Biosensors and Bioelectronics 22 (2007) 2546–2553 Single-chip microelectronic system to interface with living cells F. Heer a,∗ , S. Hafizovic a , T. Ugniwenko b , U. Frey a , W. Franks a , E. Perriard c , J.-C. Perriard c , A. Blau b , C. Ziegler b , A. Hierlemann a a Physical Electronics Laboratory, ETH Z¨ urich, ETH H¨ onggerberg, HPT H 4.2, Wolfgang-Pauli-Strasse 16, CH-8093 Zurich, Switzerland b Department of Physics, University of Kaiserslautern, D-67663 Kaiserslautern, Germany c Department of Biology, ETH Z¨ urich, ETH H¨ onggerberg, CH-8093 Zurich, Switzerland Received 19 July 2006; received in revised form 25 September 2006; accepted 3 October 2006 Available online 13 November 2006 Abstract A high degree of connectivity and the coordinated electrical activity of neural cells or networks are believed to be the reason that the brain is capable of highly sophisticated information processing. Likewise, the effectiveness of an animal heart largely depends on such coordinated cell activity. To advance our understanding of these complex biological systems, high spatiotemporal-resolution techniques to monitor the cell electrical activity and an ideally seamless interaction between cells and recording devices are desired. Here we present a monolithic microsystem in complementary metal oxide semiconductor (CMOS) technology that provides bidirectional communication (stimulation and recording) between standard electronics technology and cultured electrogenic cells. The microchip can be directly used as a substrate for cell culturing, it features circuitry units per electrode for stimulation and immediate cell signal treatment, and it provides on-chip signal transformation as well as a digital interface so that a very fast, almost real-time interaction (2 ms loop time from event recognition to, e.g., a defined stimulation) is possible at remarkable signal quality. The corresponding spontaneous and stimulated electrical activity recordings with neuronal and cardiac cell cultures will be presented. The system can be used to, e.g., study the development of neural networks, reveal the effects of neuronal plasticity and study cellular or network activity in response to pharmacological treatments. © 2006 Elsevier B.V. All rights reserved. Keywords: Microelectrode array; CMOS; Neuronal networks; In vitro; Stimulation and recording 1. Introduction Methods to directly measure the electrical activity of cultured electrogenic cells like cardiomyocytes (heart cells) or neurons include two fundamentally different techniques: (a) transmem- brane measurements by inserting one of the electrodes into the cell, the so-called “patch clamp” technique (Cole, 1949; Neher and Sakmann, 1976) and (b) extracellular recordings, e.g., by means of external microtransducers (DeBusschere and Kovacs, 2001; Fromherz, 2002; Jimbo and Robinson, 2000; Kleber and Rudy, 2003; Kovacs, 2003; Marom and Shahaf, 2000; Morefield et al., 2000; Olsson et al., 2005; Pancrazio et al., 2003; Rutten, 2002; van Pelt et al., 2004; Wise et al., 2004). Additionally, there are indirect methods like optical measurements using voltage- ∗ Corresponding author. Tel.: +41 44 633 3494; fax: +41 44 633 1054. E-mail address: fheer@phys.ethz.ch (F. Heer). sensitive or fluorescent dyes (Baker et al., 2005; Obaid et al., 2004; Peterlin et al., 2000). The patch clamp technique yields very accurate information on the electrophysiological proper- ties of entire cells, or, alternatively, on currents flowing through single ion channels. However, it is an invasive method and is limited in the cell viability time (usually hours) and in the overall number of cells that can be simultaneously recorded from. For extracellular recordings, the cells are cultured directly on top of a transducer or an array of transducers (Fig. 1a). When an electrical activity or a so-called “action potential” occurs in a cell, ions flow across the cell membrane within milliseconds. When the cell is close enough to a transducer structure these moving ions generate an electric field or volt- age, which either directly influences the open-gate region of the field-effect transistor or can be recorded by the metallic micro- electrode. Extracellular recordings are non-invasive (no punc- turing of the cell membrane), which entails a potentially long measurement time, and microtransducer arrays offer multi-site 0956-5663/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2006.10.003