Plasmonic engineering of singlet oxygen generation

Abstract

In this article, we report metal-enhanced singlet oxygen generation (ME 1 O2). We demonstrate a direct relationship between the singlet oxygen yield of a common photosensitizer (Rose Bengal) and the theoretical electric field enhancement or enhanced absorption of the photosensitizer in proximity to metallic nanoparticles. Using a series of photosensitizers, sandwiched between silver island films (SiFs), we report that the extent of singlet oxygen enhancement is inversely proportional to the free space singlet oxygen quantum yield. By modifying plasmon coupling parameters, such as nanoparticle size and shape, fluorophore/particle distance, and the excitation wavelength of the coupling photosensitizer, we can readily tune singlet oxygen yields for applications in singlet oxygen-based clinical therapy.metal-enhanced fluorescence ͉ metal-enhanced phosphorescence ͉ photodynamic therapy ͉ surface-enhanced fluorescence P hotodynamic therapy (PDT) has been widely used in both oncological (e.g., tumors and dysplasias) and nononcological (e.g., age-related macular degeneration, localized infection, and nonmalignant skin conditions) applications (1-4). Three primary components are involved in PDT: light, a photosensitizing drug, and oxygen. The photosensitizer adsorbs light energy, which it then transfers to molecular oxygen to create an activated form of oxygen called singlet oxygen (1). The singlet oxygen is a cytotoxic agent and reacts rapidly with cellular components to cause damage that ultimately leads to cell death and tumor destruction (4). PDT treatments are only effective within a specific range of singlet oxygen supply (5). For example, for solid tumors, too little singlet oxygen cannot effectively treat the tumor cells, but too much singlet oxygen can damage and kill surrounding healthy cells (6). Currently, the intensity of light is commonly adjusted to control the extent of singlet oxygen generation, but there are some limitations to this method. High fluency rates of the exposure light will lead to oxygen depletion and photosensitizer photobleaching (3). However, low fluency rates of exposure light lends to a long exposure time and can cause vascular shutdown, a precursory condition to hypoxia in the tissue (5, 7). One notable approach to controlling the fluency rate of exposure light is called interstitial PDT, where a precise amount of light is delivered locally to tumors through inserted optical fibers (8). The interstitial PDT also allows the real-time monitoring of the progression of the treatment via online collection of assessment parameters through the optical fibers (8). It is important to note that despite the better control over fluency rate, the photobleaching of the photosensitizers remains an issue. In this regard, our laboratory has introduced a metalenhanced phenomenon as a means to control the extent of singlet oxygen generation via metal-photosensitizer interactions, an alternative approach as compared with exposure settings and sensitizer dose, which we believe is a significant improvement...

Effects of light irradiation upon photodynamic therapy based on 5-aminolevulinic acid–gold nanoparticle conjugates in K562 cells via singlet oxygen generation

“…Through nonradiative energy transfer and coupling to the surface plasmons of GNPs, more PSs are excited to their triplet and singlet states, which results in more singlet oxygen generation. 44 However, the emission spectra of other light sources do not fit with the absorption peak of GNPs. Hence, they cannot cause a strong surface plasmon effect to occur in GNPs.…”

Nanodrug applications in photodynamic therapy

“…When luminescent nanoparticles are used in vivo no external light source is necessary and thus, a more localized treatment might become possible. For example, Zhang and co-workers [92] gave evidence for a relationship between electric field enhancements around metallic nanoparticle and the increase in triplet yields for the photosensitizer and also a higher production of singlet oxygen. Interaction of fluorophores with metallic nanoparticles are called metal-enhanced fluorescence.…”

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