How the optical fibre pH microsensors work?

Just browsed through the chemical sensor products of the company, called PreSens (<https://www.presens.de/products/ph/sensors>) in order to look for a precise method to measure pH change in a physiological solution (Dulbecco's Phosphate Buffer Saline 1M).


I just would like to know how the "Sensor Spot" and "Needle type" optical sensors work exactly. According to the brochure on the aforementioned page, the Sensor Spots seem to based on fluorescence quenching: basically a quencher (I believe the hydrogen ions or the hydronium ions? I'm not sure) reduce the detected fluorescence intensity of the fluorophore (some pH dependent dye incorporated into a membrane "spot").


I would like to know more about this mechanism, I leafed through numerous reviews, but I have not be able to find any detailed information about pH detection based on fluorescence quenching. What is the quencher here? Could you tell me what is the mechanism in this particular case?


Thank you for your time.


