RESUMEN
Image contrast is often limited by background autofluorescence in steady-state bioimaging microscopy. Upconversion bioimaging can overcome this by shifting the emission lifetime and wavelength beyond the autofluorescence window. Here we demonstrate the first example of triplet-triplet annihilation upconversion (TTA-UC) based lifetime imaging microscopy. A new class of ultra-small nanoparticle (NP) probes based on TTA-UC chromophores encapsulated in an organic-inorganic host has been synthesised. The NPs exhibit bright UC emission (400-500â nm) in aerated aqueous media with a UC lifetime of ≈1â µs, excellent colloidal stability and little cytotoxicity. Proof-of-concept demonstration of TTA-UC lifetime imaging using these NPs shows that the long-lived anti-Stokes emission is easily discriminable from typical autofluorescence. Moreover, fluctuations in the UC lifetime can be used to map local oxygen diffusion across the subcellular structure. Our TTA-UC NPs are highly promising stains for lifetime imaging microscopy, affording excellent image contrast and potential for oxygen mapping that is ripe for further exploitation.
RESUMEN
Light-responsive particle-stabilised (Pickering) emulsions can in principle be selectively emulsified/demulsified on-demand through the remote application of light. However, despite their wide-ranging potential in applications such as drug delivery and biphasic catalysis, their rational design is extremely challenging and there are very few examples to date. Herein, we investigate a model system based on silica particles functionalised with azobenzene photoswitches to understand the key factors that determine the characteristics of light-responsive Pickering emulsions. The particle hydrophobicity is tuned through judicious variation of the spacer length used to graft the chromophores to the surface, the grafting density, and irradiation to induce trans-cis photoisomerisation. For select emulsions, and for the first time, a reversible transition between emulsified water-in-oil droplets and demulsified water and oil phases is observed with the application of either UV or blue light, which can be repeatedly cycled. A combination of surface energy analysis and optical microscopy is shown to be useful in predicting the stability, and expected light-response, of a given emulsion. Using the observed trends, a set of design rules are presented which will help facilitate the rational design, and therefore, more widespread application of light-responsive Pickering emulsions.
RESUMEN
Melt-quenched metal-organic framework (MOF) glasses have gained significant interest as the first new category of glass reported in 50 years. In this work, an amine-functionalized zeolitic imidazolate framework (ZIF), denoted ZIF-UC-6, was prepared and demonstrated to undergo both melting and glass formation. The presence of an amine group resulted in a lower melting temperature compared to other ZIFs, while also allowing material properties to be tuned by post-synthetic modification (PSM). As a prototypical example, the ZIF glass surface was functionalized with octyl isocyanate, changing its behavior from hydrophilic to hydrophobic. PSM therefore provides a promising strategy for tuning the surface properties of MOF glasses.
RESUMEN
Organic-inorganic core-shell nanocomposites have attracted increasing attention for applications in imaging, controlled release, biomedical scaffolds and self-healing materials. While tunable properties can readily be achieved through the selection of complementary building blocks, synergistic enhancement requires management of the core-shell interface. In this work, we report a one-pot method to fabricate hybrid core-shell nanocomposite particles (CSNPs) based on ureasils. The native structure of ureasils, which are poly(oxyalkylene)/siloxane hybrids, affords formation of an organic polymer core via nanoprecipitation, while the terminal siloxane groups act as a template for nucleation and growth of the silica shell via the Stöber process. Through optimisation of the reaction conditions, we demonstrate the reproducible synthesis of ureasil CSNPs, with a hydrodynamic diameter of â¼150 nm and polydispersity <0.2, which remain electrostatically stabilised in aqueous media for >50 days. Selective functionalisation, either through the physical entrapment of polarity-sensitive fluorescent probes (coumarin 153, pyrene) or covalent-grafting to the silica shell (fluorescein isothiocyanate) is also demonstrated and provides insight into the internal environment of the particles. Moreover, preliminary studies using a live/dead cell assay indicate that ureasil CSNPs do not display cytotoxicity. Given the simple fabrication method and the structural tunability and biocompatability of the ureasils, this approach presents an efficient route to multifunctional core-shell nanocomposite particles whose properties may be tailored for a targeted application.