Metal Nanoparticles Sensitize the Formation of Singlet Oxygen

Abstract

Singlet oxygen ( 1 O 2 ) is known to play an indispensible role in the photodynamic therapy (PDT) treatment of cancer, [1][2][3][4][5] and is an important oxidant for hydroperoxidation of olefins in organic synthesis. [6,7] Singlet O 2 is conventionally formed by sensitization by organic photosensitizers, such as Rose Bengal, silicon phthalocyanine, etc. [1][2][3][4][5][6][7] These organic or organometallic dyes are, however, prone to photoinduced degradation and enzymatic degradation, which becomes problematic in PDT treatments, and reduces the efficiency of the generation of singlet O 2 . [5,8] It is, therefore, important to search for photosensitizers with highly efficient singlet O 2 generation and large absorption coefficients that are photochemically more stable and less prone to enzymatic degradation.Previously, it was reported that the yield of singlet oxygen production by a photosensitizer, namely, Rose Bengal, was enhanced by a silver island film through the metal-enhanced absorption of photosensitizer. [9,10] It was also reported that a gold nanodisk could enhance the phosphorescence decay rate of singlet oxygen, leading to a larger characteristic phosphorescence emission band of singlet oxygen at 1270 nm. [11] In another two studies, it was observed that the quantum yield of singlet O 2 formation generated by phthalocyanine photosensitizers can be enhanced by the presence of gold nanoparticles. [12,13] Herein we report an unprecedented observation that singlet oxygen can be formed through direct sensitization by metal nanoparticles (M NPs, M = Ag, Pt, and Au) without the presence of any organic photosensitizers. Unambiguous experimental evidence includes direct observation of singlet oxygen emission at roughly 1268 nm, hydroperoxidation of cyclohexene, green fluorescence from a selective singlet oxygen fluorescent sensor, namely, Singlet Oxygen Sensor Green (SOSG, Molecular Probe), and quenching of singlet oxygen phosphorescence by sodium azide.As shown in Figure 1, photoexcitation of M NPs at the surface plasmon resonance absorption bands of Ag (d = 55, 42 nm), Pt (10 nm), and Au (22 nm) in D 2 O results in characteristic singlet oxygen emission at 1264 and 1268 nm, respectively. Control experiments show that in the absence of metal nanoparticles, photoexcitation of poly(vinyl pyrrolidone (PVP) in D 2 O using either 254 or 508 nm light did not result in any detectable singlet O 2 emission signal (see the Figure 1. a) Phosphorescence emission spectra of singlet oxygen sensitized by Au, Ag or Pt nanoparticles in D 2 O, and a control experiment with PVP in D 2 O in the absence of metal nanoparticles (purple line, l ex = 254 nm and blue line, l ex = 508 nm). b) The extinction spectra (solid lines) of Ag, Pt, and Au NPs, and the excitation spectra (dashed lines) of singlet O 2 phosphorescence at 1270 nm in the presence of Ag, Pt, and Au NPs, respectively. A longpass filter of 850 nm was put between the sample and the detector for all experiments (unless otherwise mentioned) to filter away any stray light ...

A graphene quantum dot photodynamic therapy agent with high singlet oxygen generation

“…2f (refs 38, 39). This result agrees very well with that obtained using the chemical trapping method above.…”

Mechanistic understanding of surface plasmon assisted catalysis on a single particle: cyclic redox of 4-aminothiophenol

“…Therefore, the reaction of 4ATP to DMAB, which involves loss of 4 electrons and 4 protons, proceeds much faster in an environment where both O 2 and H 2 O are present under identical optical conditions. An alternate mechanism that involves nucleophilic addition of 4-ATP to 4-nitrosobenzenethiol (the latter being formed by oxidation of 4-ATP by O 2 or singlet oxygen2324 in the SPAC reaction, see Fig. S9), is analogous to the oxidation of anilines in solution2125.…”

Evaluation of the Catalytic Activity and Cytotoxicity of Palladium Nanocubes: The Role of Oxygen

“…12,15 SOSG becomes strongly fluorescent with an emission maximum at 525 nm upon oxidation of its anthracene moiety by 1 O 2 *. 15 Because of its high sensitivity and specificity towards singlet oxygen 12 , SOSG has been already used in direct detection of singlet oxygen produced by metal nanoparticles 7, 8 and by porous silicon nanoparticles. 16 It has even been used in detection of singlet oxygen inside mammalian cells 17 and in quantitative measurements of singlet oxygen generation.…”