Environmental Engineering Reference
In-Depth Information
34.2.2 Electrochemical Sensors
Electrochemical sensors are one of the largest classes of chemical sensors where a relation-
ship between electricity and chemistry is used for sensing. In general, this category of sen-
sors can be deined as devices that extract information about a sample from measurement
of parameters such as potential difference, current, resistance/conductance. On the basis
of this, electrochemical sensors can be categorized as voltammetric or amperometric sen-
sors (where current in amperes is measured), potentiometric sensors (where a difference
of two potentials in volts is measured), and chemiresistors or conductometric sensors (if
resistance in ohms or conductance is measured). Graphene has found huge potential in
this category of sensors as well. A short summary is presented in the following section.
34.2.2.1 Graphene-Based Electrodes for Voltammetric and Amperometric Sensors
In this category of electroanalytical sensors, analyte species that can become oxidized or
reduced are detected from the sudden changes in current. In voltammetric sensors, cur-
rent is measured by varying the potential. In amperometric sensors, a given potential is
applied between two electrodes placed inside the solution containing the analyte, and the
change in current is measured as the analyte is oxidized at the anode or reduced at the cath-
ode. Graphene composites have found application as electrodes for both voltammetric and
amperometric sensors. A strategy for the simultaneous voltammetric detection of catechol
(CC) and hydroquinone (HQ) using a graphene-modiied electrode was reported recently.
172
A graphene-modiied glassy carbon electrode (GR/GCE) exhibited a well-deined peak and
a signiicant increase of current, clearly demonstrating the utility of graphene as an eficient
promoter to enhance the kinetics of the electrochemical process of catechol and hydroqui-
none. Yuan et al.
173
also reported graphenic MC electrodes for the simultaneous detection
of HQ and CC. The detection limit for HQ and CC was reported to be 3.7 × 10
−7
and 3.1 ×
10
−7
M in this study. A glassy carbon electrode modiied with a β-CD-RGO composite was
used for the determination of nitrophenol isomers. Detection limits of 0.05, 0.02, and 0.1 mg/
dm
3
were reported for
para
-,
ortho
-, and
meta
-nitrophenols, respectively.
174
Electropolymerized
graphene-naion ilm-modiied GCE was used for the detection of nitroaniline isomers
recently.
175
Three nitroaniline isomers (2-nitroaniline, 3-nitroaniline, and 4-nitroaniline) were
detected with a detection limit of 0.022 μg/mL using a simple pulse voltammetry technique. A
novel Ni/Al layered double-hydroxide decorated graphene NS hybrid (LDHs-GNs) prepared
on a cathodic substrate was used as an SPE phase for stripping voltammetric detection of
organophosphate pesticides (OPs) such as MP recently.
176
The detection limit for MP in aque-
ous solutions was reported to be 0.6 ng/mL. A zirconia NP-graphene hybrid, prepared by a
one-step co-electrodeposition approach, anchored on a cathodic substrate, was recently used
for the sensitive square-wave voltammetry detection of OPs taking MP as the model pollut-
ant.
177
A detection limit of 0.6 ng/mL was achieved in this study. An enzymeless OP sensor
using Au NP-decorated GNs modiied glass carbon electrode (GCE) is also reported.
178
Liu et al.
179
recently developed a novel amperometric biosensor by anchoring acetylcho-
linesterase (AChE) on a 3-carboxyphenylboronic-RGO-Au NP hybrid-modiied electrode
for the detection of OPs and carbamate pesticides. Different pesticides such as chlorpyri-
fos, malathion, carbofuran, and isoprocarb showed a detection limit of 0.1, 0.5, 0.05, and
0.5 ppb respectively. Recently, Choi et al.
180
reported a freestanding lexible conductive
RGO-naion (RGON) hybrid ilm having superior synergistic electrochemical charac-
teristics (such as high conductivity [1176 S/m], facile electron transfer, and low interfa-
cial resistance). These hybrid ilms were used as electrochemical biosensing platforms
