Rhodamine-modified upconversion nanoprobe for distinguishing Cu2+ from Hg2+ and live cell imaging

Abstract

It is greatly important to seek a fast and sensitive method for the detection of Cu²⁺ ions because of their vital role in the human body. Fluorescent probes, especially the rhodamine derivatives, have been considered as promising candidates for detection of Cu²⁺ ions due to their attractive features. However, one problem frequently encountered in rhodamine-based fluorescent probes is that some of them could not distinguish Cu²⁺ from Hg²⁺ and these drawbacks limit their application in biological samples. In this paper, a rhodamine B derivative (RBH) was grafted to mesoporous silica coated upconversion nanoparticles (CS-UCNP) to fabricate a new organic–inorganic hybrid nanoprobe. On addition of Cu²⁺ ions, an emission band at about 580 nm appeared while the intensity of the green emission at about 545 nm of the nanoprobe decreased upon excitation of a 980 nm laser, implying that a luminescence resonance energy transfer (LRET) happened from the CS-UCNP to the RBH–Cu²⁺ complex. The obtained LRET nanoprobe could detect Cu²⁺ exclusively even in the presence of Hg²⁺ with a detection limit of 0.82 μM in absolute ethanol solution. Most importantly, this nanoprobe can be used for monitoring subcellular distribution of Cu²⁺ in living cells based on upconversion luminescence and downconversion fluorescence.