Smoothly shifting fluorescent windows: a tunable off-on-off micellar sensor for pH

The position of the window in an off-on-off fluorescent pH sensor may be shifted at will along a pH axis by changing the overall charge of the micellar container. This is obtained by using non-ionic Triton X-100 as the surfactant, and by increasing the molar fraction of the anionic sodium dodecyl sulfate (chi(SDS)) as co-surfactant, with pyrene as the fluorophore and a lipophilic tertiary amine and a lipophilic pyridine as pH-switchable quenchers. As the negative micellar charge increases by increasing cSDS, the observed pKa of the protonated bases move to higher pH values, followed by the dumb-bell shaped off-on-off fluorescence intensity vs. pH profile.