Electrochimica Acta 82 (2012) 109–114 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Modified working electrodes for electrochemical whole-cell microchips Hadar Ben-Yoav a,∗,1 , Rakefet Ofek Almog a , Yelena Sverdlov a , Marek Sternheim b , Shimshon Belkin c , Amihay Freeman d , Yosi Shacham-Diamand a,∗∗,1 a Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University, Tel-Aviv 69978, Israel b The Center for Nanoscience and Nanotechnology, Tel Aviv University, Tel-Aviv 69978, Israel c Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel d Department of Molecular Microbiology and Biotechnology, Faculty of Life Sciences, Tel Aviv University, Tel-Aviv 69978, Israel a r t i c l e i n f o Article history: Received 2 December 2011 Received in revised form 9 March 2012 Accepted 12 March 2012 Available online 20 March 2012 Keywords: Whole-cell biosensor Electrochemical biochip Three-dimensional electrode Polypyrrole Pillar structure a b s t r a c t The electrode geometry and material have a significant effect on the electrochemical biochip transduction of chemical signals into electrical current or voltage. In this work we focus on the working electrode aiming to improve the signal level of live cell sensors integrated on solid-state microchips. We present here a model and measurements describing the effect of the electrode material and dimensions on the biochip performance. The research hypothesis was that the electrode transduction efficiency increases as its effective area increases. Therefore, we investigated two methods to increase the electrode effective area: 3D structures and a polymer modified electrode. An electrochemical microchip was fabricated with a working electrode that was further modified, resulting in two structure types: 3D metallic pillar-based and polypyrrole-coated. The electrochemical performance of both modified electrodes was characterized and their utilization as working electrodes in whole-cell biochips for toxicity sensing was studied. Bio- detection efficiency analysis demonstrated higher biosensing performance for the metallic (e.g. Cu/Au) pillar-based microchip than for the polypyrrole-modified and the non-modified microchips. Therefore, we conclude that the enhanced signal of the modified geometry electrode is most probably due to the increased effective surface area and the improved charge transfer efficiency. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction The last decade has witnessed an unprecedented convergence of biological, physical, chemical and engineering sciences that allows the construction of hybrid devices that could not have been feasible earlier. The advances in micro-technology systems and biotechnologies introduced novel biochips, biosensors, biomimetic systems and diverse arrays [1–7]. Such miniaturized integrated systems repeatedly break new records regarding the interface of biological entities with diverse hardware platforms especially the introduction of biochips dealing with biomolecular sensing. Microbial cells can generate a large variety of specific responses to chemical and biological stimulations. Taking advantage of this ∗ Corresponding author at: Institute for Systems Research, Department of Elec- trical and Computer Engineering, University of Maryland, College Park, MD 20742, USA. Tel.: +1 301 405 2168; fax: +1 301 314 9920. ∗∗ Corresponding author at: School of Electrical Engineering, Department of Physi- cal Electronics, Faculty of Engineering, Tel Aviv University, Ramat Aviv 69978, Israel. Tel.: +972 3 640 8064; fax: +972 3 642 3508. E-mail addresses: benyoav@umd.edu (H. Ben-Yoav), yosish@post.tau.ac.il (Y. Shacham-Diamand). 1 ISE member. inherent specificity can yield target-specific sensors and alle- viate one of the major challenges of chemical and biological sensor design. In the biotic micro-electro-mechanical systems (biotic-MEMS) sensor, which integrates live microbial cells with micro-fabricated structures, the main sensing element is the microbial cell which typically converts the chemical or biological excitation onto an electrical signal [8,9]. Microbial biosensors have been utilized for environmental monitoring [6,10], food monitoring e.g. sensing of alcohol [11], glucose [12] or fatty acids [13], mon- itoring of microbial growth rate [14] and biocide measurements [15]. Electrochemical biosensors are based on a bio-electrochemical interaction process, where electrochemical species are consumed or generated. The electrochemical reaction produces a measureable electrical signal using conventional electrical circuits. Most electro- chemical measurements detect oxidation/reduction of the product generated by biochemical conversion of the analyte. Portable inte- grated electrochemical microsystems can be easily realized using on-chip electrochemical detection in which the sense/detection electrodes are integrated directly onto the microchip. In addition to its inherent miniaturization potential, this approach yields good signals and relatively low noise; hence it has a detection limit that is satisfactory for many practical applications. Additionally, it has low cost, and, above all, the flexibility to customize electrode shape, 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2012.03.042