Mounting of biological microsamples on protein coats for TaOTO non-coated scanning electron microscopy.

Gelatin-coated glass cover slips were immersed in a mixture of glutaraldehyde and tannic acid, and rinsed in bovine or human serum. The gelatin-coated cover slips were first placed in a human blood cell suspension, and subsequently placed in a solution of glutaraldehyde or osmium tetroxide. This preliminary mounting of the blood cells eliminated troublesome centrifugations in the tannin-osmium-thiocarbohydrazide-osmium (TaOTO) impregnation. The blood cells seldom detached from the cover slips even when the specimens were dehydrated with ethanol and critical point dried with liquid carbon dioxide. Both the mounting media as well as the mounted cells were intensely stained by the TaOTO method, and exhibited no charging in the scanning electron microscope even at acceleration voltages of 25 kV. The scanning images of the white blood cells with their microvilli were clearly visible with sharp contrast.