| A. photophysical
activation |
| 1. photothermal conversion |
indocyanine green (ICG, FDA-approved) |
introducing
molecular dyes (ICG) into the liposomes leads to
the conversion of NIR into heat upon light irradiation at a definite
wavelength, destabilizing the liposomal structure and, eventually,
releasing the payloads at the tumor site |
(49) |
| 2. incorporation of plasmonic nanostructures |
plasmonic nanoparticles such as gold nanoparticles
(Au NPs) |
including plasmonic nanoparticles (Au NPs)
in the liposomal
system |
(50) |
| upon light illumination
(at a specific wavelength), the plasmonic
nanoparticles induce heat (surpassing the lipid phase transition (Tm) through the surface plasmon resonance (SPR)
effect, dismantling the liposomal lipid bilayers and releasing the
loaded therapeutic moieties |
| 3. incorporation of inorganic nanostructures |
upconverting nanoparticles (UCNPs) such as graphene
oxide (GO) |
using UCNPs during the engineering of PTL
can absorb NIR radiation
and convert it to UV–vis energy |
(51) |
| for instance, GO (a two-dimensional (2D) nanostructure) can
absorb NIR radiation and transform it into strong thermal energy via
delocalizing the electron |
| the released thermal
energy exceeds the Tm of the phospholipids
and leads to the disassembly of the
liposomes upon phototriggering and light-controlled effluxing of their
cargos |
| B. photochemical activation |
| 1. photocleavage |
photocleavable molecules such as coumarin
derivatives and the o-nitrobenzyl group |
the photocleavable entities included in the light-responsive
liposomes can irreversibly disrupt the integrity of the liposomes
through photocleavage, rearrangement, and electron transfer reactions
upon light illumination |
(52) |
| 2. photoisomerization |
photoisomerizable entities such as azobenzene |
the photoisomerizable compound incorporated in the liposomal
lipid bilayer leads to photoinduced conformational modifications when
irradiated by NIR radiation |
(53) |
| these conformational changes then result in the disassembly
of the liposomal bilayer membrane and consequent payload release |
| 3. photochemical internalization |
photosensitizers (PS) such as porphyrins derivatives
(verteporfin) |
when exposed to light stimulation, the
PS incorporated in the
liposomes generate reactive oxygen species, which oxidize the liposomal
phospholipids |
(54) |
| this leads to the rupture
of the lipid bilayer and the subsequent
release of the loaded therapeutic molecules. |
