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

Abstract

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) asa bridging ligand (to sensitize the Eu3+ fluorescence) and terephthalic acid (TA) acting as a functional ligand to recognize the hydroxy radical (•OH). The quenching of Eu3+ fluorescence (measured at excitation/emission wavelengths of 288/615nm) 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, the fluorescence of Eu/DPA-TA showed ratiometric changes in that the TA sensitized fluorescence (peaking at 445nm) is switched on, while the plain Eu3+ fluorescence (peaking at 615nm) decreases. This finding led to a method for the ratiometric (2-wavelength) detection of OH˙ with a 0.5μM detection limit. The method also allows OH˙ to be detected with bare eyes at OH˙ concentrations as low as 10μM. In our perception, this study paves the way towards the design of new functionalized lanthanide coordination polymers for fluorometric assays and biomedical imaging. Graphical abstract Schematic of a ratiometric fluorescent assay for the detection of hydroxy radical (•OH) based onthe use of a europium(III)/dipicolinic acid coordination polymer (Eu/DPA CP) functionalized with terephthalic acid (TA). A gradual color change from red to blue can be observed and correlated to •OH concentrations.