Singlet oxygen feedback delayed fluorescence of protoporphyrin IX in organic solutions

Abstract

Delayed fluorescence (DF) of protoporphyrin IX (PpIX) has been recently proposed as a tool for monitoring of mitochondrial oxygen tension in vivo as well as for observation of the effectiveness of photodynamic therapy (PDT) [E. G. Mik, Anesth. Analg., 2013, 117, 834-346; F. Piffaretti et al., J. Biomed. Opt., 2012, 17, 115007]. However, the efficiency of the mechanism of thermal activation (E-type DF), which was considered in the papers, is limited due to a large energy gap between the first excited singlet and the first triplet state of PpIX at room or body temperatures. Moreover, the energy gap is roughly equal to other porphyrinoid photosensitizers that generate DF mostly through the Singlet Oxygen Feedback-Induced mechanism (SOFDF) under certain conditions [M. Scholz and R. Dědic, Singlet Oxygen: Applications in Biosciences and Nanosciences, 2016, vol. 2, pp. 63-81]. The mechanisms of delayed fluorescence of PpIX dissolved either in dimethylformamide (DMF) or in the mixture of DMF with ethylene glycol (EG) were investigated at atmospheric partial pressure of oxygen by means of a simultaneous time-resolved detection of O phosphorescence and PpIX DF which makes a direct comparison of the kinetics and lifetimes of both the luminescence channels possible. Samples of PpIX (100 μM) exhibit concave DF kinetics, which is a typical footprint of the SOFDF mechanism. The dramatic decrease in the DF intensity after adding a selective O quencher sodium azide (NaN, 10 mM) proves that >90% of DF is indeed generated through SOFDF. Moreover, the analysis of the DF kinetics in the presence of NaN implies that the second significant mechanism of DF generation is the triplet-triplet annihilation (P-type DF). The bimolecular mechanism of DF was further confirmed by the decrease of the DF intensity in the more viscous mixture DMF/EG and by the increase of the ratio of DF to the prompt fluorescence (PF) intensity with the increasing excitation intensity. These results show the significant role of the SOFDF mechanism in the DF of PpIX at high concentrations and at atmospheric partial pressure of oxygen and should be considered when developing diagnostic tools for clinical applications.

Oxygen‐dependent delayed fluorescence of protoporphyrin IX measured in the stomach and duodenum during upper gastrointestinal endoscopy

“…For the interpretation of the signal in terms of quantitative oxygen measurements additional research into the localization of PpIX and the photo‐physical properties of the delayed fluorescence would be very helpful. For example, Vinklárek et al described a Singlet Oxygen Feedback‐Induced mechanism (SOFDF) that influences the delayed fluorescence of PpIX under certain non‐physiological circumstances . It is currently unknown to what extent other mechanisms than T‐type delayed fluorescence, like this SOFDF mechanism, contribute to the in vivo delayed fluorescence signal.…”

Imaging of singlet oxygen feedback delayed fluorescence and lysosome permeabilization in tumor in vivo during photodynamic therapy with aluminum phthalocyanine

“…Although SOFDF cannot be applied to all photosensitizers, it was reported that a wide range of other photosensitizers are also capable of SOFDF emission (TPPS 4 , TMPyP, porphycenes, eosin, rose Bengal, etc. ), 20,26 including protoporphyrin IX, 27 which is currently the most frequently used photosensitizer in clinical PDT (it is formed endogenously in cells after administration of δ-aminolevulinic acid). Therefore, SOFDF-based singlet oxygen sensing could be potentially performed with a wide range of photosensitizers.…”

“…14 Recently, we proposed a completely different approach to monitoring singlet oxygen. [20][21][22] It is based on the mechanism of singlet oxygen feedback delayed fluorescence (SOFDF), [23][24][25] which is intrinsic to a number of different photosensitizers (protoporphyrin IX, ionic porphyrins, porphycenes, eosin, Rose Bengal, and others), 20,[26][27][28] and hence no additional probe molecule is required. The triplet state of a photosensitizer (T 1 ) can interact with the previously generated 1 O 2 , which leads to a reverse intersystem crossing (RISC) of the photosensitizer molecule and repopulation of the S 1 state that can subsequently emit a photon.…”

Understanding delayed fluorescence and triplet decays of Protoporphyrin IX under hypoxic conditions

“…The thermDF is first order in the concentration of excited states, while the TTADF and SOFDF are second order, which makes their individual contributions dependent on the concentration of triplet states, which, itself, depends on the photosensitizer concentration and excitation intensity. 1 A great example for examination of the described phenomena is Protoporphyrin IX (PpIX), which has been reported to exhibit all three of the above-mentioned RISC reactions, as manifested by DF emission [21][22][23][24]. PpIX is one of the most common photosensitizers that is used in a range or clinical applications, such as fluorescence-guided tumor resection, or photodynamic therapy (PDT) of skin diseases and cancer [25][26][27].…”