Biocompatible Probes Based on Rare-Earth Doped Strontium Aluminates with Long-Lasting Phosphorescent Properties for In Vitro Optical IMAGING.

In recent decades, the demand for biomedical imaging tools has grown very rapidly as a key feature for biomedical research and diagnostic applications. Particularly, fluorescence imaging has gained increased attention as a non-invasive, inexpensive technique that allows real-time imaging. However, tissue auto-fluorescence under external illumination, together with a weak tissue penetration of low wavelength excitation light, largely restricts the application of the technique. Accordingly, new types of fluorescent labels are currently being investigated and, in this search, phosphorescent nanoparticles promise great potential, as they combine the interesting size-dependent properties of nanoscale materials with a long-lasting phosphorescence-type emission that allows optical imaging well after excitation (so avoiding autofluorescence). In this work, core-shell structures consisting of SrAlO:Eu,Dy luminescent cores encapsulated within a biocompatible silica shell were prepared, showing a green persistent phosphorescence with an afterglow time of more than 1000 s. A high-energy ball milling procedure was used to reduce the size of the starting phosphors to a size suitable for cellular uptake, while the silica coating was produced by a reverse micelle methodology that eventually allows the excitation and emission light to pass efficiently through the shell. Confocal fluorescence microscopy using HeLa cancer cells confirmed the potential of the all-ceramic composites produced as feasible labels for in vitro optical imaging.

Tailoring the visible light photoactivity of un-doped defective TiO2 anatase nanoparticles through a simple two-step solvothermal process.

Anatase TiO2 has become a material of great interest for photocatalytic production of hydrogen, environmental purification and solar energy conversion. Among the key parameters boosting the photocatalytic efficiency of the anatase nanoparticles, an increased light absorption to expand its optical response to the visible region, together with an improved charge separation of the photo-generated electrons and holes, can be enumerated. In this work, yellow-coloured, single-phase anatase nanoparticles have been obtained using a simple two-step solvothermal routine which requires no external addition of dopants, nor the use of a harassing/aggressive synthesis atmosphere. The obtained powders display a lowered bandgap (<3.0 eV) and significantly reduce the recombination processes, eventually leading to an improved photocatalytic performance under visible light, as exemplified by an enhanced degradation of phenol. This exceptional response is linked to the presence of intrinsic defects in the yellowish particles and, hence, the specific conditions of the proposed methodology become crucial to produce a propitious TiO2-defective nanomaterial capable of photo-degrade the phenol molecule, in contrast with the lack of photocatalytic activity currently exhibited by commercial photocatalysts under visible light.

Adsorption properties of trifluoroacetic acid on anatase (101) and (001) surfaces: a density functional theory study.

The interaction of trifluoroacetic acid with anatase TiO2(101) and TiO2(001) surfaces has been studied by means of periodic density functional theory based calculations. On the former, the interaction is weak with the adsorbed molecules in a configuration almost indistinguishable from the gas phase structure. On the latter, the interaction is very strong; the molecule adsorbs as trifluoroacetate and releases a proton that binds an oxygen surface atom with a significant distortion of the substrate. The difference in adsorption the mode and strength can be understood from the different structural features of both surfaces and provides arguments to the role of trifluoroacetic as a morphological control agent in the solvothermal synthesis of TiO2 nanoparticles with predominant (001) facets. This, in turn, has a very significant impact on industrial production strategies of value-added TiO2 for photocatalytic applications. Analysis of calculated core level binding energies for F(1s) confirms the experimental assignment to F at the surface as F(-) at Ti surface sites and to F in -CF3 groups of the adsorbed molecule.

Hybrid Hierarchical Heterostructures of Nanoceramic Phosphors as Imaging Agents for Multiplexing and Living Cancer Cells Translocation.

Existing fluorescent labels used in life sciences are based on organic compounds with limited lifetime or on quantum dots which are either expensive or toxic and have low kinetic stability in biological environments. To address these challenges, luminescent nanomaterials have been conceived as hierarchical, core-shell structures with spherical morphology and highly controlled dimensions. These tailor-made nanophosphors incorporate Ln:YVO4 nanoparticles (Ln = Eu(III) and Er(III)) as 50 nm cores and display intense and narrow emission maxima centered at ∼565 nm. These cores can be encapsulated in silica shells with highly controlled dimensions as well as functionalized with chitosan or PEG5000 to reduce nonspecific interactions with biomolecules in living cells. Confocal fluorescence microscopy in living prostate cancer cells confirmed the potential of these platforms to overcome the disadvantages of commercial fluorophores and their feasibility as labels for multiplexing, biosensing, and imaging in life science assays.

Microwave-induced fast crystallization of amorphous hierarchical anatase microspheres.

The fabrication of hierarchical anatase microspheres with potential photocatalytic properties eventually comprises a consolidation step in which a high degree of crystalline order is typically achieved through conventional electric heating treatments. This however entails a substantial reduction in the specific surface area and porosity of the powders, with the consequent deterioration in their photocatalytic response. Here, we have tested the employ of microwave heating as an alternative energy-saving sintering method to promote fast crystallization. The results obtained suggest that under the microwave radiation, the TiO2 hierarchical structures can effectively crystallize in a drastically reduced heating time, allowing the specific surface area and the porosity to be kept in the high values required for an improved photocatalytic performance.