13-02-2016, 01:09 PM
ABSTRACT
Graphene, a single-atom-thick monolayer of sp2 carbon atoms perfectly arranged in a honeycomb lattice, is an emerging sensing material because of its extraordinary properties, such as exceptionally high specific surface area, electrical conductivity, and electrochemical potential window. In this study, we demonstrate that three-dimensional (3D), macroporous, highly conductive, and monolithic graphene foam synthesized by chemical vapor deposition represents a novel architecture for electrochemical electrodes. Being employed as an electrochemical sensor for detection of dopamine, 3D graphene electrode exhibits remarkable sensitivity (619.6 μA mM−1 cm−2 ) and lower detection limit (25 nM at a signal-to-noise ratio of 5.6), with linear response up to ∼25 μM. And the oxidation peak of dopamine can be easily distinguished from that of uric acid − a common interferent to dopamine detection. We envision that the graphene foam provides a promising platform for the development of electrochemical sensors as well as other applications, such as energy storage and conversion.
INTRODUCTION
Graphene, a single-atom-thick monolayer of sp2 carbon atoms perfectly arranged in a honeycomb lattice, is an emerging sensing material because of its extraordinary structural, electrical, optical, and mechanical properties.1−6 In particular, this new carbonaceous material, which exhibits large specific surface area, high charge carrier capacity and mobility, and unique electrochemical properties, has recently attracted tremendous interest to be employed as the electrode material in various novel electrochemical sensors.7−11 In most of the current developments, graphene derivative (reduced graphene oxide, rGO) is used, sometimes hybridizing with other functional materials, to coat the conventional electrode (e.g., glassy carbon electrode).12−14 Conventionally, the electrochemical electrode is planar. Therefore, the active surface area is limited. To tackle this problem, nanostructure materials (e.g., carbon nanotube) are used to coat the flat electrode surface in order to increase the specific surface area, thus, sensitivity of detection.15−17 However, such surface expansion is still inherently limited by the two-dimensional (2D) nature of the planar electrodes. Some attempts have thus been made to construct threedimensional (3D) electrodes. For example, electrochemical electrode based 3D polymeric matrix with embedded enzymes and gold nanoparticles has been developed to detect lactic acid.18 However, nanoporous composites of such kind are not adequately efficient in charge transfer and mass transport. And their architecture and morphology cannot be precisely controlled. Alternatively, photolithographic microfabrication has been used to make 3D electrode with regular array of standing nanopillars.19 But this method involves sophisticated lithographic techniques in a clean room. In the present work, we demonstrate the use of chemical vapor deposition (CVD) grown three-dimensional (3D) graphene foam20,21 as a novel free-standing and monolithic electrochemical electrode. With large specific surface area, 3D multiplexed and highly conductive pathways, and well-defined macroporous structure, this new electrode architecture holds great promise for various electrochemical sensing. To demonstrate its potential, we used it here for the detection of dopamine. Dopamine is a critical neurotransmitter, deficiency of which leads to various neurological diseases, such as Parkinson’s disease.