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. Author manuscript; available in PMC: 2013 Jan 1.
Published in final edited form as: Biophys Chem. 2011 Sep 8;160(1):12–19. doi: 10.1016/j.bpc.2011.08.006

Figure 2.

Figure 2

Single-oligomer spectroscopy. A) Light (488 nm) from a Kr-Ar laser is focused to a diffraction-limited spot by the objective of an inverted fluorescence microscope. A nanopositioning stage scans the sample over the laser, which excites individual surface-tethered peptide species. Fluorescence is collected by the objective, filtered by dichroic (D) and notch (N) filters to remove laser light, and detected by an avalanche photodiode (APD) detector. B) During laser excitation, a monomer exhibits one characteristic fluorescence intensity (broadened by shot noise) until irreversible photobleaching occurs, returning the measured intensity to background levels. C) A dimer displays two distinct intensity levels above background. Initially, laser excitation results in fluorescence from both dyes, until one photobleaches, causing a discrete drop in measured intensity. Photobleaching of the second dye results in a return to background intensities.