testing MEAs

I have been given several MEAs (three 500/30iR-Ti and two 200/30-Ti) for electrophysiology studies. I tested them with the amplifier and after 30-40 seconds individual electrodes would begin to saturate with noise. (when making the scale to 500uV, the signal would be the same over the various electrodes) I would add diH2o bath and that would level them out for 3 to 5 minutes max before electrodes would begin to saturate. I ruled out any issues with the amplifier using the model test probe and wanted to do an impedance test on MEAs with simple digital multimeter.


I used a silicone ring filled with about 400ul of diH2O on
each of the electrode arrays (amplifier not involved with this) .I
used a craftsmen digital multimeter to assist with testing. On each
array, I would test three to five contact pads with both leads
touching the individual contact pad and registering zero impedance.
When I then switched one of the probes to the diH2O bath, the results
were 1 all the time for any contact pad and the bath. (on this
multimeter, a 1 usually indicates infinite impedance). I suspect my "hand me down" MEAs have been used too many
times and the TiN electrodes may have been worn out. Do my results confirm that I have bad MEAs? Do I need a special type of multimeter for TiN electrodes?

Appreciate any thoughts anyone may have.

Regards,

Mat

Dear Mat,
any kind of measurement /recording in ddH2O is useless. To do an electrical recording, you need a condcting solution like PBS.

Regards Frank MCS

Thanks Frank for the prompt reply. I went through my trials with PBS solution with the same results. As you probably noticed, I am new to working with MEA equipment. Is there an average usage associated with an array life span? I read over a several of the posts, which indicated to keep a count on cleaning cycles. Any metrics on longevity of the arrays and cleaning I should take into account moving forward?

Mat

Dear Mat,

MEAs can be used upto 40 times approximatey. However it depends on many factors ike cuture time, accuracy of handing and storage etc.

You might want to have a ook in the MEA & MEA ceaning manuas to get an idea of proper MEA handing.

http://www.multichannelsystems.com/fileadmin/user_upload/Manuals/MEA-CleaningQuickGuide.pdf
http://www.multichannelsystems.com/fileadmin/user_upload/Manuals/MEA_Manual.pdf

However, a noise eve of about 500uV on al electrodes is extremey high even for an od MEA.

Please check foowing typical probems:
- Grounding: are you using internal reference or Ag/AgCl pellet? Are those properly connected?
- clean contact pads and gold spring contacts with a cotton bud with EtOh and check that springs are moving easily.
- if you are in doubt about your system, test the amplifier with the test model probe.

Greetings

Thomas