Different nanoparticles, such as Ag 2 S nanodots and graphene oxide, have also
been used to build UCNH-based pH sensors. As an example, Xian et al. [52] built a
case (iii) LRET-based nanosensor based on the interaction of NaYF 4 :Yb,Er dense
silica-coated UCNPs and a NIR Ag 2 S nanodot pH probe (Table 1 entry 17). The
higher the pH (up to 10), the higher the emission of the probe (due to higher RET
efficiency between the UCNP and the nanodot). The ratio between the nanodot
emission at 800 nm and the emission band of Er at 540 nm showed a linear response
from pH 4 to 10 and good reversibility. In addition, it allowed for pH imaging in
living cells and in Zebrafish model.
Other dye-UCNP-based pH sensors can be found in Table 1. Please, check
references cited therein for further information.
3.4 Biomolecules and Ions Sensing
Recently Zhang et al. [67] reported a UCNH case (iii) RET-based sensor for the
synchronous detection of glutathione (GSH) and H 2 O 2 in vivo (Fig. 7a). The UCNH
consisted of a NaYF 4 :Yb,Er,Tm UCNP co-functionalized with two probes: a thiolcoumarin-based GSH-sensitive probe (TCG) and a benzopyrylium-coumarin-based
H 2 O 2 -responsive probe (BCH), respectively (Chart 1).
The probes were selected to quench different emissions of the UCNP,
540 (Er) and 650 nm (Tm), respectively, and each signal was referenced to another
unaffected upconversion emission at 800 nm (Tm) (Fig. 7b). The resulting sensing
proved to be selective and reached limits of detection (LOD) in the order of 10
À3 M
for GSH and 10
À6 M for H 2 O 2 .
Similarly, Li et al. [68] built a case (i) and (ii) hypochlorite (ClO
À ) nanosensor
which was based on the interaction between an Er core-shell nanoparticle, specifically β-NaYF 4 ;Yb,Nd,Er@β-NaYF 4 :Nd, and a cyanine 3 (Cy3; Fig. 3, Chart 1)
ClO
À probe. The absorption of the ClO
À -sensitive Cy3 affects the intensity of the
540 nm Er emission band, while that of the 650 nm Er emission remains identical. As
a result, the ratiometric response was obtained between those bands. This sensor
showed good linearity, a LOD of 27 ppb, high selectivity and a rapid response.
Moreover, it was successfully tested in vitro and in vivo.
Other nanoparticles have also been used as acceptors to develop sensors. Even if
it is out of the scope of the present chapter, a representative example is commented
below. Zourob et al. [69] designed a case (iii) complex DNA sensor based on
the quenching of the UCNP emissions by a gold nanoparticle (AuNP). The
nanoplatform consists of polystyrene-co-acrylic acid core capped with dense silica
and functionalized with α-NaYF 4 :Yb,Tm UCNPs. The platform is attached to a
AuNP nanoparticle through a single-strand DNA probe. When the specific singlestrand DNA sequence hybridizes the DNA probe, it induces a lengthening in the
AuNP-UCNP distance, and, consequently, the UCNP emissions are recovered.
Functional Nanohybrids Based on Dyes and Upconversion Nanoparticles
385
been used to build UCNH-based pH sensors. As an example, Xian et al. [52] built a
case (iii) LRET-based nanosensor based on the interaction of NaYF 4 :Yb,Er dense
silica-coated UCNPs and a NIR Ag 2 S nanodot pH probe (Table 1 entry 17). The
higher the pH (up to 10), the higher the emission of the probe (due to higher RET
efficiency between the UCNP and the nanodot). The ratio between the nanodot
emission at 800 nm and the emission band of Er at 540 nm showed a linear response
from pH 4 to 10 and good reversibility. In addition, it allowed for pH imaging in
living cells and in Zebrafish model.
Other dye-UCNP-based pH sensors can be found in Table 1. Please, check
references cited therein for further information.
3.4 Biomolecules and Ions Sensing
Recently Zhang et al. [67] reported a UCNH case (iii) RET-based sensor for the
synchronous detection of glutathione (GSH) and H 2 O 2 in vivo (Fig. 7a). The UCNH
consisted of a NaYF 4 :Yb,Er,Tm UCNP co-functionalized with two probes: a thiolcoumarin-based GSH-sensitive probe (TCG) and a benzopyrylium-coumarin-based
H 2 O 2 -responsive probe (BCH), respectively (Chart 1).
The probes were selected to quench different emissions of the UCNP,
540 (Er) and 650 nm (Tm), respectively, and each signal was referenced to another
unaffected upconversion emission at 800 nm (Tm) (Fig. 7b). The resulting sensing
proved to be selective and reached limits of detection (LOD) in the order of 10
À3 M
for GSH and 10
À6 M for H 2 O 2 .
Similarly, Li et al. [68] built a case (i) and (ii) hypochlorite (ClO
À ) nanosensor
which was based on the interaction between an Er core-shell nanoparticle, specifically β-NaYF 4 ;Yb,Nd,Er@β-NaYF 4 :Nd, and a cyanine 3 (Cy3; Fig. 3, Chart 1)
ClO
À probe. The absorption of the ClO
À -sensitive Cy3 affects the intensity of the
540 nm Er emission band, while that of the 650 nm Er emission remains identical. As
a result, the ratiometric response was obtained between those bands. This sensor
showed good linearity, a LOD of 27 ppb, high selectivity and a rapid response.
Moreover, it was successfully tested in vitro and in vivo.
Other nanoparticles have also been used as acceptors to develop sensors. Even if
it is out of the scope of the present chapter, a representative example is commented
below. Zourob et al. [69] designed a case (iii) complex DNA sensor based on
the quenching of the UCNP emissions by a gold nanoparticle (AuNP). The
nanoplatform consists of polystyrene-co-acrylic acid core capped with dense silica
and functionalized with α-NaYF 4 :Yb,Tm UCNPs. The platform is attached to a
AuNP nanoparticle through a single-strand DNA probe. When the specific singlestrand DNA sequence hybridizes the DNA probe, it induces a lengthening in the
AuNP-UCNP distance, and, consequently, the UCNP emissions are recovered.
Functional Nanohybrids Based on Dyes and Upconversion Nanoparticles
385