Preparation of visible-light-excited europium biolabels for time-resolved luminescence cell imaging application

By using a visible-light-excited ternary Eu3+ complex, BHHBCB-Eu3+-BPT (BHHBCB: 1,2-bis[4′-(1“,1“,1“,2“,2“,3“,3“-heptafluoro-4″,6″-hexanedion-6″-yl)-benzyl]-4-chlorosulfobenzene; BPT: 2-(N,N-diethylanilin-4-yl)-4,6-bis(pyrazol-1-yl)-1,3,5-triazine), as a luminophore, two kinds of novel visible-light-excited europium materials, the silica-encapsulated BHHBCB-Eu3+-BPT (Eu@SiO2) nanoparticles and BHHBCB-Eu3+-BPT-conjugated bovine serum albumin (BSA–BHHBCB-Eu3+-BPT), were prepared for biolabeling and time-resolved luminescence cell imaging applications. The Eu@SiO2 nanoparticles, prepared by the copolymerization of 3-aminopropyl(triethoxy)silane–BHHBCB-Eu3+-BPT conjugate, free 3-aminopropyl(triethoxy) silane and tetraethyl orthosilicate in a water-in-oil reverse microemulsion, are monodispersed, spherical and uniform in size, and strongly luminescent with an excitation peak at ∼400 nm and a long luminescence lifetime of 346 μs. The BSA–BHHBCB-Eu3+-BPT, prepared by covalent binding of BHHBCB-Eu3+-BPT to BSA, shows also strong visible-light-excited luminescence with a excitation peak at ∼400 nm and a long luminescence lifetime of 402 μs. The two materials were used for labeling transferrin and folic acid. Using the time-resolved luminescence imaging of living HeLa cells, the cell-surface receptors of transferrin and folic acid were successfully visualized by the prepared biolabels based on the ligand–receptor affinity binding interaction. The results demonstrated the feasibility of the new materials as visible-light-excited biolabels for the time-resolved luminescence cell imaging.