A sodium ion sensor based on a covalently-linked aminorhodamine B–calix[4]arene chromoionophore

A fluorescent sodium optode based on a chromoionophore consisting of aminorhodamine B covalently-linked through an amide bond to a calix[4]arene has been developed. The optode, fashioned by incorporation of the chromoionophore into a single component polymer matrix, operates on the basis of on/off switching of aminorhodamine B fluorescence emission as a result of photo-induced intramolecular electron transfer, the efficiency of which is mediated by the complexation of sodium ions. The fluorescence intensity increased linearly with increasing sodium ion concentration in the range 0.01–2.0 M, exhibiting a three-fold enhancement over this range. The optode provides selectivity for sodium ions compared to potassium ions that is sufficient for clinical determinations of sodium ion concentration.