Dear Salvatore 

KPFM in liquids is doable; however, the process of scanning in liquids is more complex than in the air.

Attached is a nice paper that explains some of the details about KPFM in non-polar liquids, like decane.

Good luck!

Article Kelvin Probe Force Microscopy in Nonpolar Liquids

HI Reza,

thank you for your answer and the paper....however, I forgot to specify that measurements should be done in polar liquids, such as water and buffers...do you think it is doable? is the measurements have any physical meaning.

Cheers,

Salvatore

I am planning to do similar experiments. EFM & KPFM should be possible as long as the probe holder is suitable for liquid usage. 

Current-voltage measurements in liquid are however very challenging.