ToF‐SIMS imaging and depth profiling of HeLa cells treated with bromodeoxyuridine

Time‐of‐flight (ToF) SIMS 2D images and molecular depth profiles of human HeLa cells treated with bromodeoxyuridine (BrdU) were acquired in the dual beam mode (Bi 3 + analysis beam, C 60 + etching beam). Several preparation protocols were investigated and were compared to a simple wash‐and‐dry method. The feasibility of using C 60 to clean the samples prior to imaging with Bi was also investigated quantitatively by calibrating full depth profiles of the cells using atomic force microscopy. BrdU was used as a marker for the cell nucleus, facilitating identification and localization of subcellular features during depth profiling. Results show that C 60 can be used to remove the surface contamination and to access different layers within the cells for 2D imaging. For a 1 nA, 10 keV C 60 + beam incident at 45° and rastered over a 500 × 500 µm 2 area, ∼1 nm of biological material was sputtered every second. Our results show that HeLa cells were completely removed after etching with 1.3 × 10 15 C 60 + ions per cm 2 , giving an average etching rate of 3.9 nm for every 10 13 C 60 per cm 2 at 10 keV and 45° incidence. Copyright © 2010 John Wiley & Sons, Ltd.