[Show abstract][Hide abstract] ABSTRACT: Efficient single photon sources (SPSs) are now catching the scientific community attention. Quantum information technology algorithms are based on antibunched photon fluxes and on the fine control of their quantum states and polarization properties. Among the proposed approaches for SPSs based devices, actually two technologies are in competitions: the Stranski-Krastanov epitaxial quantum dots (QDs) and wet-chemically synthesized colloidal nanocrystals (NCs). Epitaxial QDs have been deeply studied in past years and antibunched photon fluxes up to a temperature of ~200 K have been achieved by using either GaN QDs  or a single QD embedded in a single quantum wire . In spite of the possibility to simply achieve electrical injection  and positioning inside photonic crystals nanocavities , room temperature single photon emission in epitaxial nanostructures has not been demonstrated so far. On the other hand, colloidal core/shell NCs are efficient sources of antibunched photons at room temperature  and show several advantages which let us envision their application to final devices. It has been demonstrated that the shape and size of the NCs can be tailored to overcome the drawbacks which so far limited the nanocrystals applications, such as blinking  and unpolarized emission . Beside the characterization of their physical properties [8,9], the compatibility with the nano-engineering techniques has been recently demonstrated  and the first evidence of SPSs based on single nanocrystal coupled to a cavity mode has been demonstrated . In this work we report on efficient SPSs based on a particular type of nanocrystals, in which a CdSe rod-like shell surround a CdS spherical core (Fig.1(a)). The polarization properties of these nanoparticles make them suitable for the implementation of quantum information technology algorithms based on photon polarization, such as BB84 and B92 for private cryptography keys distribution . The CdSe/CdS core/shell dot-in-rod (DR) nanocrystals have been synthesized with a seeded growth approach , which yields nanorods with narrow distributions of both lengths and diameters. A DR mono-molar solution (in toluene) was dropcasted on a microscope glass coverslip and excited using a picosecond pulsed laser. By means of a high sensitivity Hanbury-Brown and Twiss setup, based on two avalanche photodiodes, we performed time and polarization resolved measurements. In order to proof the non classical behavior of the light emitted from the single DR, the coincidence histogram (proportional to the autocorrelation function g (2) (τ)) was measured for several nanocrystals, showing a near perfect antibunching (see Fig.1(b)): the few coincidences near zero delay mean that the probability to detect more than one photon at the same time is extremely low and the sharp periodic peaks indicate that two photons are usually spaced of a multiple of the period of the laser pulses.
[Show abstract][Hide abstract] ABSTRACT: The challenges in replacing synthetic polymers with biopolymers in food packaging is discussed. It is almost impossible to imagine a biopolymer or a bioplastic that can meet all the demanding requirements at the same time and this is the challenge in replacing conventional packaging materials with more renewable biomaterials and resources. The potential for using cellulose, the most abundant polymer on the planet, as a biopolymer for food packaging is one of the most challenging areas in developing bioplastic packaging materials. This is because cellulose is highly crystalline and prone to hydrolysis. Smart and cost effective ways to blend biopolymers with synthetic polymers should be at the forefront of research and development. Synthetic thermoplastic polyurethanes can be blended or copolymerized with bioplastics or biopolymers. Barrier and mechanical properties of certain cellulose derivatives should be improved with certain food grade nano-inclusions to make them suitable for food packaging applications.
[Show abstract][Hide abstract] ABSTRACT: Nanoparticles, named cutinsomes , have been prepared from aleuritic (9,10,16-trihidroxipalmitic) acid and tomato fruit cutin monomers (a mixture of mainly 9(10),16-dihydroxypalmitic acid (85%, w/w) and 16-hydroxyhexadecanoic acid (7.5%, w/w)) with pectin in aqueous solution. The process of formation of the nanoparticles of aleuritic acid plus pectin has been monitored by UV-Vis spectrophotometry, while their chemical and morphological characterization was analyzed by ATR-FTIR, TEM, and non-contact AFM. The structure of these nanoparticles can be described as a lipid core with a pectin shell. Pectin facilitated the formation of nanoparticles, by inducing their aggregation in branched chains and favoring the condensation between lipid monomers. Also, pectin determined the self-assembly of cutinsomes on highly ordered pyrolytic graphite (HOPG) surfaces, causing their opening and forming interconnected structures. In the case of cutin monomers, the nanoparticles are fuse
[Show abstract][Hide abstract] ABSTRACT: Abstract Highly stretchable polyvinyl alcohol (PVA) films with a strain at break of around 700% were obtained from solutions in trifluoroacetic acid (TFA). Structural and chemical analysis by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (ATR-FTIR) showed that TFA is retained by PVA via hydrogen bonds between the carboxylic acid groups and the hydroxyl groups of the polymers causing a strong plasticizing effect. Additionally, composites of PVA with cellulose could be developed using TFA as common solvent. The morphological and mechanical properties of the polymer composites could be accurately tuned by modifying the relative concentrations of the two polymers. Data from water adsorption isotherms and wetting measurements indicated that the presence of trifluoromethyl groups in PVA render the composite films relatively hydrophobic.
Full-text · Article · Apr 2015 · The Chemical Engineering Journal
[Show abstract][Hide abstract] ABSTRACT: Solution-processed inorganic and organic materials have been pursued for more than a decade as low-threshold, high-gain lasing media, motivated in large part by their tunable optoelectronic properties and ease of synthesis and processing. Although both have demonstrated stimulated emission and lasing, they have not yet approached the continuous-wave pumping regime. Two-dimensional CdSe colloidal nanosheets combine the advantage of solution synthesis with the optoelectronic properties of epitaxial two-dimensional quantum wells. Here, we show that these colloidal quantum wells possess large exciton and biexciton binding energies of 132 meV and 30 meV, respectively, giving rise to stimulated emission from biexcitons at room temperature. Under femtosecond pulsed excitation, close-packed thin films yield an ultralow stimulated emission threshold of 6 μJ cm(-2), sufficient to achieve continuous-wave pumped stimulated emission, and lasing when these layers are embedded in surface-emitting microcavities.
No preview · Article · Oct 2014 · Nature Nanotechnology
[Show abstract][Hide abstract] ABSTRACT: Bioplastics with a wide range of mechanical properties were directly obtained from industrially processed edible vegetable and cereal wastes. As model systems, we present bioplastics synthesized from wastes of parsley and spinach stems, rice hulls, and cocoa pod husks by digesting in trifluoroacetic acid (TFA), casting, and evaporation. In this way, amorphous cellulose-based plastics are formed. Moreover, many other natural elements present in these plants are carried over into the bioplastics rendering them with many exceptional thermo-physical properties. Here, we show that, due to their broad compatibility with cellulose, amorphous cellulose can be naturally plasticized with these bioplastics by simply mixing during processing. Comparison of their mechanical properties with that of various petroleum based synthetic polymers indicates that these bioplastics have equivalent mechanical properties to the nondegrading ones. This opens up possibilities for replacing some of the nondegrading polymers with the present bioplastics obtained from agro-waste.
[Show abstract][Hide abstract] ABSTRACT: The cuticle is one of the most important plant barriers. It is an external and continuous lipid membrane that covers the surface of epidermal cells and whose main function is to prevent the massive loss of water. The spectroscopic characterization of the plant cuticle and its components (cutin, cutan, waxes, polysaccharides and phenolics) by infrared and Raman spectroscopies has provided significant advances in the knowledge of the functional groups present in the cuticular matrix and on their structural role, interaction and macromolecular arrangement. Additionally, these spectroscopies have been used in the study of cuticle interaction with exogenous molecules, degradation, distribution of components within the cuticle matrix, changes during growth and development and characterization of fossil plants.
Full-text · Article · Jun 2014 · Frontiers in Plant Science
[Show abstract][Hide abstract] ABSTRACT: The assessment of the risks exerted by nanoparticles is a key challenge for academic, industrial, and regulatory communities worldwide. Experimental evidence points towards significant toxicity for a range of nanoparticles both in vitro and in vivo. Worldwide efforts aim at uncovering the underlying mechanisms for this toxicity. Here, we show that the intracellular ion release elicited by the acidic conditions of the lysosomal cellular compartment - where particles are abundantly internalized - is responsible for the cascading events associated with nanoparticles-induced intracellular toxicity. We call this mechanism a lysosome-enhanced Trojan horse effect since, in the case of nanoparticles, the protective cellular machinery designed to degrade foreign objects is actually responsible for their toxicity. To test our hypothesis, we compare toxicity for similar gold particles whose main difference is in the internalization pathways. We show that particles known to pass directly though cell membranes be
[Show abstract][Hide abstract] ABSTRACT: Li-ion rechargeable batteries have enabled the wireless revolution
transforming global communication. Future challenges, however, demands
distributed energy supply at a level that is not feasible with the current
energy-storage technology. New materials, capable of providing higher energy
density are needed. Here we report a new class of lithium-ion batteries based
on a graphene ink anode and a lithium iron phosphate cathode. By carefully
balancing the cell composition and suppressing the initial irreversible
capacity of the anode, we demonstrate an optimal battery performance in terms
of specific capacity, i.e. 165 mAhg-1, estimated energy density of about 190
Whkg-1 and life, with a stable operation for over 80 charge-discharge cycles.
We link these unique properties to the graphene nanoflake anode displaying
crystalline order and high uptake of lithium at the edges, as well as to its
structural and morphological optimization in relation to the overall battery
composition. Our approach, compatible with any printing technologies, is cheap
and scalable and opens up new opportunities for the development of
high-capacity Li-ion batteries.
[Show abstract][Hide abstract] ABSTRACT: Technologies able to handle microvolumes of liquids, like microfluidics and liquid marbles, are attractive for applications that include miniaturized biological and chemical reactors, sensors, microactuators, and drug delivery systems. Inspired from natural fibrous envelopes, here we present an innovative approach for liquid encapsulation and manipulation by using electrospun nanofibers. We demonstrated the realization of not-wetting soft solids consisting of a liquid core wrapped in a hydrophobic fibrillar cloak of a fluoroacrylic copolymer and cellulose acetate. By properly controlling the wetting and mechanical properties of the fibers, we created final architectures with tunable mechanical robustness that were stable on a wide range of substrate (from paper to glass) and floated on liquid surfaces. Remarkably, the realized fiber-coated drops endured vortex mixing in a continuous oil phase at high stirring speed without bursting or water losses, favouring mixing processes inside the entrapped liquid volume. Moreover, the produced cloak can be easily functionalized by incorporating functional particles, active molecules or drugs inside the nanofibers.
[Show abstract][Hide abstract] ABSTRACT: We have studied in vitro toxicity of iron oxide nanoparticles (NPs) coated with a thin silica shell (Fe3O4/SiO2 NPs) on A549 and HeLa cells. We compared bare and surface passivated Fe3O4/SiO2 NPs to evaluate the effects of the coating on the particle stability and toxicity. NPs cytotoxicity was investigated by cell viability, membrane integrity, mitochondrial membrane potential (MMP), reactive oxygen species (ROS) assays, and their genotoxicity by comet assay. Our results show that NPs surface passivation reduces the oxidative stress and alteration of iron homeostasis and, consequently, the overall toxicity, despite bare and passivated NPs show similar cell internalization efficiency. We found that the higher toxicity of bare NPs is due to their stronger in-situ degradation, with larger intracellular release of iron ions, as compared to surface passivated NPs. Our results indicate that surface engineering of Fe3O4/SiO2 NPs plays a key role in improving particles stability in biological environments reducing both cytotoxic and genotoxic effects.
[Show abstract][Hide abstract] ABSTRACT: Plasmonic resonators have generated much interest in recent years due to their ability to localize optical energy into thin continuous metallic regions. We present the integration of such resonators into flexible polydimethylsiloxane-gold nanocomposite materials that couple light efficiently, in order to prepare a totally optical layout for tactile sensors, able to detect low applied pressure forces. The development of plasmonic nanostructured resonators of thin gold layers onto polydimethylsiloxane is achieved using light texturing. In particular, this technique creates uniform patterns of gold nanoparticles forming quasi continuous gold thin layers behaving as plasmonic resonators. The excitation of the resonators and the detection of the signal after the application of the pressure are done through optical fibers avoiding electrical connections or circuits embedded into the elastomer. The proposed totally optical tactile sensor is easily processable and ideal for upscaling oriented towards humanoid robotics and biocompatible elastomeric human interface skin prostheses.
[Show abstract][Hide abstract] ABSTRACT: In recent years, education in nanotechnology has evolved to reflect the
new skill set required to perform multidisciplinary research. As the
field further develops, it will need to evolve again.
No preview · Article · Nov 2013 · Nature Nanotechnology
[Show abstract][Hide abstract] ABSTRACT: In this work, we propose a quantitative assessment of nanoparticles toxicity in vivo. We show a quantitative ranking of several types of nanoparticles (AuNPs, AgNPs, cadmium-based QDs, cadmium-free QDs, and iron oxide NPs, with different coating and/or surface chemistries), providing a categorization of their toxicity outcomes. This strategy may offer an innovative high-throughput screening tool of nanomaterials, of potential and broad interest to the nanoscience community.
Full-text · Article · Sep 2013 · Journal of Nanoparticle Research
[Show abstract][Hide abstract] ABSTRACT: We demonstrate the generation of natural polymeric structures of complex shapes and controlled composition, starting from the collision of aqueous drops of alginate with the surface of a calcium ion-based liquid. We prove that by tuning the impact velocity of the alginate drops on the target surface one can control the floating state of the drops inducing the formation of mushroom-like structures, upon alginate gelation. Besides the geometric peculiarity, the presented approach allows us to provide dual functionality to the polymeric objects, attaching different kinds of functional molecules onto their surface areas, which are immersed or not in the liquid, making such architectures attractive for the development of a novel class of bionanocomposites.
[Show abstract][Hide abstract] ABSTRACT: Fatigue resistance of the photochromic diarylethene molecules 1,2-bis[2-methylbenzo[b]thyophen-3-yl]-3,3,4,4,5,5-hexafluoro-1-cyclopentene embedded in three different acrylic polymers is studied upon multiple coloration–decoloration cycles. The resistance to photofatigue is found to be different in the three polymeric materials when one-photon excitation was used for the reversible photoconversion experiment. In particular, the photochromic molecules lose their photoisomerization ability faster if they are embedded in poly(methyl methacrylate) (PMMA) with respect to poly(ethyl methacrylate-co-methyl acrylate) (PEMMA) and poly(ethyl methacrylate) (PEMA). We propose several explanations based on the physico-chemical properties of the matrix and of the photochromic molecules. In the case of two-photon excitation, which is necessary for 3D optical writing, the fatigue resistance is found to be poorer than in the one-photon case. The accelerated photodegradation can be assigned to the non-linear nature of interaction between the polymeric composite material and light.
No preview · Article · Jun 2013 · Materials Science and Engineering B