acceptor distances were controlled by building an inactive silica shell around the
UCNP core. The thickness of the silica shell bears an influence on the upconversion
luminescence (in particular, increasing brightness by reducing superficial defects
and quenching by solvent molecules) as well as in ET efficiency. Interestingly,
shorter distances between the UCNP surface and rose bengal did not translate into
higher ET efficiency which was achieved when the separation was about 6 nm.
We have also prepared an UCNH consisting of a NaYF 4 :Yb,Er UCNP, capped
with polyethylene glycol (PEG), and a diiodo-substituted BODIPY (IBDP) as the
photosensitizer, i.e., UCNP-IBDP@PEG UCNHs [2]. The IBDP absorption spectrum overlaps the green luminescence of NaYF 4 :Yb,Er. This UCNH showed a
decrease in its green to red emission compared to that of the precursor (NaYF 4 :Er
3
+
,Yb
3+ UCNP) upon NIR excitation. Time-resolved experiments demonstrated that
the quenching of the green upconverted emission was due to resonance ET from the
UCNP to the IBDP [37]. Moreover, singlet oxygen was detected by using a chemical
probe, and then, the UCNH was tested to check its feasibility for cell killing. In vitro
assays with SH-SY5Y human neuroblastoma-derived cells proved that the UCNH
induced about 50% cancer cell death after NIR light irradiation (Fig. 8).
Remarkably, the combination of PSs with UCNPs has been optimized to make
the most out of it by simultaneously activating two photosensitizers for enhanced
PDT. For example, Zn-PC and merocyanine 540 has been encapsulated in NaYF 4 :
Yb,Er nanoparticles coated with mesoporous silica. The UCNP efficiently
upconverted the energy of NIR light to Vis light (green and red emissions) and
transferred it to the encapsulated photosensitizers since their absorption matched
perfectly well the upconversion emission. The results of this study showed that this
nanohybrid was capable of enhancing the therapeutic efficacy of PDT when activated at a single 980 nm wavelength [114].
Later on, IR-808-sensitized UCNHs carrying dual PSs as PDT agent have been
designed [115]. The UCNH consisted of a core-shell NaGdF 4 :Yb,Er@NaGdF 4 :Nd,
Yb nanoparticle, Ce6 covalently conjugated to mesoporous silica shell and MC540
loaded inside the silica channels via electrostatic interactions. This UCNH enabled
the generation of cytotoxic ROS under 808 nm light thanks to the absorption of the
upconverted green and red light by each PS (MC540 and Ce6, respectively) [115].
5 Theragnosis
Theragnosis has emerged as a new concept in next-generation medicine to include
combinations of simultaneous imaging (e.g. for diagnosis) and targeted therapy.
Cutting-edge nanotheranostic agents are designed to contain those combinations in
single integrated nanohybrids aiming to offer individualized treatments based on
in vivo molecular images to allow for a comprehensive diagnosis [116–118]. Several
NPs have been used as platforms for theragnosis based on nanoparticles [119, 120],
such as magnetic NPs [121], gold nanoparticles [122], silica NPs [123, 124], carbon
nanotubes [125, 126], quantum dots [127] and UCNPs [6, 128] among others.
388
J. Ferrera-González et al.
UCNP core. The thickness of the silica shell bears an influence on the upconversion
luminescence (in particular, increasing brightness by reducing superficial defects
and quenching by solvent molecules) as well as in ET efficiency. Interestingly,
shorter distances between the UCNP surface and rose bengal did not translate into
higher ET efficiency which was achieved when the separation was about 6 nm.
We have also prepared an UCNH consisting of a NaYF 4 :Yb,Er UCNP, capped
with polyethylene glycol (PEG), and a diiodo-substituted BODIPY (IBDP) as the
photosensitizer, i.e., UCNP-IBDP@PEG UCNHs [2]. The IBDP absorption spectrum overlaps the green luminescence of NaYF 4 :Yb,Er. This UCNH showed a
decrease in its green to red emission compared to that of the precursor (NaYF 4 :Er
3
+
,Yb
3+ UCNP) upon NIR excitation. Time-resolved experiments demonstrated that
the quenching of the green upconverted emission was due to resonance ET from the
UCNP to the IBDP [37]. Moreover, singlet oxygen was detected by using a chemical
probe, and then, the UCNH was tested to check its feasibility for cell killing. In vitro
assays with SH-SY5Y human neuroblastoma-derived cells proved that the UCNH
induced about 50% cancer cell death after NIR light irradiation (Fig. 8).
Remarkably, the combination of PSs with UCNPs has been optimized to make
the most out of it by simultaneously activating two photosensitizers for enhanced
PDT. For example, Zn-PC and merocyanine 540 has been encapsulated in NaYF 4 :
Yb,Er nanoparticles coated with mesoporous silica. The UCNP efficiently
upconverted the energy of NIR light to Vis light (green and red emissions) and
transferred it to the encapsulated photosensitizers since their absorption matched
perfectly well the upconversion emission. The results of this study showed that this
nanohybrid was capable of enhancing the therapeutic efficacy of PDT when activated at a single 980 nm wavelength [114].
Later on, IR-808-sensitized UCNHs carrying dual PSs as PDT agent have been
designed [115]. The UCNH consisted of a core-shell NaGdF 4 :Yb,Er@NaGdF 4 :Nd,
Yb nanoparticle, Ce6 covalently conjugated to mesoporous silica shell and MC540
loaded inside the silica channels via electrostatic interactions. This UCNH enabled
the generation of cytotoxic ROS under 808 nm light thanks to the absorption of the
upconverted green and red light by each PS (MC540 and Ce6, respectively) [115].
5 Theragnosis
Theragnosis has emerged as a new concept in next-generation medicine to include
combinations of simultaneous imaging (e.g. for diagnosis) and targeted therapy.
Cutting-edge nanotheranostic agents are designed to contain those combinations in
single integrated nanohybrids aiming to offer individualized treatments based on
in vivo molecular images to allow for a comprehensive diagnosis [116–118]. Several
NPs have been used as platforms for theragnosis based on nanoparticles [119, 120],
such as magnetic NPs [121], gold nanoparticles [122], silica NPs [123, 124], carbon
nanotubes [125, 126], quantum dots [127] and UCNPs [6, 128] among others.
388
J. Ferrera-González et al.