(Keynote) Single Gold Nanowire Electrodes for Electrochemical Based Biosensing Applications
Authors: O' Riordan Alan , Barry Sean , Creedon Niamh , Montrose Armelle , O'Sullivan Benjamin 
Published: February 2020

Compared to traditional macroelectrodes, nanoscale electrodes have tremendous potential as electrochemical sensors exhibiting enhanced performance.  As critical dimensions of the electrodes enter the nano regime, 3D analyte diffusion profiles to the electrode dominate with a corresponding increase in mass transport, higher current densities giving rise to an increase in the ratio of faradaic to charging current, higher signal to noise ratios, steady-state sigmoidal voltammograms, low depletion of target molecules, low supporting electrolyte concentration requirements and shorter RC time constant 1-3. We and others have previously reported fabrication and in-depth electrochemical analysis of discrete gold nanowire electrodes for use in electrochemical applications.  The single nanowire electrodes and nanowire electrode arrays were fabricated using a hybrid E-beam / photolithography approach, providing electrodes with well-defined and reproducible dimensions.  Finite element diffusion domain simulation studies were employed to explore mass transport to nanowire electrodes.  Simulation results suggested that radial diffusion to nanowires should be present at fast scan rates 4,5.  This behavior was confirmed experimentally where CVs obtained in FcCOOH, were observed to be steady-state, with high currents (nA) and sigmoidal up to 50,000 mV s-1.  The electrochemical responses of single and diffusionally independent arrays of nanowires, in model redox mediators, were excellently described by Butler-Volmer kinetics.  To date we have employed these nanowire devices for highly sensitive detection of biochemical and chemical species including glucose and explosives 6-8.

Herein we extend this work and explore the application of single on-chip gold nanowires for use as electrochemical biosensors with specificity provided by modifying the nanowire surface with polymer overlayers both with and without encapsulated biomolecules (application specific). We show highly sensitive dopamine with a measured limit of detection of 10 pM.  We show real-time detection of glucose using an enzyme encapsulated within a polymer host without the need for a mediator.  Finally we show label-free detection using electrochemical impedance spectroscopy of antibody-antigen binding events at a single nanowire electrode; see figure 1.

Figure 1: Schematic showing the label-free detection of antibody-antigen binding at a single nanowire electrode

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Acknowledgements This work was supported by Science Foundation Ireland under the US-Ireland programme (SFI12/US/I2476), by the Department of Agriculture Food and the Marine (13S405) and the Irish Higher Education Authority PRTLI programs (Cycle 3 “Nanoscience” and Cycle 4 “INSPIRE”).

Figure 1