Case Studies
Single Molecule Excitation Spectroscopic Imaging
Prof. Juergen Koehler of University of Bayreuth, Germany, has used a back-illuminated
EMCCD to probe spectral absorption characteristics of single molecules. Prof. Koehler
has interrogated the photophysics of light harvesting complex (LH2) of photosynthetic
purple bacterium, performing extensive probing of many single molecules in parallel.
Typically 40 to 60 LH2 complexes are imaged by the EMCCD at any one time.
Nominal spectral bandwidth of excitation is dictated by the mutual relationship
of the scanning laser with the frame rate of the EMCCD, and amounts to ~ 0.1nm,
~ 300 exposures per spectrum. For each imaged sample region, a series of 50 successive
laser scans was recorded, where the polarization of the incident laser field was
rotated by 18 percent between two scans, corresponding to five complete turns of
polarization.
The enhanced statistical relevance of the results obtained through parallel measurement
has lead to higher quality measurements and drastically improved experimental throughput
compared with experiments using sequential scanning spectroscopy and a single-channel
APD for detection.
Surface intensity plot from a region of the illuminated field. A wavelength vs polarization
vs intensity analysis is shown for one single LH2 molecule from within this field.