Environmental Engineering Reference
In-Depth Information
for organophosphate detection (Figure 34.5a through c), with a sensitivity of 10.7 nA/M,
detection limit of 1.37 × 10 −7 M, and response time of <3 s. The device was found to be
reusable for >100 cycles as well. Amino-functionalized exfoliated graphite nanoplatelet-
modiied electrodes were used for the determination of Pb on vegetables using differential
pu l s e volt a m m e t r y. 181 A detection limit of 0.001 μg/L was attained in this approach. An
amperometric biosensor based on AChE immobilized on CdS-decorated graphene (CdS-
graphene) nanocomposite was reported by Wang et al. 182 In this study, a rapid inhibition
time (2 min) was obtained due to the integration of the CdS-graphene nanocomposite.
A voltammetric strategy to selectively detect Hg 2+ from water in the presence of various
other ions, using graphene-based hybrid electrode, was reported by Gong et al. 183 First,
graphene was mixed with chitosan to make a homogenous dispersion and drop-casted
onto the electrode surface followed by deposition of Au NPs. It was noted that the compos-
ite ilm greatly facilitates electron transfer, resulting in a remarkably improved sensitivity
and selectivity. The detection limit of this method was found to be 6 ppt. Highly toxic
Cd 2+ was also detected using a similar method. 184 The device consisted of naion-graphene
nanocomposite ilm and a differential pulse anodic stripping voltameter. Cui et al. 185 fab-
ricated a composite comprising graphene, Au NPs, and ionic liquids and modiied GCE
with the composite. This modiied electrode was employed for the detection of paraquat,
a herbicide widely used in agriculture. A detection limit of 7.3 × 10 −10 M was reported. Wu
et al. 186 also used a reduced β-cyclodextrin-graphene (β-CD-graphene) hybrid as a sorbent
for the preconcentration and electrochemical sensing of MP.
Graphene-based materials have also been used for cyclic voltammetry-based ultrasensi-
tive detection strategies. An electrochemical sensor using graphene-CNT-Pt NP hybrid
for the determination of bisphenol A with a detection limit of 4.2 × 10 −8 M is reported. 187
Graphene-CD hybrid (CD-GNs) were used as an enhanced material for ultrasensitive
detection of carbendazim by cyclic voltammetry recently. 188 An increase in peak currents
was observed when GNs modiied GCE and the CD-GNs/GCE was used, indicating that
the nanocomposite ilm not only shows the excellent electrical properties of GNs but also
exhibits high supramolecular recognition capability of CDs. The detection limit of carben-
dazim was reported to be 2 nM with a signal-to-noise ratio of 3. Good recoveries (98.9%
and 104.5%) were also observed.
34.2.2.2 Potentiometric Sensors
In this category of sensors, the signal is measured as the voltage difference (potential)
between the working electrode and the reference electrode and the concentration of the
analyte modulates the potential of the working electrode. Yuan et al. 189 recently reported
a GO-based electrode for the potentiometric detection of Cu 2+ . GO sheets grafted with
2-amino-5-mercapto-1,3,4-thiiodiazole were used as a neutral carrier in this process. A
detection limit of 4.0 × 10 −8 M, applicability over a wide pH range (3.0-7.0), and fast response
time (15 s) were reported. A noncovalent graphene-based composite was also used for the
potentiometric sensing of Zn 2+ ions. 190 Using the π-π interaction between GO and a Zn 2+
ions complexing ligand 1-(2-pyridylazo)-2-naphthol, a hybrid sensing membrane for the
potentiometric determination of zinc ions was fabricated. A highly selective and sensi-
tive determination of Zn 2+ was possible using this strategy. An interesting electrochemical
sensor for the selective and sensitive detection of bacteria using graphene was reported by
Wan et al. 191 In this method, the nanomaterial-promoted reduction of silver ions resulting
in the signal ampliication of GO coupled device was used for the sensing.
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