the sensing material is discussed for detection and the methodology of fabrication of
sensor. The level of detection is the key aspect of any developed sensor for heavy
metals since they can be harmful even at extreme low concentrations. We have
included lead (Pb), cadmium (Cd), mercury (Hg), chromium (Cr) and arsenic
(As) for the current discussion since they happen to be most important among all
HMIs.
3.2 Detection of Lead
Lead is one of the most common HMI contaminants due to its widespread utilization as battery electrodes and water pipelines. It is non-biodegradable and can
continue to accumulate inside the body leading to disturbed immune, reproductive
and neurosystem [31]. It is an essential pollutant to be monitored specially for
drinking water. Some excellent review exist for detection of lead ions in water [36,
41–44]. There are a variety of ways in which it can be detected include colorimeter,
electrochemical sensing, fluorescence spectroscopy and others [40, 42–44]. Some
of them are detailed in the following paragraphs.
Colorimetric sensors for Pb detection are most useful due their applicability in
field operations. Kim et al. [42] and Terra et al. [40] have provided a good review of
different available techniques for fluorescent and colorimetric sensors. Nanofibers
based colorimetric sensors have been reported by many researchers. One of the
most commonly used material for colorimetric sensor is polydiacetylene owing to
its unique optical property resulting from the delocalized p-electrons and the
restricted conformational movements along the backbone [45, 46]. Since the biocompatibility of the nanofiber too plays a role during the detection process, Raj
et al. [47] have reported a biocompatible curcumin based colorimetric sensor for
lead detection. Electrospinning was utilized to fabricate Curcumin loaded cellulose
acetate nanofiber membrane and a visual detection limit of 20 lM is reported with
color changing from yellow to orange. The advantage of this method is the usage of
a biocompatible material thus reducing the chance of secondary contamination of
water.
Li et al. [48] prepared a sensor strip utilizing electrospun polyamide-6/
nitrocellulose nanofiber nets as membrane to assemble bovine serum albumin
decorated Au nanoparticle (BAu probe) for colorimetric detection of Pb
2+ . It was
possible to have a naked eye detection of Pb
2+ even at a concentration of 0.20 lM.
Pb
2+ could accelerate the specific leaching reaction, thus causing a color change
from pink to white (fading gradually with the increasing concentration of Pb
2+ )
which could be observed by the naked eye. In another work, Li et al. [49] have also
developed pink to purple chromatic strips wherein they have utilized electrospun
nylon-6/polyvinylene fluoride nanofiber nets with l-glutathione-conjugated Au
nanoparticle based probes. The sensor strips showed a response time of 10 min and
detection range 10–500 lg/dL. In both these works, the large surface area provided
Nanofiber Based Sensors for Water Pollution Monitoring
305
sensor. The level of detection is the key aspect of any developed sensor for heavy
metals since they can be harmful even at extreme low concentrations. We have
included lead (Pb), cadmium (Cd), mercury (Hg), chromium (Cr) and arsenic
(As) for the current discussion since they happen to be most important among all
HMIs.
3.2 Detection of Lead
Lead is one of the most common HMI contaminants due to its widespread utilization as battery electrodes and water pipelines. It is non-biodegradable and can
continue to accumulate inside the body leading to disturbed immune, reproductive
and neurosystem [31]. It is an essential pollutant to be monitored specially for
drinking water. Some excellent review exist for detection of lead ions in water [36,
41–44]. There are a variety of ways in which it can be detected include colorimeter,
electrochemical sensing, fluorescence spectroscopy and others [40, 42–44]. Some
of them are detailed in the following paragraphs.
Colorimetric sensors for Pb detection are most useful due their applicability in
field operations. Kim et al. [42] and Terra et al. [40] have provided a good review of
different available techniques for fluorescent and colorimetric sensors. Nanofibers
based colorimetric sensors have been reported by many researchers. One of the
most commonly used material for colorimetric sensor is polydiacetylene owing to
its unique optical property resulting from the delocalized p-electrons and the
restricted conformational movements along the backbone [45, 46]. Since the biocompatibility of the nanofiber too plays a role during the detection process, Raj
et al. [47] have reported a biocompatible curcumin based colorimetric sensor for
lead detection. Electrospinning was utilized to fabricate Curcumin loaded cellulose
acetate nanofiber membrane and a visual detection limit of 20 lM is reported with
color changing from yellow to orange. The advantage of this method is the usage of
a biocompatible material thus reducing the chance of secondary contamination of
water.
Li et al. [48] prepared a sensor strip utilizing electrospun polyamide-6/
nitrocellulose nanofiber nets as membrane to assemble bovine serum albumin
decorated Au nanoparticle (BAu probe) for colorimetric detection of Pb
2+ . It was
possible to have a naked eye detection of Pb
2+ even at a concentration of 0.20 lM.
Pb
2+ could accelerate the specific leaching reaction, thus causing a color change
from pink to white (fading gradually with the increasing concentration of Pb
2+ )
which could be observed by the naked eye. In another work, Li et al. [49] have also
developed pink to purple chromatic strips wherein they have utilized electrospun
nylon-6/polyvinylene fluoride nanofiber nets with l-glutathione-conjugated Au
nanoparticle based probes. The sensor strips showed a response time of 10 min and
detection range 10–500 lg/dL. In both these works, the large surface area provided
Nanofiber Based Sensors for Water Pollution Monitoring
305