Fluorophore-Induced Plasmonic Current: Generation-Based Detection of Singlet Oxygen

Abstract

In this work, we report the surface-based electrical detection of singlet oxygen using the emerging fluorophore-induced plasmonic current (PC) technique. By this method, we utilize the fluorescent “turn on” response of the well-known singlet oxygen sensor green (SOSG) singlet oxygen (1O2) fluorescent probe for the generation of fluorophore-induced PC in a silver nanoparticle film. To demonstrate the potential utility of this new technique, a photosensitizing molecule is used to generate 1O2 in a solution containing the SOSG probe. The resulting change in SOSG fluorescence quantum yield and extinction coefficient permits stronger energy transfer from the SOSG probe to a proximal silver nanoparticle island film located in the near-electric field of the probe. This yields an increase in the induced electric current flow, allowing for the detection of the 1O2 analyte. To the author’s knowledge, this represents the first detection of the reactive oxygen species 1O2 utilizing fluorophore-induced PC methodology and even broader electrical detection of 1O2. This is significant as it opens the possibility for 1O2 detection methods which do not require a traditional “photodetector” and associated optics, simplifying the instrumentation over existing fluorescence detection methods and potentially even lowering the cost.

The Inverse Relationship between Metal-Enhanced Fluorescence and Fluorophore-Induced Plasmonic Current

“…Recent advances in the understanding of metal-enhanced fluorescence (MEF) and fluorophore-induced plasmonic current (PC) have led to the development of both optical and photovoltaic devices, respectively. These devices operate either through “plasmon to light” optical far-field detection such as in MEF and surface plasmon resonance (SPR), − or by “plasmon to current” direct electrical current generation resulting from the dephasing of plasmon resonance. − This direct electrical current generation may be accomplished using plasmon resonance in conjunction with a semiconducting material, , or through electron transport between closely spaced metal nanoparticles such as in PC. , In both MEF and PC, a fluorophore may be used for nonradiative energy transfer to a metal nanoparticle, resulting in plasmon excitation. The excited plasmon may then relax through various routes, including radiative emission, heat loss to the surroundings, and electron transport. , While extensive literature is available regarding both optical and photovoltaic techniques separately, little has been published regarding the relationship between these two phenomena.…”

“…PC is generated when a fluorophore nonradiatively transfers energy to a proximal metal nanoparticle island film, resulting in a measurable current change through the film. − This is possible because of close spacing between discrete metal nanoparticles in the film, allowing for electron transport between the particles, also known in the literature as electron “hopping” (Figure b,c). − Previous work from our laboratory has also shown the electrical current change upon fluorophore excitation to be dependent on the magnitude of the fluorophore extinction coefficient, providing information regarding the fluorophore and opening the possibility for various detection assays. This dependence of the current on fluorophore extinction coefficient is explained by the capability of a higher extinction fluorophore to bring more energy into proximity of the metal nanoparticle, allowing for increased energy transfer to the metal, and a subsequent increase in current generation through the film upon fluorophore excitation.…”

Fine‐Tuning Cu (II)‐Induced Self‐Assembly of Hydrophilic Cyanine Dyes for Enhanced Tumor Photothermal Therapy

“…The fluorescence emission of SOSG would be greatly improved when reacted with 1 O 2 . [ 19 ] Compared with monomeric Cy‐1COOH, obviously enhanced fluorescent signals of SOSG were observed when treated with Cy‐1COOH/Cu aggregates, suggesting improved 1 O 2 production of Cy‐1COOH/Cu aggregates (Figure S22A–C, Supporting Information). This could be due to partial J‐aggregates in Cy‐1COOH/Cu aggregates that would favor to boost 1 O 2 production.…”

Nanotechnologies for Reactive Oxygen Species“Turn-On” Detection

“…The presence of 1 O 2 in this system can result in change in the SOSG fluorescence quantum yield, which permits a stronger energy transfer from the SOSG probe to a proximal silver nanoparticle island film located in the near-electric field of the probe. This induces an increase in the target electric current flow, allowing for the sensing of the 1 O 2 ( Knoblauch et al, 2020 ).…”