Plasmonic Electricity: Fluorophore-Induced Plasmonic Current

Abstract

Fluorophore-induced plasmonic current is generated when an excited fluorophore in close proximity to a metal nanoparticle film nonradiatively transfers energy to the metal, resulting in an electrical current across the film. Although a growing literature reports the use of surface plasmons for fluorescence enhancement as well as plasmons for current generation, little has been published hitherto regarding the electrical current generation via the fluorophore excitation of plasmons. Our "plasmon to current" technique utilizes electron transport between closely spaced metal nanoparticles, generating a measurable electrical signal upon excitation of a proximal fluorophore. This induced electrical signal is found to be strongly dependent on the magnitude of the fluorophore extinction coefficient. In other words the electrical signal contains photophysical information pertaining to the fluorophore, potentially leading to the direct detection of fluorescence without the need for traditional detectors such as photomultiplier tubes and charge coupled devices. In addition, we demonstrate the dependence of this current on fluorophore concentration and excitation laser polarization. Fluorophore-induced plasmonic current holds potential as a novel molecular detection platform with simplified instrumentation, compatible with a variety of fluorescent probes.

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

“…As described in recent work by our laboratory, this electrical current is dependent on a number of factors including not only nanoparticle size and spacing in the film but also solvent permittivity, applied voltage, temperature, and the fluorophore extinction coefficient. , In our studies of extinction coefficient effects, an increase in the current was observed with increasing fluorophore extinction coefficient . This is thought to be due to the high extinction fluorophore absorbing more radiative energy from the far-field light (laser or LED) and bringing more energy into the near-electric field of the nanoparticles.…”

“…Silver nanoparticle island films utilized for SOSG induced current measurements were characterized, as described in a previous manuscript from our laboratory . Briefly, absorption spectra of prepared silver films were collected using a single beam Varian Cary 50-Bio UV–VIS spectrophotometer.…”

“…Briefly, absorption spectra of prepared silver films were collected using a single beam Varian Cary 50-Bio UV–VIS spectrophotometer. SEM of vapor deposited films was performed using a Nova NanoSEM 450 with secondary electron imaging, with representative film surface images displayed in previous work . All dry silver nanoparticle island films were characterized as electrically noncontinuous, displaying zero measurable current under zero applied bias voltage …”

“…Electrodes are in simultaneous contact with the metal film and solvent. [Redrawn from ref ]. (C) Modification of the PC set up from (B) for detection of singlet oxygen.…”

“…To address this limitation, herein, we investigate for the first time the use of an emerging phenomenon called plasmonic current (PC) or plasmonic electricity (PE) for the surface-based detection of 1 O 2 . Fluorophore-induced PC is generated when an excited fluorescent molecule nonradiatively transfers energy to a nearby metallic nanoparticle film, generating a measurable electrical current through the film (Scheme B) . The generated electrical current is due to electron transport between discreet metal nanoparticles in the film, also known in the literature as electron “hopping” or “tunneling” for closely spaced particles. − The ability of nanoparticles in the film to support electron transport is dependent on the charging energy required for a nanoparticle to gain an electron, which is related to the particle capacitance, that is, where E C is charging energy, e is the elementary electric charge, and C is capacitance of the particle. − …”