Pyrolyzed Photoresist Carbon Electrodes in Aprotic Solvent: Bilirubin Electrochemistry and Interaction with Electrogenerated Superoxide M. Silvestrini a , A. Mardegan b , R. Kamath c , M. Madou c, d, e , L.M. Moretto a , S. Passamonti f , P. Scopece b , P. Ugo a, * a Department of Molecular Sciences and Nanosystems, University Ca’Foscari of Venice, Santa Marta 2137, 30123 Venice, Italy b Veneto Nanotech, via delle Industrie 5, 30175 Venice-Marghera, Italy c Department of Biomedical Engineering, University of CA, Irvine, CA 92697, USA d Materials and Manufacturing Technology, University of CA, Irvine, CA 92697, USA e Department of Mechanical and Aerospace Engineering, University of CA, Irvine, CA 92697, USA f Department of Life Sciences, University of Trieste, 34127 Trieste, Italy A R T I C L E I N F O Article history: Received 9 July 2014 Received in revised form 25 August 2014 Accepted 9 September 2014 Available online 28 September 2014 Keywords: Pyrolyzed photoresist carbon Bilirubin Superoxide Dimethyl sulfoxide Voltammetry A B S T R A C T Pyrolyzed photoresist carbon electrodes (PPCEs) are fabricated by the photopatterning of a negative tone epoxy-based photoresist, SU-8, through optimized standard UV photolithography. The electrochemical characteristics of PPCEs are investigated in dimethyl sulfoxide (DMSO), observing a wider accessible potential window and a smaller capacitance with respect to glassy carbon electrodes. PPCEs are used to study the cyclic voltammetric behavior of bilirubin (BR) in DMSO. Detailed information is obtained on the multiple steps involved both in the electrochemical oxidation and reduction of BR. Interesting points concerning the electrochemical oxidation of BR to biliverdin are clarified, identifying the formation of an intermediate whose fate depends on the time scale of the electrochemical experiment. PPCEs are also used to electrogenerate the superoxide anion O 2  in DMSO for studying possible reactions between BR and O 2  . The results obtained demonstrate that BR is an efficient superoxide scavenger and that a concentration 2 mM of BR is high enough to consume all the O 2  generated by oxygen reduction at the PPCE/DMSO interface. ã 2014 Published by Elsevier Ltd. 1. Introduction Carbon electrodes possess many advantages including low fabrication cost, wide accessible potential window, chemical and electrochemical stability [1] so that, in many cases, these electro- des are superior with respect to noble metal electrodes [2]. Among common carbon electrode materials, such as pyrolytic graphite, carbon fibers or carbon paste [3–6], glassy carbon (GC) is the most widely used [7,8]. Glassy carbon is impermeable to gases and liquids, has a very small porosity and can be polished to a mirror- like finish an almost infinitive number of times. Moreover, it is very resistant both to high oxidizing and reducing potentials thereby allowing one to perform electrochemistry in a 4–5 V wide potential window [9], when suitable electrolytes are used. Recently, a new procedure to fabricate carbon electrodes based on the controlled pyrolysis of polymeric photoresist has been introduced, obtaining so-called pyrolyzed photoresist carbon electrodes (PPCEs) [10]. This is a very promising approach since, by using simple UV photo-lithography it is possible to pattern high-performance carbon electrodes with complex geometries, such as interdigitated arrays of microelectrodes [11,12]. The optimization of the pyrolysis conditions allows one to obtain PPCEs in which the carbon is mostly amorphous GC [13]. Studies performed in aqueous media demonstrated that the electrochem- ical behavior of PPCEs compares with that of classical electrodes prepared from bulk glassy carbon rods, with the advantage of being cheaper and with the possibility to customize their design [13]. In this paper we report, for the first time, the application of PPCEs for voltammetric measurements in an aprotic solvent, namely dimethyl sulfoxide (DMSO), used here as medium to dissolve bilirubin (BR) and to study its electrochemical behavior together with its reactivity towards electrogenerated superoxide radical anions. * Corresponding author. E-mail address: ugo@unive.it (P. Ugo). http://dx.doi.org/10.1016/j.electacta.2014.09.046 0013-4686/ ã 2014 Published by Elsevier Ltd. Electrochimica Acta 147 (2014) 401–407 Contents lists available at ScienceDirect Electrochimica Acta journa l home page : www.e lsevier.com/loca te/ele cta cta