Finding molecules with Ambient Mass Spectrometry Imaging

Published on
October 6, 2017

The Ambient Mass Spectrometry Imaging (MSI) seminar on October 5 was focused on finding the molecule. From the examples and results during the seminar it became apparent that MSI can cover a sheer spectrum of research domains. The presentations covered metabolites in plant materials, contaminants in and on food products, drugs in hair and the surface of synthetic fibres.

Business developer Edda Neuteboom kicked off by outlining the Shared Research Facilities activities within Wageningen University & Research. They invest in and provide access to advanced research equipment, organise facility-sharing within WUR and with other parties, and organise seminars to stimulate facility sharing.

Introduction to Ambient Mass Spectrometry Imaging

In his presentation, Michel Nielen zoomed in to Ambient Mass Spectrometry Imaging, placing it in the spectrum of chemical ‘microscopies’ in 2D and 3D, how Mass Spectrometric Imaging (MSI) works, what the difference is between ambient versus vacuum MSI, and the available ambient MSI technologies at WUR. In short, the differences in MSI technologies are that DESI uses particles has a (sub-)mm spatial resolution and is experimentally tricky, DART uses gas, has a mm-resolution and is experimentally simple and robust, and LAESI, which uses photons has a >150 µm spatial resolution and is experimentally in the middle.

DART MSI of drugs of abuse in hair

Teris van Beek presented the research of Wilco Duvivier in which DART (Direct Analysis in Real Time) technology was used to find out if this technology could be used as a fast and easy analysis scan method to test drugs in hair, without a destructive sample preparation and with intact hair locks. This method is forensically interesting as many compounds accumulate in hair and conventional analysis uses sensitive LC- or GC-MS(/MS) analysis, segmentation is used to estimate time of drug intake, sample preparation is destructive and inefficient and offers only a rough estimated time of drug intake. The results not only showed a direct analysis of the intact locks of hair, within minutes, but it was sensitivity-sufficient, additional hits of different drugs were found using retrospective data analysis.

Ambient Characterization of Synthetic Fibres

Fred van Geenen presented results from his PhD research whereby LAESI-MS (Laser Ablation Electrospray Ionization – Mass spectroscopy) was tested as an analysis technique for the surfaces of synthetic fibres under ambient conditions. It is highly desired to identify the polymer, the finishes applied and irregularities that may compromise performance and value of the fibre.

LAESI-MSI of foods and food ingredients

Food contaminants are usually measured as an average in a sample, whereas contaminant levels may vary locally to a large extent. LAESI-MSI is a method in 2D and 3D in which large and irregular sample surfaces can be tackled. It does not need precise tissue slicing nor a MALDI matrix, as other methods do. Michel Nielen showed the opportunities the method can offer to the audience, via examples of fungicides on citrus peel, pesticides on rose leaves, and mycotoxins on rye (ergot poisoning). The main drawback of the technology was discussed as high water content in e.g., cherry tomatoes demands a lower laser power. And like any MSI technique, handling and quantifying data are major challenges.

Metabolic mapping in plants: LAESI-MS imaging

Some metabolites in plants are located in islands, with high or lower concentrations. Why they are there is unknown. Robert Hall presented the results of research, in which LAESI-MSI was used to map metabolites in plants. Some metabolites are visible to the naked human eye, but many fall in the visual spectrum of pollinating insects. The glucosinlates found the outer parts and the midrib of the leaf in Arabidopsis taste bitter, which stops caterpillars from eating. MSI results portray the presence of these metabolites. In phalaenopsis orchids distinct purple areas show a cyanidin derivative, while the compounds from the same metabolic route, apigenin derivatives avoid the area. Next step is to combine these results with genetic research. Hall concludes that LAESI-MSI is an easy and powerful method to localise the invisible molecules to the human eye, about 99,9% of in plants.