Environmental Engineering Reference
In-Depth Information
create electron-deicient centers and aid in electron transfer between the hybrid and the
nitroaromatic, leading to the quenching. A competitive adsorption-based method for
the sensitive detection of synthetic organic dyes on RGO was also reported. The higher
adsorption capacity of a dye compared with the one already anchored onto RGO was
used to detect the former.
231
Wang et al.
232
proposed a graphene-conjugated oligomer
hybrid probe for the detection of lectin and
E.
coli.
Lee et al.
233
reported a metal-organic
framework/azobenzoic acid-functionalized GO composite hydrogel (MOF/A-GO), which
in the presence of Zn
2+
can function as a chemosensor for the detection of TNT. A label-
free surface plasmon resonance-based sensing strategy for the biological warfare agent
Salmonella typhi
, based on electrochemically synthesized GNS, is also available in the
literature.
234
Catalytic chemiluminescence and ECL are other phenomena used for selective sensing.
Graphene-Al
2
O
3
composites were fabricated through a facile one-step process involving
supercritical CO
2
(SCCO
2
), which displayed high catalytic chemiluminescence sensitivity
and high selectivity to ethanol gas.
235
An appreciable response was obtained for a low con-
centration of 9.6 mg/mL ethanol at 200°C, indicating the promise of the nanocomposite.
Ampliied ECL-based sensing of acetylcholine using an RGO-quantum dots (QDs) com-
posite was reported by Deng et al.
236
The ECL emission of QDs coated on a GO-modiied
electrode will be quenched by the structural defects of GO. When the double bonds are
getting restored by the reduction, RGO-QDs exhibit ECL emission. ECL biosensors for
choline and acetylcholine were fabricated by covalently cross-linking choline oxidase
(ChO) or ChO-acetylcholinesterase on the RGO-QDs modiied electrode. Linear response
ranges and detection limits of 10-210 and 8.8 μM for choline, and 10-250 and 4.7 μM for
acetylcholine, respectively, were obtained using these electrodes.
34.2.4 Graphene as SPE Material in Chromatographic Sensors
This section illustrates the use of graphene and its composites as the adsorbent for the SPE
of pollutants and subsequent chromatography or mass spectroscopy (MS)-based sensing/
detection strategy. Zhang and coworkers reported a graphene-coated solid-phase micro-
extraction (SPME) iber where GO was covalently bonded to the fused-silica substrate
using 3-aminopropyltriethoxysilane as a cross-linking agent and subsequently reduced
by hydrazine to make a graphene coating. Coupled with gas chromatography (GC)-MS,
they used this composite structure as a high-performance SPME for polycyclic aromatic
hydrocarbons (PAHs) leading to sensitive detection of PAH with good precision (<11%),
low detection limits (1.52-2.72 ng/L), and wide linearity (5-500 ng/L) under the optimized
conditions.
237
GO-bonded fused-silica iber was also used as the SPME for the GC-based
detection of PAH by Xu et al.
238
Use of graphene to create a high-eficiency adsorbent
coating on ibers for the SPME of four triazine herbicides (atrazine, prometon, ametryn,
and prometryn) from water is also reported.
239
Coupled with high-performance liquid
chromatography-diode array detection (HPLC-DAD), these graphene-coated ibers were
used to determine the presence of the above-mentioned four triazine herbicides. A detec-
tion limit of 0.05-0.2 ng/mL was reported in the process. Liu et al.
240
illustrated the advan-
tages of using graphene as an adsorbent for SPE, taking eight different chlorophenols as
model analytes. Luo et al.
241
recently proposed the utility of a substrate-less graphene iber
prepared by a hydrothermal process as an SPME sorbent. This was demonstrated using
ive different organochlorine pesticides as the model systems. The results pointed to the
superiority of graphene ibers over commercial ibers with higher extraction eficiencies,
higher thermal stability (up to 310°C), better reproducibility, and longer service life (more
