Biophotonic Detection of N2

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Biophotonic Detection of N2

• Tilden Hagan

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Goal

• Precise detection of Nitrogen N2
• Preferably in living tissue
• Otherwise in solution or gaseous

Purpose

• For use in a safety device for SCUBA diving to
  assist in preventing the bends

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The Bends

• Nitrogen buildup in the body increases with
  pressure, from depth
• If too much N2 is absorbed into the body, when
  the diver surfaces bubbles can form inside the
  body - just like carbonation when opening a can
  of soda
• The bends can be fatal in severe cases

Application

• Allow SCUBA divers to know when they are at risk
  of having the bends
• Eliminate guesswork of dive tables, allowing
  divers to dive longer if they are not yet at risk
• Dive boats can ensure that none of the divers are
  at dangerous nitrogen levels after diving, and
  before beginning another dive

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Methods Used

• Absorbance
• In solution with white light
• Gaseous with white light, Ti-Saph laser, and HeNe
  laser
• Two photon with Ti-Saph laser
• Raman Scattering
• Gaseous with Ti-Saph laser and HeNe laser
• Both lasers also with acetone and ethanol

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Absorbance

• Absorbance in Solution
• Bubbled pure N2 through water to increase the N2
  absorbed by water
• Measured the spectrum of transmitted white light
  before and after increasing N2 levels

PC
Light Source
USB2000 Spectrometer
Lens
Collimator
Fiber
Fiber
Cuvette
Fiber Coupler
Fiber Coupler

• Absorbance Gaseous
• Measured the spectrum of transmitted white light
  with atmospheric air and high pressure N2

PC
Light Source
USB2000 Spectrometer
Lens
Collimator
Fiber
Fiber
Gas Cell
Fiber Coupler
Fiber Coupler
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Ti-Saph Absorbance

• Absorbance Gaseous
• Measured the power of transmitted Ti-Saph laser
  beam at different wavelengths with atmospheric
  air and high pressure N2

Ti-Saph Laser
Voltmeter
Beam Splitter
Gas Cell
Neutral Density Filter
Mirror
Differential Detector
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Ti-Saph Two Photon Absorption

• Two Photon Absorption
• Two photons absorbed at almost the same moment,
  by one atom, excite it to an energy state
  equivalent to a single photon with twice the
  energy (half the wavelength)
• Focused Two Photon Gaseous Absorbance
• Focused laser beam in cell to induce two photon
  absorption and measured transmitted power

Ti-Saph Laser
Voltmeter
Beam Splitter
10cm Focal Length Lens
Gas Cell
Neutral Density Filter
Differential Detector
3cm Focal Length Lens
Mirror
Mirrors
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Raman Scattering

• Inelastic scattering of light
• A monochromatic light source excites the
  molecules
• Most of the absorbed energy excites electrons,
  but some causes vibrational motion or rotation
• This induces a virtual state where the electron
  resides, when it settles the emitted photon is at
  a different wavelength
• Stokes Raman Scattering will cause the photon to
  be at a higher wavelength (lower energy),
  equivalent to the energy lost in the vibrational
  transition
• Anti-Stokes Scattering will cause the photon to
  be at a lower wavelength (higher energy), due to
  the already vibrating molecule adding the
  additional energy to the emitted photon

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Raman Scattering

• Ethanol and Acetone
• Excite with a 632nm HeNe laser to observe raman
  shifts

Mirror
HeNe Laser
10cm Focal Length Lens
Spectrometer
PC
Quartz Cuvette
3cm Focal Length Lens
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• Large raman peaks of glass make it difficult to
  detect raman spectra of contents
• Quartz has very little raman spectra, making it
  more practical for use in raman spectroscopy

Examples of ethanol peaks http//www.chem.sc.edu/a
nalytical/ chem621/labs2005/raman.pdf
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• Ethanol raman in quartz cuvette
• Listed peaks are at 883, 1050, 1230, and 1400
  cm-1
• http//www.chem.sc.edu/analytical/chem621/labs2005
  /raman.pdf
• http//www.deltanu.com/labs/dnlab5.pdf

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• Acetone raman in quartz cuvette
• Listed peaks are at 1700, 2950 cm-1
• http//www.deltanu.com/labs/dnlab2.pdf
• http//www.deltanu.com/presentations/acswork2.pdf

Image from deltanu showing corresponding acetone
peaks
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Raman Scattering

• Nitrogen
• Excite with a 632nm HeNe laser to observe raman
  shifts

Mirror
HeNe Laser
10cm Focal Length Lens
Spectrometer
PC
Glass Cell
3cm Focal Length Lens
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• N2 raman spectra used water to create a raman
  baseline for zero N2 raman
• No significant differences existed between any
  two spectra
• Literature listed 2350 cm-1 as N2s raman peak,
  however we found nothing of significance at this
  wavenumber
• http//ed.augie.edu/viste/Raman/RamanQuantum.html

2350
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Conclusion

• Research should continue on accurate nitrogen
  detection because it could be very useful in some
  applications. However, nitrogens symmetric
  nature and lack of a dipole makes detection very
  difficult
• We were unable to successfully detect N2 using
  any of the described methods
• Reasons for this include not having a sensitive
  enough spectrometer, or one with a tight enough
  bandwidth
• Interference from the strong raman spectra of
  glass
• Future Work
• Use a quartz cell instead of glass
• Build a better spectrometer suited for this
  specific task so the raman signal from nitrogen
  could be detected

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Acknowledgements

• I would like to extend a thank you to my project
  advisor Adam Wax for the opportunity to conduct
  this research project
• I would also like to thank Nick Graff for the
  tremendous amount of time and help he gave me
  over the past two semesters
• This project was supported in part by NSF (BES
  03-48204)