Studying the Adsorption of Hemoglobin to a Silica Surface via Cavity Ringdown Spectroscopy

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Studying the Adsorption of Hemoglobin to a Silica
Surface via Cavity Ringdown Spectroscopy

• Andrew Haehlen

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Objectives

• Vertically orient the cavity to accommodate
  dovetail prism.
• Wanted to obtain relationship between absorbance
  and concentration.
• Develop CRDS technology overall.

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Setup
Top View
Side View
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Traditional Spectroscopy vs. CRDS

• Traditional absorption
• difference between light going into and coming
  out of a sample (not good for very dilute
  solutions)

• CRDS
• measures how long light stays in the cavity (good
  for dilute solutions)

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Evanescent wave CRDS

• When TIR occurs through a prism, an evanescent
  wave forms at the point of reflection.
• This evanescent wave can interact with a sample
  and absorb light, giving a reduction in the
  observed ringdown time.

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Absorption vs. Adsorption

• Absorption The amount of light that a sample
  takes in when irradiated
• Adsorption The process of something
  (hemoglobin) sticking to a surface
• We are measuring absorption and interpreting
  it as adsorption of hemoglobin.

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Why Normal Incidence?

• The laser was sent into the prism at a normal
  incident angle for several reasons.
• Ease of alignment
• 100 of light stays in cavity
• Refraction is wavelength dependent
• Allows both polarizations of light to pass
  through

Refraction
Normal incidence
vs.
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Experimental

• Align cavity
• Take measurements with empty cavity
• Add hemoglobin and wait for the change in signal
  to taper off

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Baseline for Experiments?

• Water was solvent.
• Should not absorb light i.e. should not see
  change in signal
• Initially, however, water alone produced
  significant change in signal.
• Solved by aerating (shaking the heck out of)
  water before mixing up solutions of hemoglobin.
• Obtained level baseline for comparison. ?

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Sample Run (10mg/L)
Empty cavity
Absorbance due to hemoglobin
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Asymptote vs. Concentration
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Possible Explanation for Observed Double
Exponential
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Future Research

• Modification of the setup, adding a flow cell to
  the prism to stir the sample solution.
• This would reduce the time dependence of
  diffusion.
• Using this setup, the sample can be aerated to
  give different oxygen-bound states.

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(More) Future Research

• Surface orientation studies
• Different polarizations of the laser light can be
  used to gather info on how a molecule is oriented
  on the surface of the prism.
• Solid phase studies
• Evanescent wave CRDS can be expanded to solid
  phase samples
• One prism has been coated with gold and platinum

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Acknowledgments

• Thank you to the financial support of the Richter
  Foundation, George Fox University, and the
  Research Corporation.
• Dr. Michael Everest, Chris Kliewer