Use of Lanthanide-Containing Polyoxometalates to Sensitise the Emission of Fluorescent Labelled Serum Albumin.

Monitoring the interaction of biomolecules is important, and the use of energy transfer is a principal technique in elucidating nanoscale interactions. Lanthanide compounds are promising luminescent probes for biological samples as their emission is longer-lived than any native autofluorescence. Polyoxometalates (POMs) are interesting structural motifs to incorporate lanthanides, offering low toxicity and a size pertinent for biological applications. Here, we employ iso-structured POMs containing either terbium or europium and assess their interaction with serum albumin by sensitisation of a fluorescent tag on the protein via LRET (luminescence resonance energy transfer) by exciting the lanthanide. Time-resolved measurements showed energy transfer with an efficiency of over 90% for the POM-protein systems. The Tb-POM results were relatively straightforward, while those with the iso-structured Eu-POM were complicated by the effect of protein shielding from the aqueous environment.