Abstract

We address a structure for surface plasmon resonance (SPR) sensing supporting a symmetric bound surface plasmon, which results in a SPR feature narrower by a factor of 2 compared with that for the conventional configuration. We demonstrate that it enables a low-cost and low-power-consumption LED to be used as a polychromatic light source, which leads to a decrease in the sensor cost and an increase in the sensor miniaturization potential. Further, we show that these advancements are not at the expense of sensor performance in terms of its sensitivity and resolution. We show that the sensor can be designed to have similar sensitivity and even better resolution compared with those for a conventional configuration.

© 2006 Optical Society of America

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References

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  1. J. Homola and R. Slavík, "Fiber-optic sensor based on surface plasmon resonance," Electron. Lett. 32, 480-482 (1996).
    [CrossRef]
  2. J. Ctyroký, J. Homola, and M. Skalský, "Tuning of spectral operation range of a waveguide surface plasmon resonance sensor," Electron. Lett. 33, 1246-1248 (1997).
    [CrossRef]
  3. A. V. Kabashin and P. I. Nikitin, "Surface plasmon resonance interferometer for bio- and chemical-sensors," Opt. Commun. 150, 5-8 (1998).
    [CrossRef]
  4. G. G. Nenninger, M. Piliarik, and J. Homola, "Data analysis for optical sensors based on spectroscopy of surface plasmons," Meas. Sci. Technol. 13, 2038-2046 (2002).
    [CrossRef]
  5. K. M. Byun and S. J. Kim, "Design study of highly sensitive nanowire-enhanced surface plasmon resonance biosensors using rigorous coupled wave analysis," Opt. Express 13, 3737-3742 (2005).
    [CrossRef] [PubMed]
  6. B. P. Nelson, T. E. Grimsrud, M. R. Liles, R. M. Goodman, and R. M. Corn, "Surface plasmon resonance imaging measurements of DNA and RNA hybridization adsorption onto DNA microarrays," Anal. Chem. 73, 1-7 (2001).
    [CrossRef] [PubMed]
  7. L. M. Zhang and D. Uttamchandani, "Optical chemical sensing employing surface plasmon resonance," Electron. Lett. 23, 1469-1470 (1988).
    [CrossRef]
  8. A. Suzuki, J. Kondoh, Y. Matsui, S. Shiokawa, and K. Suzuki, "Development of novel optical waveguide surface plasmon resonance (SPR) sensor with dual light emitting diodes," Sens. Actuators B 106, 383-387 (2005).
    [CrossRef]
  9. T. M. Chinowsky, J. G. Quinn, D. U. Bartholomew, R. Kaiser, and J. L. Elkind, "Performance of the Spreeta 2000 integrated surface plasmon resonance affinity sensor," Sens. Actuators B 91, 266-274 (2003).
    [CrossRef]
  10. H. P. Ho, S. Y. Wu, M. Yang, and A. C. Cheung, "Application of white light-emitting diode to surface plasmon resonance sensors," Sens. Actuators B 80, 89-94 (2001).
    [CrossRef]
  11. J. Homola, I. Koudela, and S. S. Yee, "Surface plasmon resonance sensor based on diffraction gratings and prism couplers: sensitivity comparison," Sens. Actuators B 54, 16-24 (1999).
    [CrossRef]
  12. F.-C. Chien and S.-J. Chen, "A sensitivity comparison of optical biosensors based on four different surface plasmon resonance models," Biosens. Bioelectron. 20, 633-642 (2004).
    [CrossRef] [PubMed]
  13. K. Matsubara, S. Kawata, and S. Minami, "Multilayer system for a high-precision surface plasmon resonance sensor," Opt. Lett. 15, 75-77 (1990).
    [CrossRef] [PubMed]
  14. 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]
  15. 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]
  16. H. Raether, Surface Plasmons on Smooth and Rough Surfaces and on Gratings (Springer, 1988), Vol. 111.
  17. J. Chilwell and I. Hodgkinson, "Thin-films field-transfer matrix theory of planar multilayer waveguides and reflection prism-loaded waveguides," J. Opt. Soc. Am. A 1, 742-753 (1984).
    [CrossRef]

2005

A. Suzuki, J. Kondoh, Y. Matsui, S. Shiokawa, and K. Suzuki, "Development of novel optical waveguide surface plasmon resonance (SPR) sensor with dual light emitting diodes," Sens. Actuators B 106, 383-387 (2005).
[CrossRef]

K. M. Byun and S. J. Kim, "Design study of highly sensitive nanowire-enhanced surface plasmon resonance biosensors using rigorous coupled wave analysis," Opt. Express 13, 3737-3742 (2005).
[CrossRef] [PubMed]

2004

F.-C. Chien and S.-J. Chen, "A sensitivity comparison of optical biosensors based on four different surface plasmon resonance models," Biosens. Bioelectron. 20, 633-642 (2004).
[CrossRef] [PubMed]

2003

T. M. Chinowsky, J. G. Quinn, D. U. Bartholomew, R. Kaiser, and J. L. Elkind, "Performance of the Spreeta 2000 integrated surface plasmon resonance affinity sensor," Sens. Actuators B 91, 266-274 (2003).
[CrossRef]

2002

G. G. Nenninger, M. Piliarik, and J. Homola, "Data analysis for optical sensors based on spectroscopy of surface plasmons," Meas. Sci. Technol. 13, 2038-2046 (2002).
[CrossRef]

2001

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]

H. P. Ho, S. Y. Wu, M. Yang, and A. C. Cheung, "Application of white light-emitting diode to surface plasmon resonance sensors," Sens. Actuators B 80, 89-94 (2001).
[CrossRef]

B. P. Nelson, T. E. Grimsrud, M. R. Liles, R. M. Goodman, and R. M. Corn, "Surface plasmon resonance imaging measurements of DNA and RNA hybridization adsorption onto DNA microarrays," Anal. Chem. 73, 1-7 (2001).
[CrossRef] [PubMed]

1999

J. Homola, I. Koudela, and S. S. Yee, "Surface plasmon resonance sensor based on diffraction gratings and prism couplers: sensitivity comparison," Sens. Actuators B 54, 16-24 (1999).
[CrossRef]

1998

A. V. Kabashin and P. I. Nikitin, "Surface plasmon resonance interferometer for bio- and chemical-sensors," Opt. Commun. 150, 5-8 (1998).
[CrossRef]

1997

J. Ctyroký, J. Homola, and M. Skalský, "Tuning of spectral operation range of a waveguide surface plasmon resonance sensor," Electron. Lett. 33, 1246-1248 (1997).
[CrossRef]

1996

J. Homola and R. Slavík, "Fiber-optic sensor based on surface plasmon resonance," Electron. Lett. 32, 480-482 (1996).
[CrossRef]

1990

1988

L. M. Zhang and D. Uttamchandani, "Optical chemical sensing employing surface plasmon resonance," Electron. Lett. 23, 1469-1470 (1988).
[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]

1984

Bartholomew, D. U.

T. M. Chinowsky, J. G. Quinn, D. U. Bartholomew, R. Kaiser, and J. L. Elkind, "Performance of the Spreeta 2000 integrated surface plasmon resonance affinity sensor," Sens. Actuators B 91, 266-274 (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]

Byun, K. M.

Chen, S.-J.

F.-C. Chien and S.-J. Chen, "A sensitivity comparison of optical biosensors based on four different surface plasmon resonance models," Biosens. Bioelectron. 20, 633-642 (2004).
[CrossRef] [PubMed]

Cheung, A. C.

H. P. Ho, S. Y. Wu, M. Yang, and A. C. Cheung, "Application of white light-emitting diode to surface plasmon resonance sensors," Sens. Actuators B 80, 89-94 (2001).
[CrossRef]

Chien, F.-C.

F.-C. Chien and S.-J. Chen, "A sensitivity comparison of optical biosensors based on four different surface plasmon resonance models," Biosens. Bioelectron. 20, 633-642 (2004).
[CrossRef] [PubMed]

Chilwell, J.

Chinowsky, T. M.

T. M. Chinowsky, J. G. Quinn, D. U. Bartholomew, R. Kaiser, and J. L. Elkind, "Performance of the Spreeta 2000 integrated surface plasmon resonance affinity sensor," Sens. Actuators B 91, 266-274 (2003).
[CrossRef]

Corn, R. M.

B. P. Nelson, T. E. Grimsrud, M. R. Liles, R. M. Goodman, and R. M. Corn, "Surface plasmon resonance imaging measurements of DNA and RNA hybridization adsorption onto DNA microarrays," Anal. Chem. 73, 1-7 (2001).
[CrossRef] [PubMed]

Ctyroký, J.

J. Ctyroký, J. Homola, and M. Skalský, "Tuning of spectral operation range of a waveguide surface plasmon resonance sensor," Electron. Lett. 33, 1246-1248 (1997).
[CrossRef]

Elkind, J. L.

T. M. Chinowsky, J. G. Quinn, D. U. Bartholomew, R. Kaiser, and J. L. Elkind, "Performance of the Spreeta 2000 integrated surface plasmon resonance affinity sensor," Sens. Actuators B 91, 266-274 (2003).
[CrossRef]

Goodman, R. M.

B. P. Nelson, T. E. Grimsrud, M. R. Liles, R. M. Goodman, and R. M. Corn, "Surface plasmon resonance imaging measurements of DNA and RNA hybridization adsorption onto DNA microarrays," Anal. Chem. 73, 1-7 (2001).
[CrossRef] [PubMed]

Grimsrud, T. E.

B. P. Nelson, T. E. Grimsrud, M. R. Liles, R. M. Goodman, and R. M. Corn, "Surface plasmon resonance imaging measurements of DNA and RNA hybridization adsorption onto DNA microarrays," Anal. Chem. 73, 1-7 (2001).
[CrossRef] [PubMed]

Ho, H. P.

H. P. Ho, S. Y. Wu, M. Yang, and A. C. Cheung, "Application of white light-emitting diode to surface plasmon resonance sensors," Sens. Actuators B 80, 89-94 (2001).
[CrossRef]

Hodgkinson, I.

Homola, J.

G. G. Nenninger, M. Piliarik, and J. Homola, "Data analysis for optical sensors based on spectroscopy of surface plasmons," Meas. Sci. Technol. 13, 2038-2046 (2002).
[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, I. Koudela, and S. S. Yee, "Surface plasmon resonance sensor based on diffraction gratings and prism couplers: sensitivity comparison," Sens. Actuators B 54, 16-24 (1999).
[CrossRef]

J. Ctyroký, J. Homola, and M. Skalský, "Tuning of spectral operation range of a waveguide surface plasmon resonance sensor," Electron. Lett. 33, 1246-1248 (1997).
[CrossRef]

J. Homola and R. Slavík, "Fiber-optic sensor based on surface plasmon resonance," Electron. Lett. 32, 480-482 (1996).
[CrossRef]

Kabashin, A. V.

A. V. Kabashin and P. I. Nikitin, "Surface plasmon resonance interferometer for bio- and chemical-sensors," Opt. Commun. 150, 5-8 (1998).
[CrossRef]

Kaiser, R.

T. M. Chinowsky, J. G. Quinn, D. U. Bartholomew, R. Kaiser, and J. L. Elkind, "Performance of the Spreeta 2000 integrated surface plasmon resonance affinity sensor," Sens. Actuators B 91, 266-274 (2003).
[CrossRef]

Kawata, S.

Kim, S. J.

Kondoh, J.

A. Suzuki, J. Kondoh, Y. Matsui, S. Shiokawa, and K. Suzuki, "Development of novel optical waveguide surface plasmon resonance (SPR) sensor with dual light emitting diodes," Sens. Actuators B 106, 383-387 (2005).
[CrossRef]

Koudela, I.

J. Homola, I. Koudela, and S. S. Yee, "Surface plasmon resonance sensor based on diffraction gratings and prism couplers: sensitivity comparison," Sens. Actuators B 54, 16-24 (1999).
[CrossRef]

Liles, M. R.

B. P. Nelson, T. E. Grimsrud, M. R. Liles, R. M. Goodman, and R. M. Corn, "Surface plasmon resonance imaging measurements of DNA and RNA hybridization adsorption onto DNA microarrays," Anal. Chem. 73, 1-7 (2001).
[CrossRef] [PubMed]

Matsubara, K.

Matsui, Y.

A. Suzuki, J. Kondoh, Y. Matsui, S. Shiokawa, and K. Suzuki, "Development of novel optical waveguide surface plasmon resonance (SPR) sensor with dual light emitting diodes," Sens. Actuators B 106, 383-387 (2005).
[CrossRef]

Minami, S.

Nelson, B. P.

B. P. Nelson, T. E. Grimsrud, M. R. Liles, R. M. Goodman, and R. M. Corn, "Surface plasmon resonance imaging measurements of DNA and RNA hybridization adsorption onto DNA microarrays," Anal. Chem. 73, 1-7 (2001).
[CrossRef] [PubMed]

Nenninger, G. G.

G. G. Nenninger, M. Piliarik, and J. Homola, "Data analysis for optical sensors based on spectroscopy of surface plasmons," Meas. Sci. Technol. 13, 2038-2046 (2002).
[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]

Nikitin, P. I.

A. V. Kabashin and P. I. Nikitin, "Surface plasmon resonance interferometer for bio- and chemical-sensors," Opt. Commun. 150, 5-8 (1998).
[CrossRef]

Piliarik, M.

G. G. Nenninger, M. Piliarik, and J. Homola, "Data analysis for optical sensors based on spectroscopy of surface plasmons," Meas. Sci. Technol. 13, 2038-2046 (2002).
[CrossRef]

Quinn, J. G.

T. M. Chinowsky, J. G. Quinn, D. U. Bartholomew, R. Kaiser, and J. L. Elkind, "Performance of the Spreeta 2000 integrated surface plasmon resonance affinity sensor," Sens. Actuators B 91, 266-274 (2003).
[CrossRef]

Raether, H.

H. Raether, Surface Plasmons on Smooth and Rough Surfaces and on Gratings (Springer, 1988), Vol. 111.

Shiokawa, S.

A. Suzuki, J. Kondoh, Y. Matsui, S. Shiokawa, and K. Suzuki, "Development of novel optical waveguide surface plasmon resonance (SPR) sensor with dual light emitting diodes," Sens. Actuators B 106, 383-387 (2005).
[CrossRef]

Skalský, M.

J. Ctyroký, J. Homola, and M. Skalský, "Tuning of spectral operation range of a waveguide surface plasmon resonance sensor," Electron. Lett. 33, 1246-1248 (1997).
[CrossRef]

Slavík, R.

J. Homola and R. Slavík, "Fiber-optic sensor based on surface plasmon resonance," Electron. Lett. 32, 480-482 (1996).
[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]

Suzuki, A.

A. Suzuki, J. Kondoh, Y. Matsui, S. Shiokawa, and K. Suzuki, "Development of novel optical waveguide surface plasmon resonance (SPR) sensor with dual light emitting diodes," Sens. Actuators B 106, 383-387 (2005).
[CrossRef]

Suzuki, K.

A. Suzuki, J. Kondoh, Y. Matsui, S. Shiokawa, and K. Suzuki, "Development of novel optical waveguide surface plasmon resonance (SPR) sensor with dual light emitting diodes," Sens. Actuators B 106, 383-387 (2005).
[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]

Uttamchandani, D.

L. M. Zhang and D. Uttamchandani, "Optical chemical sensing employing surface plasmon resonance," Electron. Lett. 23, 1469-1470 (1988).
[CrossRef]

Wu, S. Y.

H. P. Ho, S. Y. Wu, M. Yang, and A. C. Cheung, "Application of white light-emitting diode to surface plasmon resonance sensors," Sens. Actuators B 80, 89-94 (2001).
[CrossRef]

Yang, M.

H. P. Ho, S. Y. Wu, M. Yang, and A. C. Cheung, "Application of white light-emitting diode to surface plasmon resonance sensors," Sens. Actuators B 80, 89-94 (2001).
[CrossRef]

Yee, S. S.

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, I. Koudela, and S. S. Yee, "Surface plasmon resonance sensor based on diffraction gratings and prism couplers: sensitivity comparison," Sens. Actuators B 54, 16-24 (1999).
[CrossRef]

Zhang, L. M.

L. M. Zhang and D. Uttamchandani, "Optical chemical sensing employing surface plasmon resonance," Electron. Lett. 23, 1469-1470 (1988).
[CrossRef]

Anal. Chem.

B. P. Nelson, T. E. Grimsrud, M. R. Liles, R. M. Goodman, and R. M. Corn, "Surface plasmon resonance imaging measurements of DNA and RNA hybridization adsorption onto DNA microarrays," Anal. Chem. 73, 1-7 (2001).
[CrossRef] [PubMed]

Biosens. Bioelectron.

F.-C. Chien and S.-J. Chen, "A sensitivity comparison of optical biosensors based on four different surface plasmon resonance models," Biosens. Bioelectron. 20, 633-642 (2004).
[CrossRef] [PubMed]

Electron. Lett.

J. Homola and R. Slavík, "Fiber-optic sensor based on surface plasmon resonance," Electron. Lett. 32, 480-482 (1996).
[CrossRef]

J. Ctyroký, J. Homola, and M. Skalský, "Tuning of spectral operation range of a waveguide surface plasmon resonance sensor," Electron. Lett. 33, 1246-1248 (1997).
[CrossRef]

L. M. Zhang and D. Uttamchandani, "Optical chemical sensing employing surface plasmon resonance," Electron. Lett. 23, 1469-1470 (1988).
[CrossRef]

J. Opt. Soc. Am. A

Meas. Sci. Technol.

G. G. Nenninger, M. Piliarik, and J. Homola, "Data analysis for optical sensors based on spectroscopy of surface plasmons," Meas. Sci. Technol. 13, 2038-2046 (2002).
[CrossRef]

Opt. Commun.

A. V. Kabashin and P. I. Nikitin, "Surface plasmon resonance interferometer for bio- and chemical-sensors," Opt. Commun. 150, 5-8 (1998).
[CrossRef]

Opt. Express

Opt. Lett.

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]

Sens. Actuators B

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]

A. Suzuki, J. Kondoh, Y. Matsui, S. Shiokawa, and K. Suzuki, "Development of novel optical waveguide surface plasmon resonance (SPR) sensor with dual light emitting diodes," Sens. Actuators B 106, 383-387 (2005).
[CrossRef]

T. M. Chinowsky, J. G. Quinn, D. U. Bartholomew, R. Kaiser, and J. L. Elkind, "Performance of the Spreeta 2000 integrated surface plasmon resonance affinity sensor," Sens. Actuators B 91, 266-274 (2003).
[CrossRef]

H. P. Ho, S. Y. Wu, M. Yang, and A. C. Cheung, "Application of white light-emitting diode to surface plasmon resonance sensors," Sens. Actuators B 80, 89-94 (2001).
[CrossRef]

J. Homola, I. Koudela, and S. S. Yee, "Surface plasmon resonance sensor based on diffraction gratings and prism couplers: sensitivity comparison," Sens. Actuators B 54, 16-24 (1999).
[CrossRef]

Other

H. Raether, Surface Plasmons on Smooth and Rough Surfaces and on Gratings (Springer, 1988), Vol. 111.

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Figures (14)

Fig. 1
Fig. 1

(a) Sensor setup and (b) conventional SP and LLSP chips.

Fig. 2
Fig. 2

Dispersion relations of the materials used. Solid curves, the real parts of the refractive index of A) gold, B) Ta2O5, C) BK7 glass, D) SiO2, E) water, F) Teflon AF. Dashed curves, the imaginary parts of the refractive index of A) gold and B) Ta2O5; it is zero for the rest of the materials.

Fig. 3
Fig. 3

FWHM as a function of the Ta2O5 layer thickness for various gold layer thicknesses assuming perfect collimation.

Fig. 4
Fig. 4

Surface sensitivity as a function of the Ta2O5 layer thickness for various gold layer thicknesses.

Fig. 5
Fig. 5

Bulk sensitivity as a function of the Ta2O5 layer thickness for various gold layer thicknesses.

Fig. 6
Fig. 6

Field profiles [abs(Hy )2, where Hy is transversal magnetic field component parallel to the surface] for various Ta2O5 layer thicknesses. The thickness of Teflon AF is set each time to get optimum coupling, the gold layer is 30 nm thick, and the angle of incidence is set to get the SPR at 760 nm. Zero corresponds to the interface between gold and the medium under study.

Fig. 7
Fig. 7

SPR FWHM as a function of Ta2O5 layer thickness considering an input light divergence of 0.27°. The black points show where the SPR minimum reaches the value of 10%.

Fig. 8
Fig. 8

SPR FWHM as a function of Ta2O5 layer thickness considering an input light divergence of 0.135°. The black points show where the SPR minimum reaches the value of 10%.

Fig. 9
Fig. 9

SPR dips for (a) various Teflon AF thicknesses, Ta2O5 of 30 nm thickness, and for (b) Ta2O5 layer thicknesses of 0, 20, and 40 nm, and the Teflon AF thickness set to get optimum coupling (1180, 850, and 610 nm, respectively). The input light divergence is 0.135°, the gold layer thickness is 30 nm, and the angle of incidence is set to get the SPR at 760 nm.

Fig. 10
Fig. 10

SPR dip for the designed structure consisting of 720 nm of Teflon AF, 30 nm of Ta2O5, and 30 nm of gold (dip at 760 nm), and an identical structure with an additional 21 nm thin silicon dioxide film (dip at 816 nm). The dashed curve is for perfect collimation, and the full curve corresponds to an input light divergence of 0.135°.

Fig. 11
Fig. 11

SPR dips measured on three structures having a Teflon AF layer (a) 670 nm, (b) 719 nm, and (c) 783 nm thick for various angles of incidence. The solid curve shows optimum coupling into the LLSP.

Fig. 12
Fig. 12

SPR dips for the sample shown in Fig. 11(a). The angle of incidence is set to get the SPR at 760 nm (solid curve). The dashed curve is for an identical structure with the SiO2 overlayer.

Fig. 13
Fig. 13

Spectral position of the SPR dip for a medium under study with various refractive indices for the gold-surface structure (solid curve) and for the structure with a 21 nm thick SiO2 overlayer (dashed curve). The numbers refer to the refractive index of the medium under study given at 760 nm. The sensitivities are 7300 and 5800 nm∕RIU, respectively.

Fig. 14
Fig. 14

TE-polarized light (dashed curve) and TM-polarized light (dotted curve) from a LED reflected from the SPR structure and captured by the spectrograph and its fraction—SPR response (solid curve).

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