A new SIMS paradigm for 2D and 3D molecular imaging of bio-systems |
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Authors: | John S Fletcher John C Vickerman |
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Institution: | (1) Manchester Interdisciplinary Biocentre, School of Chemical Engineering and Analytical Science, The University of Manchester, Manchester, M1 7DN, UK; |
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Abstract: | With the implementation of focused primary ion beams, secondary ion mass spectrometry (SIMS) has become a significant technique
in the rapidly emerging field of mass spectral imaging in the biological sciences. Liquid metal ion guns (LMIG) offered the
prospect of sub-100 nm spatial resolution, however this aspiration has yet to be reached for molecular imaging. This brief
review shows that using LMIG the limitations of the static limit and low ionization probability will restrict useful imaging
to around 2 μm spatial resolution with high-yield molecules. The only prospect of going beyond this in the absence of factors
of 100 increase in ionization probability is to use polyatomic ion beams such as C60+, for which bombardment induced damage is low. In these cases sub-micron imaging becomes possible, using voxels together with
molecular depth profiling and 3D imaging. The discussion shows that conventional ToF-SIMS instrumentation then becomes a limitation
in that the pulsed ion beam has a very low duty cycle which results in inordinately long analysis times, and pulsing the beam
means that high-mass resolution and high spatial resolution are mutually incompatible. New instrumental configurations are
described that allow the use of a dc ion beam and separate the mass spectrometry for the ion formation process. Early results
from these instruments suggest that sub-micron analysis and imaging with high mass resolution and good ion yields are now
realizable, although the low ion yield issue still needs to be solved. |
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