Reactions of Singlet Oxygen and Half-reduced Oxygen which are Produced Simultaneously by the Interaction of Triplet Dye and Oxygen

Abstract

Under experimental conditions in which the interaction between triplet dye and oxygen is an initiating process (D–O mechanism), the photosensitized oxidation of leucofluorescein in the aqueous solution (reaction (1)) has been found to decrease in rate with the increasing oxygen concentration and that the magnitude of the retarding effect of oxygen is almost the same independent of sensitizing dye. This is in sharp contrast to the kinetic feature of the oxidative photobleaching of dye (reaction (2)), where the rate becomes constant beyond a certain small oxygen concentration. On the basis of these findings, it has been proposed that in reaction (1), 1O2 plays a dominant role and it is deactivated by process 1O2+3O2→23O2. As to reaction (2), strong evidence has been presented for the view that the interaction of triplet dye and oxygen in the aqueous solution produces a rather stable D+···O2− of which only a small portion decomposes irreversibly. The principal evidence is as follows; 1) the free half-oxidized dye (produced by the reaction between triplet dye and [Co(Ox)3]3− was found to oxidize FH2 with a high rate and its decay was found to be accelerated by the addition of FH2; 2) the decay of the half-oxidized species (first order decay!) produced in the aerated aqueous solution, on the other hand, was not affected by FH2 under otherwise similar conditions as in (1).

Exponential Amplification Using Photoredox Autocatalysis

“…As can be seen in Figure 2, when EYH2 is activated by EY under light, EY •─ is generated as an intermediate species and reacts further to give EY. Given that triplet dyes and oxidizing radicals can oxidize other dihydroxanthene dyes, [11][12][13][14][15][16] two potential activating substances in the system are 3 EY * and EY •+ . As discussed earlier, the radical cation may not be produced at enough concentration to oxidize EYH2, otherwise the self-bimolecular reaction of EY •+ can lead to photobleached EY (Figure S6), which is S−9 inconsistent with 100% EYH2-to-EY recovery observed (Figure 2B).…”

“…[3][4][5] On the other hand, PCR can detect low-abundance target nucleic acids 6 or antigens (via immuno-PCR) 7 by amplifying specific nucleic acids exponentially, but this method often takes several hours, and is not easily translated to resource-limited settings due to reliance on laboratory instruments (thermal cyclers and analyzers), poor stability of enzyme-based reagents, and requirement of trained personnel. [8][9][10] To address these issues, efforts have been made to develop isothermal nucleic acid amplification strategies, 9,11 long-term storage methods for reagents, 12 and automated formats. 9,11,13 Alternatively, several research groups have dedicated to developing non-PCR exponential molecular amplification methods by carefully designing small molecule amplification reagents.…”

Exponential Amplification Using Photoredox Autocatalysis

“…To address this deviation, we focused on the reactivity of 1 O2, which is one of the most reactive species that is generated in the system and has higher energy by 94 kJ/mol than the ground-state oxygen. 23 The singlet oxygen has been proposed as an activating molecule for other dihydroxanthene dyes previously, 12,16 and is known to oxidize hydroquinone to benzoquinone, 24 so 1 O2 is plausible to contribute to EYH2 oxidation (Eq. 24).…”

“…[3][4][5] On the other hand, PCR can detect low-abundance target nucleic acids 6 or antigens (via immuno-PCR) 7 by amplifying specific nucleic acids exponentially, but this method often takes several hours, and is not easily translated to resource-limited settings due to reliance on laboratory instruments (thermal cyclers and analyzers), poor stability of enzyme-based reagents, and requirement of trained personnel. [8][9][10] To address these issues, efforts have been made to develop isothermal nucleic acid amplification strategies, 9,11 long-term storage methods for reagents, 12 and automated formats. 9,11,13 Alternatively, several research groups have dedicated to developing non-PCR exponential molecular amplification methods by carefully designing small molecule amplification reagents.…”

Exponential Amplification Using Photoredox Autocatalysis

“…As can be seen in Figure 2, when EYH2 is activated by EY under light, EY •─ is generated as an intermediate species and reacts further to give EY. Given that triplet dyes and oxidizing radicals can oxidize other dihydroxanthene dyes, [11][12][13][14][15][16] two potential activating substances in the system are 3 EY * and EY •+ . As discussed earlier, the radical cation may not be produced at enough concentration to oxidize EYH2, otherwise the self-bimolecular reaction of EY •+ can lead to photobleached EY (Figure S6), which is S−9 inconsistent with 100% EYH2-to-EY recovery observed (Figure 2B).…”