Submicron molecular imaging of cells by combined use of MeV SIMS and STIM

(1) Divisiont of experimental phyisics, Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
(2) Division of molecular medicine, Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia

In order to understand biochemistry processes governed in the cells, molecular composition at the submicron level has to be determined. For chemical imaging, different analytical imaging techniques can be used, and one among them is TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) with MeV ions. Heavy ion beams in the MeV energy range can eject large molecular fragments (~1000 amu) with a yield that is several orders of magnitude larger than if keV ions are used for excitation. Thus, due to high sensitivity of MeV TOF-SIMS, measured biological samples and other materials remain intact.

For molecular imaging we installed in 2012 linear TOF SIMS spectrometer at the Heavy Ion Microbeam Facility in Zagreb [1]. TOF measurement is normally performed using START signal from the pulsed beam, and STOP from the MCP detector positioned at the end of the TOF telescope. With this setup high sensitive molecular imaging with lateral resolution of ~10 can be achieved.
In the new setup, presented here, trigger for the START is replaced with the timing signal from the STIM (Scanning Transmission Ion Microscopy) detector placed behind the transparent target.

This allows us to perform measurements with continuous beam in the low current mode (~1000 Hz), and significantly reduce beam dimension (below 1µm) with small opening of the object slits. Due to well defined submicron beam focus, molecular imaging of the single cell on a sub-cellular level is possible. Also, besides the molecular imaging, STIM image of the cell is also recorded providing additional information about distribution of cell density. Imaging of Na+, K+, and lipids inside single HeLa cells will be demonstrated (HeLa cell culture was grown on 100 nm thin Si3N4 window).

[1] T. Tadić, I. Bogdanović Radović, Z. Siketić, D. D. Cosic, N. Skukan, M. Jakšić and J. Matsuo, Nucl. Instr. Meth. Phys. Res., B 332 (20014), 234