Current trends in mass spectrometry imaging.

Abstract

Mass spectrometry imaging provides spatial and molecular information for a wide range of analyte ions. The ability to map the distribution of biomolecules without labeling of target compounds has made imaging one of the most dynamic fields in mass spectrometry. In continuation of the ABC special issue BMALDI Imaging^ in 2011 (Vol. 401, Issue 1), we cover recent trends in mass spectrometry imaging. The community has been very active and we have seen a number of exiting developments in instrumentation and applications. While MALDI is still the most widely used technique for mass spectrometry imaging, a number of alternative approaches, including ambient ionization sources, have been used increasingly in the last few years. In addition, sample preparation and data processing strategies have received increased interest in the MS imaging community. Sample preparation includes on-tissue chemistry, e.g., for digestion of proteins. This is related to a continuing shift away from imaging of (unidentified) intact proteins towards imaging of Bmetabolites^ and drug compounds in the lower mass range. This was enabled by the increased use and availability of high resolution mass spectrometers, which allow differentiation of analyte signals from matrix background (without the need for MS/MS). In addition, a growing number of studies include complementary techniques such as LCMS/MS for the reliable identification of the imaged compounds. Another trend has been the use of multimodal approaches by employing multiple instrument platforms for mass spectrometry imaging and/or by integrating spectroscopic imaging techniques. The (absolute) quantitation of imaged compounds and the related issue of ion suppression have become one of the most discussed topics in the field. Finally, the rapidly increasing number of samples and size of data sets has boosted the development of strategies for analyzing and handling data. These general trends and developments in mass spectrometry imaging are also reflected in the contributions to this topical collection as discussed in the following. A key parameter for MS imaging experiments is spatial resolution. A few years ago pixel sizes of 10 μm and below had only been demonstrated by very few groups for mammalian tissue sections. Several approaches are now being employed in order to obtain more detailed spatial information from a more diverse of set of samples. Bhandari et al. present the application of Bmass spectrometry imaging with high resolution in mass and space^ for the localization of metabolites in whole insects and individual insect organs at 10 μm pixel size. Lee et al. investigate metabolites in maize leaves with a pixel size of 5 μm and high resolution MALDI-MS with a modified commercial system. Zavalin et al. have significantly increased measurement speed for their transmission geometry approach and present the analysis of intact proteins at a pixel size of 2.5 μm in MALDI-ToF-MS. Appropriate sample preparation is a key requirement for any high spatial resolution imaging method. In this context Anderson et al. Published in the topical collectionMass Spectrometry Imagingwith guest editors Andreas Rompp and Uwe Karst.