Hello Ciaran Daly

Lasers illuminate the stream with coherent, focused light of specific wavelength and power. This illumination facilitates the generation of fluorescence signals from cells labelled with fluorophores and light scatter signal from redirected laser light.

Filters placed in front of the detectors, function to restrict the light that is introduced to the detectors so that each detector can be dedicated to measure fluorescence from a specific set of fluorophores.

Most flow cytometers use separate channels and detectors to detect emitted light, the number of which vary according to the instrument. Photomultiplier tubes are the most commonly used detectors.

The specificity of detection is controlled by the optical filters, which block certain wavelengths whilst transmitting others. As you may know that there are three filter types:

Long pass filters allow light through above a cutoff wavelength.

Short pass filters permit light below a certain wavelength.

Band pass filters transmit light within a specified narrow range of wavelengths.

So, each set of filter serves to direct the specific wavelengths of light to their matching detector.

For instance, in a parallel laser arrangement, lasers excite the same cell at different times and each laser has its own detector.

Let us say, you might consider using two fluorophores that have the same emission but are excited at different wavelengths. For example, PE-AF647 excited at 488nm and APC excited at 633nm. Both dyes emit in the 680nm region. The PE-AF647 dye would be excited only by the 488nm laser and the emission light would be collected by the detector designated for that laser line. On the same cell, the APC dye would be excited only by 633nm laser after the first dye was excited and the emission would be collected by its designated detector.

It is important that you understand the setup of your instrument before planning your experiment.

Best.

Typically, the 488/8 filter is used for FSC or SSC