The Enzymatic Oxidation of Graphene Oxide

Abstract

Two-dimensional graphitic carbon is a new material with many emerging applications, and studying its chemical properties is an important goal. Here, we reported a new phenomenon -the enzymatic oxidation of a single layer of graphitic carbon by horseradish peroxidase (HRP). In the presence of low concentrations of hydrogen peroxide (~40 µM), HRP catalyzed the oxidation of graphene oxide, which resulted in the formation of holes on its basal plane. During the same period of analysis, HRP failed to oxidize chemically reduced graphene oxide (RGO). The enzymatic oxidation was characterized by Raman, UV-Vis, EPR and FT-IR spectroscopy, TEM, AFM, SDS-PAGE, and GC-MS. Computational docking studies indicated that HRP was preferentially bound to the basal plane rather than the edge for both graphene oxide and RGO. Due to the more dynamic nature of HRP on graphene oxide, the heme active site of HRP was in closer proximity to graphene oxide compared to RGO, thereby facilitating the oxidation of the basal plane of graphene oxide. We also studied the electronic properties of the reduced intermediate product, holey reduced graphene oxide (hRGO), using field-effect transistor (FET) measurements. While RGO exhibited a V-shaped transfer characteristic similar to a single layer of graphene that was attributed to its zero band gap, hRGO demonstrated a p-type semiconducting behavior with a positive shift in the Dirac points. This p-type behavior rendered hRGO, which can be conceptualized as interconnected graphene nanoribbons, as a potentially attractive material for FET sensors. Keywords graphene; oxidation; microscopy; peroxidase; field-effect transistor Graphene has captured the attention of the scientific community due to its novel electronic properties 1,2 coupled with its mechanical strength, 2,3 both of which may make graphene integral in future generations of electronics, batteries, sensors, and composites.1 , 2 , 4 -6 One of the current methods of synthesizing graphene entails exfoliating graphite through astar@pitt.edu. Supporting Information Available: Supplemental TEM micrographs for the graphene oxide and RGO experiments ( Figure S1); Amplex Red assay for days 1 and 20 of RGO oxidation ( Figure S2); electron paramagnetic resonance (EPR) spectroscopy data ( Figure S3); AFM images with section analysis of graphene oxide, HRP, and RGO ( Figure S4); details of the predicted interaction sites for RGO, graphene oxide, and holey graphene oxide on HRP (Table S1); back gate FET data for hRGO and RGO ( Figure S5); and FT-IR and UV-vis spectra of hRGO, RGO, and graphene oxide ( Figure S6). This material is available free of charge via the Internet at

Hypochlorite degrades 2D graphene oxide sheets faster than 1D oxidised carbon nanotubes and nanohorns

“…Similar observations were demonstrated in other CNM degradation studies. 17 Later on for GO, the I D /I G ratio began to decrease noticeably (Day 3) and the spectra started to lose the characteristic Raman signature of GO (Days 5 and 7). This was expected and is confirmation of degradation.…”

“…Regarding degradability, several studies have investigated and demonstrated the degradation of CNMs including graphene using enzymes, such as lignin peroxidase 16 or horseradish peroxidase. 17 Chemical strategies such as Fenton-based chemistry have also been tested. 18 However, studies directly comparing the degradation kinetics of CNMs of different geometries in an oxidative environment are lacking.…”

“…45 This may contribute to the observed hole formation (Fig. 4) in the GO sheets [16][17][18] where epoxides arise. Interestingly, ClO − can form epoxides from alkene double bonds.…”

“…These observations are similar to that reported previously when the horseradish peroxidase enzyme was incubated with H 2 O 2 and GO. 17 The enzyme was able to bind to GO and induce structural defects by catalysing the conversion of H 2 O 2 to stronger oxidative species. For OxMWNT and as expected, the degradation pattern was different with evident exfoliation of the OxMWNT outer walls at Days 5 and 7 ( Supplementary Fig.…”

Interactions of graphene and graphene oxide with proteins and peptides

“…The adsorption of the protein (enzyme) molecules on graphene and GO, in turn, may improve their biocompatibilities or accelerate their chemical process or biodegradation. Kotchey et al studied systematically the enzymatic oxidation of GO and CRGO by HRP in the presence of hydrogen peroxide [133] . As shown in Figures 15 and 16 , with electron microscopy, it was found that the HRP could catalyze the oxidation of GO, but not the CRGO.…”