Ultrasensitive Simultaneous Electrochemical Detection of Uric Acid, Dopamine and Ascorbic Acid on Pristine Epitaxial Graphene Nanowalls
Pradip Kumar Roy1*, Abhijit Ganguly2, Wei-Hsun Yang2, Kuei-Hsien Chen2,3, Li-Chyong Chen2, Surojit Chattopadhyay1,4
1Institute of Biophotonics, National Yang-Ming University, Taipei, Taiwan
2Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
3Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
4Biophotonics and Molecular Imaging Research Centre, National Yang Ming University, Taipei, Taiwan
* presenting author:Pradip Kumar Roy, email:Pradipkumarrkm@gmail.com
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), fabricated by microwave plasma enhanced chemical vapour deposition process. This hetero-architecture is created by growing edge-oriented SiC nanowalls on silicon substrates, and subsequent surface graphitization resulting in a hetero junction composed of a 2H-SiC nanowalls sheathed by few-layer strained graphene. 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 geometrical area (EAA/GA ≈ 134%), as evident from the Fe(CN)₆ ³-/⁴- redox kinetic study. The hexagonal sp²-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 high sensitivity of 476.2 µA/µM/cm² for UA which are orders of magnitude superior other graphene based electrochemical detection methods.

We propose a reaction kinetic model, where at low analyte concentrations (C-analyte) the sensitivity is attributed to a Direct Electron transfer (DET) at the EGNW edges favouring the electrode-analyte interaction and demonstrates an unprecedented sensitivity. With increasing C-analyte, the EGNW edges are nearly exhausted with the adsorbed analytes, and DET occurs predominantly at the unmodified “basal-planes”, as well as indirect electron transfer, through the analyte-modified edge-planes of the electrode. At the next transition region at even higher C-analyte, the EGNWs electrode surface was saturated with the analyte residues, and DET slowed down, hence the slope of the sensitivity curve is the least.

Acknowledgements: National Science Council, NSC-101-2112-M-010-003-MY3.

Keywords: Epitaxial Graphene Nanowalls, Simultaneous detection , Uric Acid, Dopamine and Ascorbic Acid, Reaction kinetic model, Edge and basal plane