Sensor Group (Judy, Tai, Ho, Harmon)

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Sensor Group (Judy, Tai, Ho, Harmon)

• environmentally robust sensors (stationary and
  mobile deployment)
• initial emphasis or chemical species (ionic)
• specifically nitrate
• achievements and timeline
• nitrate ISE, demonstrate scaleability
• higher performance amperometric nitrate sensor
• general ion separation/identification
  capabilities (IC-on-a-chip)
• a more general chemical sensor based on surface
  plasmon resonance
• transitioning to gas/atmospheric project CO2

the river is receiving excessive nutrients from
adjacent groundwater (not from surface runoff,
not from atmospheric deposition)...
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Potentiometric nitrate selective electrode

• Carbon electrode coated with a doped-conducting
  polymer (ion selective membrane)
• Advantages
• simple, passive, inexpensive
• effective at nitrate gt 2 ppm
• amenable to diversity of form factors
• good starter for ENS testbeds
• Challenges
• need to longer lifespan, lower det. lim., less
  drift
• develop robust packaging
• in situ calibration protocols

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Potentiometric packaging for the environment,
experimenting with form factor

• epoxy and simple protective plastic sheaths
• demonstration on soil samples collected at
  Palmdale
• conventional soil nitrate analysis (1.5 days) vs.
  direct soil moisture readings (first-time to our
  knowledge! 1.5 h!)
• direct measurements revealed previously
  unobserveable degree of heterogeneity in soil
  nitrate concentrations
• Next steps
• scale up to 10-20 sensor deployment
• in situ calibration and testing
• alternative conducting polymers

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Micromachined Amperometric Nitrate Sensor

• Amperometric nitrate sensor
• Silver working electrode sensitive for nitrate
• NaOH electrolyte minimize nitrogen interference
• Anion-permeable membrane for selectivity
• Advantages
• Simple sensor design and operation (easily
  minaturized)
• more sensitive than potentiometric (40-50x lower)
• Challenges
• requires microfluidics (not as easily
  minitiarized)
• associated power requirements

SEM Picture of Electrodes and Microfluidic
Channels
Microfabricated Sensor Chip
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Micromachined Amperometric Nitrate Sensor

• Prototype sensor units have been designed,
  fabricated, assembled, and tested under ideal
  laboratory settings.
• Next steps
• prototype refinement
• in situ calibration and testing

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Ion Liquid Chromatography On-a-Chip

• First Integrated Ion Liquid Chromatography Chip
• Advantages
• selectivity through chromatographic process
• multiple ion sensing simultaneously
• sensor internal (protected)
• Challenges
• detection limit in ppm range
• microfluidics required

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For higher performance

1. Longer separation column greater separation
   power
2. Tandem column multi-dimensional separation
3. High pressure LC (HPLC) conceivable for wider
   array of analytes, including organic solutes

6.5 cm-long Column
100 um-Deep Anchored Column
Wafer Thickness
100um-Deep Anchor
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Molecular Detection Using Plasmonic Band Gap

• Surface Plasmon EM waves propagating on surface
  of metal
• Wavelength strongly dependent on molecular
  binding
• Surface Plasmon Wave propagation forbidden in a
  grating whose period is equal to half the
  wavelength Plasmonic Band Gap

Epolariton
Concept
PMMA grating
Surface plasmon dispersion relation on a grating
Motivation
Plasmonic Band Gap sensing necessitates only
rudimentary optics gt On-chip molecular
detection possible!
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Proof of concept
Numerical calculation of the characteristics of
such a sensor
Dispersion Relations of SPW on gratings
sensor characteristics at 800 nm
No Binding
Working Range
Sensor output
Plasmonic Band Gap propagation impossible
Binding
Molecular Binding
Working range and sensitivity of the sensor can
be tuned by the filling ratio and period of the
grating
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Next sensor group effort carbon dioxide?
CO2

• Obvious, widespread drivers carbon cycling,
  sequestration, climate change
• Again, commercial sensors available, but large
  and/or costly
• Can we create sensors that scale to large
  spatially distributed problems?

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Infrared CO2 Sensing

• Uses wavelength-sensitive IR absorption by CO2
  molecules

• Proof of concept using filtered pyroelectric
  sensor

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Potential to increase sensitivity

• Sensor Sensitivity critical ? Novel
  pyrolyzed-parylene carbon bolometer (measures
  infrared light via the induced temperature change
  observed when absorbing the infrared light on
  thermally-insulated element)
• Next steps
• initial prototype completed
• prototype refinement
• in situ calibration and testing

Example of fabricated device