Probing Matter at small length scales:

1. Mark E. ReevesDepartment of PhysicsPh:(202) 994-6279http://home.gwu.edu/~reevesme/reevesme@gwu.edu

2. Probing Matter at small length scales: • Submicron imaging with long photons • How to beat diffraction – SNOM (or NSOM) • Developing electronic probes through nanoparticle assembly

3. The protein microscope: imaging proteins via cellular level assays

4. to Mass Spec Laser beam SNOM tip SNOM-MALDI Sampling • Laser energy is absorbed by matrix surrounding biomolecules • Biomolecules release, intact, from the surface • Are collect by capillary headed into mass spectrometer Illustration of principle Drawing of instrument

5. Use SNOM to probe the intramuscular junction With direct illumination, diffraction limits our spot size to 10 mm The Elements: • IR light (3 micron)– allows water to be the matrix • SNOM – allows light to be focused down to 0.1 micron spot. • Atmospheric pressure – allows investigation of live cells. With SNOM, the spot size is 0.1 mm (0.5 mm scale bar) Human hair 100 mm Burden, S.J., et al.. J. Cell Biol. 1979

6. Scanning Near-Field Optical MicroscopySNOM • 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

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 • Piled up material again forms a concentric circle around the pit

8. 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.

9. Self-Assembled Nanoparticle wires

10. Nanoparticles have unique properties • At left are CdSe nanoparticles, the small size gives them quantum properties “electron in a box” • The emission for the excited state to ground goes to longer wavelength (lower energy) for larger particles (bigger boxes) • Color can change also by attachment of proteins But they are difficult to electrically connect

11. Here’s how to wire up nanotechnology • Atomic force microscope image of a wire made of plastic spheres • 2 micron-wide gold wire (scanning electron micrograph) • Parallel 10 micron x 1 cm gold wires • Square array of crossing gold wires. • ---- once the gold dries, it stays put

12. W All-electronic molecular detection: • VCD deposited nanowire placed in a solution of thiol-derivatized molecules (ODT – a molecule used for biofunctionalization, HS(CH)CH ) • Clear signal in the resistance observed as ODT molecules attach to gold nanowires Onset of attachment

13. Collaborations • Biological problems • Akos Vertes (KIPTA, GWU) • Fatah Kashanchi (KIPTA, GWU) • Eric Hoffmann (CNMRC) • Joan Hoffmann (post doc, GWU) • Jeff Byers, Marc Raphael (NRL) • Microwave Materials • David Norton (U. of Florida) • Hans Christen (ORNL) • Nanomaterials • Lynn Kurihara (NRL)