Preparation and functionalization of a visible-light-excited europium complex-modified luminescent protein for cell imaging applications

Lanthanide complex-based luminescent bioprobes have shown great utility in a variety of time-resolved luminescence bioassays, but these bioprobes often require UV excitation and suffer from problems related to bioaffinity and biocompatibility for in vivo applications. In this work, a new visible-light-excited europium(III) complex with the maximum excitation wavelength over 400 nm, BHHBB-Eu3+-BPT{BHHBB: 1,2-bis[4'-(1 '',1 '',1 '',2 '',2 '',3 '',3 ''-heptafluoro-4 '',6 '' -hexanedion-6 ''-yl)-benzyl]-benzene; BPT: 2{N,N-diethylanilin-4-yl)-4,6-bis(pyrazol-1-yl)-1,3,5-triazine}, has been synthesized for the preparation of an artificial luminescent protein that can be used as a visible-light-excited luminescent bioprobe for cell imaging. By encapsulating BHHBB-Eu3+-BPT into apoferritin with a simple dissociation-reassembly method, the luminescent protein, Eu@AFt, with a maximum excitation peak at 420 nm and a long luminescence lifetime of 365 mu s was fabricated and successfully used for visible-light-excited time-resolved luminescence cell imaging. Moreover, by conjugating a mitochondria-targeting molecule, (5-N-succinimidoxy-5-oxopentyl)-triphenylphosphonium bromide (SPTPP), onto the surface of Eu@AFt, a mitochondria-specifically-tracking luminescent probe, Eu@AFt-SPTPP, was further prepared and used for visible-light-excited confocal luminescence microscopy imaging to visualize the mitochondria of living cells.