Targeted pH switched europium complexes monitoring receptor internalisation in living cells

Abstract

We report the design and evaluation of pH responsive luminescent europium(III) probes that allow conjugation to targeting vectors to monitor receptor internalisation in cells. The approach adopted here can be...

A ratiometric luminescence pH sensor based on YAG:V3+,V5+ nanoparticles

“…Recent studies have shown that, among lanthanide ions, Eu 3+ ions are the most prevalent in the development of new pH sensors having a MOF or a complex structure. 44,63,[65][66][67][68][69][70] As presented, these sensors can exhibit a wide usable pH range, covering 2-8, 66 1.05-9.85 67 and 1.06-10.99; 63 however, in this case, their sensing performance exploits a single emission intensity of Eu 3+ ions, which has been found to significantly reduce their reliability, especially when concerning biological applications. 36 From the sensing perspective, the ratiometric approach has been stated to be much more favorable in terms of highly sensitive and accurate pH measurements.…”

The design of responsive luminescent lanthanide probes and sensors

“…This approach has been described to follow the agonist-induced internalisation of the glucagon-like peptide-1 receptor (GLP-1R): a 5-fold increase in europium emission intensity was observed 1 h after agonist-induced internalisation of the receptor labelled with [EuL 23 ] 2À , (Scheme 8). 125 The GLP-1R receptor is a target for anti-diabetic drugs because it is involved in the metabolic pathway for insulin production.…”

“…Reproduced with permission from the Royal Society of Chemistry. 125 lifetime of the Eu 5 D 0 excited state, as the pH rises loss of a proton from the protonated amine or phenol group occurs, allowing fast electron transfer to the Eu ion, quenching its emission and shortening the 'time-averaged' observed lifetime. An alternative viewpoint is to say that there is a potential energy surface crossing of the 5 D 0 Eu excited state with the internal ligand to metal charge transfer state (LMCT) that involves the conjugated heteroatom and the extended p system.…”

“…12 pH Variation of europium emission of [EuL 23 ] 2À (l exc 332 nm, 295 K, 0.1 M NaCl); showing the variations of the europium emission intensity and lifetime (l exc 332 nm, l em 613 nm) with a pK a value of 6.18(03). Reproduced with permission from the Royal Society of Chemistry 125.…”

Comparative analysis of lanthanide excited state quenching by electronic energy and electron transfer processes

“…16 The large lifetime and emission intensity variations in these complexes has led to the creation of targeted luminescent pH probes for cells being developed to monitor receptor internalisation and endosomal acidication in real time. 11 The rate of proton transfer to and from nitrogen in aqueous solution (typically 10 10 s À1 ) occurs much more quickly than both the rate of decay of the excited europium ion (Table 1, 10 3 s À1 ) and the intermediate ligand ICT or triplet excited states. Furthermore, the rate of electron transfer from the lone pair orbital to the excited Eu ion is faster than the rate of energy transfer populating the Eu* 5 D 0 state, and much faster than the rate of decay of the Eu excited state itself.…”