the sensing ability up to 0.67 nM using SERS method and 10–7 nM based on the
colorimetric method in acidic conditions [83] (Fig. 16).
Borthakur et al. utilized Cu(0) nanoparticles decorated hydrophilic glucose
functionalized graphene oxide nanocomposite (Cu-frGO) for the detection of toxic
Cr(VI) ions present in wastewater system. To explored the sensitivity of the proposed colorimetric probe, they have studied the peroxidase-like activity towards the
oxidation of chromogenic peroxidase substrate TMB to it’s blue colored oxidized
(oxTMB) product. For the quantitative determination of Cr(VI), the absorbance of
oxTMB is monitored by UV-vis spectrometer at 652 nm wavelength in presence of
Cr(VI) ions, which enhances the peroxidase oxidation of TMB. They reported that
the proposed colorimetric probe is highly selective and had sensitivity for Cr(VI) up
to the lower concentration of 67.13 nM (Fig. 17b). They also reported the removal
of Cr(VI) ion from environmental spiked samples [84].
Fig. 14 UV-visible spectra of Au nanoparticles/rGO at various concentrations of NO
2− (a), plot
of absorbance versus [NO
2− ] (b), calibration curve for NO
2− ion detection (c) linear plot of No
2−
range 0.1–20 µM (reproduced with permission from Ref. [81])
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