Plasmon-Enhanced Energy Transfer in Photosensitive Nanocrystal Device

Abstract

Förster resonance energy transfer (FRET) interacted with localized surface plasmon (LSP) gives us the ability to overcome inadequate transfer of energy between donor and acceptor nanocrystals (NCs). In this paper, we show LSP-enhanced FRET in colloidal photosensors of NCs in operation, resulting in substantially enhanced photosensitivity. The proposed photosensitive device is a layered self-assembled colloidal platform consisting of separated monolayers of the donor and the acceptor colloidal NCs with an intermediate metal nanoparticle (MNP) layer made of gold interspaced by polyelectrolyte layers. Using LBL assembly, we fabricated and comparatively studied seven types of such NC-monolayer devices (containing only donor, only acceptor, Au MNP-donor, Au MNP-acceptor, donor-acceptor bilayer, donor-Au MNP-acceptor trilayer, and acceptor-Au MNP-donor reverse trilayer). In these structures, we revealed the effect of LSP-enhanced FRET and exciton interactions from the donor NCs layer to the acceptor NCs layer. Compared to a single acceptor NC device, we observed a significant extension in operating wavelength range and a substantial photosensitivity enhancement (2.91-fold) around the LSP resonance peak of Au MNPs in the LSP-enhanced FRET trilayer structure. Moreover, we present a theoretical model for the intercoupled donor-Au MNP-acceptor structure subject to the plasmon-mediated nonradiative energy transfer. The obtained numerical results are in excellent agreement with the systematic experimental studies done in our work. The potential to modify the energy transfer through mastering the exciton-plasmon interactions and its implication in devices make them attractive for applications in nanophotonic devices and sensors.

A Self‐Assembled Plasmonic Substrate for Enhanced Fluorescence Resonance Energy Transfer

“…These competitive effects are controlled by several experimental parameters, such as the spectral overlap between absorption/emission of the fluorophores and the extinction of metal nanostructures, the distance between the metal surface and the fluorophores, and the absorption/scattering ratio of the nanostructures . In plasmon‐modulated FRET, the interactions between different entities are even more complicated . Single‐particle experiments have suggested that the FRET channel is turned on when the LSPR of plasmonic nanocrystal lies between the emission peak of the donor and absorption peak of the acceptor or right at the emission wavelength of the acceptor, and is turned off, while the LSPR is at the emission wavelength of the donor .…”

“…Despite these advantages incurred by plasmon modulation, there is still no planar plasmonic substrate available to serve as a universal platform for tailored on‐surface FRET enhancement, which is highly desirable for biosensing, optical imaging, and solar energy conversion applications. 2D substrates, such as electrostatically adsorbed metal nanoparticle monolayers and plasmonic gratings have been used to study plasmon‐controlled FRET at a fundamental level. However, these plasmonic substrates, along with other possible choices, such as gold‐island films, show at least three interconnected problems in practical applications.…”

“…However, these plasmonic substrates, along with other possible choices, such as gold‐island films, show at least three interconnected problems in practical applications. First, there is limited structural control over homogeneity of nanoparticle distribution and interparticle distance in the plasmonic substrates fabricated by adsorbing metal nanoparticles, causing problems when homogenous optical properties are required. Second, the LSPR bands are either too broad or lack of the flexibility to be tuned to desired spectral positions, such as in the cases of gold‐island films and plasmonic gratings that depend on the change of incident light angles to tune the spectral peak wavelength .…”

“…[9][10][11][12][13] In plasmon-modulated FRET, the interactions between different entities are even more complicated. [14][15][16][17][18][19] Single-particle experiments have suggested that the FRET channel is turned on when the LSPR of plasmonic nanocrystal lies between the emission peak of the donor and absorption peak of the acceptor or right at the emission wavelength of the acceptor, and is turned off, while the LSPR is at the emission wavelength of the donor. [20] Both theoretical and experimental studies have found that the plasmonfluorophore interactions increase the Förster distance (the distance where the possibility of energy transfer is 50%), [21][22][23][24] modify FRET efficiency, [21,[25][26][27] and enable forbidden Förster dipole-dipole energy transfer by the strongly inhomogeneous local fields.…”

“…However, these plasmonic substrates, along with other possible choices, such as gold-island films, [30][31][32][33][34][35] show at least three interconnected problems in practical applications. First, there is limited structural control over homogeneity of nanoparticle distribution and interparticle distance in the plasmonic substrates fabricated by adsorbing metal nanoparticles, [15][16][17][18]23] causing…”