Edge promoted ultrasensitive electrochemical detection of organic bio- molecules on epitaxial graphene nanowalls Pradip Kumar Roy a , Abhijit Ganguly b,c , Wei-Hsun Yang d , Chien-Ting Wu e , Jih-Shang Hwang f , Yian Tai d , Kuei-Hsien Chen b,c,n , Li-Chyong Chen c,nn , Surojit Chattopadhyay a,g,nnn a Institute of Biophotonics, National Yang-Ming University, Taipei, Taiwan b Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan c Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan d Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan e Nano Device Materials Characterization Division, National Nano Device Laboratories, Hsinchu, Taiwan f Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, Taiwan g Biophotonics and Molecular Imaging Research Centre, National Yang Ming University, Taipei, Taiwan article info Article history: Received 23 December 2014 Received in revised form 27 February 2015 Accepted 11 March 2015 Available online 14 March 2015 Keywords: Three dimensional (3D) epitaxial graphene Electrochemical detection Dopamine Sensitivity Reaction kinetics Limit of detection abstract We report the simultaneous electrochemical detection of dopamine (DA), uric acid (UA) and ascorbic acid (AA) on three dimensional (3D) unmodified ‘as-grown’ epitaxial graphene nanowall arrays (EGNWs). The 3D few layer EGNWs, unlike the 2D planar graphene, offers an abundance of vertically oriented nano- graphitic-edges that exhibit fast electron-transfer kinetics and high electroactive surface area to geo- metrical area (EAA/GA E134%), as evident from the Fe(CN) 6 3 /4 redox kinetic study. The hexagonal sp 2 -C domains, on the basal plane of the EGNWs, facilitate efficient adsorption via spontaneous π–π interaction with the aromatic rings in DA and UA. Such affinity together with the fast electron kinetics enables simultaneous and unambiguous identification of individual AA, DA and UA from their mixture. The unique edge dominant EGNWs result in an unprecedented low limit of detection (experimental) of 0.033 nM and highest sensitivity of 476.2 mA/mM/cm 2 , for UA, which are orders of magnitude higher than comparable existing reports. A reaction kinetics based modeling of the edge-oriented 3D EGNW system is proposed to illustrate the superior electro-activity for bio-sensing applications. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Graphene (Novoselov et al., 2004) is being considered as one of the most promising materials for next generation nanotechnolo- gical applications spanning the field of nanoelectronics (Wester- velt, 2008), energy devices (Gwon et al., 2011) and sensors (Mo- hanty and Berry, 2008). For sensing applications mainly graphene oxide (GO) (Liu et al., 2010) and reduced GO (Zhou et al., 2009) are the popular choices, with limited use of chemical vapor deposited (CVD) graphene (Huang et al., 2010). Although GO is being used widely for sensing, its performance should be limited by the pre- sence of abundant oxygen moieties and high defect sites (Ganguly et al., 2011), which would induce high resistance to the charge- transfer from the bio-analytes and hence reduce the efficiency of electrocatalytic behavior. Metal nano particle modified highly sensitive carbon materials have been used successfully for differ- ent sensing applications with a very low limit of detection (LoD) (Huang et al., 2008; Oztekin et al., 2012). However, pure carbon based sensors, such as graphene with a hexagonal sp 2 structure, should be a better choice for the detection of organic analytes (Shang et al., 2008; Huang et al., 2011; Ping et al., 2012; Sheng et al., 2012; Niu et al., 2013; Yan et al., 2013; Zhang et al., 2013; Du et al., 2014; Yue et al., 2014), having aromatic or heterocyclic ring structures, that facilitate a strong π–π interaction between the two. Intuitively, better graphitic nature should provide improved interaction, at least those with molecular structures promoting the π–π interaction, required for bio-sensing applications unless other factors or experimental difficulty presents insurmountable Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/bios Biosensors and Bioelectronics http://dx.doi.org/10.1016/j.bios.2015.03.027 0956-5663/& 2015 Elsevier B.V. All rights reserved. n Corresponding author at: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan. nn Corresponding author at : Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan. nnn Corresponding author at: Institute of Biophotonics, National Yang-Ming University, Taipei, Taiwan. E-mail addresses: chenkh@pub.iams.sinica.edu.tw (K.-H. Chen), chenlc@ntu.edu.tw (L.-C. Chen), sur@ym.edu.tw (S. Chattopadhyay). Biosensors and Bioelectronics 70 (2015) 137–144