Scanning electron-stimulated desorption microscopy of red blood cells.

Scanning electron-stimulated desorption (SESD) has been used to image the surface of unfixed red blood cells with high surface specificity and with a lateral spatial resolution of less than or equal to 1 micron. The micrographs were obtained using a scanning Auger microprobe with an appended secondary ion mass spectrometer (SIMS). The instrument was operated at low electron beam energies (2 kV) to maximize electron-stimulated desorption probabilities and minimize the interaction of the electrons with the biological substrate. ESD spectra from the surface of red blood cells prepared from smears of whole blood show H+ as the predominant desorbed positive ion and O+, OH+, H3O+, Na+, and Cl+ as secondary species. SESD images and line-scans obtained with the above ion signals demonstrate that SESD can be used to map the surface chemistry of cells at submicron resolution. The parent molecules contributing to the desorbed ion signals are shown to originate from the first few atomic layers of the cell surface and are believed to be components of the blood plasma (H2O, NaCl, etc.) which coalesced onto the cells as they dehydrated in the vacuum chamber of the microprobe. An interesting extension of this work is the possibility of mapping the concentration of adsorption sites of specific cell-surface binding species using ESD labels.