Abstract
To investigate fluorescence lifetime spectroscopy in tissue-like scattering, measurements of phase modulation as a function of modulation frequency were made using two fluorescent dyes exhibiting single exponential decay kinetics in a 2% intralipid solution. To experimentally simulate fluorescence multiexponential decay kinetics, we varied the concentration ratios of the two dyes, 3,3-diethylthiatricarbocyanine iodide and indocynanine green (ICG), which exhibit distinctly different lifetimes of 1.33 and 0.57 ns, respectively. The experimental results were then compared with values predicted using the optical diffusion equation incorporating 1) biexponential decay, 2) average of the biexponential decay, as well as 3) stretched exponential decay kinetic models to describe kinetics owing to independent and quenched relaxation of the two dyes. Our results show that while all kinetic models could describe phase-modulation data in nonscattering solution, when incorporated into the diffusion equation, the kinetic parameters failed to likewise predict phase-modulation data in scattering solutions. We attribute the results to the insensitivity of phase-modulation measurements in nonscattering solutions and the inaccuracy of the derived kinetic parameters. Our results suggest the high sensitivity of phase-modulation measurements in scattering solutions may provide greater opportunities for fluorescence lifetime spectroscopy.
Full Text
The Full Text of this article is available as a PDF (304.3 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Andersson-Engels S., Johansson J., Svanberg K., Svanberg S. Fluorescence imaging and point measurements of tissue: applications to the demarcation of malignant tumors and atherosclerotic lesions from normal tissue. Photochem Photobiol. 1991 Jun;53(6):807–814. doi: 10.1111/j.1751-1097.1991.tb09895.x. [DOI] [PubMed] [Google Scholar]
- Fishkin J. B., Gratton E. Propagation of photon-density waves in strongly scattering media containing an absorbing semi-infinite plane bounded by a straight edge. J Opt Soc Am A. 1993 Jan;10(1):127–140. doi: 10.1364/josaa.10.000127. [DOI] [PubMed] [Google Scholar]
- Gratton E., Limkeman M., Lakowicz J. R., Maliwal B. P., Cherek H., Laczko G. Resolution of mixtures of fluorophores using variable-frequency phase and modulation data. Biophys J. 1984 Oct;46(4):479–486. doi: 10.1016/S0006-3495(84)84044-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hawrysz D. J., Sevick-Muraca E. M. Developments toward diagnostic breast cancer imaging using near-infrared optical measurements and fluorescent contrast agents. Neoplasia. 2000 Sep-Oct;2(5):388–417. doi: 10.1038/sj.neo.7900118. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lakowicz J. R., Laczko G., Cherek H., Gratton E., Limkeman M. Analysis of fluorescence decay kinetics from variable-frequency phase shift and modulation data. Biophys J. 1984 Oct;46(4):463–477. doi: 10.1016/S0006-3495(84)84043-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Russell R. J., Pishko M. V., Gefrides C. C., McShane M. J., Coté G. L. A fluorescence-based glucose biosensor using concanavalin A and dextran encapsulated in a poly(ethylene glycol) hydrogel. Anal Chem. 1999 Aug 1;71(15):3126–3132. doi: 10.1021/ac990060r. [DOI] [PubMed] [Google Scholar]
- Sevick E. M., Chance B., Leigh J., Nioka S., Maris M. Quantitation of time- and frequency-resolved optical spectra for the determination of tissue oxygenation. Anal Biochem. 1991 Jun;195(2):330–351. doi: 10.1016/0003-2697(91)90339-u. [DOI] [PubMed] [Google Scholar]
- Szmacinski H., Lakowicz J. R. Optical measurements of pH using fluorescence lifetimes and phase-modulation fluorometry. Anal Chem. 1993 Jul 1;65(13):1668–1674. doi: 10.1021/ac00061a007. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Weissleder R., Tung C. H., Mahmood U., Bogdanov A., Jr In vivo imaging of tumors with protease-activated near-infrared fluorescent probes. Nat Biotechnol. 1999 Apr;17(4):375–378. doi: 10.1038/7933. [DOI] [PubMed] [Google Scholar]