Use of advantageous, volatile matrices enabled by next-generation high-speed matrix-assisted laser desorption/ionization time-of-flight imaging employing a scanning laser beam.

RATIONALE:In mass spectrometry imaging (MSI) it is often desirable to analyse the same sample in both polarities to extract the most information. However, many matrices that produce high-quality spectra in matrix-assisted laser desorption/ionization (MALDI) are volatile, greatly limiting their use in long imaging experiments. We demonstrate that using a new high speed MALDI-MSI instrument, volatile matrices, including those that produce intense lipid signals in both positive and negative ion mode, can now be effectively used in MSI. METHODS:A prototype Bruker rapifleX MALDI Tissuetyper™ time-of-flight (TOF) instrument was used for high-speed imaging. This allows acquisition rates up to 50 pixels/s made possible by use of a 10 kHz laser and two rotating mirrors that allow the laser beam to be moved over, and synchronised with, the rapidly moving sample. MSI experiments were performed on mouse brain sections using non-vacuum stable dithranol and 2,6-dihydroxyacetophenone (DHA) matrices with pixel sizes ranging from 10 × 10 µm(2) to 50 × 50 µm(2). RESULTS:Both DHA and dithranol produced rich, complementary lipid spectra in both positive and negative ion modes. Due to the rapid acquisition speed of the instrument, both matrices could be effectively used for MSI despite their volatility. For example, an entire mouse brain could be imaged consecutively in both positive and negative ion mode with 50 × 50 µm(2) pixels in ~35 min. We demonstrate that these speeds make possible both faster and higher resolution imaging of biological tissues on practical timescales. CONCLUSIONS:These high acquisition speeds now make possible whole new classes of matrices that are unstable under high vacuum for MALDI-MSI studies. This provides researchers with far greater range and flexibility in choosing the best matrix for the given sample and analytes that they wish to detect. In addition, such instruments allow MSI to be performed at higher resolution across larger areas on practical time scales.