S. Grandi

Synthesis of GeO2-doped SiO2 aerogels and xerogels

Abstract This work describes a new rapid method for preparation by sol–gel method of GeO2–SiO2 glass with GeO2 doping level varied from 0 to 10 mol%. From the same wet gels, both aerogels and xerogels were synthesized and different thermal treatments were performed in order to obtain the corresponding glasses. Bulk glasses were obtained by the aerogel route that is shown to be the most convenient method in terms of time saving. Instrumental neutron activation analysis (INAA) was employed to determine germanium concentration in the gels. Inductively coupled plasma mass spectroscopy (ICP-MS) was utilized to check the composition of the gels used as precursors for optical glasses. The porosity of both aerogels and xerogels was measured by adsorption isotherms. Solid-state 29 Si nuclear magnetic resonance at the magic angle ( 29 Si MAS-NMR) was employed to characterize the local bonding structure in both gels and glasses.

Sol-Gel GeO2-Doped SiO2 Glasses for Optical Applications

Optical and structural properties of silica materials with controlled Ge-content were investigated in aerogels samples with Ge concentration up to 100000 molar ppm prepared by a sol-gel method and densified at 1150°C. An optical absorption band centered at 242 nm, commonly ascribed to an under-coordinated germanium point defect, was observed in all doped samples, and its amplitude was found to be almost linearly correlated with the Ge-content. This feature may be ascribed to the new preparation technique so that this is potentially useful to produce materials with controlled defect content for specific optical applications.

OH-dependence of ultraviolet emission in porous silica

Abstract Photoluminescence and Raman measurements have been performed on sol–gel synthesized porous silica monoliths. Porous silica and polyethilenglycole/silica hybrids thermally treated at different temperatures have been analyzed. By exciting at 5.6 eV a structured photoluminescence emission centered at 3.7 eV is found in the whole set of samples. Hydration treatment of the pore surfaces increases the H-bonding interaction between silanols, inhibits the isolated silanols vibrations and changes the photoluminescence spectrum increasing the emission peaked at 3.7 eV.

Biocompatibility of functionalized boron phosphate (BPO4) nanoparticles for boron neutron capture therapy (BNCT) application.

UNLABELLED Boron neutron capture therapy (BNCT) is a radiotherapy treatment based on the accumulation in the tumor of a (10)B-containing drug and subsequent irradiation with low energy neutrons, which bring about the decay of (10)B to (7)Li and an α particle, causing the death of the neoplastic cell. The effectiveness of BNCT is limited by the low delivery and accumulation of the used boron-containing compounds. Here we report the development and the characterization of BPO4 nanoparticles (NPs) as a novel possible alternative drug for BNCT. An extensive analysis of BPO4 NP biocompatibility was performed using both mature blood cells (erythrocytes, neutrophils and platelets) and a model of hematopoietic progenitor cells. A time- and concentration-dependent cytotoxicity study was performed on neoplastic coloncarcinoma and osteosarcoma cell lines. BPO4 functionalization with folic acid, introduced to improve the uptake by tumor cells, appeared to effectively limit the unwanted effects of NPs on the analyzed blood components. FROM THE CLINICAL EDITOR Boron neutron capture therapy (BNCT) is a radiotherapy treatment modality based on the accumulation of a (10)B-containing drug and subsequent irradiation with low energy neutrons, inducing the decay of (10)B to (7)Li and an α particle, causing neoplastic cell death. This team of authors reports on a folic acid functionalized BPO4 nanoparticle with improved characteristics compared with conventional BNCT approaches, as demonstrated in tumor cell lines, and hopefully to be followed by translational human studies.

On the formation of aggregates in silica – rhodamine 6G type II hybrids

The spectroscopic features of dye aggregates in organic–inorganic Rhodamine 6G–silica hybrids are investigated in sol–gel prepared type II bulk and thick film samples in the 10−4–10−3 mol l−1 concentration range. No aggregates are observed in film samples irrespective of the dye concentration and the spectroscopic features are ascribed to fluorescent monomers. On the contrary, by means of excitation and emission fluorescence measurements and the analysis of fluorescence decay kinetics the formation of fluorescent aggregates is reported in bulk samples and the geometry of the formed aggregates at the silica surface is discussed on the single exciton theory framework. Beside the distribution of a single emitting specie observed in bulk samples and individuated as oblique J dimers, the analysis of the excitation spectra indicate also the presence of “dark” monomer units. An energy transfer mechanism is hypothesized to explain the interaction of the monomer–dimer pair.

Twofold coordinated Ge defects induced by gamma-ray irradiation in Ge-doped SiO 2

We report an experimental study by photoluminescence, optical absorption and Electron Paramagnetic Resonance measurements on the effects of exposure of Ge-doped amorphous SiO2 to γ ray radiation at room temperature. We have evidenced that irradiation at doses of the order of 1 MGy is able to generate Ge-related defects, recognizable from their optical properties as twofold coordinated Ge centers. Until now, such centers, responsible for photosensitivity of Ge-doped SiO2, have been induced only in synthesis procedures of materials. The found result evidences a role played by γ radiation in generating photosensitive defects and could furnish a novel basis for photosensitive pattern writing through ionizing radiation.

Ultraviolet emission lifetime in Si and Ge oxygen deficient centers in silica

We have measured the temperature dependence, in the range 10–295 K, of the lifetimes of the ultraviolet emissions associated with twofold coordinated Si and Ge, in pure and Ge-doped silica under excitation by synchrotron radiation. The Si-related fluorescence, centered at 4.4 eV, has a single exponential decay and its lifetime decreases from 4.0 ± 0.2 to 3.5 ± 0.2 ns on increasing the temperature. The luminescence at 4.2 eV, associated with the Ge defect, decays with a single exponential dependence below 150 K and with a more complex dependence at higher temperatures, its lifetime reducing from 7.8 ± 0.2 to 3.4 ± 0.2 ns. These features give evidence of the effectiveness of the thermally activated intersystem crossing in the relaxation of the excited singlet states, which is larger in the Ge-related center.

Synthesis and characterisation of functionalized borosilicate nanoparticles for boron neutron capture therapy applications

Boron Neutron Capture Therapy (BNCT) is a promising therapy for the cure of diffuse tumors. The successful clinical application of BNCT requires finding new boron-based compounds suitable for an efficient 10B delivery to the cancerous tissues. The purpose of this work is to synthesize borosilicate nanoparticles by a sol–gel recipe, and to functionalize them with folic acid in order to promote their capture by the tumor cells. Whereas sol–gel is a promising technique for the synthesis of nanoparticles, in case of borosilicate systems this approach is affected by significant boron loss during preparation. Here we show that functionalization of borosilicate nanoparticles with folic acid can reduce the boron loss. Moreover, preliminary biocompatibility tests indicate that functionalization strongly changes the reactivity of NPs towards blood cells, so favouring the potential use of these materials for clinical applications.

Bone reconstruction: Au nanocomposite bioglasses with antibacterial properties

Bioglasses are of wide interest since they spontaneously bond and integrate with living bone in the body. By varying the glass chemistry and/or by adding some dopants, it is possible to improve their clinical applications. Gold nanoparticles (Au NPs) are a well-known antibacterial agent, as well as a unique probe for sensing and imaging applications. We report on the synthesis of a 58S bioglass doped with Au NPs at two doping levels: 0.1% wt. and 1% wt. Antibacterial properties were observed on the Gram-positive Staphylococcus aureus, whereas no significant effects were found on the Gram-negative Escherichia coli. A possible mechanism of action of Au NPs towards bacteria has been described.

Ge related centers induced by gamma irradiation in sol–gel Ge-doped silica

Abstract Investigation of sol–gel silica samples with different Ge-doping content and with concentration of oxygen deficient centers (ODC) less than 1016 centers/cm3 was carried out after γ ray irradiation by electron paramagnetic resonance, optical absorption (OA) and photoluminescence measurements. It is found that in the dose range below 5 kGy paramagnetic centers with the characteristic resonance line of Ge(1) defects are induced in all the investigated samples, whereas no signatures of other Ge related centers or E′-Si are detected. Optical measurements detect two absorption bands peaked at 4.5 and 5.8 eV and no variation in the emission spectra of highly doped materials. From these results new suggestions arise for the correlation between the Ge(1) centers and the OA bands at 4.5 and 5.8 eV and for the absence of correlation of Ge(1) with Ge-ODC.