Sample preparation for MALDI-MS

What is MALDI Imaging?

The application of Matrix Assisted Laser Desorption Ionization (MALDI) mass spectrometry has been changed in the recent years. Whereas before the focus of MALDI was on the analysis of peptides and proteins (proteomics), the development and progress of MALDI Imaging has clearly expanded the amount of applications. The aim of MALDI Imaging is to provide localized information on diverse analytes in various materials. The examined samples are mostly thin tissue slices of different materials. MALDI Imaging mass spectrometry enables the visualization of the spatial distribution of proteins, peptides, pharmaceutical compounds and their metabolites, biomarkers or other compounds within thin slices of samples such as human, animal or plant tissue. It is a promising tool for putative biomarker characterization and drug development.
For gaining usable results in the process of MALDI Imaging the sample preparation is crucial. Essential is how the matrix is applied onto the sample.


Crystal size of the matrix in MALDI Imaging

 Currently the smallest MALDI matrix crystals worldwide !


The sample preparation is often the limiting factor in spatial resolution. Limiting factors include crystal size and homogeneity of the matrix coverage and the undesirable migration/diffusion of analytes. In order to detect large bio-molecules such as proteins or peptides, or small molecules such as drugs or their metabolites, it is necessary to remove the lipids with a washing procedure. If the washing procedure is not performed in a fast and efficient manner, spatial resolution can be lost.In the following description we will not handle how fresh frozen or FFPE tissue samples can be cut in tiny slices or fixed on targets like standard microscope glasses, rather we will give descriptions and recommendations how matrix or enzyme solutions can be applied on tissues in order to achieve a maximum of sensitivity and resolution. The matrix compounds are applied in water/organic solvent mixture. If a certain area of tissue remains wet longer than a few seconds during the application of matrix, the spatial resolution will be lost due to diffusion of the molecules of interest. A diffusion based migration will be higher, if
  • the compounds of interest are small; e.g. peptides are much more affected than proteins
  • the solubility of the analytes very good in the matrix solvent. Proteins in ethanol will be less affected than smaller peptides or pharmaceuticals in aqueous organic solvents
  • the temperature is higher and the viscosity of the solvent lower

Influence of crystal size on resolution in MALDI Imaging

Methods for MALDI Imaging sample preparation

Matrix application methods

The application method or coverage with matrix depends on the target analyte. Bio molecules such as peptides or proteins or compounds other than lipids need to be extracted. Unlike the previously mentioned compounds lipids do not need an extraction step. Lipids can be analyzed without extraction and only need an application of matrix.


Why a graduated spray procedure is so important

 Other coverage methods

TLC sprayer or other manual spray methods
Micro Spotting Technique
Ultrasonic sprayer
Modified Airbrush Technique
Electrospray Technique

SunCollect System for MALDI Imaging

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