Detection of electrical signal

I am very interested in you multielectrode system. I understand the electrodes are made from indium tin oxide. This, I think, is a very basic question, but how is current injected into a sample, or how are local field potentials measured? When using a silver wire electrode I understand how the flow of chloride ions from solution form AgCl on a silver wire microelectrode, so how is the equivalent electrical signal detected with the indium tin oxide?

Roman

Dear Roman

The main difference is that you measure extracellular potentials with a passive metal conductor (= electrode). The extracellular space is conductive as well, and though the resistance is very low, it is not zero. According to Ohm's law (U=RxI, where U=voltage, R=resistance, and I=current), the extracellular current results in a small voltage that can be measured with extracellular electrodes.

The electrode material is Titanum Nitride (TiN). The main advantage of this material is that it has a high surface area (forming folded microstructures) and therefore has a low impedance and a high signal-to-noise ratio.

I hope this helps, Christine

Hi Christine,
I've been reading your reply with interest.

Can you confirm that MEAs are therefore suitable for recording cell membrane potential variations? I understand that this would imply an indirect measurement of the plasma membrane potential through a direct measure of the extracellular potential between the cell and the close electrodes. Of course I should keep the electrodes at a fixed voltage.

Am I right?
Thank you for your kind comments and suggestions!

Arianna