Photochemical mechanisms of light-triggered release from nanocarriers

Abstract

Over the last three decades, a handful of photochemical mechanisms have been applied to a large number of nanoscale assemblies that encapsulate a payload to afford spatio-temporal and remote control over activity of the encapsulated payload. Many of these systems are designed with an eye towards biomedical applications, as spatio-temporal and remote control of bioactivity would advance research and clinical practice. This review covers five underlying photochemical mechanisms that govern the activity of the majority of photoresponsive nanocarriers: 1. photo driven isomerization and oxidation, 2. surface plasmon absorption and photothermal effects, 3. photo driven hydrophobicity changes, 4. photo driven polymer backbone fragmentation and 5. photo driven de-crosslinking. The ways in which these mechanisms have been incorporated into nanocarriers and how they affect release are detailed, as well as the advantages and disadvantages of each system.

Figure 1

Structure of amphiphatic azobenzene moiety utilized in the study by Kano et al [7].

Figure 2

Schematic representation of a cross-section of lipid bilayer packed with trans-azobenzenes that photoisomerize upon irradiation into the cis-form and cause distortions in the lipid packing.

Figure 3

A) Schematic representation of the formation of ionomer vesicles from AzoC10 and PEG-PAA. B) fluorescence emission spectra of pyrene sulfonic acid, a) before, b) after UV, and c) after visible irradiation [17].

Figure 4

Scheme showing the generation of a net dipole moment on photoisomerization.

Figure 5

Schematic representation of non-covalently crosslinked azo-dextran nanogels, AD [22].

Figure 6

Photoresponsive materials functionalized with azobenzene derivatives. (a) nano-impellers prepared by the co-condensation ethod derivatized with AzoH; (b) triggered release materials prepared by the post-synthesis modification method derivatized with AzoG1 [23].

Figure 7

Schematic representation of the proposed mechanism of laser triggered release of entrapped solutes form liposomes. Light treatment of DOX-loaded DPPC:DC_8,9PC liposomes results in release of DOX. The effective concentration of the free drug is increased in the vicinity of cells. DOX is subsequently taken up by cells by passive diffusion leading to improved cell killing. [26]

Figure 8

Schematic representation of size change behavior of P(3,4DHCA-co-4HCA) nanoparticles with UV irradiation. Chemical structure of UV-induced [2+2] cycloaddition formation (cross-linking) and deformation (cleavage) [29-30].

Figure 9

Singlet oxygen mediated photo-oxidation of plasmenylcholine leading to cleavage of vinyl ether linkages [40-41].

Figure 10

Multi-stimuli responsive PEGylated nanogels composed of a PEG shell and PEAMA core with gold nanoparticles immobilized in the core [62].

Figure 11

Formation of gold nanoparticle-liposome assemblies for NIR light-triggered release of carboxyfluorescein. [58].

Figure 12

Gold nanoparticles with DNA bound to the surface for NIR light-triggered release [63-64].

Figure 13

A) Diazonaphthoquinone-based molecules undergoing an amphiphilic to hydrophilic switch upon UV and NIR irradiation. [69] B) DNQ-based system modified by incorporation of dendritic polyester to install multiple DNQ moieties [73].

Figure 14

A) Block copolymer with masked carboxyl groups undergoing amphiphilic to hydrophilic switch upon light exposure and examples of light-sensitive protecting groups. (B) Amphiphilic block-copolymer micellar disassembly upon irradiation.

Figure 15

Light-induced hydrophobicity switch of spiropyran-containing block copolymer [74].

Figure 16

Ionization of Malachite green derivative upon UV light exposure. [76]

Figure 17

Polyion complex formed between chitosan and pyrene derivative undergoes a hydrophobic to hydrophilic switch upon light exposure [77].

Figure 18

Schematic of triggered liposomal release through an engineered channel protein [78].

Figure 19

Schematic representation of degradation of polymeric particles by light and release of cargo. Nile Red release from the polymeric particles upon A) UV irradiation at 300-400 nm B) NIR irradiation at 750nm. [87]

Figure 20

Schematic of quinone-methide-based polymer [83] degradation after cleavage of o-nitrobenzyl triggering group with UV or NIR light.

Figure 21

Schematic representation of the “graft-through and “click-to” approach. A) Bivalent macromonomer on which “graft-through” ROMP with catalyst 1 was performed followed by in situ chloride-azide exchange. B) The resulting azido-bivalent-brush polymer functionalized with DOX-alkyne by click chemistry allows controlled release of the anticancer agent doxorubicin (DOX) in response to 365 nm UV light [89].

Figure 22

A) Schematic illustration of the preparation and photo-controlled volume change of nanogel [90]. B) Designed diblock copolymer bearing coumarin side groups for the reversible photo-cross-linking reaction.

Figure 23

A) Photo-controlled release of encapsulated guest molecules upon light irradiation of polymer micelles. B) Synthesis of photocleavable cross-linked block copolymers and their light-triggered dissociation [92].