Mark E. ReevesDepartment of Physics

Ph:(202) 994-6279http://home.gwu.edu/~reevesme/

reevesme@gwu.edu

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 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

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

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ethanol100 M ODT1 mM ODT

10 mM ODT

Change in

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Time (s)

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)