F. Iovino, A. Spyrogianni, G.A. Sotiriou
Keywords: fluorescence bioimaging, pathogen-host interactions, S. pneumoniae
Summary:Luminescent rare-earth-based inorganic nanoparticles (nanophosphors) are promising bioimaging agents due to their high photostability, sharp emission bands and high biocompatibility overcoming toxicity-related concerns associated with the commonly-used heavy-metal containing quantum dots. Flame aerosol technology provides a scalable and highly reproducible process for production of such nanophosphors (e.g. Y2O3:Eu3+,Tb3+) with precise control of their composition and properties [1,2,3]. Nanophosphors that can be excited in the near- ultraviolet and visible region, such as YVO4:Eu3+,Bi3+, provide a useful tool for bioimaging and in vitro dosimetry studies using conventional fluorescence microscopes. Here, YVO4:Eu3+,Bi3+ nanophosphors are made by flame spray pyrolysis. The optimal Bi content for maximum red- shift of their excitation band edge towards the visible region is identified through systematic experiments. The nanophosphors with the optimal composition are highly crystalline and appear bright red under a conventional fluorescence microscope. Their photostability during dynamic imaging of cells in vitro is confirmed, contrary to commercial fluorescent (organic-dye labeled) SiO2 nanoparticles that exhibit 50% photobleaching within 3.5 h. Furthermore, the feasibility of the developed nanoparticles as superior bioiamging agents is demonstrated by studying the pathogen-host interactions of human lung endothelial cells with S. pneumoniae over time upon (i) the nanoparticle labelling of the cells incubated with GFP-expressing S. pneumoniae bacteria, and (ii) by the biofunctionalization of the luminescent nanoparticles with targeting antibodies. The nanobiointeractions are examined in both upright and inverted cell culture orientations , validating the antibody selectivity towards the targeted cells.  Sotiriou, G.A., Schneider, M., & Pratsinis, S.E., J. Phys. Chem. C 115, 1084-1089 (2011) .  Sotiriou, G.A., Schneider, M., & Pratsinis, S.E., J. Phys. Chem. C 116, 4493-4499 (2012).  Sotiriou, G.A., Franco, D., Poulikakos, D., & Ferrari, A., ACS Nano 6, 3888-3897 (2012).  Spyrogianni, A., Herrmann, I.K., Lucas, M.S., Leroux, J.C., & Sotiriou, G.A., Nanomedicine 11, 2483-2496 (2016).