(615h) Highly-Stable and Near-UV Activated YVO4:Eu3+,Bi3+ Nanophosphors for Bioimaging and in vitro Dosimetry

Luminescent rare-earth-based inorganic
nanoparticles (nanophosphors)
are promising bioimaging agents due to
their high photostability, sharp emission bands and relatively low toxicity (Escudero et al, 2016a).
Flame aerosol technology provides
a scalable (Mueller et al, 2003) and
highly reproducible
(Strobel & Pratsinis, 2007) process
for production of such nanophosphors (e.g. Y₂O₃:Eu^3+,Tb3+) with precise control of their composition and properties (Sotiriou et al,
2011; Sotiriou et al, 2012). Nanophosphors that can be
excited in the near-ultraviolet and visible region, such as YVO₄:Eu^3+,Bi3+ (Takeshita
et al, 2008), provide a useful
tool for bioimaging (Escudero et al, 2016b) and in
vitro dosimetry (Halamoda-Kenzaoui
et al, 2015) studies using conventional
fluorescence microscopes.

         Here, YVO₄:Eu^3+,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 HeLa cells in vitro is confirmed, contrary to commercial
fluorescent (organic-dye labeled)
SiO₂nanoparticles that
exhibit 50% photobleaching within 3.5 h (Fig. 1).

Figure 1. Dynamic fluorescence microscopy imaging of HeLa cells co-incubated with YVO₄:Eu^3+,Bi3+nanophosphors
and fluorescent SiO₂nanoparticles.
The fluorescence intensity
of images corresponding to
YVO₄:Eu^3+,Bi3+
is stable with time (circles and red images), while that for
fluorescent SiO₂decreases down to 50% within 3.5 h (triangles and green images). The corresponding optical microscopy image in transmission mode at 0 h is also shown.

Furthermore, the deposition rate of these nanophosphors is measured by optical
absorption spectroscopy, indicating slower deposition rate in serum-containing than serum-free cell culture
medium, consistent with previous
studies for different nanomaterials
(Allouni et al, 2009; Spyrogianni
et al, 2016). This is also confirmed in vitro by monitoring the fluorescence intensity of images of HeLa cells after incubation
with nanophosphor
suspensions in the presence
and absence of serum for various time points (Halamoda-Kenzaoui
et al, 2015).

Allouni, Z.E., Cimpan, M.R., Hol, P.J., Skodvin,
T., & Gjerdet, N.R. (2009) Coll. Surf. B 68,
83-87.

Escudero, A., Carrillo-Carrion, C., Zyuzin,
M.V., & Parak, W.J. (2016a) Topics Curr. Chem. 374.

Escudero, A., Carrillo-Carrion, C., Zyuzin,
M.V., Ashraf, S., Hartmann,
R., Nunez, N.O., Ocana, M.,
& Parak, W.J. (2016b) Nanoscale
8, 12221-12236.

Halamoda-Kenzaoui,
B., Ceridono, M., Colpo,
P., Valsesia, A., Urban, P., Ojea-Jimenez,
I., Gioria, S., Gilliland,
D., Rossi, F., & Kinsner-Ovaskainen, A. (2015)
PLOS ONE 10, e0141593.

Mueller, R., Madler, L., & Pratsinis, S.E.
(2003) Chem. Eng. Sci. 58,
1969-1976.

Sotiriou, G.A.,
Schneider, M., & Pratsinis, S.E. (2011) J. Phys. Chem. C 115, 1084-1089.

Sotiriou, G.A., Franco, D., Poulikakos, D., &
Ferrari, A. (2012) ACS Nano 6, 3888-3897.

Spyrogianni, A., Herrmann, I.K., Lucas, M.S., Leroux,
J.C., & Sotiriou, G.A. (2016) Nanomedicine (Lond.) 11, 2483-2496.

Strobel, R.,
& Pratsinis, S.E. (2007) J. Mater. Chem. 17, 4743-4756.

Takeshita, S., Isobe, T., & Niikura, S.
(2008) J. Lumin. 128, 1515-1522.