FCS Measurement Example

FCS measurement of freely diffusing Atto 655 molecules in ethylene glycol. The dye was excited with the cw-laser of the FluoView 1000 from Olympus at 633 nm and the fluorescence emission was detected through a 690 nm longpass filter by a single photon avalanche diode (SPAD), which was coupled to a corresponding emission port of the microscope using a multimode fiber. The signal from the SPAD was processed by the TimeHarp 200 using the PDL 800-B running at a repetition rate of 40 MHz as a synchronisation signal source, in order to form the necessary start-stop pulses for TCSPC. The confocal pinhole was set to 165 µm and the measurement time for this curve was 60 seconds.

The whole measurement could have also been done using the pulsed picosecond lasers of the LDH-series, which would have provided the additional opportunity to do TCSPC-FCS.