Abstract

A theoretical analysis and an experimental demonstration are presented to show the increase in collected evanescent fluorescence for a fiber-optic sensor having a high refractive-index (nr), titanium sol-gel, thin-film coating. Simulations indicated that the maximum collected fluorescence should increase and shift to smaller film thicknesses as nr increases and also predicted an interference color-filtering effect. Experimentally, collected fluorescence increased by as much as 6× over that from a bare fused-silica fiber having a numerical aperture of 0.60. Simulations and experimental data were consistent with a decrease in the effective nr as film thickness increases. Electron micrographs of the sol-gel structure supported this observation and showed that the structure differs significantly from that of films formed on a planar glass substrate. High nr, sol-gel thin films are a potentially inexpensive approach to significantly increasing the signal from fiber sensors.

© 1998 Optical Society of America

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References

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  1. H. P. Kao, J. Biwersi, A. S. Verkman, “Fiber optic halide sensor based on fluorescence quenching,” in Fiber Optic Medical and Fluorescent Sensors and Applications, D. R. Hansman, F. P. Milanovich, G. G. Vurek, D. R. Walt, eds., Proc. SPIE1648, 194–201 (1992).
    [CrossRef]
  2. R. P. Ekins, “Competitive, noncompetitive and multianalyte microspot immunoassays,” in Immunochemistry of Solid-Phase Immunoassay, J. E. Butler, ed., (CRC Press, Boca Raton, Fla.,1991), pp. 105–139.
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    [CrossRef]
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    [CrossRef] [PubMed]
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    [CrossRef]
  6. E. H. Hellen, D. Axelrod, “Fluorescence emission at dielectric and metal-film interfaces,” J. Opt. Soc. Am. B 4, 337–350 (1987).
    [CrossRef]
  7. D. Axelrod, T. P. Burghardt, N. L. Thompson, “Total internal reflection fluorescence,” Annu. Rev. Biophys. Bioeng. 13, 247–268 (1984).
    [CrossRef] [PubMed]
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    [CrossRef]
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    [CrossRef]
  10. C. J. Brinker, A. J. Hurd, P. R. Schunk, G. C. Frye, C. S. Ashley, “Review of sol-gel thin film formation,” J. Non-Cryst. Solids 147 and 148, 424–436 (1992).
    [CrossRef]
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  14. N. J. Harrick, Internal Reflection Spectroscopy (Wiley, New York, 1967), pp. 13–63.
  15. R. W. Boyd, Radiometry and the Detection of Optical Radiation (Wiley, New York, 1983), p. 23.
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  17. H. P. Kao, J. S. Schoeniger, “Hollow cylindrical waveguides for use as evanescent fluorescence-based sensors: effect of numerical aperture on collected signal,” Appl. Opt. 36, 8199–8205 (1997).
    [CrossRef]

1997 (1)

1996 (1)

C. A. Browne, D. H. Tarrant, M. S. Olteanu, J. W. Mullens, E. L. Chronister, “Intrinsic sol-gel clad fiber-optic sensors with time-resolved detection,” Anal. Chem. 28, 2289–2295 (1996).
[CrossRef]

1992 (1)

C. J. Brinker, A. J. Hurd, P. R. Schunk, G. C. Frye, C. S. Ashley, “Review of sol-gel thin film formation,” J. Non-Cryst. Solids 147 and 148, 424–436 (1992).
[CrossRef]

1987 (2)

1985 (1)

J. D. Andrade, R. A. Van Wagenan, D. E. Gregonis, K. Newby, J. N. Lin, “Remote fiber-optic biosensors based on evanescent-excited fluoro-immunoassay: concept and progress,” IEEE Trans. Electron Devices 32, 1175–1179 (1985).
[CrossRef]

1984 (1)

D. Axelrod, T. P. Burghardt, N. L. Thompson, “Total internal reflection fluorescence,” Annu. Rev. Biophys. Bioeng. 13, 247–268 (1984).
[CrossRef] [PubMed]

1981 (1)

C. J. Brinker, M. S. Harrington, “Sol-gel derived antireflective coatings for silicon,” Sol. Energy Mater. 5, 159–172 (1981).
[CrossRef]

1979 (1)

1972 (1)

Andrade, J. D.

J. D. Andrade, R. A. Van Wagenan, D. E. Gregonis, K. Newby, J. N. Lin, “Remote fiber-optic biosensors based on evanescent-excited fluoro-immunoassay: concept and progress,” IEEE Trans. Electron Devices 32, 1175–1179 (1985).
[CrossRef]

Ashley, C. S.

C. J. Brinker, A. J. Hurd, P. R. Schunk, G. C. Frye, C. S. Ashley, “Review of sol-gel thin film formation,” J. Non-Cryst. Solids 147 and 148, 424–436 (1992).
[CrossRef]

Ashley, Carol S.

Carol S. Ashley, Sandia National Laboratories, Albuquerque, N. Mex. 87185-1349 (personal communication, 1997).

Axelrod, D.

E. H. Hellen, D. Axelrod, “Fluorescence emission at dielectric and metal-film interfaces,” J. Opt. Soc. Am. B 4, 337–350 (1987).
[CrossRef]

D. Axelrod, T. P. Burghardt, N. L. Thompson, “Total internal reflection fluorescence,” Annu. Rev. Biophys. Bioeng. 13, 247–268 (1984).
[CrossRef] [PubMed]

Benner, R. E.

Biwersi, J.

H. P. Kao, J. Biwersi, A. S. Verkman, “Fiber optic halide sensor based on fluorescence quenching,” in Fiber Optic Medical and Fluorescent Sensors and Applications, D. R. Hansman, F. P. Milanovich, G. G. Vurek, D. R. Walt, eds., Proc. SPIE1648, 194–201 (1992).
[CrossRef]

Born, M.

M. Born, E. Wolf, Principles of Optics, 6th ed. (Pergamon, Oxford, UK, 1980), p. 62.

Boyd, R. W.

R. W. Boyd, Radiometry and the Detection of Optical Radiation (Wiley, New York, 1983), p. 23.

Brinker, C. J.

C. J. Brinker, A. J. Hurd, P. R. Schunk, G. C. Frye, C. S. Ashley, “Review of sol-gel thin film formation,” J. Non-Cryst. Solids 147 and 148, 424–436 (1992).
[CrossRef]

C. J. Brinker, M. S. Harrington, “Sol-gel derived antireflective coatings for silicon,” Sol. Energy Mater. 5, 159–172 (1981).
[CrossRef]

Browne, C. A.

C. A. Browne, D. H. Tarrant, M. S. Olteanu, J. W. Mullens, E. L. Chronister, “Intrinsic sol-gel clad fiber-optic sensors with time-resolved detection,” Anal. Chem. 28, 2289–2295 (1996).
[CrossRef]

Burghardt, T. P.

D. Axelrod, T. P. Burghardt, N. L. Thompson, “Total internal reflection fluorescence,” Annu. Rev. Biophys. Bioeng. 13, 247–268 (1984).
[CrossRef] [PubMed]

Carniglia, C. K.

Change, R. K.

Chronister, E. L.

C. A. Browne, D. H. Tarrant, M. S. Olteanu, J. W. Mullens, E. L. Chronister, “Intrinsic sol-gel clad fiber-optic sensors with time-resolved detection,” Anal. Chem. 28, 2289–2295 (1996).
[CrossRef]

Drexhage, K. H.

Ekins, R. P.

R. P. Ekins, “Competitive, noncompetitive and multianalyte microspot immunoassays,” in Immunochemistry of Solid-Phase Immunoassay, J. E. Butler, ed., (CRC Press, Boca Raton, Fla.,1991), pp. 105–139.

Fenn, J. B.

Frye, G. C.

C. J. Brinker, A. J. Hurd, P. R. Schunk, G. C. Frye, C. S. Ashley, “Review of sol-gel thin film formation,” J. Non-Cryst. Solids 147 and 148, 424–436 (1992).
[CrossRef]

Glass, T. R.

Gregonis, D. E.

J. D. Andrade, R. A. Van Wagenan, D. E. Gregonis, K. Newby, J. N. Lin, “Remote fiber-optic biosensors based on evanescent-excited fluoro-immunoassay: concept and progress,” IEEE Trans. Electron Devices 32, 1175–1179 (1985).
[CrossRef]

Harrick, N. J.

N. J. Harrick, Internal Reflection Spectroscopy (Wiley, New York, 1967), pp. 13–63.

Harrington, M. S.

C. J. Brinker, M. S. Harrington, “Sol-gel derived antireflective coatings for silicon,” Sol. Energy Mater. 5, 159–172 (1981).
[CrossRef]

Heavens, O. S.

O. S. Heavens, Optical Properties of Thin Solid Films (Dover, New York, 1991), p. 57.

Hellen, E. H.

Hirschfeld, T.

Hurd, A. J.

C. J. Brinker, A. J. Hurd, P. R. Schunk, G. C. Frye, C. S. Ashley, “Review of sol-gel thin film formation,” J. Non-Cryst. Solids 147 and 148, 424–436 (1992).
[CrossRef]

Kao, H. P.

H. P. Kao, J. S. Schoeniger, “Hollow cylindrical waveguides for use as evanescent fluorescence-based sensors: effect of numerical aperture on collected signal,” Appl. Opt. 36, 8199–8205 (1997).
[CrossRef]

H. P. Kao, J. Biwersi, A. S. Verkman, “Fiber optic halide sensor based on fluorescence quenching,” in Fiber Optic Medical and Fluorescent Sensors and Applications, D. R. Hansman, F. P. Milanovich, G. G. Vurek, D. R. Walt, eds., Proc. SPIE1648, 194–201 (1992).
[CrossRef]

Lackie, S.

Lee, E.-H.

Lin, J. N.

J. D. Andrade, R. A. Van Wagenan, D. E. Gregonis, K. Newby, J. N. Lin, “Remote fiber-optic biosensors based on evanescent-excited fluoro-immunoassay: concept and progress,” IEEE Trans. Electron Devices 32, 1175–1179 (1985).
[CrossRef]

Mandel, L.

Mullens, J. W.

C. A. Browne, D. H. Tarrant, M. S. Olteanu, J. W. Mullens, E. L. Chronister, “Intrinsic sol-gel clad fiber-optic sensors with time-resolved detection,” Anal. Chem. 28, 2289–2295 (1996).
[CrossRef]

Newby, K.

J. D. Andrade, R. A. Van Wagenan, D. E. Gregonis, K. Newby, J. N. Lin, “Remote fiber-optic biosensors based on evanescent-excited fluoro-immunoassay: concept and progress,” IEEE Trans. Electron Devices 32, 1175–1179 (1985).
[CrossRef]

Olteanu, M. S.

C. A. Browne, D. H. Tarrant, M. S. Olteanu, J. W. Mullens, E. L. Chronister, “Intrinsic sol-gel clad fiber-optic sensors with time-resolved detection,” Anal. Chem. 28, 2289–2295 (1996).
[CrossRef]

Schoeniger, J. S.

Schunk, P. R.

C. J. Brinker, A. J. Hurd, P. R. Schunk, G. C. Frye, C. S. Ashley, “Review of sol-gel thin film formation,” J. Non-Cryst. Solids 147 and 148, 424–436 (1992).
[CrossRef]

Tarrant, D. H.

C. A. Browne, D. H. Tarrant, M. S. Olteanu, J. W. Mullens, E. L. Chronister, “Intrinsic sol-gel clad fiber-optic sensors with time-resolved detection,” Anal. Chem. 28, 2289–2295 (1996).
[CrossRef]

Thompson, N. L.

D. Axelrod, T. P. Burghardt, N. L. Thompson, “Total internal reflection fluorescence,” Annu. Rev. Biophys. Bioeng. 13, 247–268 (1984).
[CrossRef] [PubMed]

Van Wagenan, R. A.

J. D. Andrade, R. A. Van Wagenan, D. E. Gregonis, K. Newby, J. N. Lin, “Remote fiber-optic biosensors based on evanescent-excited fluoro-immunoassay: concept and progress,” IEEE Trans. Electron Devices 32, 1175–1179 (1985).
[CrossRef]

Verkman, A. S.

H. P. Kao, J. Biwersi, A. S. Verkman, “Fiber optic halide sensor based on fluorescence quenching,” in Fiber Optic Medical and Fluorescent Sensors and Applications, D. R. Hansman, F. P. Milanovich, G. G. Vurek, D. R. Walt, eds., Proc. SPIE1648, 194–201 (1992).
[CrossRef]

Wolf, E.

M. Born, E. Wolf, Principles of Optics, 6th ed. (Pergamon, Oxford, UK, 1980), p. 62.

Anal. Chem. (1)

C. A. Browne, D. H. Tarrant, M. S. Olteanu, J. W. Mullens, E. L. Chronister, “Intrinsic sol-gel clad fiber-optic sensors with time-resolved detection,” Anal. Chem. 28, 2289–2295 (1996).
[CrossRef]

Annu. Rev. Biophys. Bioeng. (1)

D. Axelrod, T. P. Burghardt, N. L. Thompson, “Total internal reflection fluorescence,” Annu. Rev. Biophys. Bioeng. 13, 247–268 (1984).
[CrossRef] [PubMed]

Appl. Opt. (3)

IEEE Trans. Electron Devices (1)

J. D. Andrade, R. A. Van Wagenan, D. E. Gregonis, K. Newby, J. N. Lin, “Remote fiber-optic biosensors based on evanescent-excited fluoro-immunoassay: concept and progress,” IEEE Trans. Electron Devices 32, 1175–1179 (1985).
[CrossRef]

J. Non-Cryst. Solids (1)

C. J. Brinker, A. J. Hurd, P. R. Schunk, G. C. Frye, C. S. Ashley, “Review of sol-gel thin film formation,” J. Non-Cryst. Solids 147 and 148, 424–436 (1992).
[CrossRef]

J. Opt. Soc. Am. (1)

J. Opt. Soc. Am. B (1)

Sol. Energy Mater. (1)

C. J. Brinker, M. S. Harrington, “Sol-gel derived antireflective coatings for silicon,” Sol. Energy Mater. 5, 159–172 (1981).
[CrossRef]

Other (7)

M. Born, E. Wolf, Principles of Optics, 6th ed. (Pergamon, Oxford, UK, 1980), p. 62.

O. S. Heavens, Optical Properties of Thin Solid Films (Dover, New York, 1991), p. 57.

N. J. Harrick, Internal Reflection Spectroscopy (Wiley, New York, 1967), pp. 13–63.

R. W. Boyd, Radiometry and the Detection of Optical Radiation (Wiley, New York, 1983), p. 23.

Carol S. Ashley, Sandia National Laboratories, Albuquerque, N. Mex. 87185-1349 (personal communication, 1997).

H. P. Kao, J. Biwersi, A. S. Verkman, “Fiber optic halide sensor based on fluorescence quenching,” in Fiber Optic Medical and Fluorescent Sensors and Applications, D. R. Hansman, F. P. Milanovich, G. G. Vurek, D. R. Walt, eds., Proc. SPIE1648, 194–201 (1992).
[CrossRef]

R. P. Ekins, “Competitive, noncompetitive and multianalyte microspot immunoassays,” in Immunochemistry of Solid-Phase Immunoassay, J. E. Butler, ed., (CRC Press, Boca Raton, Fla.,1991), pp. 105–139.

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Figures (8)

Fig. 1
Fig. 1

Structure of a fiber-optic sensor having a sol-gel, thin-film coating.

Fig. 2
Fig. 2

Coordinate system for describing the path of a light ray in the fiber-optic sensor.

Fig. 3
Fig. 3

Schematic of epifluorescence optical setup for excitation and collection of fluorescence and the preparation of the sensor.

Fig. 4
Fig. 4

Dependence of collected fluorescence on excitation and collection optics N.A. for different film refractive indices and thicknesses. Numerical simulations are shown for a fiber having no thin film (solid curve), a 20-nm film and nr=2.1 (long-dashed curve), and a 120-nm film and nr=1.8 (short-dashed curve). Experimental data points are the average±sample standard deviation for three fiber film thicknesses of 0 nm (crosses), 16 nm (filled circles), and 119 nm (open circles). Numerical simulations were carried out by assuming average excitation and emission wavelengths at 600 and 690 nm, respectively: All data are normalized to the value measured for the sample at N.A.=0.6.

Fig. 5
Fig. 5

Dependence of collected fluorescence on film thickness and refractive index. A, Numerical simulations (solid curves) and experimental data at N.A.=0.6 and B, N.A.=0.4. Numerical simulations were carried out by assuming average excitation and emission wavelengths at 600 and 690 nm, respectively. Each data point is the average±sample standard deviation of three fibers.

Fig. 6
Fig. 6

Thickness of different sol-gel thin films. A, FESEM images of thin films fabricated from an indicated number of sol-gel coats. Unless otherwise indicated, thin films were fabricated on the surface of a 400-µm diameter fused-silica fiber optic. The scale indicated in the lower right micrograph is the same for all images. B, Measured thickness as a function of number of coatings. Thicknesses were measured along the crystal grain of the thin film and corrected for the viewing angle of 20°. Data points are mean±sample standard deviation of five measurements taken from a single scanning electron-micrograph image. Note that for some data points the error bars are smaller than the marker.

Fig. 7
Fig. 7

Crystallinity and porosity of sol-gel films. A, HRTEM image of a section of 10-sol-coat fiber demonstrates porosity at the center of the film but not at the surface. The bottom of the image is the fused-silica fiber core, and the central band is the sol layer. The arrow indicates boundary of the porous zone within the sol layer. The thickness of this section is reduced in comparison with those in Fig. 6 by damage associated with ion-milling sectioning. B, 10× magnification of the boxed area in A, shows polycrystalline microdomains within the film. C, FESEM images of sol-gel films at 5- and 15-coat thicknesses. The scale indicated in the lower right micrograph is the same for both images. Image resolution was 2 nm.

Fig. 8
Fig. 8

Dependence of the collected fluorescence on the fluorescence excitation and emission wavelengths. Numerical simulations at N.A.=0.6 for the collected fluorescence as a function of film thickness are shown for fluorescein (average wavelengths assumed for simulations: excitation=490 nm, emission=530 nm), rhodamine (555 nm, 580 nm), and Cy 5 (600 nm, 690 nm). The refractive index of the film was taken as 2.1.

Equations (13)

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S=kAeEc,
N(r, α, β)=L tan(α)2a{1-[(r/a)sin β]2}1/2,
cos(η)=sin(α){1-[(r/a)sin β]2}1/2.
sin(θ)=(ncore/nfilm)sin(η).
|T(θ)|V2=nsamplencore|tV(θ)|2,
|T(θ)|H2=nsamplencore|tH(θ)|2(sin2 θ-cos2 θ),
tV,H(θ)=tcorefilmV,H(η)tfilmsampleV,H(θ)exp[i(2nfilmhπ(cosθ)/λ)]1+rcorefilmV,H(η)rfilmsampleV,H(θ)exp[i(4nfilmhπ(cosθ)/λ)],
|T(θ)|avg2=nsample2ncore[|tV(θ)|2+|tH(θ)|2(sin2 θ-cos2 θ)].
Ievanescent|T(θ)|avg2 exp(-2x/dp),
Ae(αmax)
0θ0N(r, α, β)Pi|T(θ)|avg2 exp(-2x/dp)dxdθ0αmax02π0ar×sin2 α{[1-(r sin β/a)2][sin2 θ-(nsample/nfilm)2]}1/2×|T(θ)|avg2drdβdα.
Ec(αmax)
0θ0N(r, α, β)|T(θ)|avg2 exp(-2x/dp)dxdθ0αmax02π0ar ×tan α{[1-(r sin β/a)2][sin2 θ-(nsample/nfilm)2]}1/2×|T(θ)|avg2drdβdα.

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