Pyrene (PYR) is a rigid, carcinogenic, unreactive, and nonelectrooxidizable compound. A multiwalled carbon nanotube (MWCNT)-modified gold electrode surface-bound electrochemical oxidation of PYR to a highly redox-active surface-confined quinone derivative (PYRO) at an applied potential of 1 V versus Ag/AgCl in pH 7 phosphate buffer solution has been demonstrated in this work. Among various carbon nanomaterials examined, the pristine MWCNT-modified gold electrode showed effective electrochemical oxidation of the PYR. The MWCNT's graphite impurity promotes the electrochemical oxidation reaction. Physicochemical and electrochemical characterizations of MWCNT@PYRO by Raman spectroscopy, FT-IR, X-ray photoelectron spectroscopy, and GC-MS reveal the presence of PYRO as pyrene-tetrone within the modified electrode. The quinone position of PYRO was identified as ortho-directing by an elegantly designed ortho-isomer-selective complexation reaction with copper ion as an MWCNT@PYRO-Cu(2+/1+)-modified electrode. Finally, a cytochrome c enzyme-modified Au/MWCNT@PYRO (i.e., Au/MWCNT@PYRO-Cyt c) was also developed and further demonstrated for the selective biosensing of hydrogen peroxide.

Highly stable biomolecule supported by AuNPs assisted with graphene nanocomposite as a sensing platform for H2O2 biosensor application.

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Polyaromatic hydrocarbon (PAH) oxidation: PAHs, which are considered major environmental pollutants, are carcinogenic, and cannot be electrochemically oxidized on conventional electrodes (gold, platinum, and glassy carbon), can be electrochemically oxidized on multiwalled carbon nanotube surfaces at a potential of 1 V versus Ag/AgCl at pH 7. This results in the formation of stable surface-confined quinone systems (see scheme; AN = anthracene; AQ = anthraquinone).

A hemoglobin (Hb) modified glassy carbon electrode consisting of low cost as commercially received impure-multiwalled carbon nanotube (i-MWCNT, 90% purity) and nafion (GCE/i-MWCNT@Hb/Nf) has been demonstrated for improved electric wiring of Hb and efficient direct electrontransfer characteristics. This report is the first attempt for coupling i-MWCNT with Hb for the biosensor purpose. The Hb electrode was assembled by a simple preparation procedure within 38.3 (±2.5) min of time, without any linker, surfactant, promoters, and extensive functionalization of the MWCNT. Impurities within the i-MWCNT such as metal oxides (Fe 3 O 4 , Co 3 O 4 , and NiO), graphite, and amorphous carbon were quantitatively identified by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The metal oxide impurities were found to assist the binding of Hb onto i-MWCNT, whereas the graphitic impurity facilitated the direct electron-transfer reaction. The measured surface excess value of the Hb on the GCE/CNT@Hb/Nf with respect to different CNTs are in the sequences of i-MWCNT > purified-MWCNT > impure single-walled carbon nanotube > functionalized-MWCNT. The GCE/i-MWCNT@Hb/Nf shows enhanced and selective H 2 O 2 electrocatalytic reduction signal without interference from cysteine, ascorbic acid, uric acid, nitrite, and nitrate. Note that Hb can mediate the nitrite reduction reaction too; however, no interference has been observed in this work. Various types of milk, cosmetic bleaching cream, and medical real samples were successfully analyzed with recovery values closer to 100%. The electrode has been found to be stable for 110 days.