Metal nanoparticle-enhanced radiative transitions: Giving singlet oxygen emission a boost

Abstract

The fabrication and use of metal nanoparticles to influence electronic transitions in a given molecule is of growing interest; there is much to be gained by developing and exploiting methods to enhance weak optical signals. Singlet molecular oxygen, O 2 (a 1 Δ g ), which is an important intermediate in many oxidation reactions, particularly in biological systems, is ideally monitored by the 1275-nm O 2 (a 1 Δ g ) → O 2 (X 3 Σ g -) phosphorescent transition. Unfortunately, the latter is highly forbidden and, as such, often presents a severe limitation in the application of this optical probe. In this paper, we describe how this weak phosphorescent transition can be enhanced by using localized surface plasmons (LSPs) from specially engineered gold nanostructures. In an attempt to elucidate the mechanism of this process, data were recorded from samples in which we decoupled the component of the plasmon resonance that absorbs incident light from the component that scatters incident light. We find that the latter appears to be the feature of significance in the process through which singlet oxygen phosphorescence is enhanced. In this work, we also illustrate how the singlet oxygen system provides an ideal model for a general study of metal-enhanced radiative rate constants.

Amplified Production of Singlet Oxygen in Aqueous Solution Using Metal Enhancement Effects

“…). This specific characteristic not only allows for an overlap with the absorption of RB, a requirement for metal enhancement effect , but is also within the size range (40–70 nm) for optimum enhancement efficiency as reported previously for MEF .…”

“…As 1 O 2 is the excited form of molecular oxygen, with a finite lifetime of 10 À6 -10 À3 s in solution (27,28), and is highly reactive, it has been used in a broad range of applications including organic chemical synthesis (29)(30)(31), wastewater treatment (28,32,33) and photodynamic therapy (34)(35)(36). Interestingly, it has been shown that the metal enhancement effect is not limited to fluorescence, and enhancement of both 1 O 2 production, and phosphorescence quantum yield have been observed (12,(37)(38)(39)(40)(41)(42). For instance, an increase in 1 O 2 radiative decay will lead to an enhancement of its phosphorescence quantum yield (38,39).…”

Silica-Coated Gold Nanostars for Combined Surface-Enhanced Raman Scattering (SERS) Detection and Singlet-Oxygen Generation: A Potential Nanoplatform for Theranostics

“…8,30 The plasmonic effect of the gold nanostars may also be contributing to the observed enhancement of singlet oxygen generation. 31-33 These results indicate that such nanocomposites can effectively be used to carry the photosensitizer MB and generate singlet oxygen when excited at the appropriate wavelength.…”

Functionalized phosphorescent nanoparticles in (bio)chemical sensing and imaging – A review

“…An alternative mechanism producing enhanced phosphorescence is related to the generation of localized plasmon resonance using metallic nanoparticles that resonate with the O2(a 1 Δg) → O2(X 3 Σg -) transition, and an oxygen sensitizer such as tetraphenylporphyrin (TTP) [50]. The metal nanostructure was extremely relevant for the efficiency of this phenomenon: nanosandwiches, gold nanorods or gold nanoshells do not generate an increase on the phosphorescence, whereas gold nanodiscs produce more than 3.5-fold increase in phosphorescence, and no increase of the fluorescence is observed, indicating that there is no metal-enhanced effect.…”