NeuroProbes - Development of Modular Multifunctional Probe Arrays for Neuroscience P. Ruther 1a , S. Herwik 1a , S. Kisban 1a , K. Seidl 1a , S. Spieth 2 , B. Rubehn 1b , N. Haj-Hosseini 1a , J. Steigert 1c , M. Daub 1c , O. Paul 1a , T. Stieglitz 1b , R. Zengerle 1c,2 , H. Neves 3 1 Department of Microsystems Engineering (IMTEK), a Microsystems Materials Laboratory, b Laboratory for Biomedical Microtechnology, c Laboratory for MEMS Applications, University of Freiburg, Germany 2 Hahn-Schickard-Gesellschaft, Institute of Micromachining and Information Technology (HSG-IMIT), Germany 3 Interuniversity Microelectronics Center (IMEC), Leuven, Belgium Abstract For decades, recordings from the brain have been performed to investigate the activity of individual neurons. However, the complex interactions between electrical and chemical signals with respect to short and long term changes of morphology and information transfer of large cellular networks are still poorly understood. In an ef- fort to provide new tools to investigate related questions, this paper introduces a new modular approach for mul- tifunctional probe arrays with high special resolution for cerebral applications. The approach allows the individ- ual assembly of probes into three-dimensional arrays to address specific brain regions, including sulci of highly folded cortices such as those of humans. We introduce a system approach allowing for the integration of re- cording and stimulation electrodes as well as microfluidics and integrated microelectronics, all sharing a com- mon slim backbone. We present the first prototypes of (i) probes with multichannel electrodes, (ii) probes with fluidic functionality realized using deep reactive ion etching combined with silicon fusion bonding and wafer grinding, (iii) highly flexible polyimide ribbon cables and the respective assembly technology, (iv) a backbone platform that allows to assemble the electrodes to three-dimensional electrode arrays and (v) the first telemetry unit. In contrast to existing systems, this new approach enables the following features: (i) compatibility with a float- ing device operation due to a flexible ribbon cable, (ii) possibility to assemble probes of multiple lengths and configurations, (iii) opportunity to assemble probes of different functionalities (drug delivery, biosensors) along with electrical probes for recording and stimulation as well as (iv) scalability nearly independent of the probe technology. 1 Introduction Extracellular recording of neurons constitutes the only possible tool to investigate the link between neu- ral ensemble activity and subject behavior. Much of the work done in this area today utilizes wire elec- trodes [1]. However, silicon-based probes have been introduced in recent years to facilitate their implemen- tation as arrays. The prevalent silicon-based devices are the Michigan probes [2] and the Utah array [3]. While the Utah array contains a single electrode per probe shaft, comb-like probes are implemented in the Michigan probes in which each comb shaft has a row of electrodes. As a consequence, only laminar infor- mation can be retrieved from the Utah array. An even- tual extension of the Michigan approach to allow three-dimensional coverage entails the stacking of a plurality of probe combs together. This however re- sults in a thick connecting structure sitting on the brain surface and incompatible with the required floating character of arrays for chronic use. The EU-funded NeuroProbes project proposes a three-dimensional implementation for probe arrays that allows three-dimensional (3D) recording and is conducive to chronic applications. The novel modular approach is based on a thin platform for probe assem- bly. In this way, the integration of multiple functions in a fully reconfigurable fashion makes it possible to suit a wide variety of experimental conditions. By splitting the design between that of the probe and the platform, a multitude of configurations can be at- tained, also allowing the scaling of the device to sat- isfy needs for denser or sparser electrode distribu- tions. Aside from electrical recording and stimulation, the project envisages the development of probes for drug delivery and sensing of chemical substances in the brain. To be compatible with the platform concept, these probes follow the same design philosophy as their electrical counterparts. In association with elec- trical recording and stimulation, such devices will en- able us to inject substances in the brain, simultane- ously observe their effects and correlate these with the neural activity. NeuroProbes strives to provide a system solution that includes front-end electronics (pre-amplifiers, Mikrosystemtechnik Kongress 2007 · 15. bis 17. Oktober 2007 in Dresden · VDE VERLAG GMBH · Berlin-Offenbach 739