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Institute of Complex Systems
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Electrical methods

In order to establish a “communication” with neuronal networks one must be able to "listen" first. Neurons are electrogenic cells, which produce electronic potentials, so-called action potentials (APs). These APs are the building blocks of neuronal communication and thus brain activity. Being able to record and stimulate the APs paves the way for understanding the brain on a deeper level. Modern micro/nano-electronics provide us with a set of devices to fulfil this purpose, starting with patch-clamp and microelectrode arrays (MEAs) and moving towards transistors and miniaturization.

Patch clamp

The most established electrical method for the investigation of electrogenic cells is the patch clamp technique. In this technique, a small needle penetrates the cell membrane and measures the intrinsic potential drop. While this method enables very high signal amplitudes it is not suitable for long-term measurements, with its invasive nature making it single-use only.


Microelectrode arrays are the gold standard in the field of extracellular recordings and stimulation. A large variety of MEAs can be fabricated, using standard gold, more advanced porous materials, or using graphene. We improve the charge transfer of MEAs by testing new materials and shapes, and characterize the stimulation range of different electrode designs. We also design MEAs for highly specific applications such as enabling bidirectional communication with retinal tissue.


Transistors are active devices used in modern electronics and can also be used for biological applications. They provide a high degree of freedom to fine-tune different parameters towards engineering a well-suited device. Such devices, fabricated using silicon, graphene, or organic materials, can record the neuronal signal with the advantage that they can be scaled down to the nanoscale and provide an intrinsic amplification. Therefore, this approach poses the ability of creating hyper-high density device arrays which, in a long-term goal, can be implantable into the brain tissue. We are working with different concepts, ranging from field effect transistors to organic electrochemical transistors to establish the ideal architecture. Transistors are promising to provide the answers for human society on how our brain actually works and maybe even partially substitute some brain activity, i.e. for the treatment of Parkinson’s disease.

Measurement set-up

To be able to record signals from the developed arrays, there is the need to develop a measurement set-up which is able to measure all the electrodes simultaneously with a good time resolution below milliseconds. Our pico-amp set-up was developed for this purpose. The signal is recorded simultaneously on up to 64 channels. All devices can be characterized directly in the set-up in order to find optimal measurement conditions. The recorded signal can be amplified with a variable amplification factor and then be converted to a digital signal in order to evaluate the recorded data. With this set-up, it is possible to analyze cell systems like neurons and cardiomyocytes over long periods of time as well as perform repeated measurements to correlate different biological conditions as well as different electrode architectures.

Flexible and implantable electronics

A logical step towards electrophysiological measurements is the in vivo recording of the extracellular activity of whole tissues. However, a stable interface between living tissue and electronics is still a big challenge for research and industry, an aspect which impedes long-term studies. One arising problem is the immune response and the insulating scar tissue resulting from the tissue’s damage during insertion of penetrating probes as well as due to the mechanical mismatch between the device and the tissue and resulting inflammatory response. In our institute, we try to tackle the problem from many different angles. We fabricate and characterize in vivo probes that can establish a tight interface with the tissue and record the electrical activity for a long period of time (months). Furthermore, we establish a platform for a biodegradable insertion shuttle for the flexible devices in order to minimize any inflammation response of the tissue, thereby increasing the lifetime of the probes. The probes, fabricated and tested in our institute, are of different shape in order to find a versatile tool for implant applications: from large brain implants to much smaller visual prosthesis.