title: Laser dissection sampling modes for direct mass spectral analysis.
abstract: BACKGROUND
  Laser microdissection coupled directly with mass spectrometry provides the capability of on-line analysis of substrates with high spatial resolution, high collection efficiency, and freedom on shape and size of the sampling area. Establishing the merits and capabilities of the different sampling modes that the system provides is necessary in order to select the best sampling mode for characterizing analytically challenging samples.
  
  
  METHODS
  The capabilities of laser ablation spot sampling, laser ablation raster sampling, and laser 'cut and drop' sampling modes of a hybrid optical microscopy/laser ablation liquid vortex capture electrospray ionization mass spectrometry system were compared for the analysis of single cells and tissue.
  
  
  RESULTS
  Single Chlamydomonas reinhardtii cells were monitored for their monogalactosyldiacylglycerol (MGDG) and diacylglyceryltrimethylhomo-Ser (DGTS) lipid content using the laser spot sampling mode, which was capable of ablating individual cells (~4-15 μm) even when agglomerated together. Turbid Allium Cepa cells (~150 μm) having unique shapes difficult to precisely measure using the other sampling modes could be ablated in their entirety using laser raster sampling. Intact microdissections of specific regions of a cocaine-dosed mouse brain tissue were compared using laser 'cut and drop' sampling. Since in laser 'cut and drop' sampling whole and otherwise unmodified sections are captured into the probe, 100% collection efficiencies were achieved. Laser ablation spot sampling has the highest spatial resolution of any sampling mode, while laser ablation raster sampling has the highest sampling area adaptability of the sampling modes.
  
  
  CONCLUSIONS
  Laser ablation spot sampling has the highest spatial resolution of any sampling mode, useful in this case for the analysis of single cells. Laser ablation raster sampling was best for sampling regions with unique shapes that are difficult to measure using other sampling modes. Laser 'cut and drop' sampling can be used for cases where the highest sensitivity is needed, for example, monitoring drugs present in trace amounts in tissue.
authors: Mass Spectrometry and Laser Spectroscopy Group, Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831-6131, USA.
authors: John F
authors: JF
authors: Cahill
authors: Mass Spectrometry and Laser Spectroscopy Group, Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831-6131, USA.
authors: Vilmos
authors: V
authors: Kertesz
authors: Mass Spectrometry and Laser Spectroscopy Group, Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831-6131, USA.
authors: Gary J
authors: GJ
authors: Van Berkel
mesh_terms: D000818:Animals; D001921:Brain / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects; D016825:Chlamydomonas reinhardtii / Q000737:chemistry* / Q000166:cytology; D003042:Cocaine / Q000494:pharmacology; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology; D038983:Galactolipids / Q000032:analysis*; D061346:Laser Capture Microdissection / Q000295:instrumentation*; D053685:Laser Therapy / Q000295:instrumentation; D051379:Mice; D057054:Molecular Imaging; D019697:Onions / Q000737:chemistry* / Q000166:cytology; D061848:Optical Imaging; D013048:Specimen Handling; D021241:Spectrometry, Mass, Electrospray Ionization / Q000295:instrumentation*; D014280:Triglycerides / Q000032:analysis*
chemical_list: C021660:1(3),2-diacylglyceryl-3(1)-O-4'-(N,N,N-trimethyl)homoserine; D018765:Dopamine Uptake Inhibitors; D038983:Galactolipids; D014280:Triglycerides; C009909:monogalactosyldiacylglycerol; D003042:Cocaine