Robert Mauricot

New nanoplatform based on Gd2O2S:Eu3+ core: synthesis, characterization and use for in vitro bio-labelling

The synthesis of Gd2O2S:Eu3+ nanoparticles (NPs), from hydroxycarbonate precursor precipitation followed by sulfuration in a H2S/Ar atmosphere at 750 °C; is reported. It is the first time that the size of Gd2O2S:Eu3+ NPs can be finely tuned from 60 nm to more than 200 nm by controlling the precipitation medium, the maturation time and the sulfuration route. The oxysulfide Gd2O2S:Eu3+ NPs emit strong red luminescence at 624 nm when excited by near UV (363 nm) or by X-rays. They may thus be considered as nano-phosphors and nano-scintillators. Then, the surface of oxysulfide NPs has been modified by an amino-silica or by a mesoporous silica shell (thickness 10–15 nm). The luminescence intensity of europium in gadolinium oxysulfide NPs has been maintained in the amino-silica coated particles Gd2O2S:Eu3+@SiO2-APTMS, whereas it has been significantly enhanced in the mesoporous silica coated Gd2O2S:Eu3+@mSiO2. This versatile new nanoplatform can be easily internalized in living NIH3T3 mouse cells. It is not cytotoxic up to 1 mg mL−1 and can be easily imaged by epifluorescence microscopy with excitation in the NUV. Consequently this spherical monodispersed Gd2O2S:Eu3+ nanophosphor could be considered as a very promising new fluorescent probe for bio-labelling, better than the corresponding oxide or fluoride nanoparticles.

APTES-Modified RE2O3:Eu3+ Luminescent Beads: Structure and Properties

Europium-doped lanthanide oxide RE(2)O(3):Eu(3+) (RE = Y or Gd) luminescent beads, with a spherical shape and a diameter of 150 ± 15 nm, have been modified by reaction with 3-aminopropyltriethoxysilane (APTES), in order to introduce reactive amine groups at their surfaces. The direct silanation has resulted in the formation of a nanometric layer at the surface of the beads, with an optimum grafting rate of 0.055 ± 0.005 mol APTES/mol RE(2)O(3). Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies confirmed the condensation of an organosilane layer, made of cross-linked -O-Si-O-Si- and of groups -O-Si-R (with R = (CH(2))(3)NH(2) or O-Et). Titration of the accessible amine groups has been performed by simultaneously measuring the luminescence of grafted fluorescein isothiocyanate and that of core particles: there are about 2.3 × 10(4) (2.8 × 10(4)) -NH(2) per Y(2)O(3):Eu(3+) (Gd(2)O(3):Eu(3+)) bead. The isoelectronic point was shifted by one pH unit after APTES modification. The surface modification by APTES at least preserved (for Gd(2)O(3):Eu(3+)) or improved (for Y(2)O(3):Eu(3+)) the red emission of the beads.

Elaboration by spray pyrolysis and characterization in the VUV range of phosphor particles with spherical shape and micronic size

Y2O3 : Eu and Zn2SiO4 : Mn are the red and green phosphors actually used in plasma display panels. These phosphors have been prepared by spray pyrolysis synthesis and thermal post-treatments. Their optical properties in the vacuum ultraviolet (VUV) energy range have been investigated. The absorption coefficients have been extracted from electron energy loss spectroscopy. The luminescence properties of phosphors from spray pyrolysis have been characterized under UV or VUV excitations with different dedicated experimental set-ups: excitation spectroscopy, measurements of luminescence efficiencies under Hg lamp, pure Xe and Ne–Xe discharges, determinations of luminescence decay times under plasma excitation. The characteristics have been compared with those of corresponding commercial phosphors.

Decontamination Efficiency of a DBD Lamp Containing an UV-C Emitting Phosphor.

Among different physical and chemical agents, the UV radiation appears to be an important route for inactivation of resistant microorganisms. The present study introduces a new mercury‐free Dielectric Barrier Discharge (DBD) flat lamp, where the biocide action comes from the UV emission produced by rare‐earth phosphor obtained by spray pyrolysis, following plasma excitation. In this study, the emission intensity of the prototype lamp is tuned by controlling gas pressure and electrical power, 500 mbar and 15 W, corresponding to optimal conditions. In order to characterize the prototype lamp, the energetic output, temperature increase following lamp ignition and ozone production of the source were measured. The bactericidal experiments carried out showed excellent results for several gram‐positive and gram‐negative bacterial strains, thus demonstrating the high decontamination efficiency of the DBD flat lamp. Finally, the study of the external morphology of the microorganisms after the exposure to the UV emission suggested that other mechanisms than the bacterial DNA damage could be involved in the inactivation process.

Multimodal gadolinium oxysulfide nanoparticles: a versatile contrast agent for mesenchymal stem cell labeling

Despite a clear development of innovative therapies based on stem cell manipulation, the availability of new tools to better understand and follow stem cell behavior and improve their biomedical applications is not adequate. Indeed, an ideal tracking device must have good ability to label stem cells as well as complete neutrality relative to their biology. Furthermore, preclinical studies imply in vitro and in vivo approaches that often require several kinds of labeling and/or detection procedures. Consequently, the multimodality concept presented in this work may present a solution to this problem as it has the potential to combine complementary imaging techniques. Spherical europium-doped gadolinium oxysulfide (Gd2O2S:Eu3+) nanoparticles are presented as a candidate as they are detectable by (1) magnetic resonance (MRI), (2) X-ray and (3) photoluminescence imaging. Whole body in vivo distribution, elimination and toxicity evaluation revealed a high tolerance of nanoparticles with a long-lasting MRI signal and slow hepatobiliary and renal clearance. In vitro labeling of a wide variety of cells unveils the nanoparticle potential for efficient and universal cell tracking. Emphasis on mesenchymal stromal cells (MSCs) leads to the definition of optimal conditions for labeling and tracking in the context of cell therapy: concentrations below 50 μg mL-1 and diameters between 170 and 300 nm. Viability, proliferation, migration and differentiation towards mesodermal lineages are preserved under these conditions, and cell labeling appears to be persistent and without any leakage. Ex vivo detection of as few as five thousand Gd2O2S:Eu3+-labeled MSCs by MRI combined with in vitro examination with fluorescence microscopy highlights the feasibility of cell tracking in cell therapy using this new nanoplatform.

Preliminary studies on biocidal activities of UV-C emitting phsphors under plasma excitations

Summary form only given. In this paper, we investigate the UVC light emission from phosphors under plasma excitation for anti-microbial testing on Escherichia coli (E-coli).