MEA storage

I have noticed that the noise level on my arrays has gone way down after storage for a few months. This would be great, but signal amplitude is even more diminished. Does this indicate a general erosion of the insulation? If so, could it be caused by storage in a slightly alkaline solution? Our ddH2O typically has a pH between 7.5 and 8.0 (although these measurements may not be very accurate). Would it be better to store the arrays long term in a pH 7.0 buffered solution? If so, what would you recommend?

Dear Jay

storing the MEA in an alkiline solution for does cause a deterioration of the Si3N4 insulation layer. This is consistent with your findings that the noise level decreases (due to increase of the stray capacitance of the leads. This results in a low-pass filter chracteristics and diminishes the recording quality of faster signals in the kHz range, i.e. action potentials.

Please store the MEA in distilled water and make sure the pH is not in the alkaline range.

I have noticed that my MEA probes/electrodes have diminished fEPSP responses after many uses too. I have tried to clean the electrodes with a collagense solution but they have a visible layer of tisue on the surface. I think this layer is requiring me to stimulate with much higher currents and leading to less detectable fiber volleys and EPSP. The fiber volleys seem like the 1st thing to go.

I am considering storing my electrodes in contact lense cleaning solution and once a week clean the electrode with a contact lense "enzymic cleaner" solution. Has anyone done this? If so what brands do you recommend?

Thanks,
Ammar Hawasli
UT Southwestern Medical Center

Dear Amar,

Unfortunately I do not have personal experience using the contact lense cleaning solution for MEA storage / cleaning.
However I remember a discussion with Chris from ALA who mentioned that one of our customers used contact lense cleaner for this purpose. So it seems to be a good idea - but we have no experiences with this up to now.

My experience is, that cleaning protocols depend mostly on the coating of the MEAs. The more sticky the coating - the more problematic it is to remove cell debris after use. I try to work mostly with cellulose nitrate coating, as this can be easily removed with MetOH.

For all others enzymatic digestion of cell debris in combination with (carefull!) ultrasonic treatment had good results in our lab.

Greetings

Thomas