Hydrogen peroxide (H2O2) is an enzymatic product of many biological processes. Therefore, detection of H2O2 is of great importance. A H2O2 sensor was fabricated using a RGO–chitosan composite film entrapped with hemoglobin (Hb) molecules. It exhibits a lower limit of detection (LOD) (0.51 mM) and a wider linear range (6.5–230 mM) as compared with the conventional H2O2 detection methods. This is because the RGO–chitosan matrix can be abundantly loaded with Hb molecules and provide a biocompatible microenvironment to retain the enzyme in its native structure. Furthermore, RGO facilitates the electron transfer between the matrix and the electroactive center of hemoglobin and the percolating 3D network of RGOs provide multiplexed paths to rapidly conduct away the charges.
In another H2O2 sensor, horseradish peroxidase (HRP) was used to hydrolyze H2O2. Small graphene sheets, non-covalently exfoliated by the aromatic molecules (tetrasodium 1,3,6,8-pyrenetetrasulfonic acid) were used to anchor the enzymes with large capacity and to efficiently mediate the charge transfer. This sensor gives a detection limit of 0.106 mM and a linear range from 0.63 mM to 16.8 mM.
A novel hierarchical nanostructure formed by layer-by-layer assembly of HRP and sodium dodecylbenzene sulfonate (SDBS) functionalized RGO has been demonstrated for H2O2 detection. An impressively low detection limit (0.1 mM) was achieved due to the high enzyme loading and the fact that enzymes intercalated in RGOs retain high catalytic efficiency towards H2O2 with low diffusion barrier. Single-stranded DNAs (ssDNA) which can interact with graphene or RGO through p–p stacking have been utilized to assist material dispersion, to electrostatically attract reactants, or to enhance the loading of enzymes.
Electrochemical detection of H2O2 can also be catalyzed by metal nanoparticles. Using one-step microwave-assisted thermal reduction, a sensing mechanism was fabricated using a platinum nanoparticle/RGO hybrid for H2O2 detection. The detection limit of this sensor (80 nM) is several orders lower than other carbon-based electrodes, such as the CNTs/chitosan modified electrode (10.3 mM), the highly ordered mesoporous carbon modified electrode (1.61 mM), CNTs/silica/Au/Pt hybrid nanomaterial (0.5 mM). A broad range of linear response is achieved (1 mM–500 mM). The high performance of this sensor can be attributed to the facts that platinum nanoparticles can be uniformly deposited on RGO nanosheets with high density, and rapid charge transfer is ensured by the intimate interaction between metal nanoparticles and RGO and their highly conductive nature. A similar sensor based on a gold nanoparticle/RGO hybrid was also demonstrated. RGO with both nanoparticles (gold) and enzymes (microperoxidase-11) was demonstrated, in which gold nanoparticles not only act as the catalyst but also act synergistically with RGO sheets to facilitate charge transfer. The highest sensitivity (45 nM) in all H2O2 sensors is realized by decorating the RGO thin-film with in situ grown Prussian blue which is a superior electrocatalyst (artificial peroxidase) for H2O2 reduction.
Figure: Graphene-material based electrochemical sensor for detection of Hydrogen per Oxide. (a) Schematic of the construction of Hb-graphene–chitosan/ GCE. Hb = hemoglobin; GCE = glassy carbon electrode; graphene here is actually RGO (b) Illustration of a RGO sheet decorated with Prussian blue (PB) nanocubes.
Extracted and edited from “Biological and chemical sensors based on graphene materials by Yuxin Liu, Xiaochen Dong and Peng Chen in Chemical Society Reviews, 2012″