Environmental Engineering Reference
In-Depth Information
properties and was used for the ultralow concentration detection (detection limit of 9 nM)
of folic acid. A biosensor based on the SERS properties of a chalcogenide prism-anchored
graphene multilayer is also reported.
252
The incorporation of graphene in the biosensor
signiicantly increased the sensitivity, and the detection accuracy also increased by >100%
because of high index chalcogenide glass as compared with silica glass.
34.3 New Directions
New graphene-based structures such as graphene QDs (GQDs) and graphene nanorib-
bons (GNRs) and carbon NPs have emerged recently with several possibilities. Sensors
based on these materials are one of the newest classes of sensors. The availability of a
band gap in these structures can help in constructing ultrafast transistors and electrical
sensors. Representative examples of some new directions where novel graphenic struc-
tures are being used for pollutant sensing are noted here. Valentini et al.
253
recently used
modiied screen-printed electrodes composed of oxidized GNRs for the selective elec-
trochemical detection of several molecules, including potassium ferricyanide, catechol,
hexaammineruthenium(III) chloride, sodium hexachloroiridate(III) hydrate, dopamine,
epinephrine, l-tyrosine, 3,4-dihydroxyphenylacetic acid, ascorbic acid, uric acid, 4-aceta
midophenol(acetaminophen), NADH, H
2
O
2
, caffeic acid, guanine, and serotonin (5-HT)
hydrochloride. Hydrothermally synthesized luorescent carbon NPs were found to be a
good sensor for mercury ions.
254
A carbon QD-polyamine composite was used as a Cu
ion sensor as well.
255
A detection limit of 6 nm was attained in this strategy. Recently,
Dong and coworkers
256
used GQDs for the detection of free chlorine in drinking water. The
destruction of the passivated surface of GQDs through oxidation by free chlorine, result-
ing in sudden quenching of their luorescence, led to the sensing (Figure 34.5i and j). Goh
and Pumera
257
recently developed a graphene-based electrochemical sensor for detection
of 2,4,6-TNT in seawater. The sensor was constructed using single-, few-, and multilayer
GNRs and graphite microparticles and the performance was compared. A detection limit
of 1 μg/mL was obtained in this approach. Graphdiyne (GD) is a carbon allotrope strik-
ingly similar to graphene but contains two diacetylenic linkages between repeating carbon
hexagon units. This is considered as the most stable of the various man-made diacetyl-
enic carbon allotropes. A GD-based photocatalyst containing P25 has also been reported
to have high eficiency for photocatalysis.
258
Compared with simple P25, the composite
GD-P25 showed enhanced photocatalytic activity for degrading MB under UV irradia-
tion. A study conducted by Akahvan and Ghaderi
259
recently reported the antibacterial
activity of GO nanowell structures on both gram-positive and gram-negative bacteria.
Nanowell structures were fabricated by electrophoretic deposition of Mg
2+
-GO. The cell
membrane damage of the bacteria caused by contact of the bacteria with the sharp edges
of the nanowalls was suggested to be the mechanism of the bacterial inactivation. Gram-
negative
E. coli
bacteria with an outer membrane were more resistant to this inactivation,
whereas gram-positive
Staphylococcus aureus
, which does not have an outer membrane,
was highly susceptible. Also, RGO nanowalls were more toxic to the bacteria than the
unreduced GO nanowalls, owing to the better charge transfer between the bacteria and
the more sharpened edges.
