Just washing with water didn't solved the problem??? lisine is a highly polar aminoacid. You could try sonicating the electrode, probably it should enhance the solubility of the polymer!

Have you considered co-incubation with a strong cation exchange resin? If you do this at slightly acidic pH >99% of the poly-L--lysine should be protonated and bind to the solid phase exchanger. Then just wash off...

Thanks for the quick responses!

Sergio, washing with water doesn't seem to work for our lab or for many other people in the literature that I've found. A lot of poly-L-lysine gets left behind and seems to be detrimental to cell growth the next time around. Sonication may be a cleaning method worth looking into though!

Wayne, we haven't done any co-incubation like you've described. Did you mean at the same time as coating the pol-L-lysine onto the chips? The acidic environment would likely be difficult for the cells to live in.

Hi Michael - I was thinking more about removing excess PLL (poly-L-Lysine) post the coating process. I'm assuming you want some PLL left on the electrode(s) to facilitate cell binding - - is the issue that you need to remove the PLL to enable electrical measurement post cellular adhesion?

Hi Wayne,

The issue is that once I have done my cell culture, stimulated the cells, made measurements, and discarded them I would like to remove the PLL entirely so that I can use the chips again. It seems that if we don't remove the PLL sufficiently it makes it difficult for the next batch of cells to grow even after a new layer of PLL has been applied.

I hope that makes sense. I appreciate your thoughts on this!

Thanks - I get it now - you want to strip off the PLL, expose the native surface and re-coat to allow reuse of the electrode. - right? With out knowing the nature of the dielectric (simple double layer of water??) or the metals present, Is there a specific chemistry you use to get the PLL to adsorb to the dielectric? If you simply incubate with aqueous PLL solutions then I might consider using a serine protease (trypsin comes to mind...) to digest the PLL on the electrode, followed by a brief wash with dilute acid followed with an extensive water/buffer wash. assuming the electrode/dielectric is stable to a brief exposure to dilute acid this intermediate step should pose little problem to subsequent cell adhesion post regeneration of the PLL electrode surface. I'm willing to be the number of times you can regenerate the surface will be limited by S/N (signal/noise) issues, but could be wrong. Hope this helps??

Wayne,

That's correct. I would like to strip off the PLL so that the original dielectric (SU8, which is a negative photoresist used in standard photolithography techniques) and the metal electrodes (gold) are exposed for re-coating and reuse. The electrodes are exposed to solution which the traces leading to them are coated to minimize interference.

In terms of coating the PLL, we simply place aqueous PLL in the dishes and let them sit for 30 minutes before removing the solution, rinsing, and drying overnight in preparation for cell plating.

I think that the trypsin/acid wash is a very good option, although it sounds like some in our lab have not had amazing results using trypsin or tergazyme (some residue is left behind. We're also looking into a bleach option discussed in the paper below:

http://www.sciencedirect.com/science/article/pii/S0165027098001563

Thanks again for all your help!

Hi! I have a similar question and it got me here, did you succeed with any of the methods suggested? I also thought about using trypsin but I ´m not sure it will work.

Thank you!

Hello, we tried to remove PLL via different methods, but it turns out it can be removed in the basic solution, we used KOH and ultrasonic, it worked.