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

Abstract

In this work we investigate the relationship between metal-enhanced fluorescence (MEF) and fluorophore-induced plasmonic current (PC). This is accomplished through measurements of both radiative emission (MEF) and direct electrical current generation between discrete metal nanoparticles upon fluorophore excitation (PC). We have conducted these measurements on silver and gold nanoparticle island films, over a range of nanoparticle sizes and spacing in the films. We have observed an inverse relationship in the magnitude of MEF with PC, where larger and more closely spaced metal nanoparticles are found to result in increased PC and subsequently a decreased MEF. We attribute this effect to the relatively high capacitance and low charging energy of large and closely spaced particles, providing an outlet for plasmon relaxation in the form of electron flow and electrical current generation. These results are significant as they open potential for controlling for and the optimization of both MEF and PC.

Thermoplasmonic-Assisted Cyclic Cleavage Amplification for Self-Validating Plasmonic Detection of SARS-CoV-2

“…Before diffusing into the bulk solution, the released fluorophores were in the vicinity of the AuNI biosensing surface (about 14.9 nm based on the B-DNA structural form). Since the randomly distributed AuNI nanophotonic chip has a broad absorbance superimposing over both the excitation and emission peak of the ATTO532 fluorophore, this distance (<15 nm) could facilitate the direct energy transfer between the fluorophore and AuNIs, therefore stimulating a transient LSPR phase response through the near-field interaction as shown in the real-time sensorgram (Figure B and C) . In comparison with the background phase response (without laser excitation) in the first 500 s of the reaction, the near-field interaction (500 to 1200 s) between the released fluorophores (gain molecules) and LSPR AuNIs produced transient phase jumps with high amplitudes.…”

“…Since the randomly distributed AuNI nanophotonic chip has a broad absorbance superimposing over both the excitation and emission peak of the ATTO532 fluorophore, this distance (<15 nm) could facilitate the direct energy transfer between the fluorophore and AuNIs, therefore stimulating a transient LSPR phase response through the nearfield interaction as shown in the real-time sensorgram (Figure 4B and C). 48 In comparison with the background phase response (without laser excitation) in the first 500 s of the reaction, the near-field interaction (500 to 1200 s) between the released fluorophores (gain molecules) and LSPR AuNIs produced transient phase jumps with high amplitudes. Different from the molecular binding, the instantaneous phase responses caused by this energy transfer and gain medium stimulation demonstrated a wider phase distribution (Figure 4D).…”

Fluorophore-Induced Plasmonic Current Generation from Aluminum Nanoparticle Films

“…We observed that there is no linear relationship between V and I as the current tends to show a Coulombic staircase as a result of a Coulombic blockade . This is thought to be due to the charge building up on individual nanoparticles until capacitance is reached, at which point it discharges its energy to the closest nanoparticle in a process known as electron hopping. − Figure shows the results of this voltage sweep experiment, and what can be noted is the overall increase in current as the thickness of the film increases and also that they all share a similar Coulombic staircase effect. A thicker film is likely to have more closely spaced particles, so the overall resistance of the films should decrease as the thickness increases, which was observed.…”

“…We found that all the rates above 0.1 Å/s resulted in films that were mirror-like in appearance, as also confirmed from the film absorption measurements. Voltage sweep experiments for these films yielded a linear relationship between V and I , indicating that the surface of these films might be populated with large nanoparticle clusters that had grown into each other, resulting in continuous films, which are known to not be effective at generating PC. − The films produced by the 0.1 Å/s deposition rate were found to be ideal candidates for fluorophore-induced PC. Figure shows the absorption spectra as a result of increasing deposition rate for three 8 nm Al Films as well as the voltage sweep analysis and a basic PC experiment detailing the use of 50 μM 2-AP and deionized water.…”

“…This current change is thought to be due to the product of energy transfer from the excited-state fluorophore to an individual nanoparticle, which when its capacitance is reached, it discharges its energy to a nearby (closely spaced) adjacent particle in a process known as electron hopping. − The constant hopping of electrons from discrete nanoparticles to adjacent nanoparticles leads to a directly observable change in the current for the overall film system, induced by the excited fluorophore . The magnitude of the induced current has been shown to be proportional to the molar extinction coefficient of the fluorophore; the concentration of the fluorophore; its position relative to the film; the capacitance of the MNF film; and the polarization of the incidental light exciting the fluorophore-induced coupled system .…”