Supramolecular Strategies To Construct Biocompatible and Photoswitchable Fluorescent Assemblies

Abstract

We designed and synthesized an amphiphilic copolymer with pendant hydrophobic decyl and hydrophilic poly(ethylene glycol) chains along a common poly(methacrylate) backbone. This macromolecular construct captures hydrophobic boron dipyrromethene fluorophores and hydrophobic spiropyran photochromes and transfers mixtures of both components in aqueous environments. Within the resulting hydrophilic supramolecular assemblies, the spiropyran components retain their photochemical properties and switch reversibly to the corresponding merocyanine isomers upon ultraviolet illumination. Their photoinduced transformations activate intermolecular electron and energy transfer pathways, which culminate in the quenching of the boron dipyrromethene fluorescence. As a result, the emission intensity of these supramolecular constructs can be modulated in aqueous environments under optical control. Furthermore, the macromolecular envelope around the fluorescent and photochromic components can cross the membrane of Chinese hamster ovarian cells and transport its cargo unaffected into the cytosol. Indeed, the fluorescence of these supramolecular constructs can be modulated also intracellularly by operating the photochromic component with optical inputs. In addition, cytotoxicity tests demonstrate that these supramolecular assemblies and the illumination conditions required for their operation have essentially no influence on cell viability. Thus, supramolecular events can be invoked to construct fluorescent and photoswitchable systems from separate components, while imposing aqueous solubility and biocompatibility on the resulting assemblies. In principle, this simple protocol can evolve into a general strategy to deliver and operate intracellularly functional molecular components under optical control.

Characterization of the Thermal and Photoinduced Reactions of Photochromic Spiropyrans in Aqueous Solution

“…Additional examples are the redox energies, 2 molecular structure, 3 and charge distribution, 4 to mention a few. Altogether, the light-induced changes in these and other properties have been harnessed for applications in, for example, the photocontrol of biological functions, 5−13 bioimaging, 14−18 optical signal processing, and photoswitching in general, 19−30 as well as in chemosensing. 31−38 In many of these situations, aqueous media is required and, hence, also spiropyran derivatives that are readily dissolved in water.…”

Reversible Fluorescence Photoswitching in DNA

“…27,28 The DNA scaffold, which is nuclease resistant, 17 provides a biocompatible and photoswitchable macromolecule that is of great interest for advanced microscopy of cellular components. 29 Moreover, sequence specificity in labeling, which is crucial for applications such as fluorescence in situ hybridization (FISH) and the study of chromosome structure, 30 can be achieved by using the appropriate template in PCR-mediated synthesis of CyDNA. Fluorescence photoswitching in CyDNA can greatly improve imaging of chromosome loci with advanced fluorescence microscopy methods such as OLID and super-resolution imaging in combination with FISH and fiber-FISH, 31 offering great potential for high-resolution cytogenetics.…”

Reversible Photoswitching of Spiropyran-Conjugated Semiconducting Polymer Dots

“…15–21 Various strategies, including emulsion polymerization, copolymerization, and core-shell embedding, have been used to build a hydrophobic core with a hydrophilic surface. 16,22,23 In those studies, the photochrome, for example spiropyran (SP) or diarylethene molecules, served as photoswitchable quencher: Once it was converted to its colored form by the absorption of ultraviolet (UV) light, it efficiently quenched the emission of its partnering fluorophore. The quenching mechanism was generally due to the electron or energy transfer from the fluorophore to the photochrome.…”

“…For example, Callan and coworkers reported the use of an amphiphilic copolymer that captured a mixture of boron dipyrromethene fluorophores (energy donor) and SP photochromes (energy acceptor) as photoswitchable assemblies. 23 Similarly, Chen et al used one-step miniemulsion polymerization to attach fluorescent dyes (4-methamino-9-ally-1,8-naphthalimide) and photochromic SP derivatives into individual nanoparticles. 22 In comparison to fluorescent dyes, these nanoparticle-based assemblies were much brighter because many dye molecules were embedded inside a single nanoparticle.…”