Fluorescence emission polarization

Pulsed method. Using a pulsed or modulated excitation light source instead of constant illumination allows investigation of the time dependence of emission polarization. In the case of pulsed excitation, the measured quantity is the time decay of fluorescent emission polarized parallel and perpendicular to the excitation plane of polarization. Emitted light polarized parallel to the excitation plane decays faster than the excited state lifetime because the molecule is rotating its emission dipole away from the polarization plane of measurement. Emitted light polarized perpendicular to the excitation plane decays more slowly because the emission dipole moment is rotating towards the plane of measurement. 

Effect of polarity on fluorescence emission. Polarity probes... 

Alternatively, an ordered, stable array of macromolecules may evolve at the surface with increasing time and/or bulk concentration. Since the excitation light is plane-polarized, the decay in emission signal may be a reflection of preferential orientation of 7-globulin molecules with time or enhanced surface packing densities. Fluorescence emission polarization studies should tell us more about this in the future. 

One of the easiest and most commonly used techniques to study the anisotropic optical properties of dye molecules is fluorescence anisotropy (FA). A dilute solution of the dye is excited with vertically polarized light and the fluorescence emission polarized parallel (I ) and perpendicular (I ) to the electric field vector of the exciting beam are detected with a 90 -scattering geometry, see figure 1. The FA is defined as ... 

Figure 3.16 Illustrations of the use of a polarizing beam splitter to select fluorescence emission polarization (a) and a dichroic mirror to process two-colour fluorescence emission in experiments such as FRET (b).

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