All-optical polariton transistor Ballarini, D; De Giorgi, M; Cancellieri, E ...
Nature communications,
2013, Letnik:
4, Številka:
1
Journal Article
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Although optical technology provides the best solution for the transmission of information, all-optical devices must satisfy several qualitative criteria to be used as logic elements. In particular, ...cascadability is difficult to obtain in optical systems, and it is assured only if the output of one stage is in the correct form to drive the input of the next stage. Exciton-polaritons, which are composite particles resulting from the strong coupling between excitons and photons, have recently demonstrated huge non-linearities and unique propagation properties. Here we show that polariton fluids moving in the plane of the microcavity can operate as input and output of an all-optical transistor, obtaining up to 19 times amplification and demonstrating the cascadability of the system. Moreover, the operation as an AND/OR gate is shown, validating the connectivity of multiple transistors in the microcavity plane and opening the way to the implementation of polariton integrated circuits.
The interaction between cells and nanostructured materials is attracting increasing interest, because of the possibility to open up novel concepts for the design of smart nanobiomaterials with active ...biological functionalities. In this frame we investigated the response of human neuroblastoma cell line (SH-SY5Y) to gold surfaces with different levels of nanoroughness. To achieve a precise control of the nanoroughness with nanometer resolution, we exploited a wet chemistry approach based on spontaneous galvanic displacement reaction. We demonstrated that neurons sense and actively respond to the surface nanotopography, with a surprising sensitivity to variations of few nanometers. We showed that focal adhesion complexes, which allow cellular sensing, are strongly affected by nanostructured surfaces, leading to a marked decrease in cell adhesion. Moreover, cells adherent on nanorough surfaces exhibit loss of neuron polarity, Golgi apparatus fragmentation, nuclear condensation, and actin cytoskeleton that is not functionally organized. Apoptosis/necrosis assays established that nanoscale features induce cell death by necrosis, with a trend directly related to roughness values. Finally, by seeding SH-SY5Y cells onto micropatterned flat and nanorough gold surfaces, we demonstrated the possibility to realize substrates with cytophilic or cytophobic behavior, simply by fine-tuning their surface topography at nanometer scale. Specific and functional adhesion of cells occurred only onto flat gold stripes, with a clear self-alignment of neurons, delivering a simple and elegant approach for the design and development of biomaterials with precise nanostructure-triggered biological responses.
The detection of a few molecules in a highly diluted solution is of paramount interest in fields including biomedicine, safety and eco-pollution in relation to rare and dangerous chemicals. ...Nanosensors based on plasmonics are promising devices in this regard, in that they combine the features of high sensitivity, label-free detection and miniaturization. However, plasmonic-based nanosensors, in common with general sensors with sensitive areas on the scale of nanometres, cannot be used directly to detect molecules dissolved in femto- or attomolar solutions. In other words, they are diffusion-limited and their detection times become impractical at such concentrations. In this Article, we demonstrate, by combining super-hydrophobic artificial surfaces and nanoplasmonic structures, that few molecules can be localized and detected even at attomolar (10-18 mol l-1 ) concentration. Moreover, the detection can be combined with fluorescence and Raman spectroscopy, such that the chemical signature of the molecules can be clearly determined.
CdSe nanocrystals of well‐defined sizes (so‐called magic‐size clusters, MSCs) have been grown with progressively larger sizes. During the synthesis, the relative populations of the different families ...of MSCs vary, as smaller clusters evolve into larger clusters. The time evolution of the various MSCs (see figure) is modeled by taking into account their much higher stability over nanocrystals of any intermediate size. A blue‐light‐emitting diode based on these MSCs is also presented.
A picosecond laser ablation approach has been developed for the synthesis of ligand-free AuAg bimetallic NPs where the relative amount of Ag is controlled in situ through a laser shielding effect. ...Various measurements, such as optical spectroscopy, transmission electron microscopy combined with energy dispersive X-ray spectroscopy and inductively coupled plasma optical emission spectrometry, revealed the generation of homogenous 15 nm average size bimetallic NPs with different compositions and tunable localized surface plasmon resonance. Furthermore, ligand-free metallic nanoparticles with respect to chemically synthesized nanoparticles display outstanding properties, i.e. featureless Raman background spectrum, which is a basic requirement in many plasmonic applications such as Surface Enhanced Raman Spectroscopy. Various molecules were chemisorbed on the nanoparticle and SERS investigations were carried out, by varying the laser wavelength. The SERS enhancement factor for AuAg bimetallic NPs shows an enhancement factor of about 5.7 × 10(5) with respect to the flat AuAg surface.
We report on the temperature and size dependence of the photoluminescence of core CdTe colloidal quantum dots (QDs). We show that at temperatures lower than 170 K a thermally activated transition ...between two different states separated by about 12−20 meV takes place. At temperatures higher than 170 K, the main nonradiative process is thermal escape assisted by multiple longitudinal optical (LO) phonons absorption. Moreover, we show that quantum confinement affects both the exciton−acoustic phonons and the exciton−LO phonons coupling. The coupling constant with acoustic phonons is strongly enhanced in QDs (up to 31μeV/K) with respect bulk CdTe (0.7μeV/K). On the contrary, the exciton-LO phonons coupling constant decreases as the dot size decreases (down to 14 meV with respect 24.5 meV in the bulk).
Engineering the spectral properties of fluorophores, such as the enhancement of luminescence intensity, can be achieved through coupling with surface plasmons in metallic nanostructures. This ...process, referred to as metal-enhanced fluorescence, offers promise for a range of applications, including LEDs, sensor technology, microarrays and single-molecule studies. It becomes even more appealing when applied to colloidal semiconductor nanocrystals, which exhibit size-dependent optical properties, have high photochemical stability, and are characterized by broad excitation spectra and narrow emission bands. Other approaches have relied upon the coupling of fluorophores (typically organic dyes) to random distributions of metallic nanoparticles or nanoscale roughness in metallic films. Here, we develop a new strategy based on the highly reproducible fabrication of ordered arrays of gold nanostructures coupled to CdSe/ZnS nanocrystals dispersed in a polymer blend. We demonstrate the possibility of obtaining precise control and a high spatial selectivity of the fluorescence enhancement process.
Bright, balanced white‐light electroluminescence has been achieved from a single active oligothiophene compound. White light is created by the superposition of a broad blue–green‐light emission ...originating from the single molecule and a red‐shifted narrow peak due to dimer formation. These results open the way to the fabrication of novel, low‐cost white‐light‐emitting devices with a single molecular material as the active compound.
Semiconductor nanocrystals, or Quantum Dots (QDs), have gained considerable attention due to their unique size-dependent optical and electronic properties that make them attractive for a wide range ...of applications, including biology and nanomedicine. Their widespread use, however, poses urgent questions about their potential toxicity, especially because of their heavy metal composition that could cause harmful effects to human health and environment. In this work, we evaluated in vivo the long-term toxicity of CdSe-ZnS QDs with different surface coatings, probing oral administration in the model system Drosophila melanogaster. In particular, we found that all the differently coated QDs significantly affect the lifespan of treated Drosophila populations and induce a marked increase in reactive oxygen species (ROS) levels. Furthermore, we observed that these QDs induce severe genotoxic effects and increased rate of apoptosis in Drosophila haemocytes. These toxic effects were found to be mainly related to the in vivo degradation of QDs with consequent release of Cd(2+) ions, while the coating of QDs can modulate their bioaccumulation in the organism, partly decreasing their overall toxicity.
A hybrid white‐light‐emitting device (see figure) whose emission originates only from ternary nanocrystal (quantum dot) composites but whose luminance performance matches the requirements of the ...lighting industry is demonstrated. The bright white‐light emission is obtained by controlling the Förster energy transfer and charge‐trapping mechanisms between the different components.
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