Abstract

The enhancement of a dissolved chemical's Raman scattering by a liquid-core optical fiber (LCOF) geometry is absorption dependent. This dependence leads to a disruption of the usual linear correlation between chemical concentration and Raman peak area. To recover the linearity, we augmented a standard LCOF Raman spectroscopy system with spectrophotometric capabilities, permitting sequential measurements of Raman and absorption spectra within the LCOF. Measurements of samples with identical Raman-scatterer concentrations but different absorption coefficients are described. Using the absorption values, we reduced variations in the measured Raman intensities from 60% to less than 1%. This correction method should be important for LCOF-based Raman spectroscopy of sample sets with variable absorption coefficients, such as urine and blood serum from multiple patients.

© 2006 Optical Society of America

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References

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  1. G. W. Walrafen and J. Stone, "Intensification of spontaneous Raman spectra by use of liquid core optical fibers," Appl. Spectrosc. 26, 585-589 (1972).
    [CrossRef]
  2. E. I. du Pont de Nemours and Company, "Amorphous copolymer of perfluoro-2, 2-dimethyll, 3-dioxole," U.S. patent 4,754,009 (4 September 1988).
  3. R. Altkorn, M. Duval Malinsky, R. P. Van Duyne, and I. Koev, "Intensity considerations in liquid core optical fiber Raman spectroscopy," Appl. Spectrosc. 55, 373-381 (2001).
    [CrossRef]
  4. L. Song, S. Liu, V. Zhelyaskov, and M. A. El-Sayed, "Application of liquid waveguide to Raman spectroscopy in aqueous solution," Appl. Spectrosc. 52, 1364-1367 (1998).
    [CrossRef]
  5. R. Altkorn, I. Koev, R. P. V. Duyne, and M. Litorja, "Low-loss liquid-core optical fiber for low-refractive-index liquids: fabrication, characterization, and application in Raman spectroscopy," Appl. Opt. 36, 8992-8998 (1997).
    [CrossRef]
  6. R. Altkorn, I. Koev, and M. J. Pelletier, "Raman performance characteristics of Teflon-AF 2400 liquid-core optical-fiber sample cells," Appl. Spectrosc. 53, 1169-1176 (1999).
    [CrossRef]
  7. P. Dress and H. Franke, "A cylindrical liquid-core waveguide," Appl. Phys. B 63, 12-19 (1996).
    [CrossRef]
  8. D. Qi and A. J. Berger, "Quantitative analysis of Raman signal enhancement from aqueous samples in liquid core optical fibers," Appl. Spectrosc. 58, 1165-1171 (2004).
    [CrossRef] [PubMed]
  9. M. J. Pelletier and R. Altkorn, "Raman sensitivity enhancement for aqueous protein samples using a liquid core optical-fiber cell," Anal. Chem. 73, 1393-1397 (2001).
    [CrossRef] [PubMed]
  10. D. Qi and A. J. Berger, "Quantitative concentration measurements of creatinine dissovled in water and urine using Raman spectroscopy and a liquid core optical fiber," J. Biomed. Opt. 10, 031115 (2005).
    [CrossRef] [PubMed]
  11. D. M. Haalnd and E. V. Thomas, "Partial least-squares methods for spectral analysis. 1. Relation to other quantitative calibration methods and the extraction of quantitative information," Anal. Chem. 60, 1193-1202 (1988).
    [CrossRef]
  12. D. M. Haaland and E. V. Thomas, "Partial least-squares methods for spectral analysis. 2. Application to simulated and glass spectra data," Anal. Chem. 60, 1202-1208 (1988).
    [CrossRef]
  13. R. Altkorn, I. Koev, and A. Gottlieb, "Waveguide capillary cell for low-refractive-index liquids," Appl. Spectrosc. 51, 1554-1558 (1997).
    [CrossRef]
  14. L. H. Kou, D. Labrie, and P. Chylek, "Refractive indices of water and ice in the 0.65 µm to 2.5 µm spectral range," Appl. Opt. 32, 3531-3540 (1993).
    [CrossRef] [PubMed]

2005 (1)

D. Qi and A. J. Berger, "Quantitative concentration measurements of creatinine dissovled in water and urine using Raman spectroscopy and a liquid core optical fiber," J. Biomed. Opt. 10, 031115 (2005).
[CrossRef] [PubMed]

2004 (1)

2001 (2)

R. Altkorn, M. Duval Malinsky, R. P. Van Duyne, and I. Koev, "Intensity considerations in liquid core optical fiber Raman spectroscopy," Appl. Spectrosc. 55, 373-381 (2001).
[CrossRef]

M. J. Pelletier and R. Altkorn, "Raman sensitivity enhancement for aqueous protein samples using a liquid core optical-fiber cell," Anal. Chem. 73, 1393-1397 (2001).
[CrossRef] [PubMed]

1999 (1)

1998 (1)

1997 (2)

1996 (1)

P. Dress and H. Franke, "A cylindrical liquid-core waveguide," Appl. Phys. B 63, 12-19 (1996).
[CrossRef]

1993 (1)

1988 (2)

D. M. Haalnd and E. V. Thomas, "Partial least-squares methods for spectral analysis. 1. Relation to other quantitative calibration methods and the extraction of quantitative information," Anal. Chem. 60, 1193-1202 (1988).
[CrossRef]

D. M. Haaland and E. V. Thomas, "Partial least-squares methods for spectral analysis. 2. Application to simulated and glass spectra data," Anal. Chem. 60, 1202-1208 (1988).
[CrossRef]

1972 (1)

Altkorn, R.

Berger, A. J.

D. Qi and A. J. Berger, "Quantitative concentration measurements of creatinine dissovled in water and urine using Raman spectroscopy and a liquid core optical fiber," J. Biomed. Opt. 10, 031115 (2005).
[CrossRef] [PubMed]

D. Qi and A. J. Berger, "Quantitative analysis of Raman signal enhancement from aqueous samples in liquid core optical fibers," Appl. Spectrosc. 58, 1165-1171 (2004).
[CrossRef] [PubMed]

Chylek, P.

Dress, P.

P. Dress and H. Franke, "A cylindrical liquid-core waveguide," Appl. Phys. B 63, 12-19 (1996).
[CrossRef]

Duval Malinsky, M.

Duyne, R. P. V.

El-Sayed, M. A.

Franke, H.

P. Dress and H. Franke, "A cylindrical liquid-core waveguide," Appl. Phys. B 63, 12-19 (1996).
[CrossRef]

Gottlieb, A.

Haaland, D. M.

D. M. Haaland and E. V. Thomas, "Partial least-squares methods for spectral analysis. 2. Application to simulated and glass spectra data," Anal. Chem. 60, 1202-1208 (1988).
[CrossRef]

Haalnd, D. M.

D. M. Haalnd and E. V. Thomas, "Partial least-squares methods for spectral analysis. 1. Relation to other quantitative calibration methods and the extraction of quantitative information," Anal. Chem. 60, 1193-1202 (1988).
[CrossRef]

Koev, I.

Kou, L. H.

Labrie, D.

Litorja, M.

Liu, S.

Pelletier, M. J.

M. J. Pelletier and R. Altkorn, "Raman sensitivity enhancement for aqueous protein samples using a liquid core optical-fiber cell," Anal. Chem. 73, 1393-1397 (2001).
[CrossRef] [PubMed]

R. Altkorn, I. Koev, and M. J. Pelletier, "Raman performance characteristics of Teflon-AF 2400 liquid-core optical-fiber sample cells," Appl. Spectrosc. 53, 1169-1176 (1999).
[CrossRef]

Qi, D.

D. Qi and A. J. Berger, "Quantitative concentration measurements of creatinine dissovled in water and urine using Raman spectroscopy and a liquid core optical fiber," J. Biomed. Opt. 10, 031115 (2005).
[CrossRef] [PubMed]

D. Qi and A. J. Berger, "Quantitative analysis of Raman signal enhancement from aqueous samples in liquid core optical fibers," Appl. Spectrosc. 58, 1165-1171 (2004).
[CrossRef] [PubMed]

Song, L.

Stone, J.

Thomas, E. V.

D. M. Haaland and E. V. Thomas, "Partial least-squares methods for spectral analysis. 2. Application to simulated and glass spectra data," Anal. Chem. 60, 1202-1208 (1988).
[CrossRef]

D. M. Haalnd and E. V. Thomas, "Partial least-squares methods for spectral analysis. 1. Relation to other quantitative calibration methods and the extraction of quantitative information," Anal. Chem. 60, 1193-1202 (1988).
[CrossRef]

Van Duyne, R. P.

Walrafen, G. W.

Zhelyaskov, V.

Anal. Chem. (3)

M. J. Pelletier and R. Altkorn, "Raman sensitivity enhancement for aqueous protein samples using a liquid core optical-fiber cell," Anal. Chem. 73, 1393-1397 (2001).
[CrossRef] [PubMed]

D. M. Haalnd and E. V. Thomas, "Partial least-squares methods for spectral analysis. 1. Relation to other quantitative calibration methods and the extraction of quantitative information," Anal. Chem. 60, 1193-1202 (1988).
[CrossRef]

D. M. Haaland and E. V. Thomas, "Partial least-squares methods for spectral analysis. 2. Application to simulated and glass spectra data," Anal. Chem. 60, 1202-1208 (1988).
[CrossRef]

Appl. Opt. (2)

Appl. Phys. B (1)

P. Dress and H. Franke, "A cylindrical liquid-core waveguide," Appl. Phys. B 63, 12-19 (1996).
[CrossRef]

Appl. Spectrosc. (6)

J. Biomed. Opt. (1)

D. Qi and A. J. Berger, "Quantitative concentration measurements of creatinine dissovled in water and urine using Raman spectroscopy and a liquid core optical fiber," J. Biomed. Opt. 10, 031115 (2005).
[CrossRef] [PubMed]

Other (1)

E. I. du Pont de Nemours and Company, "Amorphous copolymer of perfluoro-2, 2-dimethyll, 3-dioxole," U.S. patent 4,754,009 (4 September 1988).

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Figures (5)

Fig. 1
Fig. 1

Schematic of the combined Raman and absorption spectroscopy system, permitting the measurement of backscattered Raman spectra and, separately, determination of absorption coefficients: BPF, bandpass filter; EF, edge filter; DM, dichroic mirror; OF, optical fiber; PM, powermeter, WL, white-light source; M, removable mirror; L's, laser light; R, Raman light; W's, white light. See text for details.

Fig. 2
Fig. 2

Measurement of power attenuation versus propagation distance in the LCOF for determination of reflection coefficient R. Data points are the average of three trials, with associated error bars. The solid curve is the fit of Eq. (5), yielding an R value of R = 0.9966 ± 0.0004.

Fig. 3
Fig. 3

LCOF Raman spectra of two samples of 8% aqueous ethanol from sample set I. System background has been subtracted. The upper spectrum corresponds to the sample with less India ink. The five indicated peaks are ethanol peaks. The starred peak was the peak chosen for the subsequent analysis.

Fig. 4
Fig. 4

Sample set I: relative Raman peak intensities of same ethanol concentration (8%) versus relative ink concentration. (a) Raman peak intensities without correction, (b) measured absorption coefficient at Raman emission wavelength; (c) values after the correction. The Raman peak intensities are normalized to the mean values in each figure. Error bars were calculated from shot noise and system error generated in both spectral acquisition and the correction procedure.

Fig. 5
Fig. 5

Sample set II: relative Raman peak intensities for several ethanol and ink concentrations. Raman peak intensities (a) without correction and (b) after correction. In each subgroup (1, 2, 3), samples have the same ethanol concentration; the ink concentration for each subgroup increases from a to b to c. In each plot the Raman intensity was normalized to the mean for subgroup 1. Error bars were calculated from shot noise and system error, generated in both spectral acquisition and correction.

Equations (5)

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P R ( ν ˜ ) c 1 exp [ ( μ a L + μ a R + 2 μ s ) L ] μ a L + μ a R + 2 μ s A P σ m 0 ,
P corr ( ν ˜ ) = P R ( ν ˜ ) { μ a L + μ a R + 2 μ s 1 exp [ - ( μ a L + μ a R + 2 μ s ) L ] } = c A P σ m 0 .
P sample ( λ ) = P 0 ( λ ) C exp [ μ a ( λ ) L ] = P 0 ( λ ) C exp { [ μ a , W ( λ ) + μ a , C ( λ ) ] L } ,
μ a ( λ ) = μ a , W ( λ ) + 1 L ln [ P water ( λ ) P sample ( λ ) ] .
P ( z ) P ( z = 0 ) = exp ( μ a z ) 2 ( γ z ) 2 exp ( γ z ) [ ( γ z 1 ) + 1 ] ,

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