Fluorescence and photobleaching dynamics of single light-harvesting complexes

Abstract

Single light-harvesting complexes LH-2 from Rhodopseudomonas acidophila were immobilized on various charged surfaces under physiological conditions. Polarized light experiments showed that the complexes were situated on the surface as nearly upright cylinders. Their f luorescence lifetimes and photobleaching properties were obtained by using a confocal f luorescence microscope with picosecond time resolution. Initially all molecules f luoresced with a lifetime of 1 ؎ 0.2 ns, similar to the bulk value. The photobleaching of one bacteriochlorophyll molecule from the 18-member assembly caused the f luorescence to switch off completely, because of trapping of the mobile excitations by energy transfer. This process was linear in light intensity. On continued irradiation the f luorescence often reappeared, but all molecules did not show the same behavior. Some LH-2 complexes displayed a variation of their quantum yields that was attributed to photoinduced confinement of the excited states and thereby a diminution of the superradiance. Others showed much shorter lifetimes caused by excitation energy traps that are only Ϸ3% efficient. On repeated excitation some molecules entered a noisy state where the f luorescence switched on and off with a correlation time of Ϸ0.1 s. About 490 molecules were examined.

Nanoantenna enhanced emission of light-harvesting complex 2: the role of resonance, polarization, and radiative and non-radiative rates

“…The total distance between the LH2 emitter and the gold is the sum of the SAM thickness (2.3 nm 42 ) and the distance between B850 and the SAM. Assuming that the LH2 cylinders lie flat on the SAM, as has been observed for various charged surfaces, 43 the B850 to SAM distance is B3.5 nm for LH2 from Rhodopseudomonas acidophila. 39,44 This gives a total spacing between the emitter and the surface of B6 nm, while the distance to the B800 ring is B1.5 nm less.…”

Photophysics of Individual Single-Walled Carbon Nanotubes

“…169 It is also possible to observe additional unique behavior such as fluorescence intermittency (i.e., blinking) that cannot be observed for bulk samples. 170 Ensemble studies benefit significantly from the clarification of fundamental photophysical behavior that is exposed on the single particle level, which has catalyzed single molecule studies for many fluorescent systems including dyes, 171-174 polymer chains, 175,176 proteins, [177][178][179] semiconductor quantum dots, 170,180,181 and single-walled carbon nanotubes. 72,77,182 The observation of fluorescence from individual SWNTs was first reported in 2003 and, importantly, confirmed spectral assignments of (n,m) made on the ensemble level.…”

Hidden Markov Model Analysis of Multichromophore Photobleaching

“…16,47 Structural fluctuations were observed to change the polarization properties of LH2 because of the sensitivity of chromophore electronic coupling on geometry. 16,47 In the case of TMRdextran conjugates each polymer is of finite size and is labeled with several dyes. The dyes can, in principle, couple.…”

“…3,15 In principle, it is possible to use this methodology to distinguish multiple dark states that are attributed to various damaged states of fluorescent probes. 16 The dark state dwell times coupled with the identification of the preceding (prior) and succeeding (posterior) bright states are the only information that can provide knowledge about the dark states. Sorting the dwell-time distributions by prior and posterior states can limit the kinetic schemes, however this approach requires a large number of observations of dark states for each possible pair of prior and posterior states.…”