Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS): A New Tool for the Analysis of Toxicological Effects on Single Cell Level

Abstract

Single cell imaging mass spectrometry opens up a complete new perspective for strategies in toxicological risk assessment and drug discovery. In particular, time-of-flight secondary ion mass spectrometry (ToF-SIMS) with its high spatial and depth resolution is becoming part of the imaging mass spectrometry toolbox used for single cell analysis. Recent instrumentation advancements in combination with newly developed cluster ion guns allow 3-dimensional reconstruction of single cells together with a spatially resolved compound location and quantification on nanoscale depth level. The exact location and quantification of a single compound or even of a set of compounds is no longer restricted to the two dimensional space within single cells, but is available for voxels, a cube-sized 3-dimensional space, rather than pixels. The information gathered from one voxel is further analysed using multivariate statistical methodology like maximum autocorrelation factors to co-locate the compounds of interest within intracellular organelles like nucleus, mitochondria or golgi apparatus. Furthermore, the cell membrane may be resolved, including adhering compounds and potential changes of the lipid patterns. The generated information can be used further for a first evaluation of intracellular target specifity of new drug candidates or for the toxicological risk assessment of environmental chemicals and their intracellular metabolites. Additionally, single cell lipidomics and metabolomics enable for the first time an in-depth understanding of the activation or inhibition of cellular biosynthesis and signalling pathways.

Keywords: MIMS; ToF-SIMS; cryopreservation; imaging mass spectrometry; lipidomics; single cell analysis.

Figure 1

Values of two discriminant scores (discriminant analysis) for the 24 yeast samples for 34 principal ions, which were selected to discriminate between S. cerevisiae (haploid strains BY4741 and BY4742) (BY71 and BY72), S. cerevisiae diploid strain BY4743 (BY73), and C. glabrata (Cglab). S. cerevisiae (haploid strain BY4741) group; +. group centroids. Figure reprinted with permission from [51]. Copyright 2005, American Chemical Society.

Figure 2

Relative abundances of characteristic ions (450–1200 Da) used to separate four different yeasts: S. cerevisiae (haploid strain BY2742), C. galbrata, S. cerevisiae (diploid strain BY4743), and S. cerevisiae (haploid strain BY4741). The x-axes shows the selected ions; the y-axes shows the relative ion abundance (calculation: S% × 1000). Figure reprinted with permission from [51]. Copyright 2005, American Chemical Society.