Complexes of rare earth ions embedded in Poly(lactic-co-glycolic acid) (PLGA) nanoparticles: Characterization and spectroscopic study

Several Eu(III) complexes [(Eu(L1)(tta)2(H2O)]∙CF3SO3, Eu(L2)(NO3)3 and Eu(L3) with L1 = N,N’-bis(2-pyridylmethylidene)-1,2-(R,R+S,S)-cyclohexanediamine, L2 = N, N’-bis(2-quinolylmethylidene)- 1,2-(R,R+S,S)-cyclohexanediamine, L3 N-quinolyl-N,N’,N’-trans-l,2-cyclohexylenediaminetriacetic acid and tta = 2-thenoyltrifluoroacetyl-acetonate] and one Y(III) complex [(Y(L1)(tta)2(H2O)]∙CF3SO3] have been embedded, with a different degree of efficiency, in Poly(lactic-co-glycolic acid) (PLGA) matrix by using two different composition [Poly(lactic(50%)-co-glycolic acid(50%), briefly PLGA 50:50 and Poly(lactic(75%)-co-glycolic acid(25%), briefly PLGA 75:25], giving nanoparticles characterized by a monodispersed distribution of the size (diameter around 200 nm). The [Eu(L1)(tta)2(H2O)]∙CF3SO3 shows the most efficient Eu(III) luminescence (ɸTot = 25%) when embedded in PLGA 75:25. The release of the complex over the time in aqueous buffered solution has been followed by means of the decrease of Eu(III) luminescence and it is faster upon increasing the temperature to 37°C, in particular for the PLGA 50:50 system, whose melting temperature (Tm) is lower (33°C) than both the Tm of PLGA 75:25 (38°C) and the basal one.