Paper AS-ThM9
Molecular Imaging of Cells and Tissues with Ar Cluster Ion Beams

Thursday, November 1, 2012, 10:40 am, Room 20

Because molecular, structural and chemical state information is considered invaluable in life science, various mass spectroscopic techniques, such as secondary ion mass spectrometry (SIMS), matrix-assisted laser desorption ionization (MALDI) and desorption electrospray ionization (DESI), have been examined intensively during the last decade,. The SIMS technique is considered to have the highest spatial resolution, but it is necessary to increase secondary ion yields of bio-molecules. It has been reported that cluster ion beams can enhance the secondary ion yields, because of the high-density energy deposition and multiple collisions near surfaces. Clusters such as SF₅, C₆₀, Au₃, and Bi₃ were found to be quite useful for SIMS of organic materials. Because these primary ion beams cause significant damage on organic surfaces, the primary ion dose is limited to a certain threshold value (known as “the static-limit”, ~10¹² ions/cm²). Therefore, the intensity of bio-molecular ions (>500 Da) is too low to obtain high-resolution mass images.

Because Ar cluster ions provide much less damage on the surface than conventional ion beams, much attention is devoted to molecular depth profiling of organic multilayer and molecular imaging with Ar cluster-SIMS. We have developed a new SIMS imaging system with focused Ar cluster ion beam. An orthogonal acceleration time-of-flight (oa-TOF) mass spectrometer, which allows the use of a continuous beam, was employed in a new bio-imaging system. There was no need to use the ion-bunching technique in this system, and therefore there was no need for tradeoff between beam diameter and mass resolution, which is a problem in mass-imaging of biological samples with conventional SIMS. SIMS spectra of cells with Ar cluster ions are quite different from that with Bi₃ ions. Lipid molecular ions found in the mass range over 600 Da, are clearly observed with Ar cluster ions. Furthermore, background level of the spectra with Ar cluster ions is much lower than that with Bi₃ ions. This is attributed to the lower velocity of the primary ions.

The latest results of this system and its performance in molecular imaging of cells and tissues will be presented and discussed.

Acknowledgements

This work is supported by the Core Research of Evolutional Science and Technology (CREST) of Japan Science and Technology Agency (JST).