Fluorescent potentiometric indicators

Other fluorescent colorants can be used to produce pH, pNHs, and pCX)2 optical sensors. One example is the trisodium salt of 8-hydroxy 1,3,6-pyrenetrisulfonic acid (called HOPS A or HPTS) whose basic form can be excited at 470 nm to emit fluorescence at 510 nm [203, 204]. The CX)2 optical sensor requires a silicone membrane to contain a bicarbonate solution, just like potentiometric pC02 electrodes. A further similarity with potentiometric electrodes is that the pH, pNHs and pC02 optical sensors serve as the bases for enzyme sensors. The appropriate enzymatic membrane is simply attached. The optical sensor for penicillin uses penicillinase to catalyse the transformation of penicillin into penicilloic acid. The acid is detectable with a pH optical sensor that uses fluorescein isothiocyanate (FITC) as a colored indicator [205]. 

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