Abstract
The fluorescence of photosystem I (PSI) trimers in proximity to bimetallic plasmonic nanostructures have been explored by single-molecule spectroscopy (SMS) at cryogenic temperature (1.6 K). PSI serves as a model for biological multichromophore-coupled systems with high potential for biotechnological applications. Plasmonic nanostructures are fabricated by thermal annealing of thin metallic films. The fluorescence of PSI has been intensified due to the coupling with plasmonic nanostructures. Enhancement factors up to 22.9 and 5.1 are observed for individual PSI complexes coupled to Au/Au and Ag/Au samples, respectively. Additionally, a wavelength dependence of fluorescence enhancement is observed, which can be explained by the multichromophoric composition of PSI.
Highlights
The effects of metallic surfaces and nanostructures on the optical properties of molecules nearby were discussed already in the late 1960s and 1970s [1,2,3]
Irregular bimetallic nanostructures fabricated by thermal annealing of thin metallic films, having different size, shape and inter-structure spacing were used to investigate the influence of plasmonic interaction on optical properties of photosystem I (PSI) [18]
The aforementioned results have shown an increased fluorescence of PSI trimers induced by the plasmonic nanostructures Au/Au and Ag/Au, fabricated by the thermal annealing process
Summary
The effects of metallic surfaces and nanostructures on the optical properties (fluorescence quenching or enhancement) of molecules nearby were discussed already in the late 1960s and 1970s [1,2,3]. The interaction of plasmonic nanostructures with fluorophores increases their radiative decay rates and quantum yield. The increased decay rates yield an increase of the photostability of fluorophores, as the fluorophores spend less time in an excited state before returning back to the ground state [13]. The ability to increase the brightness of the fluorophore with adjacent plasmonic nanostructures simplifies the detection of the fluorophores at the single-molecule level, which otherwise is difficult due to low signal intensities
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