Alessandro Pugliara

Assessing bio-available silver released from silver nanoparticles embedded in silica layers using the green algae Chlamydomonas reinhardtii as bio-sensors

Silver nanoparticles (AgNPs) because of their strong antibacterial activity are widely used in health-care sector and industrial applications. Their huge surface-volume ratio enhances the silver release compared to the bulk material, leading to an increased toxicity for microorganisms sensitive to this element. This work presents an assessment of the toxic effect on algal photosynthesis due to small (size <20nm) AgNPs embedded in silica layers. Two physical approaches were originally used to elaborate the nanocomposite structures: (i) low energy ion beam synthesis and (ii) combined silver sputtering and plasma polymerization. These techniques allow elaboration of a single layer of AgNPs embedded in silica films at defined nanometer distances (from 0 to 7nm) beneath the free surface. The structural and optical properties of the nanostructures were studied by transmission electron microscopy and optical reflectance. The silver release from the nanostructures after 20h of immersion in buffered water was measured by inductively coupled plasma mass spectrometry and ranges between 0.02 and 0.49μM. The short-term toxicity of Ag to photosynthesis of Chlamydomonas reinhardtii was assessed by fluorometry. The obtained results show that embedding AgNPs reduces the interactions with the buffered water free media, protecting the AgNPs from fast oxidation. The release of bio-available silver (impacting on the algal photosynthesis) is controlled by the depth at which AgNPs are located for a given host matrix. This provides a procedure to tailor the toxicity of nanocomposites containing AgNPs.

Controlled elaboration of large-area plasmonic substrates by plasma process

Elaboration in a controlled way of large-area and efficient plasmonic substrates is achieved by combining sputtering of silver nanoparticles (AgNPs) and plasma polymerization of the embedding dielectric matrix in an axially asymmetric, capacitively coupled RF discharge maintained at low gas pressure. The plasma parameters and deposition conditions were optimized according to the optical response of these substrates. Structural and optical characterizations of the samples confirm the process efficiency. The obtained results indicate that to deposit a single layer of large and closely situated AgNPs, a high injected power and short sputtering times must be privileged. The plasma-elaborated plasmonic substrates appear to be very sensitive to any stimuli that affect their plasmonic response.

Dielectric Engineering of Nanostructured Layers to Control the Transport of Injected Charges in Thin Dielectrics

A new concept concerning dielectric engineering is presented in this study aiming at a net improvement of the performance of dielectric layers in RF MEMS capacitive switches with electrostatic actuation and an increase of their reliability. Instead of synthesis of new dielectric materials, we have developed a new class of dielectric layers that gain their performance from design rather than from composition. Two kinds of nanostructured dielectrics are presented. They consist of 1) silicon oxynitride layers (SiOxNy:H) with gradual variation of their properties (discrete or continuous) and 2) organosilicon (SiOxCy:H) and/or silica (SiO 2) layers with tailored interfaces; a single layer of silver nanoparticles (AgNPs) is embedded in the vicinity of the dielectric free surface. The nanostructured dielectric layers were deposited in a plasma process. They were structurally characterized and tested under electrical stress and environmental conditions typical for RF MEMS operation. The charge injection and decay dynamics were probed by Kelvin force microscopy. Modulation of the conductive properties of the nanostructured layers over seven orders of magnitude is achieved. Compared to dielectric monolayers, the nanostructured ones exhibit much shorter charge retention times. They appear to be promising candidates for implementation in RF MEMS capacitive switches with electrostatic actuation, and more generally for applications where surface charging must be avoided.

Dielectric engineering of nanostructured layers preventing electrostatic charging in thin dielectrics

New dielectric-engineering concept is developed intending a net improvement of the performance of dielectric layers under electrical stress. Instead of synthesis of new dielectric materials a new class of dielectric layers that gain their performance from design rather than from composition is established. Two kinds of nanostructured dielectric layers are presented here: (i) silicon oxynitride layers (SiOxNy:H) with gradual variation of their properties (discrete or continuous), and (ii) SiO2 layers with tailored interfaces; a single layer of silver nanoparticles (AgNPs) is embedded in the vicinity of the dielectric free surface. The nanostructured layers exhibit much shorter charge retention times and appear promising candidates for general applications where surface charging of dielectrics must be avoided, in particular for implementation in RF MEMS capacitive switches with electrostatic actuation.

The use of biosensors for improving the development of nanotechnology under realistic-use scenarios: Applications for cheaper and more effective silver nanoparticles and nanostructured surfaces

The novel features, based on the exposure of a higher number of atoms on the surfaces, allow nanomaterials to exhibit new or improved features to consumer products, that should be carefully assessed. Here is presented a new method based on the use of biosensors (algal cells) to assess the release of dissolved silver from nanoparticles. Algae were exposed to a) differently coated nanoparticles, b) from nanoparticles differing in their silver content, and c) from nanostructured surfaces differing in the depth at which silver nanoparticles have been embedded. Results shown the importance of chemical coatings, the ratio protein-silver on the AgNP composition and the depth at which are implanted in surfaces, as factors modulating the release of dissolved Ag (i.e. the responsible of the biocide properties of such nanomaterials).

On the application of surface enhanced Raman scattering to study the interaction of DsRed fluorescent proteins with silver nanoparticles embedded in thin silica layers

The interaction of proteins with silver nanoparticles (AgNPs) is of primary importance to uncover silver antimicrobial efficiency and environmental hazard. This interaction can affect silver reactivity, bioavailability and, eventually, silver toxicity towards the environmental media. Detection of the interaction of DsRed fluorescent proteins with AgNPs embedded in thin silica layers is demonstrated using surface enhanced Raman spectroscopy (SERS), but deep analyses require the design and elaboration of dedicated plasmonic substrates giving a high enhancement factor.

Plasma based concept for engineering of multifunctional materials with application to synthesis of large-area plasmonic substrates and to control the charge injection in dielectrics

The proposed approach in this contribution concerns plasma deposition processes for engineering of multifunctional materials. It opens the way for transition from material level of development to system level of applications. This concept is applied for deposition of nanocomposite thin layers comprising a single layer of silver nanoparticles (AgNPs) embedded in silica-like host matrices at a controlled distance from the free surface with application in two distinguished fields, namely plasmonics to obtain large-area plasmonic embedded substrates and electrical engineering to control the charge injection in dielectrics. Structural, optical and electrical characterizations of the samples confirm the process efficiency.

Physico-Chemical Characterization of the Interaction of Red Fluorescent Protein—DsRed With Thin Silica Layers

The Discosoma recombinant red fluorescent (DsRed) protein is the latest member of the family of fluorescent proteins. It holds great promise for applications in biotechnology and cell biology. However, before being used for rational engineering, knowledge on the behavior of DsRed and the underlying mechanisms relating its structural stability and adsorption properties on solid surfaces is highly demanded. The physico-chemical analysis performed in this study reveals that the interaction of DsRed with SiO2 surfaces does not lead to complete protein denaturation after adsorption and dehydration. Nevertheless, the photoluminescence emission of dehydrated DsRed small droplets was found to be slightly red-shifted, peaking at 590 nm. The measured contact angles of droplets containing different concentration of DsRed proteins determine the interaction as hydrophilic one, however with larger contact angles for larger DsRed concentrations. The DsRed protein behavior is not pH-dependent with respect of the contact angle measurements, in agreement with previously reported studies.

Physico-chemical characterization of the interaction of red fluorescent protein — DsRed with silica layers

The Discosoma Recombinant Red Fluorescent (DsRed) protein is the latest member of the family of fluorescent proteins. It holds great promise for applications in biotechnology and cell biology. However, before being used for rational engineering, knowledge on the underlying mechanisms relating the DsRed structural stability and adsorption properties on solid surfaces is highly demanded. The physico-chemical analysis performed in this study reveals that the interaction of DsRed with SiO2 surfaces does not lead to protein denaturation. The secondary structure of DsRed is preserved after adsorption and dehydration. The measured contact angles of sessile droplets with different DsRed concentrations determine the interaction as hydrophilic one. The photoluminescence emission of dehydrated DsRed droplets is found to be slightly red-shifted, peaking at 590 nm.