IP: 83.171.253.251 On: Sat, 19 Jan 2019 10:07:55 Copyright: American Scientific Publishers Delivered by Ingenta RESEARCH ARTICLE Copyright © 2017 American Scientific Publishers All rights reserved Printed in the United States of America SENSOR LETTERS Vol. 15, 126–131, 2017 Electrochemical Optimization of Gold Nanoparticles for Efficient Electron Transfer—Implication for Highly Sensitive Biosensing Madasamy Thangamuthu ∗ , Christian Santschi, and Olivier J. F. Martin Nanophotonics and Metrology Laboratory (NAM), Swiss Federal Institute of Technology Lausanne (EPFL), CH-1015 Lausanne, 1015, Switzerland (Received: 6 December 2016. Accepted: 8 December 2016) In this work, we have optimized linker free electrodepositionof AuNPs in terms of Au salt concentra- tion and deposition time, to improve the electron transfer efficiency between the Fe 3+ /Fe 2+ crevice of cytochrome c (cyt c and screen printed carbon electrode (SPE). Scanning electron microscopy and cyclic voltammetry are used for morphological and electrochemical characterizations of the AuNPs modified electrodes. This study enables highly sensitive electrochemical biosensing of homocys- teine (HcySH) based on the electrochemical oxidation of HcySH by cyt c. Biosensor shows the linear range of response over the concentration of HcySH from 0.3 M to 600 M, with a detection limit of 0.2 ± 0.015 M and a sensitivity of 74 ± 3.5 nA M -1 cm -2 . This work paves the way towards the use of biomolecule-AuNPs assemblies for bioanalytical applications and for the development of bioelectronic devices. Keywords: Cytochrome c, Gold Nanoparticles, Electrodeposition, Electron Transfer, Biosensor, Screen Printed Electrode. 1. INTRODUCTION Gold nanoparticles (AuNPs) play a central role in many scientific fields because of their unique physicochem- ical viz. optical, electronic and catalytic properties. 1–3 Especially, the catalytic regulation of electron transfer reactions is an emerging field of interest for the develop- ment of highly sensitive electrochemical biosensors. 4 It is well established that the performance of electrochemical biosensors greatly depends on the electron transfer effi- ciency between the redox enzyme and the conducting elec- trode surface that has been achieved by anchoring enzymes onto an AuNP matrice. 5 AuNPs offer a stable environ- ment with respect to enzymic activity, improve the electron transfer rate of the enzyme/electrode system and permit electrochemical sensing without any external mediators. 6 Brown et al. reported on electron transfer mediated by AuNPs between tin dioxide (SnO 2  and cytochrome c (cyt c 7 which triggered the researchers to study the role of AuNPs in the electron transfer reaction between cyt c and different conducting electrodes. 8–10 Consequently, highly ∗ Corresponding author; E-mail: madasamy.thangamuthu@epfl.ch sensitive electrochemical biosensors for hydrogen perox- ide, nitrite and cholesterol have been developed. 11–14 Those reports suggest that the electrochemical performance of biosensing electrodes strongly rely on the size, shape, crys- tallinity and the surface structure of the AuNPs. Conse- quently, Chen et al. studied the AuNPs size-dependent electrocatalytic activity of glucose oxidase (GOx) in which GOx anchored on 10 nm AuNPs showed higher sensitivity than 30 nm particles. 15 Likewise, Cortez et al. observed a 5-fold current enhancement as a result of AuNPs elec- tron transfer between GOx and a polyelectrolyte-surfactant complex film. 16 Contrary to these reports, Pankratov et al. could not find any impact of the AuNPs size on the bioelectrocatalytic parameters of bilirubin oxidase. 17 This confusion pulled back the researchers to look into some other parameters viz. synthesis/deposition methods, and interfacing substrates to optimize the AuNPs for efficient electron transport. In order to address this issue, a size-dependent elec- tron transfer property of the AuNPs is investigated using a binder free electrodeposition method to obtain efficient electron transfer between the active site (Fe 3+ /Fe 2+  of 126 Sensor Lett. 2017, Vol. 15, No. 2 1546-198X/2017/15/126/006 doi:10.1166/sl.2017.3773