Abstract

Tryptophan is a fluorescent amino acid common in proteins. Its absorption is largest for wavelengths λ ≲ 290 nm and its fluorescence emissions peak around 300–350 nm, depending upon the local environment. Here we report the observation of red fluorescence near 600 nm emerging from 488-nm continuous-wave (CW) laser photoexcitation of dry tryptophan (Trp) particles. With an excitation intensity below 0.5 kW/cm2, dry Trp particles yield distinctive Raman scattering peaks in the presence of relatively weak and spectrally broad emissions with λ ∼500–700 nm, allowing estimation of particle temperature at low excitation intensities. When the photoexcitation intensity is increased to 1 kW/cm2 or more for a few minutes, fluorescence intensity dramatically increases by more than two orders of magnitude. The fluorescence continues to increase in intensity and gradually shift to the red when photoexcitation intensity and the duration of exposure are increased. The resulting products absorb at visible wavelengths and generate red fluorescence with λ ∼ 650–800 nm with 633-nm CW laser excitation. We attribute the emergence of orange and red fluorescence in the Trp products to a photochemical transformation that is instigated by weak optical transitions to triplet states in Trp with 488-nm excitation and which may be expedited by a photothermal effect.

© 2016 Optical Society of America

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References

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    [Crossref]
  2. C. Pöhlker, J. A. Huffman, and U. Pöschl, “Autofluorescence of atmospheric bioaerosols–fluorescent biomolecules and potential interferences,” Atmos. Meas. Tech. 5, 37–71 (2012).
    [Crossref]
  3. S. C. Hill, R. G. Pinnick, S. Niles, Y.-L. Pan, S. Holler, R. K. Chang, J. Bottiger, B. T. Chen, C.-S. Orr, and G. Feather, “Real-time measurement of fluorescence spectra from single airborne biological particles,” Field Analyt. Chem. Technol. 3, 221–239 (1999).
    [Crossref]
  4. Y.-L. Pan, “Detection and characterization of biological and other organic-carbon aerosol particles in atmosphere using fluorescence,” J. Quant. Spectrosc. Radiat. Transfer 150, 12–35 (2015).
    [Crossref]
  5. J. T. Pelton and L. R. McLean, “Spectroscopic methods for analysis of protein secondary structure,” Anal. Biochem. 277, 167–176 (2000).
    [Crossref] [PubMed]
  6. C.-Y. Huang, G. Balakrishnan, and T. G. Spiro, “Protein secondary structure from deep-UV resonance Raman spectroscopy,” J. Raman Spectrosc. 37, 277–282 (2006).
    [Crossref]
  7. R. Tuma, “Raman spectroscopy of proteins: from peptides to large assemblies,” J. Raman Spectrosc. 36, 307–319 (2005).
    [Crossref]
  8. M. W. Trucksess, “Separation and isolation of trace impurities in L-tryptophan by high-performance liquid chromatography,” J. Chromatogr. 630, 147–150 (1993).
    [Crossref] [PubMed]
  9. S. A. Asher, M. Ludwig, and C. R. Johnson, “Uv resonance raman excitation profiles of the aromatic amino acids,” J. Am. Chem. Soc. 108, 3186–3197 (1986).
    [Crossref]
  10. J. A. Sweeney and S. A. Asher, “Tryptophan UV resonance Raman excitation profiles,” J. Phys. Chem. 94, 4784–4791 (1990).
    [Crossref]
  11. H. Ren, J. D. Biggs, and S. Mukamel, “Two-dimensional stimulated ultraviolet resonance raman spectra of tyrosine and tryptophan; a simulation study,” J. Raman. Spectrosc. 44, 544–559 (2013).
    [Crossref] [PubMed]
  12. A. Campion and P. Kambhampati, “Surface-enhanced Raman scattering,” Chem. Soc. Rev. 27, 241–250 (1998).
    [Crossref]
  13. C. L. Haynes, A. D. McFarland, and R. P. Van Duyne, “Surface-enhanced Raman spectroscopy,” Anal. Chem. 77, 338–346 (2005).
    [Crossref]
  14. A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
    [Crossref]
  15. D. V. Bent and E. Hayon, “Excited state chemistry of aromatic amino acids and related peptides. III. Tryptophan,” J. Am. Chem. Soc. 97, 2612–2619 (1975).
    [Crossref] [PubMed]
  16. D. V. Bent and E. Hayon, “Excited state chemistry of aromatic amino acids and related peptides. I. Tyrosine,” J. Am. Chem. Soc. 97, 2599–2606 (1975).
    [Crossref] [PubMed]
  17. D. V. Bent and E. Hayon, “Excited state chemistry of aromatic amino acids and related peptides. II. Phenylalanine,” J. Am. Chem. Soc. 97, 2606–2612 (1975).
    [Crossref] [PubMed]
  18. J. T. Vivian and P. R. Callis, “Mechanisms of tryptophan fluorescence shifts in proteins,” Biophys. J. 80, 2093–2109 (2001).
    [Crossref] [PubMed]
  19. M. Hospes, J. Hendriks, and K. J. Hellingwerf, “Tryptophan fluorescence as a reporter for structural changes in photoactive yellow protein elicited by photo-activation,” Photochem. Photobiol. Sci. 12, 479–488 (2012).
    [Crossref] [PubMed]
  20. A. B. T. Ghisaidoobe and S. J. Chung, “Intrinsic tryptophan fluorescence in the detection and analysis of proteins: a focus on Förster resonance energy transfer techniques,” Int. J. Mol. Sci. 15, 22518–22538 (2014).
    [Crossref] [PubMed]
  21. N. A. Borisevich and T. F. Raichenok, “Absorption, fluorescence, and fluorescence excitation spectra of free molecules of indole and its derivatives,” J. Appl. Spectrosc. 74, 245–250 (2007).
    [Crossref]
  22. L. I. Grossweiner, “Photochemistry of proteins: a review,” Curr. Eye Res. 3, 137–144 (1984).
    [Crossref] [PubMed]
  23. I. Harada, T. Miura, and H. Takeuchi, “Origin of the doublet at 1360 and 1340 cm−1 in the Raman spectra of tryptophan and related compounds,” Spectrochim. Acta 42, 307–312 (1986).
    [Crossref]
  24. T. Miura, H. Takeuchi, and I. Harada, “Characterization of individual tryptophan side chains in proteins using Raman spectroscopy and hydrogen-deuterium exchange kinetics,” Biochem. 27, 88–94 (1988).
    [Crossref]
  25. T. Miura, H. Takeuchi, and I. Harada, “Tryptophan Raman bands sensitive to hydrogen bonding and side-chain conformation,” J. Raman Spectrosc. 20, 667–671 (1989).
    [Crossref]
  26. C. R. Johnson, M. Ludwig, and S. A. Asher, “Ultraviolet resonance Raman characterization of photochemical transients of phenol, tyrosine, and tryptophan,” J. Am. Chem. Soc. 108, 905–912 (1986).
    [Crossref]
  27. C.-H. Chuang and Y.-T. Chen, “Raman scattering of L-tryptophan enhanced by surface plasmon of silver nanoparticles: vibrational assignment and structural determination,” J. Raman Spectrosc. 40, 150–156 (2009).
    [Crossref]
  28. H. Takeuchi, “Raman structural markers of tryptophan and histidine side chains in proteins,” Biopolymers 72, 305–317 (2003).
    [Crossref] [PubMed]
  29. H. Rokos, J. M. Wood, S. Hasse, and K. U. Schallreuter, “Identification of epidermal L-tryptophan and its oxidation products by in vivo FT-Raman spectroscopy further supports oxidative stress in patients with vitiligo,” J. Raman Spectrosc. 39, 1214–1218 (2008).
    [Crossref]
  30. J. C. Cuq and J. C. Cheftel, “Tryptophan degradation during heat treatments: Part 1—The degradation of free tryptophan,” Food Chem. 12, 1–14 (1983).
    [Crossref]
  31. D. Creed, “The photophysics and photochemistry of the near-UV absorbing amino acids – I. Tryptophan and its simple derivatives,” Photochem. Photobio. 39, 537–562 (1984).
    [Crossref]
  32. A. Giussani, M. Merchán, D. Roca-Sanjuán, and R. Lindh, “Essential on the photophysics and photochemistry of the indole chromophore by using a totally unconstrained theoretical approach,” J. Chem. Theory Comput. 7, 4088–4096 (2011).
    [Crossref] [PubMed]
  33. P.-S. Song and W. E. Kurtin, “Photochemistry of the model phototropic system involving flavines and indoles. III. A spectroscopic study of the polarized luminescence of indoles,” J. Am. Chem. Soc. 91, 4892–4906 (1969).
    [Crossref]
  34. R. Sakurovs and K. P. Ghiggino, “Temperature dependence of tryptophan and tyrosine luminescence in poly (vinyl alcohol) films,” Aust. J. Chem. 34, 1367–1372 (1981).
    [Crossref]
  35. I. H. Leaver and F. G. Lennox, “Studies on the phtodegradation of tryptophan,” Photochem. Photobiol. 4, 491–497 (1965).
    [Crossref]
  36. J. M. Dyer, S. D. Bringans, and W. G. Bryson, “Characterisation of photo-oxidation products within photoyellowed wool proteins: tryptophan and tyrosine derived chromophores,” Photochem. Photobiol. Sci. 5, 698–706 (2006).
    [Crossref] [PubMed]
  37. N. Igarashi, S. Onoue, and Y. Tsuda, “Photoreactivity of amino acids: tryptophan-induced photochemical events via reactive oxygen species generation,” Anal. Sci. 23, 943–948 (2007).
    [Crossref] [PubMed]
  38. K. Schäfer, D. Goddinger, and H. Höcker, “Photodegradation of tryptophan in wool,” J. Soc. Dyers Colour. 113, 350–355 (2008).
    [Crossref]
  39. A. Pirie, “Fluorescence of N′-formylkynurenine and of protein exposed to sunlight,” Biochem. J. 128, 1365 (1972).
    [Crossref] [PubMed]
  40. T. A. Laurence, J. D. Bude, N. Shen, T. Feldman, P. E. Miller, W. A. Steele, and T. Suratwala, “Metallic-like photoluminescence and absorption in fused silica surface flaws,” Appl. Phys. Lett. 94, 151114 (2009).
    [Crossref]
  41. T. A. Laurence, J. D. Bude, N. Shen, W. A. Steele, and S. Ly, “Quasi-continuum photoluminescence: Unusual broad spectral and temporal characteristics found in defective surfaces of silica and other materials,” J. Appl. Phys. 115, 083501 (2014).
    [Crossref]
  42. T. Jawhari, A. Roid, and J. Casado, “Raman spectroscopic characterization of some commercially available carbon black materials,” Carbon 33, 1561–1565 (1995).
    [Crossref]
  43. M. Lazzeri, S. Piscanec, F. Mauri, A. C. Ferrari, and J. Robertson, “Phonon linewidths and electron-phonon coupling in graphite and nanotubes,” Phys. Rev. B 73, 155426 (2006).
    [Crossref]
  44. G. Nishikawa, M. Shioya, N. Iwashita, and Y. Kawahara, “Carbonization behavior of L-tryptophan and gluten,” J. Mater. Sci. 42, 2076–2080 (2006).
    [Crossref]
  45. S. Lerman and R. Borkman, “Spectroscopic evaluation and classification of the normal, aging, and cataractous lens,” Ophthalmic Res. 8, 335–353 (1976).
    [Crossref]
  46. D. Balasubramanian, “Ultraviolet radiation and cataract,” J. Ocul. Pharmacol. Ther. 16, 285–297 (2000).
    [Crossref] [PubMed]

2015 (1)

Y.-L. Pan, “Detection and characterization of biological and other organic-carbon aerosol particles in atmosphere using fluorescence,” J. Quant. Spectrosc. Radiat. Transfer 150, 12–35 (2015).
[Crossref]

2014 (2)

A. B. T. Ghisaidoobe and S. J. Chung, “Intrinsic tryptophan fluorescence in the detection and analysis of proteins: a focus on Förster resonance energy transfer techniques,” Int. J. Mol. Sci. 15, 22518–22538 (2014).
[Crossref] [PubMed]

T. A. Laurence, J. D. Bude, N. Shen, W. A. Steele, and S. Ly, “Quasi-continuum photoluminescence: Unusual broad spectral and temporal characteristics found in defective surfaces of silica and other materials,” J. Appl. Phys. 115, 083501 (2014).
[Crossref]

2013 (1)

H. Ren, J. D. Biggs, and S. Mukamel, “Two-dimensional stimulated ultraviolet resonance raman spectra of tyrosine and tryptophan; a simulation study,” J. Raman. Spectrosc. 44, 544–559 (2013).
[Crossref] [PubMed]

2012 (2)

C. Pöhlker, J. A. Huffman, and U. Pöschl, “Autofluorescence of atmospheric bioaerosols–fluorescent biomolecules and potential interferences,” Atmos. Meas. Tech. 5, 37–71 (2012).
[Crossref]

M. Hospes, J. Hendriks, and K. J. Hellingwerf, “Tryptophan fluorescence as a reporter for structural changes in photoactive yellow protein elicited by photo-activation,” Photochem. Photobiol. Sci. 12, 479–488 (2012).
[Crossref] [PubMed]

2011 (1)

A. Giussani, M. Merchán, D. Roca-Sanjuán, and R. Lindh, “Essential on the photophysics and photochemistry of the indole chromophore by using a totally unconstrained theoretical approach,” J. Chem. Theory Comput. 7, 4088–4096 (2011).
[Crossref] [PubMed]

2009 (3)

C.-H. Chuang and Y.-T. Chen, “Raman scattering of L-tryptophan enhanced by surface plasmon of silver nanoparticles: vibrational assignment and structural determination,” J. Raman Spectrosc. 40, 150–156 (2009).
[Crossref]

A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
[Crossref]

T. A. Laurence, J. D. Bude, N. Shen, T. Feldman, P. E. Miller, W. A. Steele, and T. Suratwala, “Metallic-like photoluminescence and absorption in fused silica surface flaws,” Appl. Phys. Lett. 94, 151114 (2009).
[Crossref]

2008 (2)

K. Schäfer, D. Goddinger, and H. Höcker, “Photodegradation of tryptophan in wool,” J. Soc. Dyers Colour. 113, 350–355 (2008).
[Crossref]

H. Rokos, J. M. Wood, S. Hasse, and K. U. Schallreuter, “Identification of epidermal L-tryptophan and its oxidation products by in vivo FT-Raman spectroscopy further supports oxidative stress in patients with vitiligo,” J. Raman Spectrosc. 39, 1214–1218 (2008).
[Crossref]

2007 (2)

N. A. Borisevich and T. F. Raichenok, “Absorption, fluorescence, and fluorescence excitation spectra of free molecules of indole and its derivatives,” J. Appl. Spectrosc. 74, 245–250 (2007).
[Crossref]

N. Igarashi, S. Onoue, and Y. Tsuda, “Photoreactivity of amino acids: tryptophan-induced photochemical events via reactive oxygen species generation,” Anal. Sci. 23, 943–948 (2007).
[Crossref] [PubMed]

2006 (4)

J. M. Dyer, S. D. Bringans, and W. G. Bryson, “Characterisation of photo-oxidation products within photoyellowed wool proteins: tryptophan and tyrosine derived chromophores,” Photochem. Photobiol. Sci. 5, 698–706 (2006).
[Crossref] [PubMed]

M. Lazzeri, S. Piscanec, F. Mauri, A. C. Ferrari, and J. Robertson, “Phonon linewidths and electron-phonon coupling in graphite and nanotubes,” Phys. Rev. B 73, 155426 (2006).
[Crossref]

G. Nishikawa, M. Shioya, N. Iwashita, and Y. Kawahara, “Carbonization behavior of L-tryptophan and gluten,” J. Mater. Sci. 42, 2076–2080 (2006).
[Crossref]

C.-Y. Huang, G. Balakrishnan, and T. G. Spiro, “Protein secondary structure from deep-UV resonance Raman spectroscopy,” J. Raman Spectrosc. 37, 277–282 (2006).
[Crossref]

2005 (2)

R. Tuma, “Raman spectroscopy of proteins: from peptides to large assemblies,” J. Raman Spectrosc. 36, 307–319 (2005).
[Crossref]

C. L. Haynes, A. D. McFarland, and R. P. Van Duyne, “Surface-enhanced Raman spectroscopy,” Anal. Chem. 77, 338–346 (2005).
[Crossref]

2003 (1)

H. Takeuchi, “Raman structural markers of tryptophan and histidine side chains in proteins,” Biopolymers 72, 305–317 (2003).
[Crossref] [PubMed]

2001 (1)

J. T. Vivian and P. R. Callis, “Mechanisms of tryptophan fluorescence shifts in proteins,” Biophys. J. 80, 2093–2109 (2001).
[Crossref] [PubMed]

2000 (2)

J. T. Pelton and L. R. McLean, “Spectroscopic methods for analysis of protein secondary structure,” Anal. Biochem. 277, 167–176 (2000).
[Crossref] [PubMed]

D. Balasubramanian, “Ultraviolet radiation and cataract,” J. Ocul. Pharmacol. Ther. 16, 285–297 (2000).
[Crossref] [PubMed]

1999 (1)

S. C. Hill, R. G. Pinnick, S. Niles, Y.-L. Pan, S. Holler, R. K. Chang, J. Bottiger, B. T. Chen, C.-S. Orr, and G. Feather, “Real-time measurement of fluorescence spectra from single airborne biological particles,” Field Analyt. Chem. Technol. 3, 221–239 (1999).
[Crossref]

1998 (2)

A. Campion and P. Kambhampati, “Surface-enhanced Raman scattering,” Chem. Soc. Rev. 27, 241–250 (1998).
[Crossref]

R. G. Pinnick, S. C. Hill, P. Nachman, G. Videen, G. Chen, and R. K. Chang, “Aerosol fluorescence spectrum analyzer for rapid measurement of single micrometer-sized airborne biological particles,” Aerosol Sci. Technol. 28, 95–104 (1998).
[Crossref]

1995 (1)

T. Jawhari, A. Roid, and J. Casado, “Raman spectroscopic characterization of some commercially available carbon black materials,” Carbon 33, 1561–1565 (1995).
[Crossref]

1993 (1)

M. W. Trucksess, “Separation and isolation of trace impurities in L-tryptophan by high-performance liquid chromatography,” J. Chromatogr. 630, 147–150 (1993).
[Crossref] [PubMed]

1990 (1)

J. A. Sweeney and S. A. Asher, “Tryptophan UV resonance Raman excitation profiles,” J. Phys. Chem. 94, 4784–4791 (1990).
[Crossref]

1989 (1)

T. Miura, H. Takeuchi, and I. Harada, “Tryptophan Raman bands sensitive to hydrogen bonding and side-chain conformation,” J. Raman Spectrosc. 20, 667–671 (1989).
[Crossref]

1988 (1)

T. Miura, H. Takeuchi, and I. Harada, “Characterization of individual tryptophan side chains in proteins using Raman spectroscopy and hydrogen-deuterium exchange kinetics,” Biochem. 27, 88–94 (1988).
[Crossref]

1986 (3)

C. R. Johnson, M. Ludwig, and S. A. Asher, “Ultraviolet resonance Raman characterization of photochemical transients of phenol, tyrosine, and tryptophan,” J. Am. Chem. Soc. 108, 905–912 (1986).
[Crossref]

I. Harada, T. Miura, and H. Takeuchi, “Origin of the doublet at 1360 and 1340 cm−1 in the Raman spectra of tryptophan and related compounds,” Spectrochim. Acta 42, 307–312 (1986).
[Crossref]

S. A. Asher, M. Ludwig, and C. R. Johnson, “Uv resonance raman excitation profiles of the aromatic amino acids,” J. Am. Chem. Soc. 108, 3186–3197 (1986).
[Crossref]

1984 (2)

L. I. Grossweiner, “Photochemistry of proteins: a review,” Curr. Eye Res. 3, 137–144 (1984).
[Crossref] [PubMed]

D. Creed, “The photophysics and photochemistry of the near-UV absorbing amino acids – I. Tryptophan and its simple derivatives,” Photochem. Photobio. 39, 537–562 (1984).
[Crossref]

1983 (1)

J. C. Cuq and J. C. Cheftel, “Tryptophan degradation during heat treatments: Part 1—The degradation of free tryptophan,” Food Chem. 12, 1–14 (1983).
[Crossref]

1981 (1)

R. Sakurovs and K. P. Ghiggino, “Temperature dependence of tryptophan and tyrosine luminescence in poly (vinyl alcohol) films,” Aust. J. Chem. 34, 1367–1372 (1981).
[Crossref]

1976 (1)

S. Lerman and R. Borkman, “Spectroscopic evaluation and classification of the normal, aging, and cataractous lens,” Ophthalmic Res. 8, 335–353 (1976).
[Crossref]

1975 (3)

D. V. Bent and E. Hayon, “Excited state chemistry of aromatic amino acids and related peptides. III. Tryptophan,” J. Am. Chem. Soc. 97, 2612–2619 (1975).
[Crossref] [PubMed]

D. V. Bent and E. Hayon, “Excited state chemistry of aromatic amino acids and related peptides. I. Tyrosine,” J. Am. Chem. Soc. 97, 2599–2606 (1975).
[Crossref] [PubMed]

D. V. Bent and E. Hayon, “Excited state chemistry of aromatic amino acids and related peptides. II. Phenylalanine,” J. Am. Chem. Soc. 97, 2606–2612 (1975).
[Crossref] [PubMed]

1972 (1)

A. Pirie, “Fluorescence of N′-formylkynurenine and of protein exposed to sunlight,” Biochem. J. 128, 1365 (1972).
[Crossref] [PubMed]

1969 (1)

P.-S. Song and W. E. Kurtin, “Photochemistry of the model phototropic system involving flavines and indoles. III. A spectroscopic study of the polarized luminescence of indoles,” J. Am. Chem. Soc. 91, 4892–4906 (1969).
[Crossref]

1965 (1)

I. H. Leaver and F. G. Lennox, “Studies on the phtodegradation of tryptophan,” Photochem. Photobiol. 4, 491–497 (1965).
[Crossref]

Aliaga, A. E.

A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
[Crossref]

Asher, S. A.

J. A. Sweeney and S. A. Asher, “Tryptophan UV resonance Raman excitation profiles,” J. Phys. Chem. 94, 4784–4791 (1990).
[Crossref]

S. A. Asher, M. Ludwig, and C. R. Johnson, “Uv resonance raman excitation profiles of the aromatic amino acids,” J. Am. Chem. Soc. 108, 3186–3197 (1986).
[Crossref]

C. R. Johnson, M. Ludwig, and S. A. Asher, “Ultraviolet resonance Raman characterization of photochemical transients of phenol, tyrosine, and tryptophan,” J. Am. Chem. Soc. 108, 905–912 (1986).
[Crossref]

Balakrishnan, G.

C.-Y. Huang, G. Balakrishnan, and T. G. Spiro, “Protein secondary structure from deep-UV resonance Raman spectroscopy,” J. Raman Spectrosc. 37, 277–282 (2006).
[Crossref]

Balasubramanian, D.

D. Balasubramanian, “Ultraviolet radiation and cataract,” J. Ocul. Pharmacol. Ther. 16, 285–297 (2000).
[Crossref] [PubMed]

Bent, D. V.

D. V. Bent and E. Hayon, “Excited state chemistry of aromatic amino acids and related peptides. III. Tryptophan,” J. Am. Chem. Soc. 97, 2612–2619 (1975).
[Crossref] [PubMed]

D. V. Bent and E. Hayon, “Excited state chemistry of aromatic amino acids and related peptides. I. Tyrosine,” J. Am. Chem. Soc. 97, 2599–2606 (1975).
[Crossref] [PubMed]

D. V. Bent and E. Hayon, “Excited state chemistry of aromatic amino acids and related peptides. II. Phenylalanine,” J. Am. Chem. Soc. 97, 2606–2612 (1975).
[Crossref] [PubMed]

Biggs, J. D.

H. Ren, J. D. Biggs, and S. Mukamel, “Two-dimensional stimulated ultraviolet resonance raman spectra of tyrosine and tryptophan; a simulation study,” J. Raman. Spectrosc. 44, 544–559 (2013).
[Crossref] [PubMed]

Borisevich, N. A.

N. A. Borisevich and T. F. Raichenok, “Absorption, fluorescence, and fluorescence excitation spectra of free molecules of indole and its derivatives,” J. Appl. Spectrosc. 74, 245–250 (2007).
[Crossref]

Borkman, R.

S. Lerman and R. Borkman, “Spectroscopic evaluation and classification of the normal, aging, and cataractous lens,” Ophthalmic Res. 8, 335–353 (1976).
[Crossref]

Bottiger, J.

S. C. Hill, R. G. Pinnick, S. Niles, Y.-L. Pan, S. Holler, R. K. Chang, J. Bottiger, B. T. Chen, C.-S. Orr, and G. Feather, “Real-time measurement of fluorescence spectra from single airborne biological particles,” Field Analyt. Chem. Technol. 3, 221–239 (1999).
[Crossref]

Bringans, S. D.

J. M. Dyer, S. D. Bringans, and W. G. Bryson, “Characterisation of photo-oxidation products within photoyellowed wool proteins: tryptophan and tyrosine derived chromophores,” Photochem. Photobiol. Sci. 5, 698–706 (2006).
[Crossref] [PubMed]

Bryson, W. G.

J. M. Dyer, S. D. Bringans, and W. G. Bryson, “Characterisation of photo-oxidation products within photoyellowed wool proteins: tryptophan and tyrosine derived chromophores,” Photochem. Photobiol. Sci. 5, 698–706 (2006).
[Crossref] [PubMed]

Bude, J. D.

T. A. Laurence, J. D. Bude, N. Shen, W. A. Steele, and S. Ly, “Quasi-continuum photoluminescence: Unusual broad spectral and temporal characteristics found in defective surfaces of silica and other materials,” J. Appl. Phys. 115, 083501 (2014).
[Crossref]

T. A. Laurence, J. D. Bude, N. Shen, T. Feldman, P. E. Miller, W. A. Steele, and T. Suratwala, “Metallic-like photoluminescence and absorption in fused silica surface flaws,” Appl. Phys. Lett. 94, 151114 (2009).
[Crossref]

Callis, P. R.

J. T. Vivian and P. R. Callis, “Mechanisms of tryptophan fluorescence shifts in proteins,” Biophys. J. 80, 2093–2109 (2001).
[Crossref] [PubMed]

Campion, A.

A. Campion and P. Kambhampati, “Surface-enhanced Raman scattering,” Chem. Soc. Rev. 27, 241–250 (1998).
[Crossref]

Campos-Vallette, M. M.

A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
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A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
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T. Jawhari, A. Roid, and J. Casado, “Raman spectroscopic characterization of some commercially available carbon black materials,” Carbon 33, 1561–1565 (1995).
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A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
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S. C. Hill, R. G. Pinnick, S. Niles, Y.-L. Pan, S. Holler, R. K. Chang, J. Bottiger, B. T. Chen, C.-S. Orr, and G. Feather, “Real-time measurement of fluorescence spectra from single airborne biological particles,” Field Analyt. Chem. Technol. 3, 221–239 (1999).
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R. G. Pinnick, S. C. Hill, P. Nachman, G. Videen, G. Chen, and R. K. Chang, “Aerosol fluorescence spectrum analyzer for rapid measurement of single micrometer-sized airborne biological particles,” Aerosol Sci. Technol. 28, 95–104 (1998).
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S. C. Hill, R. G. Pinnick, S. Niles, Y.-L. Pan, S. Holler, R. K. Chang, J. Bottiger, B. T. Chen, C.-S. Orr, and G. Feather, “Real-time measurement of fluorescence spectra from single airborne biological particles,” Field Analyt. Chem. Technol. 3, 221–239 (1999).
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R. G. Pinnick, S. C. Hill, P. Nachman, G. Videen, G. Chen, and R. K. Chang, “Aerosol fluorescence spectrum analyzer for rapid measurement of single micrometer-sized airborne biological particles,” Aerosol Sci. Technol. 28, 95–104 (1998).
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A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
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J. C. Cuq and J. C. Cheftel, “Tryptophan degradation during heat treatments: Part 1—The degradation of free tryptophan,” Food Chem. 12, 1–14 (1983).
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A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
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T. A. Laurence, J. D. Bude, N. Shen, T. Feldman, P. E. Miller, W. A. Steele, and T. Suratwala, “Metallic-like photoluminescence and absorption in fused silica surface flaws,” Appl. Phys. Lett. 94, 151114 (2009).
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M. Lazzeri, S. Piscanec, F. Mauri, A. C. Ferrari, and J. Robertson, “Phonon linewidths and electron-phonon coupling in graphite and nanotubes,” Phys. Rev. B 73, 155426 (2006).
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A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
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A. B. T. Ghisaidoobe and S. J. Chung, “Intrinsic tryptophan fluorescence in the detection and analysis of proteins: a focus on Förster resonance energy transfer techniques,” Int. J. Mol. Sci. 15, 22518–22538 (2014).
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A. Giussani, M. Merchán, D. Roca-Sanjuán, and R. Lindh, “Essential on the photophysics and photochemistry of the indole chromophore by using a totally unconstrained theoretical approach,” J. Chem. Theory Comput. 7, 4088–4096 (2011).
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A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
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I. Harada, T. Miura, and H. Takeuchi, “Origin of the doublet at 1360 and 1340 cm−1 in the Raman spectra of tryptophan and related compounds,” Spectrochim. Acta 42, 307–312 (1986).
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H. Rokos, J. M. Wood, S. Hasse, and K. U. Schallreuter, “Identification of epidermal L-tryptophan and its oxidation products by in vivo FT-Raman spectroscopy further supports oxidative stress in patients with vitiligo,” J. Raman Spectrosc. 39, 1214–1218 (2008).
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S. C. Hill, R. G. Pinnick, S. Niles, Y.-L. Pan, S. Holler, R. K. Chang, J. Bottiger, B. T. Chen, C.-S. Orr, and G. Feather, “Real-time measurement of fluorescence spectra from single airborne biological particles,” Field Analyt. Chem. Technol. 3, 221–239 (1999).
[Crossref]

R. G. Pinnick, S. C. Hill, P. Nachman, G. Videen, G. Chen, and R. K. Chang, “Aerosol fluorescence spectrum analyzer for rapid measurement of single micrometer-sized airborne biological particles,” Aerosol Sci. Technol. 28, 95–104 (1998).
[Crossref]

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K. Schäfer, D. Goddinger, and H. Höcker, “Photodegradation of tryptophan in wool,” J. Soc. Dyers Colour. 113, 350–355 (2008).
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S. C. Hill, R. G. Pinnick, S. Niles, Y.-L. Pan, S. Holler, R. K. Chang, J. Bottiger, B. T. Chen, C.-S. Orr, and G. Feather, “Real-time measurement of fluorescence spectra from single airborne biological particles,” Field Analyt. Chem. Technol. 3, 221–239 (1999).
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M. Hospes, J. Hendriks, and K. J. Hellingwerf, “Tryptophan fluorescence as a reporter for structural changes in photoactive yellow protein elicited by photo-activation,” Photochem. Photobiol. Sci. 12, 479–488 (2012).
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C. Pöhlker, J. A. Huffman, and U. Pöschl, “Autofluorescence of atmospheric bioaerosols–fluorescent biomolecules and potential interferences,” Atmos. Meas. Tech. 5, 37–71 (2012).
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N. Igarashi, S. Onoue, and Y. Tsuda, “Photoreactivity of amino acids: tryptophan-induced photochemical events via reactive oxygen species generation,” Anal. Sci. 23, 943–948 (2007).
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G. Nishikawa, M. Shioya, N. Iwashita, and Y. Kawahara, “Carbonization behavior of L-tryptophan and gluten,” J. Mater. Sci. 42, 2076–2080 (2006).
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T. Jawhari, A. Roid, and J. Casado, “Raman spectroscopic characterization of some commercially available carbon black materials,” Carbon 33, 1561–1565 (1995).
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C. R. Johnson, M. Ludwig, and S. A. Asher, “Ultraviolet resonance Raman characterization of photochemical transients of phenol, tyrosine, and tryptophan,” J. Am. Chem. Soc. 108, 905–912 (1986).
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S. A. Asher, M. Ludwig, and C. R. Johnson, “Uv resonance raman excitation profiles of the aromatic amino acids,” J. Am. Chem. Soc. 108, 3186–3197 (1986).
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G. Nishikawa, M. Shioya, N. Iwashita, and Y. Kawahara, “Carbonization behavior of L-tryptophan and gluten,” J. Mater. Sci. 42, 2076–2080 (2006).
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T. A. Laurence, J. D. Bude, N. Shen, W. A. Steele, and S. Ly, “Quasi-continuum photoluminescence: Unusual broad spectral and temporal characteristics found in defective surfaces of silica and other materials,” J. Appl. Phys. 115, 083501 (2014).
[Crossref]

T. A. Laurence, J. D. Bude, N. Shen, T. Feldman, P. E. Miller, W. A. Steele, and T. Suratwala, “Metallic-like photoluminescence and absorption in fused silica surface flaws,” Appl. Phys. Lett. 94, 151114 (2009).
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M. Lazzeri, S. Piscanec, F. Mauri, A. C. Ferrari, and J. Robertson, “Phonon linewidths and electron-phonon coupling in graphite and nanotubes,” Phys. Rev. B 73, 155426 (2006).
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A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
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Lindh, R.

A. Giussani, M. Merchán, D. Roca-Sanjuán, and R. Lindh, “Essential on the photophysics and photochemistry of the indole chromophore by using a totally unconstrained theoretical approach,” J. Chem. Theory Comput. 7, 4088–4096 (2011).
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Ludwig, M.

C. R. Johnson, M. Ludwig, and S. A. Asher, “Ultraviolet resonance Raman characterization of photochemical transients of phenol, tyrosine, and tryptophan,” J. Am. Chem. Soc. 108, 905–912 (1986).
[Crossref]

S. A. Asher, M. Ludwig, and C. R. Johnson, “Uv resonance raman excitation profiles of the aromatic amino acids,” J. Am. Chem. Soc. 108, 3186–3197 (1986).
[Crossref]

Ly, S.

T. A. Laurence, J. D. Bude, N. Shen, W. A. Steele, and S. Ly, “Quasi-continuum photoluminescence: Unusual broad spectral and temporal characteristics found in defective surfaces of silica and other materials,” J. Appl. Phys. 115, 083501 (2014).
[Crossref]

Mauri, F.

M. Lazzeri, S. Piscanec, F. Mauri, A. C. Ferrari, and J. Robertson, “Phonon linewidths and electron-phonon coupling in graphite and nanotubes,” Phys. Rev. B 73, 155426 (2006).
[Crossref]

McFarland, A. D.

C. L. Haynes, A. D. McFarland, and R. P. Van Duyne, “Surface-enhanced Raman spectroscopy,” Anal. Chem. 77, 338–346 (2005).
[Crossref]

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J. T. Pelton and L. R. McLean, “Spectroscopic methods for analysis of protein secondary structure,” Anal. Biochem. 277, 167–176 (2000).
[Crossref] [PubMed]

Merchán, M.

A. Giussani, M. Merchán, D. Roca-Sanjuán, and R. Lindh, “Essential on the photophysics and photochemistry of the indole chromophore by using a totally unconstrained theoretical approach,” J. Chem. Theory Comput. 7, 4088–4096 (2011).
[Crossref] [PubMed]

Miller, P. E.

T. A. Laurence, J. D. Bude, N. Shen, T. Feldman, P. E. Miller, W. A. Steele, and T. Suratwala, “Metallic-like photoluminescence and absorption in fused silica surface flaws,” Appl. Phys. Lett. 94, 151114 (2009).
[Crossref]

Miura, T.

T. Miura, H. Takeuchi, and I. Harada, “Tryptophan Raman bands sensitive to hydrogen bonding and side-chain conformation,” J. Raman Spectrosc. 20, 667–671 (1989).
[Crossref]

T. Miura, H. Takeuchi, and I. Harada, “Characterization of individual tryptophan side chains in proteins using Raman spectroscopy and hydrogen-deuterium exchange kinetics,” Biochem. 27, 88–94 (1988).
[Crossref]

I. Harada, T. Miura, and H. Takeuchi, “Origin of the doublet at 1360 and 1340 cm−1 in the Raman spectra of tryptophan and related compounds,” Spectrochim. Acta 42, 307–312 (1986).
[Crossref]

Mukamel, S.

H. Ren, J. D. Biggs, and S. Mukamel, “Two-dimensional stimulated ultraviolet resonance raman spectra of tyrosine and tryptophan; a simulation study,” J. Raman. Spectrosc. 44, 544–559 (2013).
[Crossref] [PubMed]

Nachman, P.

R. G. Pinnick, S. C. Hill, P. Nachman, G. Videen, G. Chen, and R. K. Chang, “Aerosol fluorescence spectrum analyzer for rapid measurement of single micrometer-sized airborne biological particles,” Aerosol Sci. Technol. 28, 95–104 (1998).
[Crossref]

Niles, S.

S. C. Hill, R. G. Pinnick, S. Niles, Y.-L. Pan, S. Holler, R. K. Chang, J. Bottiger, B. T. Chen, C.-S. Orr, and G. Feather, “Real-time measurement of fluorescence spectra from single airborne biological particles,” Field Analyt. Chem. Technol. 3, 221–239 (1999).
[Crossref]

Nishikawa, G.

G. Nishikawa, M. Shioya, N. Iwashita, and Y. Kawahara, “Carbonization behavior of L-tryptophan and gluten,” J. Mater. Sci. 42, 2076–2080 (2006).
[Crossref]

Onoue, S.

N. Igarashi, S. Onoue, and Y. Tsuda, “Photoreactivity of amino acids: tryptophan-induced photochemical events via reactive oxygen species generation,” Anal. Sci. 23, 943–948 (2007).
[Crossref] [PubMed]

Orr, C.-S.

S. C. Hill, R. G. Pinnick, S. Niles, Y.-L. Pan, S. Holler, R. K. Chang, J. Bottiger, B. T. Chen, C.-S. Orr, and G. Feather, “Real-time measurement of fluorescence spectra from single airborne biological particles,” Field Analyt. Chem. Technol. 3, 221–239 (1999).
[Crossref]

Osorio-Román, I.

A. E. Aliaga, I. Osorio-Román, P. Leyton, C. Garrido, J. Cárcamo, C. Caniulef, F. Célis, G. Díaz F., E. Clavijo, J. S. Gómez-Jeria, and M. M. Campos-Vallette, “Surface-enhanced Raman scattering study of L-tryptophan,” J. Raman Spectrosc. 40, 164–169 (2009).
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Y.-L. Pan, “Detection and characterization of biological and other organic-carbon aerosol particles in atmosphere using fluorescence,” J. Quant. Spectrosc. Radiat. Transfer 150, 12–35 (2015).
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S. C. Hill, R. G. Pinnick, S. Niles, Y.-L. Pan, S. Holler, R. K. Chang, J. Bottiger, B. T. Chen, C.-S. Orr, and G. Feather, “Real-time measurement of fluorescence spectra from single airborne biological particles,” Field Analyt. Chem. Technol. 3, 221–239 (1999).
[Crossref]

Pelton, J. T.

J. T. Pelton and L. R. McLean, “Spectroscopic methods for analysis of protein secondary structure,” Anal. Biochem. 277, 167–176 (2000).
[Crossref] [PubMed]

Pinnick, R. G.

S. C. Hill, R. G. Pinnick, S. Niles, Y.-L. Pan, S. Holler, R. K. Chang, J. Bottiger, B. T. Chen, C.-S. Orr, and G. Feather, “Real-time measurement of fluorescence spectra from single airborne biological particles,” Field Analyt. Chem. Technol. 3, 221–239 (1999).
[Crossref]

R. G. Pinnick, S. C. Hill, P. Nachman, G. Videen, G. Chen, and R. K. Chang, “Aerosol fluorescence spectrum analyzer for rapid measurement of single micrometer-sized airborne biological particles,” Aerosol Sci. Technol. 28, 95–104 (1998).
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M. Lazzeri, S. Piscanec, F. Mauri, A. C. Ferrari, and J. Robertson, “Phonon linewidths and electron-phonon coupling in graphite and nanotubes,” Phys. Rev. B 73, 155426 (2006).
[Crossref]

Pöhlker, C.

C. Pöhlker, J. A. Huffman, and U. Pöschl, “Autofluorescence of atmospheric bioaerosols–fluorescent biomolecules and potential interferences,” Atmos. Meas. Tech. 5, 37–71 (2012).
[Crossref]

Pöschl, U.

C. Pöhlker, J. A. Huffman, and U. Pöschl, “Autofluorescence of atmospheric bioaerosols–fluorescent biomolecules and potential interferences,” Atmos. Meas. Tech. 5, 37–71 (2012).
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Ren, H.

H. Ren, J. D. Biggs, and S. Mukamel, “Two-dimensional stimulated ultraviolet resonance raman spectra of tyrosine and tryptophan; a simulation study,” J. Raman. Spectrosc. 44, 544–559 (2013).
[Crossref] [PubMed]

Robertson, J.

M. Lazzeri, S. Piscanec, F. Mauri, A. C. Ferrari, and J. Robertson, “Phonon linewidths and electron-phonon coupling in graphite and nanotubes,” Phys. Rev. B 73, 155426 (2006).
[Crossref]

Roca-Sanjuán, D.

A. Giussani, M. Merchán, D. Roca-Sanjuán, and R. Lindh, “Essential on the photophysics and photochemistry of the indole chromophore by using a totally unconstrained theoretical approach,” J. Chem. Theory Comput. 7, 4088–4096 (2011).
[Crossref] [PubMed]

Roid, A.

T. Jawhari, A. Roid, and J. Casado, “Raman spectroscopic characterization of some commercially available carbon black materials,” Carbon 33, 1561–1565 (1995).
[Crossref]

Rokos, H.

H. Rokos, J. M. Wood, S. Hasse, and K. U. Schallreuter, “Identification of epidermal L-tryptophan and its oxidation products by in vivo FT-Raman spectroscopy further supports oxidative stress in patients with vitiligo,” J. Raman Spectrosc. 39, 1214–1218 (2008).
[Crossref]

Sakurovs, R.

R. Sakurovs and K. P. Ghiggino, “Temperature dependence of tryptophan and tyrosine luminescence in poly (vinyl alcohol) films,” Aust. J. Chem. 34, 1367–1372 (1981).
[Crossref]

Schäfer, K.

K. Schäfer, D. Goddinger, and H. Höcker, “Photodegradation of tryptophan in wool,” J. Soc. Dyers Colour. 113, 350–355 (2008).
[Crossref]

Schallreuter, K. U.

H. Rokos, J. M. Wood, S. Hasse, and K. U. Schallreuter, “Identification of epidermal L-tryptophan and its oxidation products by in vivo FT-Raman spectroscopy further supports oxidative stress in patients with vitiligo,” J. Raman Spectrosc. 39, 1214–1218 (2008).
[Crossref]

Shen, N.

T. A. Laurence, J. D. Bude, N. Shen, W. A. Steele, and S. Ly, “Quasi-continuum photoluminescence: Unusual broad spectral and temporal characteristics found in defective surfaces of silica and other materials,” J. Appl. Phys. 115, 083501 (2014).
[Crossref]

T. A. Laurence, J. D. Bude, N. Shen, T. Feldman, P. E. Miller, W. A. Steele, and T. Suratwala, “Metallic-like photoluminescence and absorption in fused silica surface flaws,” Appl. Phys. Lett. 94, 151114 (2009).
[Crossref]

Shioya, M.

G. Nishikawa, M. Shioya, N. Iwashita, and Y. Kawahara, “Carbonization behavior of L-tryptophan and gluten,” J. Mater. Sci. 42, 2076–2080 (2006).
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Figures (6)

Fig. 1
Fig. 1 Raman spectra of solid particles of L-tryptophan. The laser excitation is at 488.0 nm (blue curve) or 632.8 nm (red curve). The excitation powers (intensities) are 2 mW (0.30 kW/cm2) for 488 nm and 5.6 mW (0.53 kW/cm2) for 633 nm, respectively. The Stokes and anti-Stokes Raman scattering peaks at 755 cm−1 are identifiable under both the 488-nm and 633-nm laser excitation, and can be used to determine the effective lattice (phonon) temperature, T*. The mode at ±523 (521) cm−1 is from the silicon substrate. T* ≈ 350–400 K in the powder particles of Trp, and T* ≈ 320–340 K in the silicon substrate. Note that the detection of Raman 521 cm−1 mode from the silicon substrate suggests that the Trp particle is largely transparent under this relatively low photoexcitation intensity. The spectra shown here have not been corrected for the spectral responses of the optical setup, including the collection optics, spectrometer, and CCD, and this may result in relatively small errors in the estimation of the lattice temperature.
Fig. 2
Fig. 2 Imaging Raman spectra. (a–c) sample SA and (d–f) sample SB. The laser excitation spot (∼ 40×20 μm) is ∼2–3 times smaller than the lateral dimensions of sample SA and slightly larger than those of sample SB. (a)&(d) Raman/fluorescence images. The white rectangles represent the region of interest area as defined by the entrance slit of the spectrometer. (b)&(e) Imaging spectra. (c)&(f) Cross-sectional profiles along the vertical direction (Y-position) for selected Raman modes as labeled.
Fig. 3
Fig. 3 (a) Temporal evolution of Raman and fluorescence spectra under 488 nm excitation at P = 14.6 mW (2.2 kW/cm2) (sample SC). The interference fringes in the spectra are due to the notch filter used to reject the scattered excitation laser light. The gap from 2.5 to 2.6 eV in the spectra is due to the notch filter and the scattered laser light is removed for clarity. (b) Spectrally integrated intensity vs. exposure time (Δt). Measurements of two separate particles are shown here: (i) sample SC for P = 14.6 mW (solid circles), and (ii) sample SD for P = 17.5 mW (open circles).
Fig. 4
Fig. 4 Raman scattering and Fluorescence as a function of excitation power P (intensity): P ∼2 mW (0.3 kW/cm2) to 25 mW (3.8 kW/cm2) (sample SB) (a) emission spectra for selected excitation power and exposure time. (b) Spectrally integrated fluorescence intensity vs. P. For P ≳ 5 mW, fluorescence intensity increases with the exposure time (Δt). The arrows indicate the sequence of the measurements for laser excitation spot fixed in a location on SB. There is an approximately 5 min break to keep the particle in darkness when P is increased. The spectrally integrated fluorescence intensity increases nonlinearly with P and Δt.
Fig. 5
Fig. 5 Fluorescence/Raman microscope images of a dry Trp particle (sample SD). (a–b) Bright-field microscope image under white-light illumination of (a) pristine Try particle (sample SD), and (b) same particle after the photochemical transformation by the exposure to 488-nm excitation at P = 17.5 mW for 50 min. (c) 633-nm and (f) 488-nm laser excitation profiles as measured by the emission from the silicon substrate. (d–e) Emission images under 633-nm excitation at P = 3.2 mW: (d) before, and (d) after the photochemical transformation. (g–h) Emission images under 488-nm excitation at P = 2.1 mW: (g) before, and (f) after the photochemical transformation. (i–j) Fluorescence images under 488-nm excitation at P = 17.5 mW: (i) exposure time Δt ∼ 1 min, and (j) Δt ∼ 50 min.
Fig. 6
Fig. 6 Spatially resolved fluorescent spectra of the products of dry tryptophan (sample SC) after exposure of 488-nm excitation at P = 14.6 mW (2.2 kW/cm2) for 60 min. Laser excitation are at P = 5.6 mW for 633 nm and P = 2.1 mW for 488 nm, respectively. The spectra are integrated over an effective area of 3×20 μm2 as illustrated by the rectangles labeled as L, C, and R on the inset fluorescence images. Insets: false-color optical fluorescence and bright filed microscope images of sample SC. (Top) 488-nm excitation, P = 2.2 mW, (Middle) 633-nm excitation, P = 5.6 mW, and (Bottom) white-light illumination.

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