formation of a huge amount of coordinate bonds between GSH and aluminum
ions limited the vibration and rotation of the GSH ligands and then reduced the
non-radiative decay rate, allowing the enhancement of emission. According to
transmission electron microscopy (TEM) images, the mean diameter of CuNCs
that existed dispersedly in water was about 2–5 nm, and the dots were monodispersive both in luminescence and in size, which benefit for analytical applications
a lot. Furthermore, GSH-protected CuNCs were reported that their luminescence
intensity was responsive to changes in pH. Huang believed this phenomenon was
mostly because of the alternation of pH value, leading to the change of the aggregation state of the CuNCs. At lower pH, the CuNCs aggregated with intensive
luminesce, while at higher pH the CuNCs were dispersed, showing weak emission.
Interestingly, the reversibility of this pH-driven luminescence switch was observed
clearly, as it didn’t fatigue after five continuous cycles. Hence, Huang claimed
that CuNCs would make an excellent luminescent pH indicator and a potential
β-galactosidase probe. Huang and his team found that the luminescence of the
CuNC dots assembled by Al
3+ was gradually quenched by increasing amount of
p-nitrophenol, indicating that there was significant interaction between these two
taking place. The coordination between Al
3+ and p-nitrophenol was owing to the
highly efficient electron transfer between the CuNC dots and p-nitrophenol. And
based on that, Huang reckoned that it could be utilized to assay β-gal using
4-nitrophenyl-b-D-galactopyranoside (NPGal) as the substrate. NPGal would rapidly
hydrolyzed into galactose and p-nitrophenol in the presence of β-gal, and the latter
was going to attach on the surface of CuNC dots via a coordinate bond, causing
luminescence quenching. And the quenching behavior corresponds to the amount of
β-gal, illustrating that CuNC dots could serve as a potential monitor of β-gal in a
continuous and real-time way.
Agostini et al. [35] also used nanoclusters targeting SA-β-gal presenting specifically in senescent cells to deliver drugs for the purpose of avoiding senescencerelated disease. The activity of SA-β-gal is encoded by the GLB1 gene [36, 37],
which is a biomarker for increased lysosome number or activity and has been
associated with replicative senescence [38, 39] and organismal aging [40, 41] for a
long time. And the nano-device involved was mesoporous silica nanoparticles
(MSNs) capped with a galacto-oligosaccharide (GOS). The structure of MSNs
contained unique mesoporous materials with large specific volume and easer
functionalization [42]. It could be absorbed by living cells through endocytosis.
Moreover, using molecular/supramolecular ensemble on the external surface of
MSNs could make them functional to develop gated MSNs, which released their
cargo in response to external stimulant while not releasing the payload if there was
only the hybrid material alone, and the latter phenomenon was called “zero delivery.” In their study, Auvray et al. [43] selected MCM-41-based MSNs as the scaffold
and loaded with Rhodamine B as a model drug after calcining. Then the oligosaccharide derivative GOS was capped onto MSNs to obtain the final product (S1). The
MSN S1 nanoparticles were roughly spherical with a diameter of about 100 nm and
an average pore diameter of 2.5 nm, and the maximum loading of Rhodamine B was
approximately 0.14 g per gram SiO 2 . Moreover, S1 was capable of releasing their
Fluorescent Probes for Diagnostics of β-Galactosidase: From Micro to Macro
195
ions limited the vibration and rotation of the GSH ligands and then reduced the
non-radiative decay rate, allowing the enhancement of emission. According to
transmission electron microscopy (TEM) images, the mean diameter of CuNCs
that existed dispersedly in water was about 2–5 nm, and the dots were monodispersive both in luminescence and in size, which benefit for analytical applications
a lot. Furthermore, GSH-protected CuNCs were reported that their luminescence
intensity was responsive to changes in pH. Huang believed this phenomenon was
mostly because of the alternation of pH value, leading to the change of the aggregation state of the CuNCs. At lower pH, the CuNCs aggregated with intensive
luminesce, while at higher pH the CuNCs were dispersed, showing weak emission.
Interestingly, the reversibility of this pH-driven luminescence switch was observed
clearly, as it didn’t fatigue after five continuous cycles. Hence, Huang claimed
that CuNCs would make an excellent luminescent pH indicator and a potential
β-galactosidase probe. Huang and his team found that the luminescence of the
CuNC dots assembled by Al
3+ was gradually quenched by increasing amount of
p-nitrophenol, indicating that there was significant interaction between these two
taking place. The coordination between Al
3+ and p-nitrophenol was owing to the
highly efficient electron transfer between the CuNC dots and p-nitrophenol. And
based on that, Huang reckoned that it could be utilized to assay β-gal using
4-nitrophenyl-b-D-galactopyranoside (NPGal) as the substrate. NPGal would rapidly
hydrolyzed into galactose and p-nitrophenol in the presence of β-gal, and the latter
was going to attach on the surface of CuNC dots via a coordinate bond, causing
luminescence quenching. And the quenching behavior corresponds to the amount of
β-gal, illustrating that CuNC dots could serve as a potential monitor of β-gal in a
continuous and real-time way.
Agostini et al. [35] also used nanoclusters targeting SA-β-gal presenting specifically in senescent cells to deliver drugs for the purpose of avoiding senescencerelated disease. The activity of SA-β-gal is encoded by the GLB1 gene [36, 37],
which is a biomarker for increased lysosome number or activity and has been
associated with replicative senescence [38, 39] and organismal aging [40, 41] for a
long time. And the nano-device involved was mesoporous silica nanoparticles
(MSNs) capped with a galacto-oligosaccharide (GOS). The structure of MSNs
contained unique mesoporous materials with large specific volume and easer
functionalization [42]. It could be absorbed by living cells through endocytosis.
Moreover, using molecular/supramolecular ensemble on the external surface of
MSNs could make them functional to develop gated MSNs, which released their
cargo in response to external stimulant while not releasing the payload if there was
only the hybrid material alone, and the latter phenomenon was called “zero delivery.” In their study, Auvray et al. [43] selected MCM-41-based MSNs as the scaffold
and loaded with Rhodamine B as a model drug after calcining. Then the oligosaccharide derivative GOS was capped onto MSNs to obtain the final product (S1). The
MSN S1 nanoparticles were roughly spherical with a diameter of about 100 nm and
an average pore diameter of 2.5 nm, and the maximum loading of Rhodamine B was
approximately 0.14 g per gram SiO 2 . Moreover, S1 was capable of releasing their
Fluorescent Probes for Diagnostics of β-Galactosidase: From Micro to Macro
195