Mark E. Reeves Department of Physics Ph:(202)

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

The protein microscope: imaging proteins via cellular level assays

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

With direct illumination, diffraction limits our spot size to 10  m Use SNOM to probe the intramuscular junction With SNOM, the spot size is 0.1  m (0.5  m scale bar) 100  m Human hair 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. Burden, S.J., et al.. J. Cell Biol. 1979

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

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

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.

Self-Assembled Nanoparticle wires

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

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

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

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)