Ratiometric detection of hydroxy radicals based on functionalized europium(III) coordination polymers

A ratiometric fluorescent probe is described that is based on a functionalized europium(III) coordination polymer (Eu/DPA-TA). It can be fabricated by using dipicolinic acid (DPA) as a bridging ligand (to sensitize the Eu3+ fluorescence) and terephthalic acid (TA) acting as a functional ligand to recognize the hydroxy radical ((OH)-O-center dot). The quenching of Eu3+ fluorescence (measured at excitation/emission wavelengths of 288/615 nm) by water is strongly reduced in the presence of TA. This leads to a significant enhancement in the emission lifetime and intensity of Eu3+. Upon the addition of (OH)-O-center dot, the fluorescence of Eu/DPA-TA showed ratiometric changes in that the TA sensitized fluorescence (peaking at 445 nm) is switched on, while the plain Eu3+ fluorescence (peaking at 615 nm) decreases. This finding led to a method for the ratiometric (2-wavelength) detection of OH center dot with a 0.5 mu M detection limit. The method also allows OH center dot to be detected with bare eyes at OH center dot concentrations as low as 10 mu M. In our perception, this study paves the way towards the design of new functionalized lanthanide coordination polymers for fluorometric assays and biomedical imaging.