Ultrabright Terbium Nanoparticles for FRET Biosensing and in Situ Imaging of Epidermal Growth Factor Receptors*.

Lanthanide-doped nanoparticles (LnNPs) have become an important class of fluorophores for advanced biosensing and bioimaging. LnNPs that are photosensitized by surface-attached antenna ligands can possess exceptional brightness. However, their functional bioconjugation remains an important challenge for their translation into bioanalytical applications. To solve this problem, we designed a ligand that can be simultaneously applied as efficient light harvesting antenna for Tb surface ions and strong linker of biomolecules to the LnNPs surfaces. To demonstrate generic applicability of the photosensitized TbNP-bioconjugates, we applied them in two prototypical applications for biosensing and bioimaging. First, in-solution biorecognition was shown by time-resolved Förster resonance energy transfer (FRET) between streptavidin-functionalized TbNPs to biotinylated dyes (ATTO 610). Second, in situ detection of ligand-receptor binding on cells was accomplished with TbNP-antibody (Matuzumab) conjugates that could specifically bind to transmembrane epidermal growth factor receptors (EGFR). High specificity and sensitivity were demonstrated by time-gated imaging of EGFR on both strongly (A431) and weakly (HeLa and Cos7) EGFR-expressing cell lines, whereas non-expressing cell lines (NIH3T3) and EGFR-passivated A431 cells did not show any signals. Despite the relatively large size of TbNP-antibody conjugates, they could be internalized by A431 cells upon binding to extracellular EGFR, which showed their potential as bright and stable luminescence markers for intracellular signaling.

Ultrabright Lanthanide Nanoparticles.

Invited for this month's cover are the collaborating groups of Dr. Loïc J. Charbonnière at CNRS/Université de Strasbourg, France and Dr. Ka-Leung Wong at Hong Kong Baptist University, Hong Kong. The cover picture shows terbium-doped LaF3 nanoparticles that are surface functionalized by photon-harvesting antenna ligands. Surface capping with antenna ligands leads to ultrabright nanoparticles, with the typical green luminescence signature of the Tb atoms and very long excited-state lifetimes. These lanthanide dots can be incorporated into living cells at nanomolar concentrations for luminescence microscopy imaging. Read the full text of the article at 10.1002/cplu.201600007.

Ultrabright Lanthanide Nanoparticles.

Tb-doped La0.9 Tb0.1 F3 nanoparticles were prepared by a simple and reproducible microwave-assisted synthetic protocol in water. The nanoparticles were characterized by XRD, TEM, dynamic light scattering and inductively coupled plasma atomic emission spectroscopy elemental analysis. Eleven ligands with varying coordination and photosensitizing abilities were designed to bind at the surface of the Tb-doped nanoparticles. The photosensitizing behavior was monitored by electronic absorption spectroscopy and steady-state and time-resolved emission spectroscopy. The two most effective photosensitizing ligands were used to isolate and purify the capped nanoparticles. The composition and spectroscopic properties of these nanoparticles were measured, which revealed either 2660 and 5240 ligands per nanoparticle, molar absorptivities of 7.6×106 and 1.6×107 m-1 cm-1 and luminescence quantum yields of 0.29 and 0.13 in water, respectively. These data correspond to exceptional brightness values of 2.2×106 and 2.1×106 m-1 cm-1 , respectively. The as-prepared nanoparticles were imaged in HeLa cells by fluorescence microscopy, which showed their specific localization in lysosomes.