Photothermal Microscopy: Imaging of Energy Dissipation From Photosynthetic Complexes

Abstract

An idea of a photothermal imaging microscopy (PTIM) is proposed, along with its realization based on a dependence of fluorescence anisotropy of dye molecules on heat emission in their nearest vicinity. Erythrosine B was selected as a fluorophore convenient to report thermal deactivation of the excited pigment-protein complex isolated from the photosynthetic apparatus of plants (LHCII), owing to the relatively large spectral gap between the fluorescence emission bands of chlorophyll a and a probe. Comparison of the simultaneously recorded images based on fluorescence lifetime of LHCII and fluorescence anisotropy of erythrosine shows a high rate of thermal energy dissipation from the aggregated forms of the complex and, possibly, thermal energy transmission along the protein supramolecular structures. Relatively high resolution of this novel microscopic technique, comparable to the fluorescence lifetime microscopy, enables its application in a nanoscale imaging and in nanothermography.

Recycling of energy dissipated as heat accounts for high activity of Photosystem II

“…Such a process is highly probable in the photosynthetic apparatus, owing to the fact that the overall energy conversion efficiency in photosynthesis does not exceed 6 % and most of the energy of absorbed light quanta is dissipated as heat 21,22 . It should be emphasized that the illuminated LHCII proved to be a very efficient emitter of heat that can be transmitted over long distances in the supramolecular structures of the protein 23 . The fact that fluorescence emission from the E700 can be detected at low temperatures, enables to determine fluorescence lifetime of this state (reported in the diagram, Fig.…”

Recycling of Energy Dissipated as Heat Accounts for High Activity of Photosystem II

“…This means that the observed thermally driven up-conversion has to be combined with a thermal deactivation of chromophores electronically excited and localized in the close neighborhood. It should be emphasized that the illuminated LHCII proved to be a very efficient emitter of heat that can be transmitted over long distances in the supramolecular structures of the protein . The fact that fluorescence emission from the E700 can be detected at low temperatures enables the determination of the fluorescence lifetime of this state (Figures and S3).…”

“…It should be emphasized that the illuminated LHCII proved to be a very efficient emitter of heat that can be transmitted over long distances in the supramolecular structures of the protein. 31 The fact that fluorescence emission from the E700 can be detected at low temperatures enables the determination of the fluorescence lifetime of this state (Figures 3 and S3). It appears that the average lifetime of the E700 is substantially longer than that of the E680 state: 4.18 ns versus 2.44 ns, very close to the previous determinations of similar LHCII systems.…”