Lanthanide doped alkaline-earth fluoride nanoparticles as biomedical probes

This thesis work presents the synthesis and characterization of lanthanide doped Calcium fluoride or Strontium fluoride nanoparticles, architected to achieve long luminescence lifetimes, upconversion properties or thermometric properties. The presentes nano-systems proved to be potentially useful as probes for optical imaging and as nanothermometers to monitor a photothermal cancer treatment

A Multifunctional Nanocomposite Hydrogel for Endoscopic Tracking and Manipulation

Herein, the fabrication of multi‐responsive and hierarchically organized nanomaterial using core‐shell SrF2 upconverting nanoparticles, doped with Yb3+, Tm3+, Nd3+ incorporated into gelatin methacryloyl matrix, is reported. Upon 800 nm excitation, deep monitoring of 3D‐printed constructs is demonstrated. Addition of magnetic self‐assembly of iron oxide nanoparticles within the hydrogel provides anisotropic structuration from the nano‐ to the macro‐scale and magnetic responsiveness permitting remote manipulation. The present study provides a new strategy for the fabrication of a novel highly organized multi‐responsive material using additive manufacturing, which can have important implications in biomedicine

Luminescent and paramagnetic properties of nanoparticles shed light on their interactions with proteins

Nanoparticles have been recognized as promising tools for targeted drug-delivery and protein therapeutics. However, the mechanisms of protein-nanoparticle interaction and the dynamics underlying the binding process are poorly understood. Here, we present a general methodology for the characterization of protein-nanoparticle interaction on a molecular level. To this end we combined biophysical techniques including nuclear magnetic resonance (NMR), circular dichroism (CD), resonance energy transfer (RET) and surface plasmon resonance (SPR). Particularly, we analyzed molecular mechanisms and dynamics of the interaction of CaF2nanoparticles with the prototypical calcium sensor calmodulin (CaM). We observed the transient formation of an intermediate encounter complex involving the structural region linking the two domains. Specific interaction of CaM with CaF2NPs is driven by the N-terminal EF-hands, which seem to recognize Ca2+on the surface of the nanoparticle. We conclude that CaF2NP-CaM interaction is fully compatible with potential applications in nanomedicine. Overall, the methods presented in this work can be extended to other systems and may be useful to quantitatively characterize structural and dynamic features of protein-NP interactions with important implications for nanomedicine and nano-biotechnology

Optical Study of Diamine Coupling on Carboxyl-Functionalized Mesoporous Silicon

A functionalization strategy, consisting of a silylation reaction by acrylic acid followed by diamine coupling, preserves and stabilizes the photoluminescence (PL) of porous silicon (pSi) microparticles suspended in ethanol. We found that under the condition of efficient amine coupling, besides the orange emission typical of the native pSi, an emission band in the blue region appears. The investigation of the interaction between pSi and diamine shows that diamine quenches and shifts the orange band meanwhile it induces an increase of the intensity of the blue one. PL lifetimes of the orange and blue bands are in the micro and nano second range, respectively. These values and their wavelength dependence clearly prove that the two bands have different origin: quantum confinement and nitrogen impurities introduced at silicon/silicon oxide interface, respectively. Thus, they can be used to discriminate between the pSi microparticles obtained by silylation, which expose carboxylic groups and the pSi microparticles after the diamine coupling, which bear amine functionalities at the surface. The increase in the stability of the PL emission of pSi in aqueous solution after functionalization, with quantum yields of the order of 1\u20132%, supports the use in biological systems of these brightly emitting, largely porous microparticles, bearing positive or negative surface charg

Nanostructured CaF2:Ln3+ (Ln3+ = Yb3+/Er3+, Yb3+/Tm3+) Thin Films: MOCVD Fabrication and Their Upconversion Properties

Calcium fluoride represents one of the most efficient hosts for up-conversion or down-conversion emissions. A simple metal organic chemical vapor deposition approach is applied to the fabrication of CaF2 nanostructured thin films using the fluorinated second-generation -diketonate compound Ca(hfa)(2)center dot diglyme center dot H2O as a Ca-F single-source precursor. The versatility of the process is demonstrated for the fabrication of up-converting Yb/Er or Yb/Tm codoped CaF2 films on Si, quartz, and glass substrates. The Ln(hfa)(3)center dot diglyme (Ln = Tm, Er, Yb) precursors are used as sources of the doping ions. Structural, morphological, and compositional characterization of the films shows the formation of polycrystalline CaF2 films with a very uniform surface and suitable doping. In fact, an appropriate tuning of the mixture composition, i.e., the Ca:Ln ratio in the multicomponent source, permits the deposition of films with the desired stoichiometry. The films show promising up-conversion properties in the visible and near infrared regions upon laser excitation for both doping mixtures

Sodium niobate based hierarchical 3D perovskite nanoparticle clusters

We report a microwave assisted synthesis of NaNbO3 perovskite mesocrystals with a hierarchical morphology formed by the self-assembly of nanoparticles in particle clusters. The synthesis method combines non-aqueous sol-gel synthesis and microwave heating in a single step process that allows us to isolate crystalline single phase NaNbO3 in few minutes. A detailed investigation of the effect of the reaction temperature on the crystallinity and morphology of the product was conducted. The synthesis stabilizes the unusual orthorhombic phase Pmma, a property that can be ascribed to the crystal size (24 nm). TEM and SAED analyses show that the hierarchical polycrystalline particles behave as single crystals, a feature related to a non-classical crystallization mechanism. Moreover, the optical bandgap of this NaNbO3 phase was estimated for the first time. The results suggest the potential of this synthetic procedure for the fast production of high quality tertiary oxide nanocrystals

Novel sol-gel fabrication of Yb3+/Tm3+ co-doped \u3b2-NaYF4 thin films and investigation of their upconversion properties

An innovative sol-gel process, using a mixture of Na(hfa)\ub7tetraglyme and RE(hfa)3\ub7diglyme (RE = Y, Yb, Tm) complexes, has been optimized to produce upconverting \u3b2-NaYF4:Yb3+/Tm3+ thin films. The X-ray diffraction (XRD) analysis confirms that the new sol-gel preparation route yields reproducibly and selectively the hexagonal Na(Y1.5Na0.5)F6 structure (\u3b2-NaYF4) without any impurity phases, since no peaks of the cubic NaYF4, YOF, Y2O3 or NaF phases were observed. This final goal has been achieved through an accurate optimization of the operative parameters such as the molar ratio of the precursor mixture, the aging time of the sol, the spin coating procedure and the annealing temperature. Field-emission scanning electron microscopy (FE-SEM) images indicate that the morphology of the surfaces, grain dimensions and thickness are strongly related to the processing parameters, with the hexagonal phase films having a very uniform morphology. Energy dispersive X-ray (EDX) analyses established the film composition in terms of dopant ions, which are responsible for the upconverting properties of the material. Luminescence measurements under laser excitation at 980 nm confirmed the promising upconversion properties of the \u3b2-NaYF4:Yb3+/Tm3+ films

Luminescence of Eu3+ Activated CaF2 and SrF2 Nanoparticles: Effect of the Particle Size and Codoping with Alkaline Ions

Eu3+ doped CaF2 and SrF2 nanoparticles were synthesized through a facile hydrothermal technique, using citrate ions as capping agents and Na+ or K+ as charge compensator ions. A proper tuning of the reaction time can modulate the nanoparticle size, from few to several tens of nanometers. Analysis of EXAFS spectra indicate that the Eu3+ ions enter into the fluorite CaF2 and SrF2 structure as substitutional defects on the metal site. Laser site selective spectroscopy demonstrates that the Eu3+ ions are mainly accommodated in two sites with different symmetries. The relative site distribution for lanthanide ions depends on the nanoparticle size, and higher symmetry Eu3+ sites are prevalent for bigger nanoparticles. Eu3+ ions in high symmetry sites present lifetimes of the 5D0 level around 27 ms, among the longest lifetimes found in the literature for Eu3+ activated materials. As a proof of concept of possible use of the Eu3+ activated alkaline-earth fluoride nanoparticles in nanomedicine, the red luminescence generated by two-photon absorption using pulsed laser excitation at 790 nm (in the first biological window) has been detected. The long Eu3+ lifetimes suggest that the present nanomaterials can be interesting as luminescent probes in time-resolved fluorescence techniques in biomedical imaging (e.g., FLIM) where fast autofluorescence is a drawback to avoid. \ua9 2018 American Chemical Society

Upconverting tri-doped calcium fluoride-based thin films: a comparison of the MOCVD and sol\u2013gel preparation methods

Starting from fluorinated metal\u2013organic b-diketonates, we report the synthesis of undoped and 3+ 3+ 3+ lanthanide-doped alkaline-earth fluoride (Er ,Tm ,Yb tri-doped CaF2) thin films through two different chemical approaches: a metal\u2013organic chemical vapor deposition (MOCVD) method and a combined sol\u2013gel/ spin-coating procedure. Both chemical approaches have the advantage of being very reliable and reproducible for the fast production of thin films with a high degree of uniformity over large areas. The fluorinated metal precursors act as a single-source in both processes, and an accurate control of the process parameters allows the optimization of the doped CaF2 films. X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray analysis have been used to characterize the deposited films. Upconversion emission, typical of the lanthanide ions, in the visible and near infrared regions upon laser excitation at 980 nm is clearly observable. The emissions are in the central region of the CIE1931 color coordinate space

Colloidal nanothermometers based on neodymium doped alkaline-earth fluorides in the first and second biological windows

Strontium fluoride nanoparticles activated with Nd3+ ions were studied as nanosized optical thermometers in the first (800-950 nm) and second (1000-1300 nm) biological windows, by monitoring the Nd3+ emission as a function of the temperature. The variations of the Nd3+ emissions were correlated with the temperature changes and the thermometric properties of SrF2 nanoparticles were evaluated using a ratiometric method. The best thermal sensitivity was found to be 0.60% K-1, a value which is the highest found for water dispersible colloidal nanothermometers based on the near-infrared luminescence of Nd3+ ions only in single phase materials. The excellent thermometric performance is also demonstrated by a thermal sensitivity of 1.2 °C, that can be achieved in temperature evaluation of real systems. Temperature measurements using a phantom tissue confirmed that the samples serve as efficient ratiometric nanothermometers that can work in two biological windows