Surface plasmon resonance sensing

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Surface plasmon resonance sensing
Surface plasmon waves extend few hundred
nanometres above the metal film. They are
affected by the refractive index in this region.
Surface plasmon resonance sensors are important
for ultrasensitive immunoassays with applications
in health diagnostics

• Principle of immunoassays
• Reactions between two protein molecules can be
  extremely specific.
• One type of molecule (antibody) can be
  immobilised on gold sensor surface
• The second (antigen) will bind changing the
  refractive index
• This change is detected by changed angle of
  surface plasmon resonance

Conventional sensor system
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Simulation based on n-layer system

• Simulation based on Fresnel reflectivity
  equations for an n-layered system
• System consisted of a BK7 hemispherical prism, a
  50nm gold layer and an analyte layer
• Simulation produced R vs ? curves from system
  parameters (incident light wavelength ? and angle
  ?, layer thicknesses d and permittivities e)

Source S. Orfanidis, Electromagnetic waves and
antennas pp.81-108 R.U.S. Kurosawa et al, PRB
33,789 (1986)
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Surface Plasmon Resonance Sensing System

• Opportunities
• Surface plasmons probe ultrathin regions
  (monolayer is enough)
• System can use inexpensive components, can run
  on Palm
• Sample can be extremely small (microfluidics)

• Challenges
• LED must be stable, preferably at a level
  10-7
• Detector response must be linear, with similar
  accuracy
• Readout must be very fast

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Statistical hypothesis testing for sensitivity
improvement

• Two SPR curves Fi and Gi produce difference
  curve Di
• From the average value of D and the variance S
  define a standardised Z value
• Central Limit Theorem states that Z has
  approximately standard normal distribution
• Hypothesis that two curves Fi and Gi are the
  same
• Choose to reject hypothesis for significance
  level 0.05 (Zgt1.96)
• Probability that this was wrong decision is less
  than 5

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Test parameters used

• Input wavelength 632.8nm
• 3 layered system (BK7 glass prism, 50nm gold
  layer, analyte layer of water and isopropanol
  solutions)
• Collection device - array detector from Ames
  Photonics Inc.
• 384 simulation points (3mm laser diameter over
  1024 pixels contained in 7.99mm)
• Noise standard deviation 3 x 10-6 (based on noise
  specifics for detector, total integration time of
  100s with 1ms integration time)

• Test applied to curve regions within
• front edge of reflectance curve

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Nanotechnology approach for the optical sensing
of trace pathogens
Nanostructures increase device sensitivity
Surface plasmons are electromagnetic waves
excited by light in metal films.

• Aim
• Develop a new optical based sensor technology
  for rapid detection of trace pathogens and
  chemicals in the environment.
• Novel approach
• Apply surface nano-patterning techniques to a
  Surface Plasmon Resonance (SPR) sensing system to
  achieve unprecedented sensitivity levels

Surface plasmons sense the analyte
Sensor readout
Examples of nanostructures
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Rigorous coupled wave analysis for modelling
nano-modified surface plasmon based sensing
systems



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Simulation results
These simulations were carried out using
DiffractMOD, an RCWA based software package from
RSoft



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Surface plasmon coupled emission

• Fluorescence emission is strongly directional
• Applications for fluorescence bioassays

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Surface Plasmon Coupled Emission Excitation
scheme adapted for microscopy



Two photon SPCE demonstrated
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Schematic diagram of a model bioassay
Feasibility of bioassays in dense media
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Relevant publications

• Plastic Versus Glass Support for an Immunoassay
  on Metal-Coated Surfaces in Optically Dense
  Samples Utilizing Directional Surface
  Plasmon-Coupled Emission Evgenia G. Matveeva,
  Ignacy Gryczynski, Joanna Malicka, Zygmunt
  Gryczynski, Ewa Goldys, Joseph Howe, Klaus W.
  Berndt, and Joseph R. Lakowicz, Journal of
  Fluorescence vol.15, no.6 865-71, Nov. 2005
• Directional two-photon induced surface
  plasmon-coupled emission Gryczynski, Ignacy
  Malicka, Joanna Lakowicz, Joseph R. Goldys, Ewa
  M. Calander, Nils Gryczynski, Zygmunt, Thin
  Solid Films, 491(1-2), 173-176, (2005).
• Ultrasensitive detection in optically dense
  physiological media applications to fast
  reliable biological assays . Matveeva, Evgenia
  G. Gryczynski, Ignacy Berndt, Klaus W.
  Lakowicz, Joseph R. Goldys, Ewa Gryczynski,
  Zygmunt. Proceedings of SPIE-The International
  Society for Optical Engineering (2006), 6092
  125-133.
• Detection limit improvement of surface plasmon
  resonance based biosensors using statistical
  hypothesis testing, Barnett, Anne Goldys, Ewa
  M. Dybek, Konrad, Proceedings of SPIE-The
  International Society for Optical Engineering
  (2005), 5703(Plasmonics in Biology and Medicine
  II), 71-78. Strategies for noise reduction and
  sensitivity increase for a Surface Plasmon
  Resonance (SPR) based biosensing system, A.
  Barnett, E.M. Goldys, K. Dybek. OWLS Conference,
  Optics Within Life Sciences Melbourne 28 Nov
  2004 1 Dec 2004