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

Abstract

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 (χ_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 χ_SDS, 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.