Analytica Chimica Acta 710 (2012) 1–8 Contents lists available at SciVerse ScienceDirect Analytica Chimica Acta j ourna l ho me page: www.elsevier.com/locate/aca Microfabricated disposable lab-on-a-chip sensors with integrated bismuth microelectrode arrays for voltammetric determination of trace metals Christos Kokkinos a , Anastasios Economou a,∗ , Ioannis Raptis b a Laboratory of Analytical Chemistry, Department of Chemistry, University of Athens, Athens 15771, Greece b Institute of Microelectronics, NCSR “Demokritos”, PO Box 60228, Aghia Paraskevi, Athens 15310, Greece a r t i c l e i n f o Article history: Received 28 September 2011 Accepted 24 October 2011 Available online 3 November 2011 Keywords: Bismuth electrodes Microelectrode arrays Microfabrication Stripping analysis Trace metals a b s t r a c t This work reports the fabrication of disposable three-electrode cells with integrated metal-film elec- trodes. The devices were fabricated by a multi-step micro-fabrication approach combining sputtering for the deposition of metals and the dielectric material (SiO 2 ) on the surface of a silicon wafer and photolithography for the definition of the geometry of the sensors. The working electrode was a micro- electrode array consisting of bismuth microdisks while the reference and counter electrode strips were made of Ag and Pt, respectively. The utility of these devices was tested for the trace determination of Pb(II) and Cd(II) by anodic stripping voltammetry and Ni(II) by adsorptive stripping voltammetry. The detection of these trace metals was carried out in unstirred and undeoxygenated solutions exhibiting sub- g L -1 limits of detection and enhanced analytical characteristics compared to conventional bismuth-film electrodes. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Over the last few years, research has focused on new materi- als that could potentially replace toxic mercury in electroanalysis. Without doubt, bismuth is the most promising substitute for mer- cury since bismuth and its salts are characterised by low toxicity while recent studies have demonstrated that the performance of bismuth electrodes in stripping analysis is roughly analogous to their mercury counterparts [1–4]. Bismuth electrodes are relatively unaffected by dissolved oxygen, can safely operate in highly alka- line media and, in some cases, offer better separation between stripping peaks than mercury electrodes. The main limitation of bismuth with respect to mercury is its more positive oxidation potential which limits the anodic polarisation range of bismuth- based electrodes. By far the commonest method to prepare BiFEs is electrochemical reduction of Bi(III) either in situ or ex situ on a suitable conductive substrate [1–3]. A new approach for the gener- ation of a bismuth-film has been proposed by our group based on micro-electronic thin-film technologies (combining photolithogra- phy and sputtering) [5–8]. The application of this approach for the fabrication of a bismuth film offers several advantages compared to electroplating. In particular, a bismuth plating solution containing Bi(III) ions is not required, therefore the experimental procedure is simplified and limitations associated with the composition of ∗ Corresponding author. Tel.: +30 2107274298; fax: +30 2107274750. E-mail address: aeconomo@chem.uoa.gr (A. Economou). the plating solution (to avoid hydrolysis or complexation of bis- muth) are avoided. A conductive substrate is not necessary since the Bi layer serves as both the current transducer and the sensor. Also, the associated time consuming steps of substrate polishing and renewal are avoided. In addition, using this approach, the elec- trode geometry and the uniformity and thickness bismuth-film can be easily controlled (in contrast to electrodeposited BiFEs whose surface is not uniformly or reproducibly covered with bismuth and the structure of the deposited metal film is strongly dependent on the deposition conditions and the nature of the substrate). Finally, the use of standard thin-film technology offers increased scope of mass-production of inexpensive and disposable devices. These microfabricated electrodes have been successfully applied to the determination of various metal cations by stripping voltammetry [5–8]. Microelectrodes are generally considered as those electrodes whose critical dimension is comparable to, or smaller than, the dif- fusion layer thickness and typically range from a few m to 50 m [9,10]. Microelectrodes, owing to their small size, provide several benefits as compared to the conventional large-sized electrodes, such as enhanced rates of mass-transport and decreased ohmic drop; these characteristics result in greater sensitivity, improved response time and increased signal-to-noise ratio. The main draw- back of single microelectrodes is the extremely weak currents generated during electrochemical redox reactions. A way to address this limitation is the use of arrays of microelectrodes, whereby multiple microelectrodes are operated in parallel [11–15]. The microelectrode arrays lead to an increase of the electrochemical 0003-2670/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2011.10.048