Lipids, even uncharged zwitterionic lipids, have permanent dipoles. These can "feel" the AC field, they experiment a force and move the molecules along with it. This process is equivalent to vortexing and heating when making multilamellar vesicles: it makes it easier for water molecules to get into previously non-hydrated places, and so force the lipid molecules to come fully into contact with water. This in turn triggers the hydrophobic forces that will transform a previously dry and disordered lipid film into a bilayer, polar heads out, apolar chains inside. Regarding voltage and frequency values, these depend on the geometry of the system. You can check the literature for that. Right now I cannot remember precisely, but the numbers that come to mind are 10 Hz and 2 Volts for Pt wires separated by 4 mm. I can look it up if you need.

Lipids, even uncharged zwitterionic lipids, have permanent dipoles. These can "feel" the AC field, they experiment a force and move the molecules along with it. This process is equivalent to vortexing and heating when making multilamellar vesicles: it makes it easier for water molecules to get into previously non-hydrated places, and so force the lipid molecules to come fully into contact with water. This in turn triggers the hydrophobic forces that will transform a previously dry and disordered lipid film into a bilayer, polar heads out, apolar chains inside. Regarding voltage and frequency values, these depend on the geometry of the system. You can check the literature for that. Right now I cannot remember precisely, but the numbers that come to mind are 10 Hz and 2 Volts for Pt wires separated by 4 mm. I can look it up if you need.

Thanks Dolores! I'm also wondering how are the frequecies and voltage values determined, by experience? If I have a lipid mixture (say PS and PC), since the AC field is to provide a votex force, will negatively charged lipids (like PS) exprience a larger force comparing to PC? And will this lead to a deviation from expected lipid composition, or even composition asymmetry in the two monolayer leaflets of GUVs?

Hi Zheng,

Below is a very good review about GUVs. In particular, references 3 and 4 of this review discuss how to prepare mixtures with negatively charged lipids. You will need to change frequencies and voltages as compared with zwitterionic lipids. In general, I would say it will be very uncommon to produce asymmectric GUVs by a simple electroformation. However one common problem is that the lower-Tm lipids will be hydrated faster that the higher-Tm lipids. You can have problems if you work at a temperature that is below the Tm of one of your lipids. Make sure to be above the Tm of the mixture you are using. Also, longer times and bigger concentrations of lipids in the wires or the ITO help obtain GUVs with more homogeneous compositions. (use at least 10 mg/ml of lipids in solvent).

Biochimica et Biophysica Acta 1798 (2010) 1324–1332

GUV preparation and imaging: Minimizing artifacts

Nelson F. Morales-Penningston a, Jing Wu b, Elaine R. Farkas c, Shih Lin Goh b, Tatyana M. Konyakhina b,

Judy Y. Zheng b, Watt W. Webb c, Gerald W. Feigenson b,⁎

Hi Dolores,

That's a very informative paper, thanks very much!

Hello, Zheng. I have just started studying electroformation and I was wondering if you did get an answer for your question.

Thanks!

"Thanks Dolores! I'm also wondering how are the frequecies and voltage values determined, by experience? If I have a lipid mixture (say PS and PC), since the AC field is to provide a votex force, will negatively charged lipids (like PS) exprience a larger force comparing to PC? And will this lead to a deviation from expected lipid composition, or even composition asymmetry in the two monolayer leaflets of GUVs? "