DOI: 10.1002/adfm.200800951 Catalyst-Free Efficient Growth, Orientation and Biosensing Properties of Multilayer Graphene Nanoflake Films with Sharp Edge Planes** By Nai Gui Shang, Pagona Papakonstantinou, * Martin McMullan, Ming Chu, Artemis Stamboulis, Alessandro Potenza, Sarnjeet S. Dhesi, and Helder Marchetto 1. Introduction Although various carbon-based materials, such as highly ordered pyrolytic graphite (HOPG), glassy carbon, fullerenes, boron-doped diamond, carbon nanotubes (CNTs), etc., [1] have been used as electrodes in both electroanalysis and electro- catalysis over the past decades, the individual roles of electrochemical activity of graphitic edges and metal impurities still remain open questions. [2,3] Highly anisotropic graphene materials such as HOPG and vertically oriented CNT arrays or forests can serve as excellent electrodes because they make predominant use of the highly reactive edge planes in contrast to the nearly inert basal planes. However, HOPG is very expensive and needs careful polishing to expose the fresh edge planes while most CNT arrays or forests always possess metal nanoparticles inherited by their metal catalytic chemical vapor deposition. It was found recently that the catalytically grown CNTs even after multiple purifications in strong acids for long times still contain residual metals sheathed by multilayer graphene layers, which not only lead to potential misinter- pretations of electrochemical experiment but also can significantly affect their electrochemical repeatability and stability. [4,5] Recently, graphene has been considered as a ‘‘rising-star’’ material and has received intensive attention because of its novel properties. [6] Here we report one kind of graphene integrated nanomaterial, that is, uniform multilayer graphene nanoflake films (MGNFs, also called carbon nanowalls, nanoflakes, nanosheets, and petals). [7–9] MGNFs could com- pete with HOPG and CNTs as they are made of vertical 1–20 nm thick, two-dimensional graphenes, which contain a large amount of open graphitic edge planes with high surface activity. [10] This is especially attractive as they were proved to be fabricated without the use of catalysts, although their growth mechanism is still not well understood. Thus, in contrast to aligned CNTs, the MGNFs could be one of best electrode materials to investigate basic electrochemical FULL PAPER [*] Dr. P. Papakonstantinou, Dr. N. G. Shang, and M. McMullan Nanotechnology and Integrated Bio-Engineering Centre (NIBEC) University of Ulster Shore Road, Newtownabbey, BT37 0QB (UK) E-mail: p.papakonstantinou@ulster.ac.uk M. Chu, Dr. A. Stamboulis Department of Metallurgy and Materials, University of Birmingham Edgbaston, Birmingham, B15 2TT (UK) Dr. A. Potenza, Dr. S. S. Dhesi, Dr. H. Marchetto Diamond Light Source Chilton, Oxfordshire, OX11 0DE (UK) [**] We acknowledge supports from the European Union under the DESYGN-IT project (STREP Project 505626-1) and the National Centre for Electron Spectroscopy and Surface (NCESS) analysis at Daresbury Laboratory, UK. We thank R. McCann and A. Kumar in University of Ulster for their help in the X-ray photoelectron spectroscopy measure- ment. Supporting Information is available online from Wiley Inter- Science or from the author. We report a novel microwave plasma enhanced chemical vapor deposition strategy for the efficient synthesis of multilayer graphene nanoflake films (MGNFs) on Si substrates. The constituent graphene nanoflakes have a highly graphitized knife-edge structure with a 2–3 nm thick sharp edge and show a preferred vertical orientation with respect to the Si substrate as established by near-edge X-ray absorption fine structure spectroscopy. The growth rate is approximately 1.6 mm min 1 , which is 10 times faster than the previously reported best value. The MGNFs are shown to demonstrate fast electron-transfer (ET) kinetics for the Fe(CN) 6 3/4 redox system and excellent electrocatalytic activity for simultaneously determining dopamine (DA), ascorbic acid (AA) and uric acid (UA). Their biosensing DA performance in the presence of common interfering agents AA and UA is superior to other bare solid-state electrodes and is comparable only to that of edge plane pyrolytic graphite. Our work here, establishes that the abundance of graphitic edge planes/defects are essentially responsible for the fast ET kinetics, active electrocatalytic and biosensing properties. This novel edge-plane-based electrochemical platform with the high surface area and electrocatalytic activity offers great promise for creating a revolutionary new class of nanostructured electrodes for biosensing, biofuel cells and energy-conversion applications. 3506 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Funct. Mater. 2008, 18, 3506–3514