164
Y. Min et al.
Table 5.4 (continued)
Metal Ligand
Metal
ion
NP
diameter
TEM
References
CdTe Mercaptomethyltetrazole Cd 2+
3 nm
–
[163]
a Figure reproduced with permission from Ref. [148]
b Figure reproduced with permission from Ref. [151]
c Figure reproduced with permission from Ref. [153]
d Figure reproduced with permission from Ref. [155]
e Figure reproduced with permission from Ref. [157]
f Figure reproduced with permission from Ref. [159]
g Figure reproduced with permission from Ref. [152]
5.2.2.5 Light-Induced Self-assembly of Irreversible Nanoparticle
Networks
The use of externally manipulated light offers excellent spatial and temporal control
for the signal molecule’s activation, degradation, or creation/disruption of a selfassembled system [164]. Light-induced self-assembly (LISA) of metal NP have
thus found applications into the biomedical field. Although most of the work deals
with non-covalent interactions (mainly NP aggregation due to changes in electrostatic stabilization), some works have reported the irreversible and photochemically
activated formation of covalent NP networks (Fig. 5.25).
Zhao and coworkers reported that UV light irradiation triggers Au NP that are,
respectively, functionalized with o-nitrobenzyl alcohol and benzylamine to proceed
with a covalent ligation reaction [165]. Indeed, o-nitrobenzyl alcohol and benzylamine can undergo an aldehyde-amine ligation-like coupling reaction under UV
irradiation. This reaction leads to the assembly of Au NP into anisotropic 1-D arrays
in aqueous solution via indazolone linkages (Fig. 5.25a). The formation of anisotropic
1-D Au NP arrays was attributed to the anisotropic electrostatic repulsions during
the self-assembling of the charged NP. The self-assembly of Au NP or nanorods into
chains and networks was also achieved by a UV light in the presence of silver ions;
taking advantage of the easy photoreduction property of silver nitrate [168]. The
authors used CTAB (or citrate)-capped gold NP or nanorods that were mixed with
the required concentrations of silver salt (the assembly was strongly dependent on
the AgNO 3 content), and then exposed to a 365 nm UV lamp. From HRTEM and
XPS analyses, the authors proposed the formation of a core–shell Ag@Au structure
(near identical lattice constants of Au (0.408 Å) and Ag (0.409 Å)) on both NP and
nanorods. The group of Shi studied the light-triggered covalent coupling of gold NP
[166, 167]. They have shown that Au NP (20 nm) stabilized with photolabile diazirine
terminal group of PEG5000 (polyethyleneglycol, Mn = 5000) can be covalently
cross-linked upon 405 nm laser irradiation (Fig. 5.25b) [166]. The surface diazirine
group is first transformed into a carbene species upon laser excitation at 405 nm. Then,
the resulting reactive carbene moieties formed covalent bonds with ligands of adjacent Au NP through C–C, C–H, O–H, and X–H (X = heteroatom) insertions, leading
Y. Min et al.
Table 5.4 (continued)
Metal Ligand
Metal
ion
NP
diameter
TEM
References
CdTe Mercaptomethyltetrazole Cd 2+
3 nm
–
[163]
a Figure reproduced with permission from Ref. [148]
b Figure reproduced with permission from Ref. [151]
c Figure reproduced with permission from Ref. [153]
d Figure reproduced with permission from Ref. [155]
e Figure reproduced with permission from Ref. [157]
f Figure reproduced with permission from Ref. [159]
g Figure reproduced with permission from Ref. [152]
5.2.2.5 Light-Induced Self-assembly of Irreversible Nanoparticle
Networks
The use of externally manipulated light offers excellent spatial and temporal control
for the signal molecule’s activation, degradation, or creation/disruption of a selfassembled system [164]. Light-induced self-assembly (LISA) of metal NP have
thus found applications into the biomedical field. Although most of the work deals
with non-covalent interactions (mainly NP aggregation due to changes in electrostatic stabilization), some works have reported the irreversible and photochemically
activated formation of covalent NP networks (Fig. 5.25).
Zhao and coworkers reported that UV light irradiation triggers Au NP that are,
respectively, functionalized with o-nitrobenzyl alcohol and benzylamine to proceed
with a covalent ligation reaction [165]. Indeed, o-nitrobenzyl alcohol and benzylamine can undergo an aldehyde-amine ligation-like coupling reaction under UV
irradiation. This reaction leads to the assembly of Au NP into anisotropic 1-D arrays
in aqueous solution via indazolone linkages (Fig. 5.25a). The formation of anisotropic
1-D Au NP arrays was attributed to the anisotropic electrostatic repulsions during
the self-assembling of the charged NP. The self-assembly of Au NP or nanorods into
chains and networks was also achieved by a UV light in the presence of silver ions;
taking advantage of the easy photoreduction property of silver nitrate [168]. The
authors used CTAB (or citrate)-capped gold NP or nanorods that were mixed with
the required concentrations of silver salt (the assembly was strongly dependent on
the AgNO 3 content), and then exposed to a 365 nm UV lamp. From HRTEM and
XPS analyses, the authors proposed the formation of a core–shell Ag@Au structure
(near identical lattice constants of Au (0.408 Å) and Ag (0.409 Å)) on both NP and
nanorods. The group of Shi studied the light-triggered covalent coupling of gold NP
[166, 167]. They have shown that Au NP (20 nm) stabilized with photolabile diazirine
terminal group of PEG5000 (polyethyleneglycol, Mn = 5000) can be covalently
cross-linked upon 405 nm laser irradiation (Fig. 5.25b) [166]. The surface diazirine
group is first transformed into a carbene species upon laser excitation at 405 nm. Then,
the resulting reactive carbene moieties formed covalent bonds with ligands of adjacent Au NP through C–C, C–H, O–H, and X–H (X = heteroatom) insertions, leading