Coreactant electrochemiluminescence at nanoporous gold electrodes Elena Villani a , Giovanni Valenti a , Massimo Marcaccio a , Luca Mattarozzi b , Simona Barison b , Denis Garoli c , Sandro Cattarin b , Francesco Paolucci a, b, * a Department of Chemistry “G. Ciamician”, via Selmi 2, I-40126, Bologna, Italy b ICMATE e CNR, Corso Stati Uniti 4, I-35127, Padova, Italy c Istituto Italiano di Tecnologia, via Morego 30, I-16163, Genova, Italy article info Article history: Received 2 March 2018 Received in revised form 29 April 2018 Accepted 30 April 2018 Available online 1 May 2018 Keywords: Electrochemiluminescence Nanoporous gold Tripropylamine Peroxydisulfate abstract The electrochemiluminescence (ECL) performances were comparatively investigated at flat and nano- porous gold (NPG) electrodes of different thicknesses (120 and 200 nm) and roughness factors (f r ). The phenomena were studied using either tripropylamine (TPrA) or peroxydisulfate (S 2 O 8 2 ) as sacrificial coreactant and Ruthenium (II)-tris(2,2 0 -bipyridine) as emitting species. The experiments performed using TPrA showed, at first glance, a linear dependence of the ECL emission with respect to the effective surface area of the NPG electrodes. However, ECL signals were not stable in the measuring conditions, presumably due to amine absorption on the metal surface, leading to electrode corrosion and modifi- cation of the surface morphology. The experiments made using peroxydisulfate as coreactant provided conversely a stable ECL response, about proportional to the effective electrode surface area, in the considered range of thicknesses. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction Electrogenerated Chemiluminescence, or simply Electro- chemiluminescence (ECL), is the generation of light occurring at the electrode surface after an electrochemical stimulus [1]. Since the first observations of the phenomenon in the early 1960s [2e4], ECL has become a powerful and versatile analytical technique [5e10] thanks to the electrochemical method of the signal generation. In fact, since the light signal is achieved without the employment of an external light source, ECL shows extremely high sensitivity and selectivity compared to other light-based techniques, such as chemiluminescence (CL) or photoluminescence (PL). In addition, the light signal is generated directly in situ, enabling spatial and temporal control of the emission with extremely high spatial res- olution. This property of the ECL has been exploited for the imaging of small objects, for example micro-particles or cells, deposited directly on the electrode surface [11e 13]. To achieve the light emission the ECL coreactant strategy is usually exploited [14]. The chemical precursors employed consist of a luminophore [15], which is a species capable of generating an excited state that relaxes through the emission of a photon, and a sacrificial species called coreactant. A coreactant is an additional reactant that upon oxidation or reduction at the electrode surface generates radicals sufficiently stable to react with the reduced or oxidized form of the luminophore [16, 17]. The use of a coreactant, that is at the basis of the majority of the ECL applications in aqueous systems, is convenient when one of the radicals of the dye is not stable enough or even for some fluorescent compounds that pre- sent only a reversible electrochemical oxidation or reduction. The ECL coreactant strategy can be divided in two different pathways depending on whether the coreactant is oxidized or reduced: the “oxidative-reduction” coreactant ECL, when the coreactant is oxidized (e.g. oxalate [18] and Tripropylamine [19]) and the “reductive-oxidation” coreactant ECL, when the coreactant is reduced (e.g. peroxydisulfate [20]). Generally, the majority of the ECL applications take advantage of the “oxidative-reduction” mechanism using TPrA as coreactant [1 ,5e10,21 ,22]. Among the factors that affect the ECL sensitivity, the choice of the electrode material is one of the most crucial, because the chemical and physical state of the electrode surface and its elec- trochemical behaviour have remarkable effect on the signal gen- eration [23]. In fact, the electrode surface state strongly influences the kinetics of the heterogeneous electron transfer reaction for the * Corresponding author. Department of Chemistry “G. Ciamician”, via Selmi 2, I- 40126, Bologna, Italy. E-mail address: Francesco.paolucci@unibo.it (F. Paolucci). Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta https://doi.org/10.1016/j.electacta.2018.04.215 0013-4686/© 2018 Elsevier Ltd. All rights reserved. Electrochimica Acta 277 (2018) 168e175