AVS 56th International Symposium & Exhibition
    Applied Surface Science Thursday Sessions
       Session AS-ThA

Paper AS-ThA2
On the Understanding and Optimization of Etching Parameters for Optimal ToF-SIMS 2D and 3D Analysis of Biological Cells

Thursday, November 12, 2009, 2:20 pm, Room C2

Session: Chemical State Depth Profiling
Presenter: J. Brison, University of Washington
Authors: J. Brison, University of Washington
D.S.W. Benoit, University of Washington
M. Dubey, University of Washington
M. Robinson, University of Washington
P.S. Stayton, University of Washington
D.G. Castner, University of Washington
Correspondent: Click to Email
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with cluster ion beams is now widely used to image biological samples in two and three dimensions. Cluster ion beams (e.g., Bi3+, C60+) have indeed been shown to provide higher molecular ion yields with lower chemical damage in depth, allowing successful 2D imaging as well as molecular depth profiling of complex biological samples. In parallel, much research has been conducted to improve the sample preparation protocols to insure that the biological samples are preserved as close as possible to the living state for ToF-SIMS analysis under ultra high vacuum (UHV) conditions.

However, ToF-SIMS is not yet routinely used to solve biological problems because the data interpretation is complicated and the fundamental cluster ion/sample interaction is not fully understood. In this work, we combined ToF-SIMS with other complementary surface characterization techniques (i.e., XPS, AFM, SEM, etc.) to supplement the complex ToF-SIMS 2D and 3D datasets obtained from biological samples. For this purpose, human HeLa cells were seeded on silicon substrates and prepared according to different protocols (fixation with paraformaldehyde, cryofixation, etc.) for UHV analysis. The HeLa cells were also treated with bromine labeled small interfering RNA (siRNA) and with bromodeoxyuridine (BrdU) to provide a target for ToF-SIMS and XPS analysis. A series of ToF-SIMS experiments dealing with the different ion species (Bi1+, Bi3+, and C60+), and various beam parameters (single beam, dual beam, different energies and fluences) was designed to obtain a reproducible and reliable depth profile of single HeLa cells when analyzed by the above listed techniques. XPS along with principal component analysis, for the first time has been used to image and provide quantitative elemental information about individual cells. Our results also show that AFM and SEM provide a better understanding of the effect of topography on the ToF-SIMS data.