A novel luminescent Europium(III) complexes for citrate detection.

Rationally designed Eu(III) complexes can be exploited as probes in the detection of analytes in biological fluids, by means of luminescence.[1] These complexes must be stable in aqueous solution, absorb and efficiently transfer the UV excitation to the metal ion (antenna effect). We succeeded to obtain this goal by including isoquinoline antenna into the ligand backbone. In fact, the luminescence of [Eu(bisoQcd)]+ (Figure 1) and Eu(isoQC3A) complexes significantly increases in the presence of the main analytes which constitute the interstitial extracellular fluid (i.e. hydrogen carbonate, serum albumin (SA) and citrate).[2,3]. Eu(III) complex suitable for citrate sensing The optical response of our Eu(III)-based probes is selective towards citrate molecule, when a complex matrix is considered. Citrate molecule is a very important bio-analyte and the monitoring of its concentration is crucial in order to identify the presence of metabolic disease.[4] When a simulated interstitial extracellular fluid is employed, the change of the citrate concentration gives rise to an increase of the Eu(III) luminescence emission intensity of [Eu(bisoQcd)]+. On the other hand, negligible or no change of the luminescence intensity was detected when the concentration of both hydrogen carbonate and SA is changed. This is due to citrate capacity to displace a higher number of water molecules giving a distinctive increase of the luminescence intensity. Moreover, the Eu(III) intrinsic quantum yield of the adduct is higher. The obtained results candidate our europium complexes as viable probes for luminescence analysis of biofluids with complex matrix. Acknowledgments: The work was financially supported by PRIN project "CHIRALAB", grant n. 20172M3K5N. [1] J.-C.G. Bünzli, Chem. Rev. 2010, 110, 2729. [2] C. De Rosa, A. Melchior, M. Sanadar, M. Tolazzi, A. Giorgetti, R. P. Ribeiro, C. Nardon, F. Piccinelli, Inorg Chem. 2020, 59, 12564. [3] C. De Rosa, A. Melchior, M. Sanadar, M. Tolazzi, A. Duerkop, F. Piccinelli, Dalton Trans. 2021, 50, 4700. [4] L. C. Costello, R. B. Franklin, Prostate Cancer Prostatic Dis. 2009, 12, 17