Rhodamine-based ratiometric fluorescent ion-selective bulk optodes

We developed the highly sensitive bulk optodes with new synthesized rhodamine type of fluorescent chromoionophore. The fluorescent turn-on through spirolactam ring-opening of rhodamine dye inside the hydrophobic polymer phase can only be obtained by incorporating cation exchanger into the sensing membrane. The rhodamine-based optode containing copper ionophore exhibited nanomolar detection limit to copper ion at pH 5.5. By introducing an inert BODIPY derivative B as the reference dye, a fluorescence resonance energy transfer (FRET) process is established between the chromoionophore and the reference dye to allow the ratiometric fluorescence measurement. The discrimination between metal ions has been achieved by simply introducing different kinds of commercially available ionophores into the membrane. The proposed optodes exhibited wide response range, excellent reproducibility and fast response time.