Table 5.

Different strategies implemented into MSNs for achieving light-responsive drug delivery.

Approach	Description	Reference
Light-Responsive Bonds
o-nitrobenzyl group	Cleavable using 365 nm light. Used as linker for the grafting of proteins and pH-responsive polymers	[140,359]
Coumarin group	Cleavable using 405 nm light. Used as linker for the grafting of cationic polymers for gene delivery	[360]
Thiolated coordination bond	Cleavable using 455 nm light. Coordination bond formed by ruthenium bipyridine-based compounds that act as gatekeepers	[361]
Thymine derivatives	Reversible formation (365 nm) and cleavage (240 nm) of a cyclobutane dimer. Used as on-off gatekeeper	[362]
ROS-Responsive Bonds (ROS Generation upon Light Application)
Aminoacrylate bond	Used as linker for the grafting of a porphyrin acting simultaneously as gatekeeper and ROS generator upon visible light irradiation	[228]
(alkylthio)alkene-based bond	Used as linker for the grafting of nanovalves and proteins. Cleaved when loaded photosensitizer chlorin e6 generates ROS upon NIR light irradiation	[363,364]
Thioketal group	Used as gatekeeper. Cleaved when chlorin e6 generates ROS upon NIR light irradiation	[365]
Double bonds	Photosensitizer AsPCs2a generates ROS upon NIR light irradiation that oxidize double bonds of the lipids and increase membrane permeability	[229]
Light-Induced Conformational Changes
Perylene group	Their removal from a polymer chain upon light irradiation, 450 nm (perylene) or 365 nm (spiropyran and o-nitrobenzyl), induce a conformational change that open the pores and triggers drug release	[366]
Spiropyran group		[367]
o-nitrobenzyl group		[368]
Cinnamamide derivative	Used as stalks for grafting of nanovalves (grafted on the surface or as pendant groups in polymers). Reversible trans-to-cis conformation change when irradiated, in general, with UV light	[369]
Azobenzene derivatives		[370,371,372,373,374,375]