Photothermal release of an encapsulated therapeutic agent from polymer-wrapped gold nanoparticles.

Visible light is used to generate heat from gold nanoparticles wrapped in an amphiphilic polymer shell and trigger a reverse Diels-Alder reaction of a 'caged' tyrphostin therapeutic agent. The hydrophilic nature of the released agent results in it travelling from the polymer to the bulk medium, while the byproduct of the reaction is trapped in the hydrophobic layer of the nano-assembly.

A dual-mode visual detector for toxic hydrazine.

Hydrazine (N2H4) is one of the commonly used chemical reagents in numerous industries and applications but its toxicity to humans poses a need to develop simple visual detection methods. Herein, we demonstrate a novel dual-mode system to detect and simultaneously consume hydrazine in vapour and solution by using a small photoresponsive molecule that has altered optical response (both colourimetric and fluorescent) after reacting with hydrazine.

Probing the Microenvironments in a Polymer-Wrapped Core-Shell Nanoassembly Using Pyrene Chromophores.

The local environments within an amphiphilic polymer shell wrapped around lanthanide-doped upconverting nanoparticles were probed using steady-state and time-resolved fluorescence spectroscopy techniques. Emission lifetime measurements of pyrene chromophores trapped within the polymer shell reveal that there are at least two environments, where the organic pyrene molecules are encapsulated in hydrophobic environments that have lower polarity than in water. The migration of pyrene chromophores from their initial location to another location was also observed, demonstrating that the polymeric shell provides both hydrophobicity and mobility for entrapped molecules. These results offer insight into what outcomes can be expected when chemical reactions are carried out in these nanoassemblies, especially if they are to be used as nanoreactors for synthesis or delivery vehicles for therapeutics.

Visible-Light-Triggered Activation of a Protein Kinase Inhibitor.

A photoresponsive small molecule undergoes a ring-opening reaction when exposed to visible light and becomes an active inhibitor of the enzyme protein kinase C. This "turning on" of enzyme inhibition with light puts control into the hands of the user, creating the opportunity to regulate when and where enzyme catalysis takes place.

Using low-energy near infrared light and upconverting nanoparticles to trigger photoreactions within supramolecular assemblies.

This overview highlights how the high-energy ultraviolet or visible light required to drive photochemical reactions can be overcome by integrating the chromophores into supramolecular structures containing upconverting nanoparticles with trivalent lanthanide dopants (such as Tm(3+) and Er(3+)). These nanoparticles are particularly interesting systems because they absorb multiple photons of near infrared light and convert them into higher-energy light which is emitted in the ultraviolet and visible regions of the electromagnetic spectrum. The upconverting nanoparticles effectively act as nanoscopic 'light bulbs', and in this way, less damaging near infrared light can be used to trigger photochemical reactions for use in imaging and small molecule release. Several examples of how this phenomenon is being used in photochemistry will be presented with the focus being on self-assembled supramolecular systems, some of which are being used in cells and small animals.

A 'Plug and Play' Method to Create Water-dispersible Nanoassemblies Containing an Amphiphilic Polymer, Organic Dyes and Upconverting Nanoparticles.

In this protocol, we first describe a procedure to synthesize lanthanide doped upconverting nanoparticles (UCNPs). We then demonstrate how to generate amphiphilic polymers in situ, and describe a protocol to encapsulate the prepared UCNPs and different organic dye molecules (porphyrins and diarylethenes) using polymer shells to form stable water-dispersible nanoassemblies. The nanoassembly samples containing both the UCNPs and the diarylethene organic dyes have interesting photochemical and photophysical properties. Upon 365 nm UV irradiation, the diarylethene group undergoes a visual color change. When the samples are irradiated with visible light of another specific wavelength, the color fades and the samples return to the initial colorless state. The samples also emit visible light from the UCNPs upon irradiation with 980 nm near-infrared light. The emission intensity of the samples can be tuned through alternate irradiation with UV and visible light. Modulation of fluorescence can be performed for many cycles without observable degradation of the samples. This versatile encapsulation procedure allows for the transfer of hydrophobic molecules and nanoparticles from an organic solvent to an aqueous medium. The polymer helps to maintain a lipid-like microenvironment for the organic molecules to aid in preservation of their photochemical behavior in water. Thus this method is ideal to prepare water-dispersible photoresponsive systems. The use of near-infrared light to activate upconverting nanoparticles allows for lower energy light to be used to activate photoreactions instead of more harmful ultraviolet light.

Two-colour fluorescent imaging in organisms using self-assembled nano-systems of upconverting nanoparticles and molecular switches.

The water-insolubility of a potentially versatile photoresponsive 'turn-on' fluorescence probe was overcome by incorporating it into a nano-assembly containing an upconverting nanoparticle wrapped in an amphiphilic polymer. The appeal of the nano-system is not only in the ability to turn "on" and "off" the fluorescence from the organic chromophore using UV and visible light, it is in the fact that the nanoparticle acts as a static probe because it emits red and green light when excited by near infrared light, which is not effected by UV and visible light. This dual-functioning emission behaviour was demonstrated in live organisms.

From slow to fast--the user controls the rate of the release of molecules from masked forms using a photoswitch and different types of light.

Exposure to UV light generates a ring-closed isomer of a diarylethene, which undergoes very slow bond breaking and release even after the light is turned off. The rate of release is increased by exposing the isomer to UV and/or visible light.

Two colors of light are needed to break bonds and release small molecules from the surface of SiO2-Au core-shell nanoparticles.

The photothermal effect is not able to break bonds and release small molecules from the surface of SiO2-Au core-shell nanoparticles unless the nanosystem is first exposed to visible light. Only after this light triggers the ring-opening reaction of dithienylethene chromophores attached to the surface of the nanoparticles can the heat generated by the NIR light induce reverse Diels-Alder reactions.

Controlling a polymer adhesive using light and a molecular switch.

A thermally remendable polymer was synthesized by the Diels-Alder reaction between dithienylfuran and maleimide monomers to generate a photoresponsive diarylethene. UV light (312 nm) and visible light (>435 nm) "gate" the reversibility of the Diels-Alder reaction and turn the self-healing properties of the polymer "off" and "on", respectively. After exposure to UV light, the strength of the polymer as an adhesive is enhanced. Visible light weakens the adhesive.

A UV-blocking polymer shell prevents one-photon photoreactions while allowing multi-photon processes in encapsulated upconverting nanoparticles.

Sun block for nanoparticles: Unintentional photorelease triggered by UV light is a problem in photodynamic therapy. Encapsulating upconverting nanoparticles containing photoswitches in a UV-blocking amphiphilic polymer shuts down the one-photon process and only allows two-photon-driven photochemistry. Thus, UV light is blocked while NIR light can reach the nanoparticle core and trigger photorelease.

Photothermal release of singlet oxygen from gold nanoparticles.

Anthracene endoperoxide ligands anchored to the surfaces of gold nanoparticles undergo bond breaking and release singlet oxygen when the nanoparticles convert 532 nm laser light to heat localized near their surfaces.

Near infrared light triggered release of biomacromolecules from hydrogels loaded with upconversion nanoparticles.

Using a photosensitive hybrid hydrogel loaded with upconversion nanoparticles (UCNPs), we show that continuous-wave near-infrared (NIR) light (980 nm) can be used to induce the gel-sol transition and release large, inactive biomacromolecules (protein and enzyme) entrapped in the hydrogel into aqueous solution "on demand", where their bioactivity is recovered. This study is a new demonstration and development in harnessing the unique multiphoton effect of UCNPs for photosensitive materials of biomedical interest.

Multimodal fluorescence modulation using molecular photoswitches and upconverting nanoparticles.

The intensity and colour of the light emitted from upconverting nanoparticles is controlled by the state of photoresponsive dithienylethene ligands decorated onto the surface of the nanoparticles. By selectively activating one or both ligands in a mixed, 3-component system, a multimodal read-out of the emitted light is achieved.

Using light and a molecular switch to 'lock' and 'unlock' the Diels-Alder reaction.

Light is used to 'gate' the Diels-Alder reaction using a photoresponsive dithienylfuran backbone and turn the reversibility of the Diels-Alder reaction 'off' and 'on' at 100 °C. These features make the reported system an excellent candidate for developing the next generation of self-healing polymers and photothermal drug delivery vehicles.

Reporting the release of caged species by a combination of two sequential photoreactions, a molecular switch, and one color of light.

In the right light: UV light triggers bond breaking, liberates a caged carboxylic acid, and generates the central C=C double bond in the photoresponsive hexatriene molecule of a dithienylethene molecular switch. Light of the same wavelength converts the colorless isomer into its colored counterpart in a visually convenient method to report on the success of the release event.

Photothermal release of small molecules from gold nanoparticles in live cells.

The ability of gold (Au) nanoparticles (NPs) to generate heat efficiently by absorbing visible and near-infrared (NIR) light holds great promise as a means to trigger chemical and biochemical events near the NPs. Previous demonstrations show that pulsed laser irradiation can selectively elicit the release of a fluorescent dye covalently anchored to the NP surface through a heat-labile linker without measurably changing the temperature of the surroundings. This article reports that the authors demonstrate the biological efficacy of this approach to photodelivery by showing that the decorated Au NPs are rapidly internalized by cells, are stable under physiological conditions, are nontoxic, and exhibit nonlethal photorelease following exposure to pulsed laser radiation. These observations, further supported by the versatility of our delivery motif, reaffirm the potential for further development of nonlethal photothermal therapeutics and their future relevance to such fields as gene therapy and stem-cell differentiation.

Near-infrared light-triggered dissociation of block copolymer micelles using upconverting nanoparticles.

We demonstrate a novel strategy enabling the use of a continuous-wave diode near-infrared (NIR) laser to disrupt block copolymer (BCP) micelles and trigger the release of their "payloads". By encapsulating NaYF(4):TmYb upconverting nanoparticles (UCNPs) inside micelles of poly(ethylene oxide)-block-poly(4,5-dimethoxy-2-nitrobenzyl methacrylate) and exposing the micellar solution to 980 nm light, photons in the UV region are emitted by the UCNPs, which in turn are absorbed by o-nitrobenzyl groups on the micelle core-forming block, activating the photocleavage reaction and leading to the dissociation of BCP micelles and release of co-loaded hydrophobic species. Our strategy of using UCNPs as an internal UV or visible light source upon NIR light excitation represents a general and efficient method to circumvent the need for UV or visible light excitation that is a common drawback for light-responsive polymeric systems developed for potential biomedical applications.