Spectrally Selective Fluorescence Imaging of C. tepidum Reaction Centers Monolayer on Thiolated Silver Nanowires

Dorota Kowalskaa, Marcin Szalkowskia, Khuram Ashrafb, Heiko Loksteinb, Izabela Kaminskaa, Justyna Grzelaka, Adam Lesniewskic, Joanna Niedziolka-Jonssonc, Richard Cogdellb, Sebastian Mackowskia
aInstitute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland; bInstitute of Molecular, Cell and Systems Biology, Glasgow Biomedical Research Centre, University of Glasgow, 120 University Place, Glasgow G12 8TA, UK; cInstitute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland

Photosynthetic organisms evolved various pigment-protein complexes to absorb sunlight and convert it into biologically useful forms. In addition to light-harvesting antennae, responsible mainly for absorbing photons, there are also Reaction Centers (RCs) responsible for separating electric charge across the photosynthetic membrane. Due to their unique photovoltaic properties and thermal stability, RCs from C. tepidum may be well suited for constructing biohybrid nanostructures with the prospect of energy harvesting and solar fuel production. Developing ways of modifying RC’s spectral properties to achieve efficient function even without antennas is a key in order to turn them into building blocks of hybrid devices. Plasmonic excitations in metallic nanostructures can be applied for that purpose [1,2].

In this work, we immobilized a monolayer of RCs from green sulfur bacterium Chlorobaculum tepidum on thiolated silver nanowires. To demonstrate, qualitatively, successful binding of His-tagged RCs by the affinity to the Ni-NTA modified surface of AgNWs, we employed wide-field and confocal fluorescence microscopy, as well as atomic force microscopy. The study of spectrally selective fluorescence of such hybrid nanostructures with excitation wavelengths corresponding to absorption of bacteriochlorophylls and carotenoids reveals substantial impact of plasmon excitations in silver nanowires on the optical properties of the RC complexes. Namely, the observed enhancement of RCs emission upon conjugation to the AgNWs is accompanied with no measurable effect on the fluorescence lifetime. Thus, by coupling RC complexes to silver nanowires we can control the absorption of photosynthetic complexes.

Acknowledgement

Research was supported by the projects DEC-2013/11/B/ST3/03984 and DEC-2013/10/E/ST3/00034 funded by the National Science Center.

References

[1] S. Mackowski, Journal of Physics: Condensed Matter 2010, 22, 193102
[2] N. Czechowski, H. Lokstein, D. Kowalska, K. Ashraf, R. J. Cogdell, and S. Mackowski, Applied Physics Letters 2014, 105, 043701