Cells should be in a single-cell suspension in any conductive cell culture medium or buffer. The ideal cell suspension concentration should be at 1.5.10^5 cells/ml (i.e., 2,250 cells in total).
NOTE: If cells tend to aggregate, it is possible to optimize the medium using serum-free, Ca2+/Mg2+- free medium, or by adding chelators, DNase, or anti-clumping compounds.