The Kinetics of Exogenous Phosphors Delayed Fluorescence in Tissues
Authors: S.N. Letuta  , A.F. Kuvandykova  , S.N. Pashkevich  
Published: June 2012

The kinetics of delayed fluorescence (DF) and phosphorescence (Ph) of xanthene dyes in tumourous and normal mammary tissues of the BYRB line mice was investigated. Spontaneous mammary cancer tumours are characteristic of the mice of this line with the possible exogenous MMTV- retrovirus, found in leukocytic fraction. The kinetics of DF and Ph molecules of the dyes was measured by means of laser flash-photolysis. The molecules in basic S0→S1 absorption band were excited by the second harmonic of pulsed laser to YAG:Nd3+ with wave length 532 nm. At the expiration of the process S1→T1 intersystem crossing (IC) and the formation of triplet T1 molecule state, the registration system of delayed luminescence started. The luminescence was registered by PMT and monochromator. The parameters of the exciting pulse: pulse duration 10 ns, density of energizing power not more than 5 MWt/cm2. The DF was registered at the wave length of 560 nm, and Ph at the wave length of 680 nm. The DF of the examined molecules can occur both as the result of termoactivated reverse to T1→S1 IC and as the result of the two T1 states annihilation with the sequent formation of S1 states. Moreover under the certain conditions in the presence of oxygen the cross – annihilation of the dye and oxygen stimulated molecules can occur. It was demonstrated that the most effective quencher of the triplet T1 states of phosphors in the tissues is the molecular oxygen 3!g"(O2). In the result of the interaction of the dye T1 molecules with the molecular oxygen singlet 1∆g (O2) oxygen is formed: T1+3!g"(O2)#$#S0+1%g(O2). Then as the result of singlet-triplet T1→1∆g(O2) annihilation of the rest triplet T1 states of the dyes with 1∆g(O2): T1+1!g(O2)"#"S1+3$g%(O2) the singlet S1 states of dyes are formed, thus contributing to the DF. As a result the registered kinetics of the DF of the dyes is made up of the three signals of various nature: termoactivated DF; T1-T1 annihilated DF; and luminescence due to the singlet-triplet T1→1∆ g (O2) cross–annihilation. The kinetic curve transforms and becomes no monotonously dependent on time. It was specified that in the tissues during short periods of time the most significant contribution to the total signal was made by singlet-triplet T1→1∆ g (O2) annihilation. However, other things equal, the delayed luminescence kinetics in normal and pathogenous tissues differ. The contribution of the singlet-triplet annihilation to the total signal of the DF in the normal tissues is significantly less than in tumour, which indicates the less effectiveness of the triplet states of the dyed molecules interaction with the singlet oxygen. Unlike DF the Ph intensity of dye molecules decreases monotonously with the period of time. Phosphorescence kinetics as well as DF differs within different tissues. The luminescence peculiarity depends on the phase of the tumour, the biotissue condition and other factors. However in all our experiments the common regularity is evident, namely the Ph lifetime in tumours is shorter than that in normal tissues. Reliable registered differences in the dye tissue delayed luminescence kinetics can be used when developing an alternative method of optical diagnosis of biotissues. We assume that the method based on the measurement of lifetime of the delayed luminescence phosphor is fairly promising. Any combinations possessing delayed luminescence and meeting the requirements set to such specimen may serve as exogenous phosphor.