Abstract
We study theoretically the bio-sensing capabilities of metal nanowire surface plasmons. As a specific example, we couple the nanowire to specific sites (bacteriochlorophyll) of the Fenna-Matthews-Olson (FMO) photosynthetic pigment protein complex. In this hybrid system, we find that when certain sites of the FMO complex are subject to either the suppression of inter-site transitions or are entirely disconnected from the complex, the resulting variations in the excitation transfer rates through the complex can be monitored through the corresponding changes in the scattering spectra of the incident nanowire surface plasmons. We also find that these changes can be further enhanced by changing the ratio of plasmon-site couplings. The change of the Fano lineshape in the scattering spectra further reveals that “site 5” in the FMO complex plays a distinct role from other sites. Our results provide a feasible way, using single photons, to detect mutation-induced, or bleaching-induced, local defects or modifications of the FMO complex, and allows access to both the local and global properties of the excitation transfer in such systems.
Highlights
Photosynthesis, the transformation of light into chemical energy, is one of the most crucial bio-chemical processes for life on earth[1]
We wish to focus on the interplay between the excitation transfer and the surface plasmons (SPs) scattering; so we focus on the simplest possible model of such environmental effects
It should be noted that excitonic fluorescence relaxation is not included in the Liouville equation. This is because its time scale (~1 ns) is much longer compared with that of the excitation transfer from site 3 to the reaction center (~1 ps), the typical excitation transfer time across the complex, and the dephasing[40] (~100 fs), such that this relaxation process can be omitted for simplicity
Summary
We model a single FMO monomer as a network of N = 7 sites (see Fig. 1), which can be described by a general Hamiltonian. Where the state is the excitonic c|no〉urpelpinrgesbeenttws eaennetxhceitnat-itohnaantdsnit′e-tnh(snit ∈es 1. Has been omitted because results of molecular dynamics simulations[37] suggest that this site plays a minimal role in the processes we are interested in. The excitation from the light-harvesting antenna enters the FMO complex at sites 1 or 6 and transfers from one site to another. When the excitation gets to the site 3, it hops irreversibly to the reaction center. In the regime that the excitonic coupling Jn,n′ is large compared with the reorganization
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