1 July 2008 Effect of liposomal confinement on photothermal and photo-oximetric fluorescence lifetimes of photosensitizers with varying hydrophilicity
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J. of Biomedical Optics, 13(4), 041314 (2008). doi:10.1117/1.2952298
Abstract
The time-resolved fluorescence of photosensitizers (PSs) of varying hydrophobicities, di-and tetrasulfonated Al phthalocyanines (Al-2 and Al-4), and Photochlor® (HPPH), was investigated in liposomes used as cell-mimetic models. Using frequency-and time-domain apparatus, the fluorescence lifetime, τ fluo, was compared for PSs free in aqueous solution and in a liposome-associated state at varied temperatures (25 to 78°C) and oxygen concentrations (0–190 μM). The analysis of τ fluo revealed different decay behaviors for the free-solution and liposome-confined PSs, most significantly for the lipophilic HPPH. Hydrophilic PS drugs (Al-4, Al-2) were less affected by the liposomal confinement, depending on the relative hydrophilicity of the compound and the consequent localization in lipsomes. Changes in the emission decay due to confinement were detected as differences in the lifetime between the bulk solution and the liposome-localized PS in response to heating and deoxygenation. Specifically, hydrophilic Al-4 produced an identical lifetime trend as a function of temperature both in solu and in a liposome-confined state. Hydrophobic HPPH exhibited a fundamental transformation in its fluorescence decay kinetics, transitioning from a multiexponential (in free solution) to single-exponential (in liposome) decay. Deoxygenation resulted in a ubiquitous τ fluo increase for all PSs in free solution, while the opposite, a τ fluo decrease, occurred in all liposomal PSs.
Ozzy Mermut, Isabelle Noiseux, Jean-Pierre Bouchard, Jean-François Cormier, Patrice Desroches, Michel Fortin, Pascal Gallant, Sébastien Leclair, Marcia L. Vernon, Kevin R. Diamond, Michael S. Patterson, "Effect of liposomal confinement on photothermal and photo-oximetric fluorescence lifetimes of photosensitizers with varying hydrophilicity," Journal of Biomedical Optics 13(4), 041314 (1 July 2008). http://dx.doi.org/10.1117/1.2952298
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KEYWORDS
Picosecond phenomena

Luminescence

Oxygen

Temperature metrology

Molecules

Scattering

Photodynamic therapy

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