Wearable Electronic Sensor for Potentiometric and Amperometric Measurements Paweł Bembnowicz, Guang-Zhong Yang Hamlyn Centre, Department of Computing, Imperial College, London, UK p.bembnowicz@imperail.ac.uk Salzitsa Anastasova, Anna-Maria Spehar-Délèze, Pankaj Vadgama Queen Mary University of London, Mile End Road, London, UK (s.anastasova, a.spehar-deleze, p.vadgama)@qmul.ac.uk Abstract— To enable continuous monitoring of electrochemical sensors outside the laboratories, there is a significant demand on electrochemical measurement systems to be miniaturized. The paper presents a low-cost, portable miniature device for electrochemical measurements. The device consists of a 35mm x 20mm x 25mm wireless tag, which enables potentiometric and amperometric measurement, and a base station for data acquisition. Potentiometric performance is evaluated using solid contact ion selective electrodes for pH and sodium. High sensitivity, repeatability and fast response time have been achieved. Amperometric measurement of hydrogen peroxide shows that the measured current accuracy and sensitivity are comparable to that of a commercial potentiostat. Moreover, the device can be used for lactate concentration sensing. Keywords—portable wireless electronics; amperometry; potentiometry; biosensor; miaturisation I. INTRODUCTION Recent advances in micro and nanotechnologies have enabled development of miniaturised electrochemical sensors of different geometries, sizes and materials for environmental, clinical, healthcare, and sports applications. However, the practical applications of these sensors are often limited due to the lack of portability or wearability. Low-cost and easy-to-use potentiostats, with capability to simultaneously and wirelessly monitor in situ, are required. Thus, there is a huge demand for miniaturised electronics [1], [2]. A potentiostat is basically an electronic tool that controls the voltage difference between a working and a reference electrode. It has two main tasks: measurement of the potential difference between a working and reference electrode, and injection of current from counter to a working electrode in order to counter-act the difference between the set voltage and actual potential difference. The majority of all biosensors today operate amperometrically, e.g., current generated at the electrode surface at applied potential is proportional to the concentration of the analyte of interest. In potentiometric methods the potential between the working and reference electrodes is proportional to the analyte activity or concentration in the absence of current flow between the electrodes [3]. Thus, a miniaturised electronic device, which enables high impedance voltage as well as current measurement in micro- and nano-ampere range, should fulfil demands for wireless signal acquisition from most electrochemical sensors. Miniaturised and wearable electronic devices for electrochemical measurements have been described in the literature [1-4]. However, they are not available on the market. In this paper, we describe development of a miniaturised, portable, wireless potentiostat for simultaneous measurement of current and potential, and its application for continuous pH, ion and lactate monitoring. Potentiometric performance was evaluated using pH and sodium ion selective electrodes. Amperometric performance was evaluated by hydrogen peroxide measurement, which was compared to results achieved by a commercially available potentiostat. The test revile high coherency between data from both devices. The device was further tested for lactate sensing. II. ELECTRONICS A. Operational Amplyfire Configuratins for Potentiometric and Ampermetric Measurements A device for potentiometric (voltage) measurements should be characterized by high input impedance [5]. Impedance value in order of 10 9 Ω may be achieved by using instrumentation amplifier. However, significant noise can appear when so high impedance is applied. Moreover, instrumentation amplifier is a composition of several operational amplifiers, which makes its energy consumption higher than a single operational amplifier [6]. In this study, it was shown that a simplified circuit can be successfully used. Potentiometric measurements were made by applying operational amplifier in non-inverting mode of operation (Fig. 1A). This allowed reduction of size and energy consumption. Input impedance in this configuration was in the range of 10 6 Ω, which was found to be sufficient for potentiometric measurements [6]. The output voltage V out of this configuration can be calculated by equation:  ௢௨௧ = ௜௡ ൬1 +  ଵ  ଶ ൰ where V in is input voltage [V] and R 1 , R 2 are resistors values [Ω]. (1) 978-1-4799-0330-6/13/$31.00 ©2013 IEEE