After 30 min incubation, the cells were fixed with an equal volume of 4% glutaraldehyde in 0.2 M Na-cacodylate buffer, pH 7.4, for 3 h at 4 °C, followed by dehydration with a graded series of ethanol and dried the sample using HMDS (hexamethyl disilazane). Coating with a 20 nm thick layer of Au/Pd was applied, and the samples were examines under a scanning electron microscope (Zeiss Sigma 300).