Abstract:
A novel pH sensitive, colorimetric ionic liquid nanosensor based on phosphonium salts of
fluorescein is reported. Herein, fluorescein salts of various stoichiometries were synthesized by
use of a trihexyltetradecylphosphonium cation [TTP]
and
monoanionic [FL]
+
in combination with dianionic [FL]
2−
−
fluorescein. Nanomaterials derived from these two compounds yielded
contrasting colorimetric responses in neutral and acidic environments. Variations in fluorescence
spectra as a function of pH were also observed. Examination of TEM and DLS data revealed
significant expansion in the diameter of [TTP]2[FL] nanodroplets in acidic environments of
variable pHs. A similar trend was also observed for [TTP][FL] nanoparticles. The pH dependent
colorimetric and other optical properties of these nanomaterials are attributed to alterations in
molecular orientations and stacking as suggested by measuring the absorption, fluorescence, and
zeta potential. Since the pH is an important indicator for many diseases, including cancer, these
nanosensors are considered to be potential candidates for biomedical applications.
