Temperature-Induced Energy Transfer in Dye-Conjugated
Upconverting Nanoparticles: A New Candidate for Nanothermometry
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Abstract
Lanthanide-doped upconverting nanoparticles
(UCNPs) are highly
promising candidates for bioimaging and for cellular nanothermometry
as a novel diagnostic tool. Aiming for the diagnosis of diseases at
very early stages in order to optimize therapy and recovery of the
patient, it must be taken into account that thermal singularities
are often one of the first indicators of a disease. It is therefore
our goal to develop a nanothermometer based on UCNPs that is suitable
to detect the temperature at a subcellular level in the physiological
range. Thus, upconverting NaGdF<sub>4</sub>:Er<sup>3+</sup>,Yb<sup>3+</sup> nanoparticles that convert near-infrared (NIR) into visible
(VIS) light are synthesized by thermal decomposition. Appropriate
surface modification with a thermoresponsive polymer pNIPAM (poly(<i>N</i>-isopropylacrylamide)) guarantees dispersibility in aqueous
media required for biomedical applications. In a further step, the
combination of the obtained UCNPs with an organic dye (FluoProbe532A)
provides potential donor-acceptor-pairs allowing for energy transfer
processes, whereas the light emitted by the Er<sup>3+</sup> ions (donors)
is absorbed by the organic dye (acceptor). It has been demonstrated
that the dye-conjugated UCNPs undergo a temperature-dependent energy
transfer process inducing a temperature-dependent increase in the
thermal sensitivity when compared to unlabeled UCNPs. This result
indicates the great potential of the presented nanoprobes for applications
in nanothermometry