I have never used, or heard of anyone using copper wires for tetrodes.

If you already have the 0.01 mm wires, just try.

If not, why do you want or need to use them?

If you make your tetrodes by twisting them together and then heating them, the rigidity does not come from the metal, but from the plastic coating. Therefore I expect that it should not pose a problem in that regard. I do not know what the consequences for the impedance and recording quality will be. The surface area changes from 177 um2 to 79 um2.

Thank you very much for your reply. Currently I am recording from an insect brain with four tetrodes and an electrode diameter of 15 µm. In other words, the elctrodes span a total diameter range of about 240 µm. To minimize the invasive procedure, I wonder if I should order wires with a smaller diameter of 10 µm. Thus, ending up with a total diameter of 160 µm instead of 240 µm.

The point with the coating makes sense.

Regarding impedance, I think we should be still at the save site. In the past, I´ve recorded extracellularly with impedances in the range 2-10 megaohms (glass electrodes). With the copper wires you even won´t reach one megaohm. Worst case scenario might be to reduce the impedance by gold coating or other approaches.

Thanks again for your answer.

Cheers

Jerome

Hi Jerome,

I have only recorded in rodents. In our field we always gold plate the tetrodes to 200-300 kOhm. A lower impedance would help you resolve the spikes better.

good luck!

Nils

Dear Jerome,

I have never used copper wires for recording and I also never heard about someone using this metal for extracellular recordings. Tissue reactions to the electrode in contact with the CNS can be minimized if one uses electrode material (metal core and insulation material) which is biocompatible. I always differ between chemical and mechanical compatibility with the tissue. In case of the metal I would not recommend to use copper, because it is well known as a toxic material for biological systems. Silver and copper wires usually are proved to be the most toxic materials to brain tissue. For details see Geddes & Roeder (1).

Babb & Dymond (2) reported that tissue reaction to the implanted electrode can be minimized by proper selection of both electrode and insulation materials . The authors stated: “…Implanting in brain tissue for 2 months without passage of current showed platinum, platinum-8 percent tungsten, platinum-l0 percent rhodium, platinum-10 percent iridium, platinum-10 percent nickel, platinized platinum, a gold-nickel-chromium alloy, a gold-palladium-rhodium alloy, a chromium-nickel-molybdenum alloy (Vitallium), stainless steel, rhenium, gold and boron to be nontoxic (Dymond et al ., 1970) . Silver (Dymond et al ., 1970), silver chloride, and copper (Fischer et al ., 1961) are highly toxic…”

I understand that you are recording from an insect brain. I know from researchers using twisted wire tetrodes in insects made of 12µm diameter coated nichrome wires. (3) This might be a better choice. Please find the cited literature below:

1. Geddes LA, Roeder R. 2003. Criteria for the selection of materials for implanted electrodes. Ann Biomed Eng 31:879-90.

2. Babb MI, Dymond AM. 1975. Electrode implantation in the human body. Bull Prosthet Res:51-150.

3. Guo P, Pollack AJ, Varga AG, Martin JP, Ritzmann RE. 2014. Extracellular wire tetrode recording in brain of freely walking insects. Journal of visualized experiments : JoVE doi:10.3791/51337:51337.

I hope this information is helpful for you.

Best wishes, Dirk