MALDI Mass Spectrometry

Main content

Matrix-assisted laser desorption ionization (MALDI) is a soft ionization technique for mass spectrometry that allows for the detection of diverse chemical compounds over a broad mass range. Analytes such as high-mass molecules or fragile small molecules can be detected intact and quantified. We exploit specific advantages of MALDI-MS, such as its high-troughput capabilities, for novel analytical challenges in biotechnological process monitoring, multidimensional protein analysis or the analysis of microbial populations, with single cell sensitivity using specialized targets called microarrays for mass spectrometry (MAMS).

Mean intensity vs laser fluence (337 nm) vs. delayed extraction time  
Fig. 1 Mean intensity at individual instrument parameters on a copper target

The mechanism(s) in MALDI is/are still not fully understood. Current models still leave room for mechanistic interpretation. We are studying the MALDI mechanism(s) using a unique lab-built internal MALDI source coupled to an FT-ICR instrument. The setup offers advantages in the trapping/detection of unstable species formed immediately after laser impact, as well as the simultaneous detection of negative and positive ions, which is highly advantageous in seeking a unified mechanism for MALDI. The better understanding of ionization mechanisms can ultimately allow to extend this knowledge to routine analysis and to have better control to enhance the sensitivity of MALDI for the detection of analytes of interest. Moreover, the influence of the target substrate on the desorption process and thus on the maximum ion yield is of high interest for the mechansitic interpretation (fig.1, exemplary for copper in neg ion mode). 

The high speed of analysis in combination with the robustness of the MALDI process in samples with high salt concentrations allows us to develop methods to monitor biotechnological processes. Our methods aim at the detection and quantification of antibodies, proteins and selected metabolites from mammalian cell cultures. Moreover the microarray technology is applied to on-plate store liquid chromatography separations. The stored volumes can then be further processed for multidimensional readouts e.g. for the identification of PTM's.

The main advantages of MALDI as an ionization technique are it's sensitivity, the speed of analysis as well as the selectivity provided by the simple sample preparation steps. This makes it possible to ionize samples from complex (biological) matrices with high sensitivity. In this context our laboratory developed a microarray for mass spectrometry with self aliquoting properties. Using this microarray we are developping methods to analyze cellular activity in microbial populations with single-cell sensitivity (Fig. 2). In recent years, there has been a surge in the development and application of single-cell genomics, transcriptomics, proteomics, and metabolomics.The most interesting potential application of single-cell metabolomics may be in the area of cancer—for example, identification of circulating cancer cells that lead to metastasis.

12 black and 12 white dots, the average measurement shows a grey population.  
Fig. 2 Classical motivation for single cell measurements
Microarray for mass spectrometry; over 2000 spots with a 300 um diameter are arranged in lanes and rows on the chip  
Fig. 3 Microarray for mass spectrometry

Current Scientific projects

Single cell analysis. We have developed a MALDI-MS based population screening method with single cell resolution. The challenge when it comes to analyzing metabolites from single cells is the extremly small sample amount, which can only be sucessfully analyzed by highly sensitive methods. Using MALDI-MS, mass spectra can be collected from cells that are separated by individual target wells.

Biotechnological process monitoring. We develop a novel high-throughput method based on MALDI time-of-flight mass spectrometry to monitor mammalian cell-based biotechonological processes. 

MALDI mechanism(s). A focus of our research is elucidating the underlying mechanisms by systematically studying the influence of many experimental parameters, e.g. the substrate material’s conductive properties and the influence on the ion yield for negative and positive polarities by means of MALDI-Time-of-Flight and -Fourier-Transform Ion Cyclotron Resonance mass spectrometry.

Staff: Joanna Hajduk, Guido Zeegers, Mario Mirabelli

 

 
Page URL: http://www.zenobi.ethz.ch/research/maldi-ms.html
23.02.2017
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