Abstract

Dual-mode surface-plasmon resonance (SPR) sensors use both long- and short- range surface plasmon waves to differentiate surface binding interactions from interfering bulk effects. We have optimized the design of these sensors for minimum surface limit of detection (LOD) using a Cramer-Rao lower bound for spectral shift estimation. Despite trade-offs between resonance width, minimum reflectivity, and sensitivity for the two modes, a range of reasonable design parameters provides nearly optimal performance. Experimental verification using biotin-streptavidin binding as a model system reveals that sensitivity and LOD for dual-mode sensors remains competitive with single-mode sensors while compensating for bulk effects.

© 2007 Optical Society of America

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References

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  1. R. Slavik, J. Homola, and H. Vaisocherova, "Advanced biosensing using simultaneous excitation of short and long range surface plasmons," Meas. Sci. Technol. 17, 932-938 (2006).
    [CrossRef]
  2. R. Donipudi, S. Pochiraju, and J. T. Hastings, "Self-referenced SPR sensing via simultaneous excitation of long- and short-range surface plasmons," Proceedings of the 2006 Conference on Lasers and Electrooptics (2006).
    [CrossRef]
  3. G. G. Nenninger, J. B. Clendenning, C. E. Furlong, and S. S. Yee, "Reference-compensated biosensing using a dual-channel surface plasmon resonance sensor system based on a planar lightpipe configuration," Sens. Actuators B 51, 38-45 (1998).
    [CrossRef]
  4. J. Homola, "Present and future of surface plasmon resonance biosensors," Anal. Bioanal. Chem. 377, 528-539 (2003).
    [CrossRef] [PubMed]
  5. J. Homola, H. B. Lu, and S. S. Yee, "Dual-channel surface plasmon resonance sensor with spectral discrimination of sensing channels using dielectric overlayer," Electron. Lett. 35, 1105-1106 (1999).
    [CrossRef]
  6. J. Homola, H. B. Lu, G. G. Nenninger, J. Dostalek, and S. S. Yee, "A novel multichannel surface plasmon resonance biosensor," Sens. Actuators B 76, 403-410 (2001).
    [CrossRef]
  7. C. Boozer, Q. M. Yu, S. F. Chen, C. Y. Lee, J. Homola, S. S. Yee, and S. Y. Jiang, "Surface functionalization for self-referencing surface plasmon resonance (SPR) biosensors by multi-step self-assembly," Sens. Actuators B 90, 22-30 (2003).
    [CrossRef]
  8. J. T. Hastings, "Optimizing Surface-Plasmon Resonance Sensors for Limit of Detection based on a Cramer-Rao Bound," IEEE Sensors J. (to be published) (2007).
  9. W. C. Karl and H. H. Pien, "High-resolution biosensor spectral peak shift estimation," IEEE Trans. Signal Process 53, 4631-4639 (2005).
    [CrossRef]
  10. E. N. Economou, "Surface Plasmons in Thin Films," Phys. Rev. 182, 539-554 (1969).
    [CrossRef]
  11. J. J. Burke, G. I. Stegeman, and T. Tamir, "Surface-polariton-like waves guided by thin, lossy metal-films," Phys Rev B 33, 5186-5201 (1986).
    [CrossRef]
  12. G. G. Nenninger, P. Tobiska, J. Homola, and S. S. Yee, "Long-range surface plasmons for high-resolution surface plasmon resonance sensors," Sens. Actuators B 74, 145-151 (2001).
    [CrossRef]
  13. J. H. Lowry, J. S. Mendlowitz, and N. S. Subramanian, "Optical characteristics of Teflon Af(R) Fluoroplastic Materials," Opt. Eng. 31, 1982-1985 (1992).
    [CrossRef]
  14. G. M. Hale and M. R. Querry, "Optical constants of water in the 200-nm to 200-µm wavelength region," Appl. Opt. 12, 555 (1973).
    [CrossRef] [PubMed]
  15. P. B. Johnson and R. W. Christy, "Optical-constants of noble-metals," Phys Rev B 6, 4370-4379 (1972).
    [CrossRef]
  16. J. A. Woollam Co., "Optical Properties of Gold from 250nm to 1000nm," (1996).
  17. "Data sheet for N-BK7," (Schott North America Inc., 2001).
  18. N. H. Kim, T. J. Baek, H. G. Park, and G. H. Seong, "Highly sensitive biomolecule detection on a quartz crystal microbalance using gold nanoparticles as signal amplification probes," Anal. Sci. 23, 177-181 (2007).
    [CrossRef] [PubMed]
  19. W. M. Shu, E. D. Laue, and A. A. Seshia, "Investigation of biotin-streptavidin binding interactions using microcantilever sensors," Biosens. Bioelectron. 22, 2003-2009 (2007).
    [CrossRef]

2007

J. T. Hastings, "Optimizing Surface-Plasmon Resonance Sensors for Limit of Detection based on a Cramer-Rao Bound," IEEE Sensors J. (to be published) (2007).

N. H. Kim, T. J. Baek, H. G. Park, and G. H. Seong, "Highly sensitive biomolecule detection on a quartz crystal microbalance using gold nanoparticles as signal amplification probes," Anal. Sci. 23, 177-181 (2007).
[CrossRef] [PubMed]

W. M. Shu, E. D. Laue, and A. A. Seshia, "Investigation of biotin-streptavidin binding interactions using microcantilever sensors," Biosens. Bioelectron. 22, 2003-2009 (2007).
[CrossRef]

2006

R. Slavik, J. Homola, and H. Vaisocherova, "Advanced biosensing using simultaneous excitation of short and long range surface plasmons," Meas. Sci. Technol. 17, 932-938 (2006).
[CrossRef]

2005

W. C. Karl and H. H. Pien, "High-resolution biosensor spectral peak shift estimation," IEEE Trans. Signal Process 53, 4631-4639 (2005).
[CrossRef]

2003

C. Boozer, Q. M. Yu, S. F. Chen, C. Y. Lee, J. Homola, S. S. Yee, and S. Y. Jiang, "Surface functionalization for self-referencing surface plasmon resonance (SPR) biosensors by multi-step self-assembly," Sens. Actuators B 90, 22-30 (2003).
[CrossRef]

J. Homola, "Present and future of surface plasmon resonance biosensors," Anal. Bioanal. Chem. 377, 528-539 (2003).
[CrossRef] [PubMed]

2001

J. Homola, H. B. Lu, G. G. Nenninger, J. Dostalek, and S. S. Yee, "A novel multichannel surface plasmon resonance biosensor," Sens. Actuators B 76, 403-410 (2001).
[CrossRef]

G. G. Nenninger, P. Tobiska, J. Homola, and S. S. Yee, "Long-range surface plasmons for high-resolution surface plasmon resonance sensors," Sens. Actuators B 74, 145-151 (2001).
[CrossRef]

1999

J. Homola, H. B. Lu, and S. S. Yee, "Dual-channel surface plasmon resonance sensor with spectral discrimination of sensing channels using dielectric overlayer," Electron. Lett. 35, 1105-1106 (1999).
[CrossRef]

1998

G. G. Nenninger, J. B. Clendenning, C. E. Furlong, and S. S. Yee, "Reference-compensated biosensing using a dual-channel surface plasmon resonance sensor system based on a planar lightpipe configuration," Sens. Actuators B 51, 38-45 (1998).
[CrossRef]

1992

J. H. Lowry, J. S. Mendlowitz, and N. S. Subramanian, "Optical characteristics of Teflon Af(R) Fluoroplastic Materials," Opt. Eng. 31, 1982-1985 (1992).
[CrossRef]

1986

J. J. Burke, G. I. Stegeman, and T. Tamir, "Surface-polariton-like waves guided by thin, lossy metal-films," Phys Rev B 33, 5186-5201 (1986).
[CrossRef]

1973

1972

P. B. Johnson and R. W. Christy, "Optical-constants of noble-metals," Phys Rev B 6, 4370-4379 (1972).
[CrossRef]

1969

E. N. Economou, "Surface Plasmons in Thin Films," Phys. Rev. 182, 539-554 (1969).
[CrossRef]

Baek, T. J.

N. H. Kim, T. J. Baek, H. G. Park, and G. H. Seong, "Highly sensitive biomolecule detection on a quartz crystal microbalance using gold nanoparticles as signal amplification probes," Anal. Sci. 23, 177-181 (2007).
[CrossRef] [PubMed]

Boozer, C.

C. Boozer, Q. M. Yu, S. F. Chen, C. Y. Lee, J. Homola, S. S. Yee, and S. Y. Jiang, "Surface functionalization for self-referencing surface plasmon resonance (SPR) biosensors by multi-step self-assembly," Sens. Actuators B 90, 22-30 (2003).
[CrossRef]

Burke, J. J.

J. J. Burke, G. I. Stegeman, and T. Tamir, "Surface-polariton-like waves guided by thin, lossy metal-films," Phys Rev B 33, 5186-5201 (1986).
[CrossRef]

Chen, S. F.

C. Boozer, Q. M. Yu, S. F. Chen, C. Y. Lee, J. Homola, S. S. Yee, and S. Y. Jiang, "Surface functionalization for self-referencing surface plasmon resonance (SPR) biosensors by multi-step self-assembly," Sens. Actuators B 90, 22-30 (2003).
[CrossRef]

Christy, R. W.

P. B. Johnson and R. W. Christy, "Optical-constants of noble-metals," Phys Rev B 6, 4370-4379 (1972).
[CrossRef]

Clendenning, J. B.

G. G. Nenninger, J. B. Clendenning, C. E. Furlong, and S. S. Yee, "Reference-compensated biosensing using a dual-channel surface plasmon resonance sensor system based on a planar lightpipe configuration," Sens. Actuators B 51, 38-45 (1998).
[CrossRef]

Dostalek, J.

J. Homola, H. B. Lu, G. G. Nenninger, J. Dostalek, and S. S. Yee, "A novel multichannel surface plasmon resonance biosensor," Sens. Actuators B 76, 403-410 (2001).
[CrossRef]

Economou, E. N.

E. N. Economou, "Surface Plasmons in Thin Films," Phys. Rev. 182, 539-554 (1969).
[CrossRef]

Furlong, C. E.

G. G. Nenninger, J. B. Clendenning, C. E. Furlong, and S. S. Yee, "Reference-compensated biosensing using a dual-channel surface plasmon resonance sensor system based on a planar lightpipe configuration," Sens. Actuators B 51, 38-45 (1998).
[CrossRef]

Hale, G. M.

Hastings, J. T.

J. T. Hastings, "Optimizing Surface-Plasmon Resonance Sensors for Limit of Detection based on a Cramer-Rao Bound," IEEE Sensors J. (to be published) (2007).

Homola, J.

R. Slavik, J. Homola, and H. Vaisocherova, "Advanced biosensing using simultaneous excitation of short and long range surface plasmons," Meas. Sci. Technol. 17, 932-938 (2006).
[CrossRef]

J. Homola, "Present and future of surface plasmon resonance biosensors," Anal. Bioanal. Chem. 377, 528-539 (2003).
[CrossRef] [PubMed]

C. Boozer, Q. M. Yu, S. F. Chen, C. Y. Lee, J. Homola, S. S. Yee, and S. Y. Jiang, "Surface functionalization for self-referencing surface plasmon resonance (SPR) biosensors by multi-step self-assembly," Sens. Actuators B 90, 22-30 (2003).
[CrossRef]

G. G. Nenninger, P. Tobiska, J. Homola, and S. S. Yee, "Long-range surface plasmons for high-resolution surface plasmon resonance sensors," Sens. Actuators B 74, 145-151 (2001).
[CrossRef]

J. Homola, H. B. Lu, G. G. Nenninger, J. Dostalek, and S. S. Yee, "A novel multichannel surface plasmon resonance biosensor," Sens. Actuators B 76, 403-410 (2001).
[CrossRef]

J. Homola, H. B. Lu, and S. S. Yee, "Dual-channel surface plasmon resonance sensor with spectral discrimination of sensing channels using dielectric overlayer," Electron. Lett. 35, 1105-1106 (1999).
[CrossRef]

Jiang, S. Y.

C. Boozer, Q. M. Yu, S. F. Chen, C. Y. Lee, J. Homola, S. S. Yee, and S. Y. Jiang, "Surface functionalization for self-referencing surface plasmon resonance (SPR) biosensors by multi-step self-assembly," Sens. Actuators B 90, 22-30 (2003).
[CrossRef]

Johnson, P. B.

P. B. Johnson and R. W. Christy, "Optical-constants of noble-metals," Phys Rev B 6, 4370-4379 (1972).
[CrossRef]

Karl, W. C.

W. C. Karl and H. H. Pien, "High-resolution biosensor spectral peak shift estimation," IEEE Trans. Signal Process 53, 4631-4639 (2005).
[CrossRef]

Kim, N. H.

N. H. Kim, T. J. Baek, H. G. Park, and G. H. Seong, "Highly sensitive biomolecule detection on a quartz crystal microbalance using gold nanoparticles as signal amplification probes," Anal. Sci. 23, 177-181 (2007).
[CrossRef] [PubMed]

Laue, E. D.

W. M. Shu, E. D. Laue, and A. A. Seshia, "Investigation of biotin-streptavidin binding interactions using microcantilever sensors," Biosens. Bioelectron. 22, 2003-2009 (2007).
[CrossRef]

Lee, C. Y.

C. Boozer, Q. M. Yu, S. F. Chen, C. Y. Lee, J. Homola, S. S. Yee, and S. Y. Jiang, "Surface functionalization for self-referencing surface plasmon resonance (SPR) biosensors by multi-step self-assembly," Sens. Actuators B 90, 22-30 (2003).
[CrossRef]

Lowry, J. H.

J. H. Lowry, J. S. Mendlowitz, and N. S. Subramanian, "Optical characteristics of Teflon Af(R) Fluoroplastic Materials," Opt. Eng. 31, 1982-1985 (1992).
[CrossRef]

Lu, H. B.

J. Homola, H. B. Lu, G. G. Nenninger, J. Dostalek, and S. S. Yee, "A novel multichannel surface plasmon resonance biosensor," Sens. Actuators B 76, 403-410 (2001).
[CrossRef]

J. Homola, H. B. Lu, and S. S. Yee, "Dual-channel surface plasmon resonance sensor with spectral discrimination of sensing channels using dielectric overlayer," Electron. Lett. 35, 1105-1106 (1999).
[CrossRef]

Mendlowitz, J. S.

J. H. Lowry, J. S. Mendlowitz, and N. S. Subramanian, "Optical characteristics of Teflon Af(R) Fluoroplastic Materials," Opt. Eng. 31, 1982-1985 (1992).
[CrossRef]

Nenninger, G. G.

G. G. Nenninger, P. Tobiska, J. Homola, and S. S. Yee, "Long-range surface plasmons for high-resolution surface plasmon resonance sensors," Sens. Actuators B 74, 145-151 (2001).
[CrossRef]

J. Homola, H. B. Lu, G. G. Nenninger, J. Dostalek, and S. S. Yee, "A novel multichannel surface plasmon resonance biosensor," Sens. Actuators B 76, 403-410 (2001).
[CrossRef]

G. G. Nenninger, J. B. Clendenning, C. E. Furlong, and S. S. Yee, "Reference-compensated biosensing using a dual-channel surface plasmon resonance sensor system based on a planar lightpipe configuration," Sens. Actuators B 51, 38-45 (1998).
[CrossRef]

Park, H. G.

N. H. Kim, T. J. Baek, H. G. Park, and G. H. Seong, "Highly sensitive biomolecule detection on a quartz crystal microbalance using gold nanoparticles as signal amplification probes," Anal. Sci. 23, 177-181 (2007).
[CrossRef] [PubMed]

Pien, H. H.

W. C. Karl and H. H. Pien, "High-resolution biosensor spectral peak shift estimation," IEEE Trans. Signal Process 53, 4631-4639 (2005).
[CrossRef]

Querry, M. R.

Seong, G. H.

N. H. Kim, T. J. Baek, H. G. Park, and G. H. Seong, "Highly sensitive biomolecule detection on a quartz crystal microbalance using gold nanoparticles as signal amplification probes," Anal. Sci. 23, 177-181 (2007).
[CrossRef] [PubMed]

Seshia, A. A.

W. M. Shu, E. D. Laue, and A. A. Seshia, "Investigation of biotin-streptavidin binding interactions using microcantilever sensors," Biosens. Bioelectron. 22, 2003-2009 (2007).
[CrossRef]

Shu, W. M.

W. M. Shu, E. D. Laue, and A. A. Seshia, "Investigation of biotin-streptavidin binding interactions using microcantilever sensors," Biosens. Bioelectron. 22, 2003-2009 (2007).
[CrossRef]

Slavik, R.

R. Slavik, J. Homola, and H. Vaisocherova, "Advanced biosensing using simultaneous excitation of short and long range surface plasmons," Meas. Sci. Technol. 17, 932-938 (2006).
[CrossRef]

Stegeman, G. I.

J. J. Burke, G. I. Stegeman, and T. Tamir, "Surface-polariton-like waves guided by thin, lossy metal-films," Phys Rev B 33, 5186-5201 (1986).
[CrossRef]

Subramanian, N. S.

J. H. Lowry, J. S. Mendlowitz, and N. S. Subramanian, "Optical characteristics of Teflon Af(R) Fluoroplastic Materials," Opt. Eng. 31, 1982-1985 (1992).
[CrossRef]

Tamir, T.

J. J. Burke, G. I. Stegeman, and T. Tamir, "Surface-polariton-like waves guided by thin, lossy metal-films," Phys Rev B 33, 5186-5201 (1986).
[CrossRef]

Tobiska, P.

G. G. Nenninger, P. Tobiska, J. Homola, and S. S. Yee, "Long-range surface plasmons for high-resolution surface plasmon resonance sensors," Sens. Actuators B 74, 145-151 (2001).
[CrossRef]

Vaisocherova, H.

R. Slavik, J. Homola, and H. Vaisocherova, "Advanced biosensing using simultaneous excitation of short and long range surface plasmons," Meas. Sci. Technol. 17, 932-938 (2006).
[CrossRef]

Yee, S. S.

C. Boozer, Q. M. Yu, S. F. Chen, C. Y. Lee, J. Homola, S. S. Yee, and S. Y. Jiang, "Surface functionalization for self-referencing surface plasmon resonance (SPR) biosensors by multi-step self-assembly," Sens. Actuators B 90, 22-30 (2003).
[CrossRef]

G. G. Nenninger, P. Tobiska, J. Homola, and S. S. Yee, "Long-range surface plasmons for high-resolution surface plasmon resonance sensors," Sens. Actuators B 74, 145-151 (2001).
[CrossRef]

J. Homola, H. B. Lu, G. G. Nenninger, J. Dostalek, and S. S. Yee, "A novel multichannel surface plasmon resonance biosensor," Sens. Actuators B 76, 403-410 (2001).
[CrossRef]

J. Homola, H. B. Lu, and S. S. Yee, "Dual-channel surface plasmon resonance sensor with spectral discrimination of sensing channels using dielectric overlayer," Electron. Lett. 35, 1105-1106 (1999).
[CrossRef]

G. G. Nenninger, J. B. Clendenning, C. E. Furlong, and S. S. Yee, "Reference-compensated biosensing using a dual-channel surface plasmon resonance sensor system based on a planar lightpipe configuration," Sens. Actuators B 51, 38-45 (1998).
[CrossRef]

Yu, Q. M.

C. Boozer, Q. M. Yu, S. F. Chen, C. Y. Lee, J. Homola, S. S. Yee, and S. Y. Jiang, "Surface functionalization for self-referencing surface plasmon resonance (SPR) biosensors by multi-step self-assembly," Sens. Actuators B 90, 22-30 (2003).
[CrossRef]

Anal. Bioanal. Chem.

J. Homola, "Present and future of surface plasmon resonance biosensors," Anal. Bioanal. Chem. 377, 528-539 (2003).
[CrossRef] [PubMed]

Anal. Sci.

N. H. Kim, T. J. Baek, H. G. Park, and G. H. Seong, "Highly sensitive biomolecule detection on a quartz crystal microbalance using gold nanoparticles as signal amplification probes," Anal. Sci. 23, 177-181 (2007).
[CrossRef] [PubMed]

Appl. Opt.

Biosens. Bioelectron.

W. M. Shu, E. D. Laue, and A. A. Seshia, "Investigation of biotin-streptavidin binding interactions using microcantilever sensors," Biosens. Bioelectron. 22, 2003-2009 (2007).
[CrossRef]

Electron. Lett.

J. Homola, H. B. Lu, and S. S. Yee, "Dual-channel surface plasmon resonance sensor with spectral discrimination of sensing channels using dielectric overlayer," Electron. Lett. 35, 1105-1106 (1999).
[CrossRef]

IEEE Sensors J.

J. T. Hastings, "Optimizing Surface-Plasmon Resonance Sensors for Limit of Detection based on a Cramer-Rao Bound," IEEE Sensors J. (to be published) (2007).

IEEE Trans. Signal Process

W. C. Karl and H. H. Pien, "High-resolution biosensor spectral peak shift estimation," IEEE Trans. Signal Process 53, 4631-4639 (2005).
[CrossRef]

Meas. Sci. Technol.

R. Slavik, J. Homola, and H. Vaisocherova, "Advanced biosensing using simultaneous excitation of short and long range surface plasmons," Meas. Sci. Technol. 17, 932-938 (2006).
[CrossRef]

Opt. Eng.

J. H. Lowry, J. S. Mendlowitz, and N. S. Subramanian, "Optical characteristics of Teflon Af(R) Fluoroplastic Materials," Opt. Eng. 31, 1982-1985 (1992).
[CrossRef]

Phys Rev B

J. J. Burke, G. I. Stegeman, and T. Tamir, "Surface-polariton-like waves guided by thin, lossy metal-films," Phys Rev B 33, 5186-5201 (1986).
[CrossRef]

P. B. Johnson and R. W. Christy, "Optical-constants of noble-metals," Phys Rev B 6, 4370-4379 (1972).
[CrossRef]

Phys. Rev.

E. N. Economou, "Surface Plasmons in Thin Films," Phys. Rev. 182, 539-554 (1969).
[CrossRef]

Sens. Actuators B

J. Homola, H. B. Lu, G. G. Nenninger, J. Dostalek, and S. S. Yee, "A novel multichannel surface plasmon resonance biosensor," Sens. Actuators B 76, 403-410 (2001).
[CrossRef]

C. Boozer, Q. M. Yu, S. F. Chen, C. Y. Lee, J. Homola, S. S. Yee, and S. Y. Jiang, "Surface functionalization for self-referencing surface plasmon resonance (SPR) biosensors by multi-step self-assembly," Sens. Actuators B 90, 22-30 (2003).
[CrossRef]

G. G. Nenninger, P. Tobiska, J. Homola, and S. S. Yee, "Long-range surface plasmons for high-resolution surface plasmon resonance sensors," Sens. Actuators B 74, 145-151 (2001).
[CrossRef]

G. G. Nenninger, J. B. Clendenning, C. E. Furlong, and S. S. Yee, "Reference-compensated biosensing using a dual-channel surface plasmon resonance sensor system based on a planar lightpipe configuration," Sens. Actuators B 51, 38-45 (1998).
[CrossRef]

Other

J. A. Woollam Co., "Optical Properties of Gold from 250nm to 1000nm," (1996).

"Data sheet for N-BK7," (Schott North America Inc., 2001).

R. Donipudi, S. Pochiraju, and J. T. Hastings, "Self-referenced SPR sensing via simultaneous excitation of long- and short-range surface plasmons," Proceedings of the 2006 Conference on Lasers and Electrooptics (2006).
[CrossRef]

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Figures (8)

Fig. 1.
Fig. 1.

Schematic diagram of a self-referencing surface-plasmon resonance sensor. The sensor consists of a gold thin film on a buffer layer (Teflon-AF) that closely matches the refractive index of the solution of interest. The structure supports two surface plasmon modes excited at different wavelengths: a symmetric (long-range, LRSP) mode whose fields extend deeper into the solution and an anti-symmetric mode (short-range, SRSP) whose fields are concentrated near the surface of the metal.

Fig. 2.
Fig. 2.

Experimental reflection spectra from a BK7, Teflon AF (430 nm), Au (56 nm) SPR sensor in deionized water with an angle of incidence of approximately 65.5° (inside BK7 prism). The two reflection minima correspond to coupling to the long-range (LRSP) and the short-range (SRSP) surface plasmons. Also shown are theoretical fits to the spectrum using two different data sets for the dielectric constant of gold. Fit 1 uses Johnson and Christy’s values and fit 2 uses values provided by J.A. Woollam Co.

Fig. 3.
Fig. 3.

Optical properties of gold used for optimization. Shown are Johnson and Christies’ data and the fit to this data used for optimization.

Fig. 4.
Fig. 4.

Calculated surface and bulk sensitivities for the long- and short- range surface-plasmon modes of a BK7-Teflon AF-Au sensor illuminated with white light at 65.5° incident angle (inside BK7). Bulk sensitivity is in nm/RIU and surface sensitivity is in nm(wavelength)/nm(thickness).

Fig. 5.
Fig. 5.

Calculated surface and bulk resonance wavelengths, λ 0, and minimum reflectivities, R min, for the long-range (LRSP) and short-range (SRSP) surface-plasmon modes of a BK7-Teflon AF-Au sensor illuminated at a 65.5° incident angle (inside BK7).

Fig. 6.
Fig. 6.

Bulk (a) and surface (b) limits of detection for the dual mode SPR sensor as a function of buffer (Teflon AF) thickness and gold thickness for a source/detector combination with constant power spectral density. (c,d) LODs for the dual mode sensor when interrogated with a tungsten-halogen lamp and Si CCD detector. The angle of incidence is 65.5° inside the BK7 prism. LODs are normalized to the square root of the number of detected photons. Note that the optimal design clearly depends on the illumination and detection system and that the design for optimal surface LOD is almost identical to design for optimal bulk LOD.

Fig. 7.
Fig. 7.

Self-referenced measurement of streptavidin binding to a biotin functionalized gold surface. This experiment illustrates sensor performance for large changes in surface concentration. (a,b) SRSP and LRSP wavelengths vs. time. (c) bulk index change calculated from non-linear model (d) change in surface concentration calculed from nonlinear model. Experiments were conducted in 50mM Tris buffer (1) with 1% glycerol (2) or streptavidin (3) added. (c) and (d) clearly indicate that the dual-mode sensor compensates for changes in bulk index.

Fig. 8.
Fig. 8.

Self-referenced measurement of streptavidin binding to a biotin functionalized gold surface with a large surface concentration of streptavidin already present. This experiment illustrates sensor performance for small changes in surface concentration analyzed using the linear model. (a,b) Resonance wavelength vs. time for the long- and short-range surface plasmon modes. (c,d) Bulk refractive index and relative surface concentration change calculated from (a). Solutions are based on 50mM Tris buffer (1) with 1% glycerol (2) or streptavidin (3) added.

Equations (10)

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k sp ( λ ) = 2 π n p ( λ ) λ sin θ
Δ λ LR = S S LR Δ d + S B LR Δ n B , and
Δ λ SR = S S SR Δ d + S B SR Δ n B ,
Δ d = Δ λ LR S B LR Δ λ SR S B SR S S LR S B LR S S SR S B SR , and
Δ n B = Δ λ LR S S LR Δ λ SR S S SR S B LR S S LR S B SR S S SR .
LOD ( Δ d ) = 3 sqrt [ var ( Δ λ LR ) S B LR 2 + var ( Δ λ SR ) S B SR 2 ( S S LR S B LR S S SR S B SR ) 2 ] , and
LOD ( Δ n B ) = 3 sqrt [ var ( Δ λ LR ) S S LR 2 + var ( Δ λ SR ) S S SR 2 ( S B LR S S LR S B SR S S SR ) 2 ] .
Δ λ LR = S S LR Δ d + S B LR Δ n B + S SB LR Δ d Δ n B , and
Δ λ SR = S S SR Δ d + S B SR Δ n B + S SB SR Δ d Δ n B .
var ( Δ λ 0 ) ( i = 1 N P ( λ i ) [ dR ( λ ) d λ λ = λ i Δ λ 0 ] 2 R ( λ i Δ λ 0 ) ) 1 .

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