Abstract

A broadband, multichannel, single-mode, planar waveguide based spectrometer was developed for probing molecular monolayers. A protein sub-monolayer (thickness h ≅ 3 nm, imaginary part of refractive index kl ≤ 0.01) immobilized on the waveguide surface was characterized by the waveguide attenuated total reflection (ATR) spectrometer. A sensitivity enhancement of 4 orders of magnitude, compared to conventional transmission measurements, has been experimentally achieved in the characterization of ultra-thin films. In addition, polarized spectroscopic measurements at the TE and TM waveguide modes were implemented to determine the average orientation angle of the adsorbed molecules. The work developed here is a new research tool for the investigation of some fundamental aspects of molecular films and a novel platform to develop new technological devices of high sensitivity and selectivity such as biosensors.

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References

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  1. J. D. Swalen, D. L. Allara, J. D. Andrade, E. A. Chandross, S. Garoff, J. Israelachvili, T. J. McCarthy, R. Murray, R. F. Pease, J. F. Rabolt, K. J. Wynne and H. Yu, "Molecular monolayers and films," Langmuir 3, 932-950 (1987).
    [CrossRef]
  2. A. N. Parikh and D. L. Allara, "Quantitative determination of molecular structure in multilayer thin films of biaxial and lower symmetry from photon spectroscopies. I. Reflection infrared vibrational spectroscopy," J. Chem. Phys. 96, 927-945 (1992).
    [CrossRef]
  3. J. D. Andrade and V. Hlady, "Protein adsorption and materials biocompatibility: a tutorial review and suggested hypotheses," Advances in Polymer Science 79, 1-63 (1986).
    [CrossRef]
  4. O. S. Wolfbeis, "Fiber-optic sensors in biomedical sciences," Pure & Appl. Chem. 59, 663-672 (1987).
    [CrossRef]
  5. R. E. Dessey, "Waveguides as chemical sensors," Anal. Chem. 61, 1079A-1094A (1989).
  6. M. A. Arnold, "Fiber-optic chemical sensors," Anal. Chem. 64, 1015A-1025A (1992).
  7. S. S. Saavedra and W. M. Reichert, "In situ quantitation of protein adsorption density by integrated optical waveguide attenuated total reflection spectrometry," Langmuir 7, 995-999 (1991).
    [CrossRef]
  8. T. E. Plowman, M. D. Garrison, D. S. Walker and W. M. Reichert, "Surface sensitivity of SiON integrated optical waveguides (IOWs) examined by IOW-attenuated total reflection spectrometry and IOW-Raman spectroscopy," Thin Solid Films 243, 610-615, (1994).
    [CrossRef]
  9. J. D. Swalen, M. Tacke, R. Santo, K. E. Rieckoff and J. Fisher, "Spectra of organic molecules in thin films," Helt. Chim. Acta 61, 960-977 (1978).
    [CrossRef]
  10. D. S. Goldman, P. L. White and N. C. Anheir, "Miniaturized spectrometer employing planar waveguides and grating couplers for chemical analysis," Appl. Opt. 29, 4583-4589 (1990).
    [CrossRef] [PubMed]
  11. C. Piraud, E. K. Mwarania, J. Yao, K. ODwyer, D. J. Schiffrin and J. S. Wilkinson, "Optoelectrochemical transduction on planar optical waveguides," J. Light. Tech. 10, 693-699 (1992).
    [CrossRef]
  12. K. Kato, A. Takatsu, N. Matsuda, R. Azumi and M. Matsumoto, "A slab-optical-waveguide absorption spectroscopy of Langmuir-Blodgett films with a white light excitation source," Chem. Lett. 437-438 (1995).
    [CrossRef]
  13. S. B. Mendes, L. Li, J. J. Burke, J. E. Lee and S. S. Saavedra, "70-nm-bandwidth achromatic waveguide coupler," Appl. Opt. 34, 6180-6186 (1995).
    [CrossRef] [PubMed]
  14. S. B. Mendes, L. Li, J. J. Burke and S. S. Saavedra, "Achromatic prism-coupler for planar waveguide," Opt. Comm. 136, 320-326 (1997).
    [CrossRef]
  15. S. B. Mendes, "Broadband attenuated total reflection spectroscopy in the optical waveguide regime," Ph.D. dissertation, University of Arizona, 1997.
  16. L. Li and J. Brazas, "A method for achromatically coupling a beam of light into a waveguide," U.S. patent 5,420,947 (30 May 1995).
  17. S. B. Mendes, L. Li, J. J. Burke, J. E. Lee, D. R. Dunphy and S. S. Saavedra, "Broad-band attenuated total reflection spectroscopy of a hydrated protein film on a single mode planar waveguide," Langmuir 12, 3374- 3376 (1996).
    [CrossRef]

Other

J. D. Swalen, D. L. Allara, J. D. Andrade, E. A. Chandross, S. Garoff, J. Israelachvili, T. J. McCarthy, R. Murray, R. F. Pease, J. F. Rabolt, K. J. Wynne and H. Yu, "Molecular monolayers and films," Langmuir 3, 932-950 (1987).
[CrossRef]

A. N. Parikh and D. L. Allara, "Quantitative determination of molecular structure in multilayer thin films of biaxial and lower symmetry from photon spectroscopies. I. Reflection infrared vibrational spectroscopy," J. Chem. Phys. 96, 927-945 (1992).
[CrossRef]

J. D. Andrade and V. Hlady, "Protein adsorption and materials biocompatibility: a tutorial review and suggested hypotheses," Advances in Polymer Science 79, 1-63 (1986).
[CrossRef]

O. S. Wolfbeis, "Fiber-optic sensors in biomedical sciences," Pure & Appl. Chem. 59, 663-672 (1987).
[CrossRef]

R. E. Dessey, "Waveguides as chemical sensors," Anal. Chem. 61, 1079A-1094A (1989).

M. A. Arnold, "Fiber-optic chemical sensors," Anal. Chem. 64, 1015A-1025A (1992).

S. S. Saavedra and W. M. Reichert, "In situ quantitation of protein adsorption density by integrated optical waveguide attenuated total reflection spectrometry," Langmuir 7, 995-999 (1991).
[CrossRef]

T. E. Plowman, M. D. Garrison, D. S. Walker and W. M. Reichert, "Surface sensitivity of SiON integrated optical waveguides (IOWs) examined by IOW-attenuated total reflection spectrometry and IOW-Raman spectroscopy," Thin Solid Films 243, 610-615, (1994).
[CrossRef]

J. D. Swalen, M. Tacke, R. Santo, K. E. Rieckoff and J. Fisher, "Spectra of organic molecules in thin films," Helt. Chim. Acta 61, 960-977 (1978).
[CrossRef]

D. S. Goldman, P. L. White and N. C. Anheir, "Miniaturized spectrometer employing planar waveguides and grating couplers for chemical analysis," Appl. Opt. 29, 4583-4589 (1990).
[CrossRef] [PubMed]

C. Piraud, E. K. Mwarania, J. Yao, K. ODwyer, D. J. Schiffrin and J. S. Wilkinson, "Optoelectrochemical transduction on planar optical waveguides," J. Light. Tech. 10, 693-699 (1992).
[CrossRef]

K. Kato, A. Takatsu, N. Matsuda, R. Azumi and M. Matsumoto, "A slab-optical-waveguide absorption spectroscopy of Langmuir-Blodgett films with a white light excitation source," Chem. Lett. 437-438 (1995).
[CrossRef]

S. B. Mendes, L. Li, J. J. Burke, J. E. Lee and S. S. Saavedra, "70-nm-bandwidth achromatic waveguide coupler," Appl. Opt. 34, 6180-6186 (1995).
[CrossRef] [PubMed]

S. B. Mendes, L. Li, J. J. Burke and S. S. Saavedra, "Achromatic prism-coupler for planar waveguide," Opt. Comm. 136, 320-326 (1997).
[CrossRef]

S. B. Mendes, "Broadband attenuated total reflection spectroscopy in the optical waveguide regime," Ph.D. dissertation, University of Arizona, 1997.

L. Li and J. Brazas, "A method for achromatically coupling a beam of light into a waveguide," U.S. patent 5,420,947 (30 May 1995).

S. B. Mendes, L. Li, J. J. Burke, J. E. Lee, D. R. Dunphy and S. S. Saavedra, "Broad-band attenuated total reflection spectroscopy of a hydrated protein film on a single mode planar waveguide," Langmuir 12, 3374- 3376 (1996).
[CrossRef]

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Figures (8)

Fig: 1:
Fig: 1:

The single-mode, broadband, multichannel, planar waveguide based spectrometer. Xe lamp of 150 W, L1 = 10 cm focal length lens, Ir1, Ir2 = iris, Pol = linear polarizer, L2 = 17 cm focal length lens, Pr = prism of LaSF3 and φ = 52.2°, G1, G2, G3 = diffraction gratings, S = fused silica substrate, CCD = thermo-electrically cooled, charge-coupled array detector, L3 = 25.4 mm focal length cylindrical lens. Grating parameters: G1, period = 1.921 μm, depth = 0.34 μm; G2, period = 2.252 μm, depth = 0.12 μm; G3, period = 0.3 μm, depth = 0.12 μm. The distance between the input and output grating couplers is L = 8 mm.

Fig. 2:
Fig. 2:

Schematic representation of the waveguide structure with an absorbing dichroic molecular layer (refractive index nl - i fr kl and thickness h) on the surface of the guiding film.

Fig. 3:
Fig. 3:

Sensitivity vs. waveguide thickness. For the calculations, it was assumed: propagation length L = 1 cm, wavelength λ = 550 nm, waveguide index of refraction nw = 1.56, substrate index of refraction ns = 1.46, real part of the adsorbed layer index of refraction nl = 1.33, cladding index of refraction nc = 1.33. The molecular film is assumed isotropic (fx = fy = fz = 1). The results are for the lowest order waveguide mode and they are independent of the adlayer thickness, h, and absorption coefficient, kl .

Fig. 4:
Fig. 4:

Mismatch in the effective index of couplers and waveguides as described in [13].

Fig. 5:
Fig. 5:

Output intensity of two laser lines for spectral resolution characterization.

Fig. 6:
Fig. 6:

Performance test with a 600-nm bandpass filter measured in a transmission mode by the waveguide based spectrometer shown in Fig. 1 and a conventional transmission spectrophotometer (Cary 5-G).

Fig. 7:
Fig. 7:

Spectrum of cytochrome c adsorbed to the waveguide glass surface acquired.

Fig. 8:
Fig. 8:

Dichroic ratio over a broad spectral range for cytochrome c immobilized on a glass surface.

Equations (4)

Equations on this page are rendered with MathJax. Learn more.

A TE = 4 π k l h λ ln 10 { 2 n l f y ( n w 2 N TE 2 ) N TE ( n w 2 n c 2 ) L t eff , TE }
A TM = 4 π k l h λ ln 10 { 2 n l n w 2 ( n w 2 N TM 2 ) [ f x ( N TM 2 n c 2 ) + f z ( n c n l ) 4 N TM 2 ] N TM [ n w 4 ( N TM 2 n c 2 ) + n c 4 ( n w 2 N TM 2 ) ] L t eff , TM }
Δλ res λ = Λα π ,
Δλ det f .

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