title: Laser microdissection and atmospheric pressure chemical ionization mass spectrometry coupled for multimodal imaging.
abstract: BACKGROUND
  Improvement in spatial resolution of atmospheric pressure molecular chemical imaging is required to resolve distinct surface features in the low micrometer and sub-micrometer scale. Laser capture microdissection systems have the capability to focus laser light to a few micrometers. This type of system, when employed for laser ablation (LA) mass spectrometry (MS)-based chemical imaging, has the potential to achieve high spatial resolution with multimodal optical and chemical imaging capability.
  
  
  METHODS
  A commercially available laser capture microdissection system was coupled to a modified ion source of a mass spectrometer. This design allowed for sampling of laser-ablated material via a transfer tube directly into the ionization region. Ionization of the ablated material was accomplished using atmospheric pressure chemical ionization (APCI).
  
  
  RESULTS
  Rhodamine 6G dye of red permanent marker ink in a laser etched pattern as well as cholesterol and phosphatidylcholine in a cerebellum mouse brain thin tissue section were identified and imaged from the mass spectral data. Employing a spot diameter of 8 µm using the 10× microscope cutting objective and lateral oversampling resulted in a pixel size of about 3.7 µm in the same dimension. Distinguishing between features approximately 13 µm apart in a cerebellum mouse brain thin tissue section was demonstrated in a multimodal fashion co-registering optical and mass spectral images.
  
  
  CONCLUSIONS
  A LA/APCI-MS system was developed that comprised a commercially available laser microdissection instrument for transmission geometry LA and a modestly modified ion source for secondary ionization of the ablated material. The set-up was successfully applied for multimodal imaging using the ability to co-register bright field, fluorescence and mass spectral chemical images on one platform.
authors.affiliation: Organic and Biological Mass Spectrometry Group, Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6131, USA.
authors.forename: Matthias
authors.initials: M
authors.lastname: Lorenz
authors.forename: Olga S
authors.initials: OS
authors.lastname: Ovchinnikova
authors.forename: Vilmos
authors.initials: V
authors.lastname: Kertesz
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Van Berkel
mesh_terms: D000818:Animals; D002531:Cerebellum / Q000737:chemistry* / Q000378:metabolism; D061346:Laser Capture Microdissection; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D008297:Male; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D051379:Mice
chemical_list: D008055:Lipids