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Fluorescence upconversion

From EverybodyWiki Bios & Wiki



Fluorescence upconversion (FU) is an ultrafast laser spectroscopic technique. It is a variant of sum-frequency generation (of which the Second-harmonic generation (SHG) is a special case) but applied to the detection of the incoherent fluorescence. It is therefore closely related to the Optical Kerr Gating (OKG) technique. There is, however, some confusion about the term "fluorescence upconversion". Historically, it relates to a non-linear optical technique, which is used to detect transient fluorescence with a very high time-resolution. More recently, the term has been used to describe the sequential absorption of two (or more) photons in a material leading to the emission of light at a shorter wavelength than the excitation wavelength (Photon upconversion). Although related, the two applications should not be confused. Here only the first one will be discussed.

Description

Fluorescence upconversion (FU) is a time-resolved spectroscopic technique which relies on the use of ultrashort laser pulses, typically a hundred femtoseconds or less. It is a pump-probe technique with the two pulses separated in time by a controllable time-delay. The most striking characteristic of FU is that the time resolution is only limited by the laser pulse duration, which today easily is < 100 femtoseconds. Two early technical reviews, written by Jagdeep Shah and Paul Barbara respectively, describe the FU technique in detail [1] [2] Some more recent reviews also describe the technique. [3] [4] [5]

FU setup
Simplified scheme of a fluorescence upconversion setup

Briefly, a fairly strong pump pulse excites the sample, generating the fluorescence (at a frequency νF) which is collected and focused in a nonlinear optical crystal. In parallel, an intense probe pulse (also called gate pulse, at a frequency νG) is focused and superposed with the fluorescence in the crystal. The instantaneous interaction of the fluorescence and the probe pulse in the crystal allows the generation of sum-frequency light at a frequency νS = νG + νF (where ν is the frequency).[1] It is important that the fluorescence and the probe pulses arrive simultaneously (or nearly) in the crystal - to this purpose the probe pulse is directed through a controllable optical Delay stage.

Simply speaking, the probe (gate) pulse represents a "time window" during which the fluorescence is detected. An important advantage of this technique is that the intensity of the detected signal (the sum frequency light) is directly proportional to the intensity of the fluorescence.[6] Since the sum frequency light appears at shorter wavelengths than the fluorescence, a monochromator or an optical filter can be used to suppress both fluorescence and diffused laser light, allowing for a high signal-to-noise ratio when detected, for example, by a photo-multiplier.[1]

History

The first demonstration of the FU technique was reported by Mahr and Hirsch in 1975. [7] They used FU to characterize the 150 picosecond laser pulses generated by a mode-locked argon laser. In contrast, analyzing the red laser pulses emitted from a Rhodamine 6G dye laser pumped by the same argon laser, they found a much longer-lived (several nanoseconds) component, accordingly assigned to spontaneous emission (fluorescence). Soon after, Hirsch and coworkers applied the FU technique to bacteriorhodopsin.[8] Using a picosecond mode-locked dye laser, they measured the emission lifetime of bacteriorhodopsin at physiological temperatures to be 15 +/- 3 ps.

Since then the number of articles using this technique increases steadily every year and today more than 1200 scientific papers can be found (Web of Science 2025, but this is certainly an underestimation).

Among the first applications of FU with sub-picosecond time resolution was the study of polar solvation dynamics. Indeed, the solvent influences the solubility of a solute, the stability of a solution and even the reaction rates of different compounds in solution. The understanding of such solvent effects is fundamental in chemistry. Their equally important dynamics are called solvation dynamics. Briefly, solvation dynamics can in principle be studied by using an "inert" fluorescent probe molecule and follow the evolution of the fluorescence spectrum in time i.e. the Time-Dependent Fluorescence Stokes Shift (TDFSS). With "inert" probe molecule it is understood a molecule that does not undergo any other relaxation processes than solvation, which is far from trivial. Other possible processes that may affect the fluorescence spectrum are, for example vibrational relaxation,[6] photoisomerization,[9] conformational change[10] or charge transfer processes,[11] all of which have also been studied by FU.

Hallidy and Topp were the first to study solvation dynamics using FU. They characterized the temperature-dependence of the evolution of the fluorescence spectrum in terms of interpreted in terms of independent re!axation processes: solvation dynamics and solvent-assisted fluorescence quenching. [12]

Graham Fleming and coworkers pursued the characterization of the Time-Dependent Fluorescence Stokes Shift of chosen fluorescent probe molecules in various low-viscous solvents at room-temperature. They distinguished various solvation processes, from slower long-range diffusional processes to ultrafast inertial effects in the first solvation shell.[13][14]

Another possible origin of the observed Stokes shift is intramolecular vibrational relaxation. The group of Wolfgang Kaiser used FU to study vibrational relaxation processes in polyatomic molecules. [15] The group of Paul Barbara used FU to study solvation dynamics and vibrational relaxation but also excited-state intramolecular proton transfer in various organic molecules.[16]

The polarisation sensitivity of FU (see above) was used by several groups to record the time-dependent fluorescence anisotropy and thereby study the rotational relaxation dynamics of dyes in solution. [17]

FU in the ultraviolet region has been used to study various biomolecules such as proteins. [18] [19] [5] and the very shortlived intrinsic fluorescence of DNA constituents.[20][21][22][23]

Kinetic recordings

By scanning the optical delay (see above) between the fluorescence (i.e. the excitation pulse) and the gating pulse, kinetic traces of the fluorescence at a given wavelength can be obtained. This is the most straight-forward application of fluorescence upconversion. Typically, a mechanical delay stage controlled by a step-motor can be positioned by 1 micrometer steps. Using the formula given above it is easy to show that this corresponds to 6.67 femtoseconds.[citation needed]

Spectral recordings

In general, the FU technique provides a limited spectral bandwidth (<10 nm), much less than that of the probed fluorescence (> 100 nm). In order to monitor the time-evolution of the full fluorescence spectrum several approaches are used.

The most widely used method is to reconstruct the time-resolved fluorescence spectrum a posteriori from a number of individual kinetic traces recorded at different wavelengths.[24]

The major problem for making a direct recording of a broad fluorescence spectrum is the group-velocity dispersion; different wavelengths propagate with different velocities through the optical components (filters, lenses, crystal,..). The difference in arrival time in the crystal of the "blue" and "red" components of the fluorescence spectrum may amount to several hundreds of femtoseconds.

A step-wise scanning approach has been developed, where the monochromator is positioned in wavelength while the phase-matching angle is optimized and the optical delay adjusted for the group-velocity difference for each wavelength.[25]

Broadband detection of the upconversion signal can in principle be obtained with a spectrograph equipped with a CCD camera. However, as mentioned above, the limited bandwidth of the crystal does not allow to cover the whole fluorescence spectrum. An elegant approach to overcome is to rapidly rotate the crystal during the measuring time. [26][27] The broad spectrum recorded for a given delay time must however be corrected for the group velocity dispersion.

A much more advanced approach has been developed by Ernsting and coll. who adjust the wavelength-dependent angular dispersion of the focused fluorescence in order to fulfill phase-matching conditions over a wide spectral range.[28]

FU imaging

Femtosecond Lifetime Imaging using FU has been reported. [5] Space-resolved fluorescence decays of different tryptophan residues in a fluorescent protein were recorded on the picosecond timescale.

Caution

As mentioned in the beginning fluorescence upconversion should not be confused with photon upconversion, sometimes called upconversion fluorescence.[29] While FU is an instantaneous interaction between the fluorescence, the probe-pulse and the sum-frequency light in the nonlinear crystal, photon upconversion is based on the sequential absorption of two (or more) photons in an optical material leading to light emission at shorter wavelength than the excitation light but at a (much) later time.[29]

References

  1. ↑ 1.0 1.1 1.2 Shah, J. (1988). "Ultrafast luminescence spectroscopy using sum frequency generation". IEEE J. Quant. Electron. 24 (2): 276–288. Bibcode:1988IJQE...24..276S. doi:10.1109/3.124.
  2. ↑ Kahlow, M. A.; Jarzeba, W.; DuBruil, T. P.; Barbara, P. F. (1988). "Ultrafast emission spectroscopy in the ultraviolet by time-gated upconversion". Rev. Sci. Instrum. 59 (7): 1098–1109. Bibcode:1988RScI...59.1098K. doi:10.1063/1.1139734.
  3. ↑ Mialocq, J.-C.; Gustavsson, T. (2001). "Investigation of Femtosecond Chemical Reactivity by Means of Fluorescence Up-Conversion". In Valeur, B.; Brochon, J.-C. New Trends in Fluorescence Spectroscopy. Springer Series on Fluorescence. 1. Springer. pp. 61–80. doi:10.1007/978-3-642-56853-4_4. ISBN 978-3-642-63214-3. Search this book on
  4. ↑ Lemmetyinen, H.; Tkachenko, N. V.; Valeur, B.; Hotta, J.-I.; Ameloot, M.; Ernsting, N. P.; Gustavsson, T.; Boens, T. (2014). "Time-resolved fluorescence methods". Pure Appl. Chem. 86 (12): 1969–1998. doi:10.1515/pac-2013-0912.
  5. ↑ 5.0 5.1 5.2 Chosrowjan, H.; Taniguchi, S.; Tanaka, F. (2015). "Ultrafast fluorescence upconversion technique and its applications to proteins". The FEBS Journal. 282 (16): 3003–3015. doi:10.1111/febs.13180. PMID 25532707.
  6. ↑ 6.0 6.1 Kopainsky, B; Kaiser, W (1978). "Investigation of intra- and intermolecular transfer processes by picosecond fluorescence gating". Optics Communications. 26 (2): 219–224. Bibcode:1978OptCo..26..219K. doi:10.1016/0030-4018(78)90057-3.
  7. ↑ Mahr, H.; Hirsch, M. D. (1975). "An optical up-conversion light gate with picosecond resolution". Optics Comm. 13 (2): 96–99. Bibcode:1975OptCo..13...96M. doi:10.1016/0030-4018(75)90017-6.
  8. ↑ Hirsch, M.; Marcus, M. A.; Lewis, A.; Mahr, H.; Frigo, N. (1976). "A method for measuring picosecond phenomena in photolabile species" (PDF). Biophysical Journal. 16 (12): 1399–1409. doi:10.1016/S0006-3495(76)85783-9. PMC 1334971. PMID 990393.
  9. ↑ Flom, S. R.; Nagarajan, V.; Barbara, P. F. (1986). "Dynamic solvent effects on large-amplitude isomerisation rates. 1. 2-vinylanthracene". Journal of Physical Chemistry. 90 (10): 2085–2092. doi:10.1021/j100401a022.
  10. ↑ Brown, O. J.; Lopez, S. A.; Fuller, A. O.; Goodson, T. (2007). "Formation and reversible dissociation of coiled coil of peptide to the C-terminus of the HSVB5 protein: A time-resolved spectroscopic analysis". Biophysical Journal. 93 (3): 1068–1078. Bibcode:2007BpJ....93.1068B. doi:10.1529/biophysj.106.100958. PMC 1913165. PMID 17496024.
  11. ↑ Eilers-Koenig, Nina; Kuehne, Thomas; Schwarzer, Dirk; Voehringer, Peter; Schroeder, Joerg (1996). "Femtosecond dynamics of intramolecular charge transfer in 4-dimethylamino-4'-cyanostilbene in polar solvents". Chemical Physics Letters. 253 (1, 2): 69–76. doi:10.1016/0009-2614(96)00237-0. hdl:11858/00-001M-0000-0013-018E-7.
  12. ↑ Hallidy, L. A.; Topp, M. R. (1977). "Direct time-resolution of the Stokes fluorescence shift of a polar molecule in a polar solvent". Chem. Phys. Lett. 48 (1): 40–50. Bibcode:1977CPL....48...40H. doi:10.1016/0009-2614(77)80209-1.
  13. ↑ Castner Jr., E. W.; Maroncelli, M.; Fleming, G. R. (1987). "Subpicosecond resolution studies of solvation dynamics in polar aprotic and alcohol solvents". J. Chem. Phys. 86 (3): 1090–1097. Bibcode:1987JChPh..86.1090C. doi:10.1063/1.452249.
  14. ↑ Jimenez, R.; Fleming, G. R.; Kumar, P. V.; Maroncelli, M. (1994). "Femtosecond solvation dynamics of water". Nature. 369 (6480): 471–473. Bibcode:1994Natur.369..471J. doi:10.1038/369471a0.
  15. ↑ Kopainsky, B.; Kaiser, W. (1978). "Investigation of intra- and intermolecular transfer processes by picosecond fluorescence gating". Optics Comm. 26 (2): 219–224. Bibcode:1978OptCo..26..219K. doi:10.1016/0030-4018(78)90057-3.
  16. ↑ Ding, K.; Courtney, S. J.; Strandjord, A. J.; Flom, S.; Friedrich, D.; Barbara, P. F. (1983). "Excited-state intramolecular proton transfer and vibrational relaxation in 2-(2-hydroxyphenyl)benzothiazole". J. Phys. Chem. 87 (7): 1184–1188. doi:10.1021/j100230a018.
  17. ↑ Beddard, G. S.; Doust, T.; Porter, G. (1981). "Picosecond fluorescence depolarisation measured by frequency conversion". Chem. Phys. 61 (1): 17–23. Bibcode:1981CP.....61...17B. doi:10.1016/0301-0104(81)85044-6.
  18. ↑ Xu, J.; Knutson, J. R. (2008). "Chapter 8 Ultrafast Fluorescence Spectroscopy via Upconversion". Fluorescence Spectroscopy. Methods Enzymol. 450. pp. 159–183. doi:10.1016/S0076-6879(08)03408-3. ISBN 978-0-12-374586-6. PMC 3439200. PMID 19152860. Search this book on
  19. ↑ Biesso, A.; Xu, J.; Knutson, J. R. (2014). "Upconversion Spectrophotofluorometry". Fluorescence Spectroscopy and Microscopy. Methods Mol Biol. 1076. pp. 303–319. doi:10.1007/978-1-62703-649-8_12. ISBN 978-1-62703-648-1. PMC 4196937. PMID 24108631. Search this book on
  20. ↑ Peon, J.; Zewail, A. H. (2001). "DNA/RNA nucleotides and nucleosides: direct measurement of excited-state lifetime s by femtosecond fluorescence up-conversion". Chem. Phys. Lett. 348 (3–4): 255–262. Bibcode:2001CPL...348..255P. doi:10.1016/S0009-2614(01)01128-9.
  21. ↑ Gustavsson, T.; Sharonov, A.; Markovitsi, D. (2002). "Thymine, thymidine and thymidine 5´-monophosphate studied by femtosecond fluorescence upconversion spectroscopy". Chem. Phys. Lett. 351 (3–4): 195–200. doi:10.1016/S0009-2614(01)01375-6.
  22. ↑ Gustavsson, T.; Sharonov, A.; Onidas, D.; Markovitsi, D. (2002). "Adenine, deoxyadenosine and deoxyadenosine 5'-monophosphate studied by femtosecond fluorescence upconversion spectroscopy". Chem. Phys. Lett. 356 (1–2): 49-54. doi:10.1016/S0009-2614(02)00290-7.
  23. ↑ Gustavsson, T.; Banyasz, A.; Lazzarotto, E.; Markovitsii, D. (2006). "Singlet excited-state behavior of uracil and thymine in aqueous solution: a combined experimental and computational study of 11 uracil derivatives". J. Am. Chem. Soc. 128 (2): 607–619. Bibcode:2006JAChS.128..607G. doi:10.1021/ja056181s. PMID 16402849.
  24. ↑ Maroncelli, M.; Fleming, G. R. (1987). "Picosecond solvation dynamics of coumarin 153: the importance of molecular aspects of solvation". J. Chem. Phys. 86 (11): 6221–6239. Bibcode:1987JChPh..86.6221M. doi:10.1063/1.452460.
  25. ↑ Gustavsson, T.; Cassara, L.; Gulbinas, V.; Gurzadyan, G.; Mialocq, J.-C.; Pommeret, S.; Sorgius, M.; van der Meulen, P. (1998). "Femtosecond Spectroscopic Study of Relaxation Processes of Three Amino-Substituted Coumarin Dyes in Methanol and Dimethylsulfoxide". J. Phys. Chem. A. 102 (23): 4229–4245. Bibcode:1998JPCA..102.4229G. doi:10.1021/jp980282d.
  26. ↑ Haacke, S.; Taylor, R. A.; Bar-Joseph, I.; Brasil, M. J. S. P.; Hartig, M.; Deveau, B. (1998). "Improving the signal-to-noise ratio of femtosecond luminescence upconversion by multichannel detection". Journal of the American Optical Society B. 15 (4): 1410–1417. Bibcode:1998JOSAB..15.1410H. doi:10.1364/JOSAB.15.001410.
  27. ↑ Cannizzo, A.; Bräm, O.; Zgrablic, G.; Tortschanoff, A.; Ajdarzadeh Oskouei, A.; van Mourik, F.; Chergui, M. (2007). "Femtosecond fluorescence upconversion setup with broadband detection in the ultraviolet". Optics Letters. 12 (24): 3555–3557. Bibcode:2007OptL...32.3555C. doi:10.1364/OL.32.003555. PMID 18087540.
  28. ↑ Zhang, X. X.; Wurth, C.; Zhao, L.; Resch-Genger, U.; Ernsting, N. P.; Sajadi, M. (2011). "Femtosecond broadband fluorescence upconversion spectroscopy: Improved setup and photometric correction". Rev. Sci. Instrum. 82 (6): 063108–063108–8. Bibcode:2011RScI...82f3108Z. doi:10.1063/1.3597674. PMID 21721675.
  29. ↑ 29.0 29.1 Chatteriee, D. K.; Rufalhah, A. J.; Zhang, Y. (2008). "Upconversion fluorescence imaging of cells and small animals using lanthanide doped nanocrystals". Biomaterials. 29 (7): 937–943. doi:10.1016/j.biomaterials.2007.10.051. PMID 18061257.



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