Biosensors and Bioelectronics 32 (2012) 309–313 Contents lists available at SciVerse ScienceDirect Biosensors and Bioelectronics j our na l ho me page: www.elsevier.com/locate/bios Short communication A cost-effective and field-ready potentiostat that poises subsurface electrodes to monitor bacterial respiration Elliot S. Friedman a , Miriam A. Rosenbaum a,1 , Alexander W. Lee a,2 , David. A. Lipson b , Bruce R. Land c , Largus T. Angenent a,∗ a Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY 14853, USA b Department of Biology, San Diego State University, San Diego, CA 92182, USA c School of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853, USA a r t i c l e i n f o Article history: Received 29 October 2011 Received in revised form 6 December 2011 Accepted 8 December 2011 Available online 16 December 2011 Keywords: Bioelectrochemical systems Biosensing Arctic peat soils Microbial respiration Potentiostat a b s t r a c t Here, we present the proof-of-concept for a subsurface bioelectrochemical system (BES)-based biosensor capable of monitoring microbial respiration that occurs through exocellular electron transfer. This system includes our open-source design of a three-channel microcontroller-unit (MCU)-based potentiostat that is capable of chronoamperometry, which laboratory tests showed to be accurate within 0.95 ± 0.58% (95% Confidence Limit) of a commercial potentiostat. The potentiostat design is freely available online: http://angenent.bee.cornell.edu/potentiostat.html. This robust and field-ready potentiostat, which can withstand temperatures of -30 ◦ C, can be manufactured at relatively low cost ($600), thus, allowing for en-masse deployment at field sites. The MCU-based potentiostat was integrated with electrodes and a solar panel-based power system, and deployed as a biosensor to monitor microbial respiration in drained thaw lake basins outside Barrow, AK. At three different depths, the working electrode of a microbial three- electrode system (M3C) was maintained at potentials corresponding to the microbial reduction of iron(III) compounds and humic acids. Thereby, the working electrode mimics these compounds and is used by certain microbes as an electron acceptor. The sensors revealed daily cycles in microbial respiration. In the medium- and deep-depth electrodes the onset of these cycles followed a considerable increase in overall activity that corresponded to those soils reaching temperatures conducive to microbial activity as the summer thaw progressed. The BES biosensor is a valuable tool for studying microbial activity in situ in remote environments, and the cost-efficient design of the potentiostat allows for wide-scale use in remote areas. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Bioelectrochemical systems (BESs), including microbial fuel cells and microbial electrolysis cells, have been designed to uti- lize the ability of dissimilatory metal-reducing bacteria to respire with a solid-state electrode (Clauwaert et al., 2008; Cusick et al., 2011; Fornero et al., 2010; Hamelers et al., 2010; He et al., 2005; Liu et al., 2004; Lovley, 2006). In addition to waste treatment and energy or product recovery, BESs can be used as biosensors. Often for biosensor function, the working electrode (WE) is poised at ∗ Corresponding author. Tel.: +1 607 255 2480; fax: +1 607 255 4449. E-mail addresses: esf59@cornell.edu (E.S. Friedman), Miriam.Rosenbaum@rwth- aachen.de (M.A. Rosenbaum), awl9@cornell.edu (A.W. Lee), dlipson@sciences.sdsu.edu (David.A. Lipson), bruce.land@cornell.edu (B.R. Land), la249@cornell.edu (L.T. Angenent). 1 Present address: Institute of Applied Microbiology, RWTH Aachen University, Worringer Weg 1, 52074 Aachen, Germany. 2 Present address: The Boeing Company, Ridley Park, PA, USA. a specific potential to mimic an electron acceptor (e.g., iron[III], humic acids) or an electron donor (e.g., iron[II]). This is accom- plished with a microbial three-electrode system (M3C) for which the potential of a WE is controlled with respect to a reference electrode (RE). The current flowing into or out of the working elec- trode is measured via an equal and opposite current produced at the counter electrode (CE). A potentiostat is used to control the potential at the WE and to record the current. The resulting current produced by electrode-respiring bacteria can be directly linked to other parameters, including metabolic activity (Tront et al., 2008), biological oxygen demand (Chang et al., 2004; Kang et al., 2003), or biodegradable organic matter (Kumlanghan et al., 2007). Currently, biosensing applications of BESs are limited by the price of potentiostats, which can cost up to $6000 per chan- nel and are often unsuitable for long-term field use. Here, we present the design of an accurate, cost-effective, open-source, and field-ready potentiostat and demonstrate its use as a biosen- sor to study bacterial respiration in Arctic peat soils. Although other microcontroller-unit (MCU)-based potentiostats have been 0956-5663/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2011.12.013