IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 58, NO. 9, SEPTEMBER 2011 2521 Characterization of the Electrochemical Behavior of Gastrointestinal Fluids Using a Multielectrode Sensor Probe Karen Twomey*, Eva Alvarez de Eulate, Julian R. Marchesi, Sofia Kolida, Glenn Gibson, Damien W. M. Arrigan, and Vladimir I. Ogurtsov Abstract—A characterization of gastrointestinal fluids has been performed by means of an electrochemical sensor that has poten- tial for clinical in vivo and in vitro monitoring applications. The sensor comprised a three-electrode cell with a counter, reference, and four working electrodes, Au, Pt, Ir, and Rh. Cyclic voltam- metry was used to obtain chemical information from faecal water (in vitro) and gut model (in vivo) fluids. Stable voltammetric re- sponses were obtained for both fluids at these noble metal working electrodes. The responses differed in shape that demonstrated the discrimination capability and the potential for practical use as a tool for gastrointestinal fluid investigation. The analysis of the sta- bility profiles in faecal water over a 14-h duration has indicated a possible adsorption mechanism with the formation of a biolayer on the sensor surface. The stability in gut model fluids over a 42-h du- ration has demonstrated a more stable profile, but the mechanisms involved are more complicated to determine. Index Terms—Electrochemical, electrode, gastrointestinal fluids, voltammetry. I. INTRODUCTION G ASTROINTESTINAL diseases are growing in incidence in particular across the Western World. The gold stan- dard in diagnosis is endoscopy, an invasive technique that is not suitable for all candidates, where high-resolution color images are taken of the gut wall. Therefore, there have been significant efforts to develop reliable alternative approaches that could pro- vide a noninvasive diagnosis, e.g., by application of different Manuscript received October 27, 2010; revised March 31, 2011; accepted May 23, 2011. Date of publication June 2, 2011; date of current version Au- gust 19, 2011. This work was supported by Enterprise Ireland under Grant CFTD.05/112 and Grant IC/2006/64. Asterisk indicates corresponding author. *K. Twomey is with the Molecular Microsystems Group, Tyndall National Institute, University College Cork, Cork, Ireland (e-mail: karen.twomey@ tyndall.ie). E. Alvarez de Eulate and D. W. M. Arrigan were with the Molecular Mi- crosystems Group, Tyndall National Institute, University College Cork, Cork, Ireland. They are now with the Department of Chemistry, Nanochemistry Research Institute, Curtin University, Perth, W.A. 6845, Australia (e-mail: eva.alvarez@postgrad.curtin.edu.au; d.arrigan@curtin.edu.au). J. R. Marchesi is with the School of Biosciences, Cardiff University, Cardiff, CF10 3AT, U.K. (e-mail: marchesiJR@cardiff.ac.uk). S. Kolida and G. Gibson are with the School of Food Biosciences, Univer- sity of Reading, Reading, RG6 6UR, U.K. (e-mail: s.kolida@reading.ac.uk; g.r.gibson@reading.ac.uk). V. I. Ogurtsov is with the Molecular Microsystems Group, Tyndall Na- tional Institute, University College Cork, Cork, Ireland (e-mail: vladimir. ogourtsov@tyndall.ie). Digital Object Identifier 10.1109/TBME.2011.2158543 analytical methods for the gastrointestinal fluid analysis. For example, mass spectrometric investigation of gut fluids has de- termined differences in the spectra from healthy humans versus patients with inflammatory bowel disease (IBD) [1]. An analysis of gut lavage fluid using chromatographic techniques has also shown that mucin levels differ between samples from healthy and IBD subjects [2]. Faecal calprotectin levels in faeces have been proposed as a marker for intestinal inflammation [3], [4]. In spite of these studies, the gut environment is still poorly investigated, and this fundamental limitation, in turn, leads to difficulty in understanding the causes and behavior of diseases of the gut. This paper describes an electrochemical study of two biomimetic fluids related to the gut environment, faecal wa- ter, and gut model fluids, which have potential for in vitro and in vivo applications. For in vitro applications, faecal water was prepared from stool samples of healthy volunteers. A gut model system was used for access to gut model fluids. The electro- chemical system under investigation adapts an electronic tongue (e-tongue) approach, which is a multisensor system incorporat- ing high-sensitivity sensors and signal-processing routines [5], [6]. It has been proven that this methodology can be effectively used for the analysis of complex solutions including recognition of different flavors. This approach has been well established in the analysis of complex liquids in food and environmental ap- plications where a qualitative assessment on conditions of liquid foods [7]–[9] and waste water [10], [11] (e.g., as part of water treatment processes) is needed. The first of these e-tongue systems can be attributed to Toko, who in 1990 introduced a sensor that could distinguish between the five basic tastes salt, sweet, sour, bitter, and umami. [12]. Other sensors followed with potentiometric [13], voltammet- ric [14]–[16], and surface acoustic wave array sensors [17] being developed for applications ranging from tasting the freshness of milk, different fruit juices, and the quality of drinking water. Among these systems, the voltammetric e-tongue tends to be favored for robust applications. It consists of an array of no- ble metal electrodes that do not require selective coatings and can be cleaned in situ. These electrodes can be deposited on a sensing substrate using microfabrication techniques [18] that facilitate miniaturization, batch production, high reproducibil- ity, low cost, and a disposable option (so, surface fouling and cross contamination is not an issue). The aim of this paper is to evaluate the suitability of an e- tongue approach for the analysis of gastrointestinal fluids. To 0018-9294/$26.00 © 2011 IEEE