Atomic force microscopy study of fine structures of the entire surface of red blood cells

Glutaraldehyde-fixed red blood cells were imaged by tapping mode atomic force microscopy (TMAFM) in air at room temperature. The results show that TMAFM can visualize the morphology of the red blood cell at both cellular and nanometer scales. The scan size covers the range from several hundred nanometers to more than one hundred micrometers. TMAFM not only has a higher resolution than the optical microscope, but also can observe biological samples without precoating as required for scanning electron microscopy (SEM). The AFM images of the entire surface of an uncoated red blood cell with nanometer resolution are successfully reconstructed by 28 AFM images of the preselected subareas on the surface of the red blood cell. These images reveal directly the fine structures of the external surface of uncoated red blood cells in air. The surface exhibits a characteristic structure composed of a large number of closely-packed nanometer particles with a size ranging from a few nanometers to tens of nanometers. These "particulate" components are evenly distributed, and no jumping protrusion or depression structures were found. These particles give rise to a very smooth surface of the red blood cell as shown in a large-scan AFM image. In addition, the 28 AFM images obtained by the continuous scanning over 3 hours indicate that TMAFM can image soft biological samples such as red blood cells stably and reproducibly.