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24 Typical Applications

The luminescence light is detected the same way as for fluorescence decay measurement. The

reference pulses for the DPC-230 are obtained from a second output of the DDG-200 pulse

generator.

For microsecond lifetime measurement the DPC-230 is operated in the multiscaler mode. The

system parameters are shown in Fig. 32. The other parameters are the same as for fluorescence

decay measurement. A typical result is shown in Fig. 33.

Fig. 32: System parameters for microsecond-luminescence decay measurement

Fig. 33: Luminescence decay recorded with the system parameters shown in Fig. 32. Left: Logarithmic scale.

Right: Linear scale

Fluorescence Correlation

Fluorescence correlation spectroscopy (FCS) is based on exciting a small number of mole-

cules in a femtoliter volume and correlating the fluctuations of the fluorescence intensity. The

fluctuations are caused by diffusion, rotation, intersystem crossing, conformational changes,

or other random effects. The required femtoliter volume can be obtained one-photon excita-

tion and confocal detection or by two-photon excitation. The technique dates back to a work

of Magde, Elson and Webb published in 1972 [20]. Theory and applications of FCS are de-

scribed in [8, 27, 28, 29, 30].

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Cornelius DPC 230 Especificaciones Pagina 30