Detection of Cu2+ ions in aqueous solution via emission quenching of colloidal EuPO4 ultrasmall nanoparticles

Abstract EuPO4 and Eu3+-activated REPO4 (RE = La, Dy, Er) ultrasmall fluorescent nanoparticles (NPs) with an average diameter of 2.1 nm were prepared via colloidal synthesis and tested for sensing Cu2+ and other heavy-metal ions. The pure monoclinic monazite crystal structure (space group P121/n1) of the synthesized particles was confirmed using X-ray diffraction measurements, and transmission electron microscopy images showed round particles with a narrow particle-size distribution. The NPs exhibited intense red emission, which is characteristic of the f-f electronic transition of Eu3+, and the quenching of their emission in the presence of heavy-metal ions was revealed by dispersing colloidal particles in a TRIS buffer and then performing photoluminescence measurements. Strong quenching of the emission (at a rate of 0.195 μM−1) was observed upon the addition of Cu2+ ions over the concentration range of 0–10 μM with a limit of detection of 60 nM for Cu2+. The recovery of nearly 90% of the original emission intensity of the probe was achieved via the addition of ethylendiaminetetraacetic acid and was possible in five quenching/recovery cycles.