Tissue MALDI Imaging mass spectrometry (IMS)
Tissue MALDI imaging by MALDI-TOF mass spectrometry is a new methodology also named as molecular histology. Briefly, the tissue of interest is sliced in a 10 um section and deposited in a MALDI compatible conductive slide. The sample is then sprayed with MALDI matrix and located in a MALDI target. The MALDI-TOF analysis is done by restring the entire tissue section, getting a MALDI-TOF spectra for each of the shots and across the entire tissue. The obtained data is the special distribution of the observed analytes in the tissue.
The spray is one of the key steps along the entire process. The droplets have to be small enough to allow a good lateral resolution (also limited by the laser beam diameter). At the same time, peptide and protein MALDI imaging requires the proteins of the tissue to be extracted. This is accomplished by controlling the time of extraction and the number of times the process is repeated.
In tight collaboration with IDEKO-IK4
research center, IDEKO-IK4 has built a simple and robust sprayer that allow us to have a high quality spray comparable in performance to any commercial equipment.
Images are usually acquired in MALDI-TOF linear mode and automatic fashion, gaining in sensitivity and robustness. Once the mass spectrometry analysis is done, the images are obtained by dedicated software and statistical analysis can be performed. This information, achieved in a unbiased manner, is described to be complementary to classical staining and immune-histochemical assays.
Pilot Study: Mouse Kidney MALDI-TOF IMS
MALDI-IMS of a longitudinal slice of mouse kidney acquired at low resolution (150 um laser beam diameter). Three main areas can be observed according to differential peptide distribution: cortex (green), medulae (yellow) and pelvis (red).
Three average spectra corresponding to kidney pelvis (red), medulae (green) and cortex (blue), show differentially expressed peptides.
Total average spectrum of the full kidney slice, showing 185 signals in the range 1000 – 20000 Th, with a S/N >3 in all range. Marked peaks show differential arrangement arround the tissue.
With only the analysis of two peaks, 5443 and 11310 Th, is possible to characterize in a great extent (75%) the differences in the three regions. The most dissimilar region in this graph is the kidney pelvis.
Anybody interested in this novel type of tissue analysis, please, do not hesitate contacting us!