic pH, the absorption spectrum is not overlapping with that of PCDs. Due to the failure in meeting the criteria for IFE, a
significant enhancement in fluorescence was observed, thus acting as a fluorescent
nanoswitch.
Fluorescent Chemosensor for Detection of Water Pollutants
153