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					Optical Aspects of SNOM-MALDI
        A Funnel for Photons




                            Mark Reeves
                          Joan Hoffmann
                      Institute for Proteomics
                 Technology and Applications
                                   Mark Reeves/GWU
                       Department of Physics
                                   03/09/2006………1/7
                  SNOM-MALDI Sampling
                                      ● Laser energy is absorbed by matrix
        Illustration of principle       surrounding biomolecules
Laser                           to    ● Biomolecules release, intact, from the
beam                           Mass     surface
                               Spec
                                      ● Are collect by capillary headed into
                                        mass spectrometer

                                            Drawing of instrument
 SNOM tip




                                                           Mark Reeves/GWU
                                                           03/09/2006………2/7
                 Why not use conventional optics?

                                                         Human hair
                                                      100 μm




   Neuroscience, Edited by Purves,          5-10 μm
   Augustine, Fitzpatrick, Katz, LaMantia




●Ultimately cannot focus further
●The interference effects limit the spot size to
a 10 μm diameter for our IR illumination …
diffraction limit
                                                               Mark Reeves/GWU
                                                               03/09/2006………3/7
                                              Use SNOM to probe the
                                              intramuscular junction
                               With direct illumination,   The Elements:
                               diffraction limits our
                                                           ● IR light (3 micron)–
                               spot size to 10 μm
                                                              allows water to be the
                                                              matrix
                                With SNOM, the             ● SNOM – allows light to
                                spot size is 0.1 μm           be focused down to 0.1
                                (0.5 μm scale bar)            micron spot.
                                                           ● Atmospheric pressure –
                                                              allows investigation of
                                                              live cells.

                                                Human hair
                                            100 μm
Burden, S.J., et al.. J. Cell Biol. 1979


                                                                       Mark Reeves/GWU
                                                                       03/09/2006………4/7
Scanning Near-Field Optical Microscopy
                SNOM



                  ● Light is passed through an aperture
                  ● Object, screen, and illumination are
                    very close
                  ● This is the near-field
                  ● Light waves do not have a chance to
                    form, so diffraction is not an issue
                  ● We are limited only by how small we
                    can make the aperture – Our goal is
                    0.1 microns

                                         Mark Reeves/GWU
                                         03/09/2006………5/7
   Practical Realization               ● Sharpened optical fiber forms aperture
                                           ● Fiber is metalized except at end
AFM   (from tip’s vertical position)
                                           ● Fiber is placed on atomic force
                                             microscope platform
                                       ● Object, screen, and illumination are
                                         very close ~ 10 nm
                                       ● Fibers below are chemically etched
                                       ● Light throughput is 1000x that of
                                         commercial tips
NSOM   (amount of transmitted light)




 Images acquired simultaneously
                                                              Mark Reeves/GWU
                                                              03/09/2006………6/7
before    With conventional optics
         (Images are sample topography)
           ● Ablation of (2,5)-dihydroxybenzoic acid (DHB)
           ● Figures show ablation pit
 after
           ● Crater is about 15 microns wide– Our goal is
             0.1 microns
           ● Piled up material forms a concentric circle
             around the pit
           ● This material would be vacuumed up into the
             mass spec.
                                           Human hair
                                         100 μm




                                   http://siliconcert.com/sem.htm

                                            Mark Reeves/GWU
                                            03/09/2006………7/7
Through SNOM tips

● Image of trenches scanned through
  the DHB
● Image of pit from single laser shot
● Crater is about 0.3 microns wide– Our
  goal is 0.1 microns
● Piled up material again forms a
  concentric circle around the pit



                            Human hair
                          100 μm




                        Mark Reeves/GWU
                        03/09/2006………8/7
        Applications
                                           ● Neuromuscular Junction (current)
                                           ● Muscle repair (future)
                                             Children’s Hospital – Keck Foundation
                                           ● HIV transfection (current)
                                             GWU Medical Center – internal funds
                                           ● Signaling at chemical synapse (future)
                                             Naval Research Laboratory – NRL




Burden, S.J., et al.. J. Cell Biol. 1979
                                                                  Mark Reeves/GWU
                                                                  03/09/2006………9/7
          Applications
● Neuromuscular Junction (current)
● Muscle repair (future)
  Children’s Hospital – Keck Foundation
● HIV transfection (current)
  GWU Medical Center – internal funds
● Signaling at chemical synapse (future)
  Naval Research Laboratory – NRL




                                 New England Journal of Medicine 339:32.
                                                           Mark Reeves/GWU
                                                           03/09/2006………10/7
   Applications
                                  ● Neuromuscular Junction (current)
                                  ● Muscle repair (future)
                                    Children’s Hospital – Keck Foundation
                                  ● HIV transfection (current)
                                    GWU Medical Center – internal funds
                                  ● Signaling at chemical synapse (future)
                                    Naval Research Laboratory – NRL




http://portal.uni-freiburg.de/anatomie1/forschung

                                                         Mark Reeves/GWU
                                                         03/09/2006………11/7

				
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