Size exclusion chromatography SEC is a subset of high performance liquid chromatography in which hig

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Nanofabricated Size Exclusion Chromatograph-on-a-C
hip for Biomolecule Detection
Team members Dr. Sabrina Grannan, Mr. Jason
Feldman, Prof. Joe Wang (New Mexico State
University), Ms. Danielle Svehla, Dr. Frank
Grunthaner, Dr. Brian Hunt

• Size exclusion chromatography (SEC) is a subset
  of high performance liquid chromatography in
  which high molecular weight species are separated
  based on their retention time in a size exclusion
  column.
• We are developing a novel SEC-on-a-chip
  consisting of a nanofabricated size exclusion
  column with on-chip molecular detection.

The Nanofabricated Size Exclusion Chromatograph
will be fabricated using the new JEOL-9300 ebeam
lithography system recently acquired by the JPL
Microdevices Laboratory. This system provides
unsurpassed resolution of lt20 nm and is the only
such system in the public sector devoted to pure
research.
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Theory of size exclusion chromatography Path
length through size exclusion network depends on
molecule size
10 micron silica or polymer bead
The conventional size exclusion separation column
is packed with silica or polymer beads containing
a uniform matrix of nanopores average pore sizes
can range from 10 to 1000 nm.
Path followed by molecule with dimensions greater
than size exclusion limit (shortest transit time)
Path followed by partially permeating molecule
(intermediate transit time)
Path followed by fully permeating small molecule
with dimensions less than the permeation limit
(longest transit time)
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Theory of size exclusion chromatography, continued
Molecules that are larger than the pore size of
the packing are excluded and thus are not
retained by the column -- these molecules are the
first to be eluted. (Molecular weight greater
than exclusion limit). Molecules having
intermediate diameters can partially penetrate or
permeate throughout the pore maze and are eluted
after being retained for a characteristic
time. Molecules having diameters less than the
smallest pore size can fully penetrate the pore
maze and are last eluted in a group. NOTE
Size exclusion separations differ from other
chromatographic techniques in that no chemical or
physical interaction between analytes and the
stationary phase is required (or desired)
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Anticipated reductions in instrument dimensions
for nanofabricated size exclusion chromatograph
Conventional benchtop size exclusion
chromatograph, manufactured by Hewlett Packard
Nanofabricated SEC will be an integrated handheld
device, similar to the Sandia lab-on-a-chip shown
above
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Principles of microfluidic ion chromatograph
operation

• An AC potential waveform is applied to the
  platinum electrodes at the bottom of the
  microfluidic channel. As ions flow through the
  channel they are cyclically pulled down onto the
  electrodes (forming an electrical double layer)
  and then released. Ions with higher mobilities
  will be retained longer in the column.
• If successful, this approach allows dramatic
  miniaturization and simplification of the ion
  chromatograph instrument, and allows
  significantly greater control of the separation
  process through adjustment of the electrode
  geometry, applied voltages, and waveform
  frequency.
• The prototype devices consists of a glass
  substrate patterned with platinum electrodes, and
  a PDMS coverslip patterned with fluidic channels
  using soft lithographic techniques.

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Mask design for prototype microfluidic ion
chromatograph
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Prototype device fabricated using fluid channels
in RTV silicone over platinum electrodes on glass

• Prototype device made at the Caltech
  Nanofabrication Lab during June and July, 2001
• Currently being tested at JPL using
  microinjection pump and custom conductivity
  detection circuit