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In this study, transmission electron microscopy atomic force microscopy, and surface enhanced Raman spectroscopy are combined through a direct imaging approach, to gather structural and chemical information of complex molecular systems such as ion channels in their original plasma membrane. Customized microfabricated sample holder allows to characterize Na

The effect of direct or indirect binding of intercalant molecules on DNA structure is of fundamental importance in understanding the biological functioning of DNA. Here we report on self-suspended DNA nanobundles as ultrasensitive nanomechanical resonators for structural studies of DNA-ligand complexes. Such vibrating nanostructures represent the smallest mechanical resonator entirely composed of DNA. A correlative analysis between the mechanical and structural properties is exploited to study the intrinsic changes of double strand DNA, when interacting with different intercalant molecules (YOYO-1 and GelRed) and a chemotherapeutic drug (Cisplatin), at different concentrations. Possible implications of our findings are related to the study of interaction mechanism of a wide category of molecules with DNA, and to further applications in medicine, such as optimal titration of chemotherapeutic drugs and environmental studies for the detection of heavy metals in human serum., Intercalating molecules can significantly change the conformation of DNA. Here, the authors fabricated resonators fully composed of DNA forming bundles between microfabricated pillars to study the vibration property of the DNA bundles with/without intercalant molecules.

Superhydrophobic surfaces display an extraordinary repulsion to water and water-based solutions. This effect emerges from the interplay of intrinsic hydrophobicity of the surface and its morphology. These surfaces have been established for a long time and have been studied for decades. The increasing interest in recent years has been focused towards applications in many different fields and, in particular, biomedical applications. In this paper, we review the progress achieved in the last years in the fabrication of regularly patterned superhydrophobic surfaces in many different materials and their exploitation for the manipulation and characterization of biomaterial, with particular emphasis on the issues affecting the yields of the fabrication processes and the quality of the manufactured devices.

Methods to produce protein amyloid fibrils, in vitro, and in situ structure characterization, are of primary importance in biology, medicine, and pharmacology. We first demonstrated the droplet on a super-hydrophobic substrate as the reactor to produce protein amyloid fibrils with real-time monitoring of the growth process by using combined light-sheet microscopy and thermal imaging. The molecular structures were characterized by Raman spectroscopy, X-ray diffraction and X-ray scattering. We demonstrated that the convective flow induced by the temperature gradient of the sample is the main driving force in the growth of well-ordered protein fibrils. Particular attention was devoted to PHF6 peptide and full-length Tau441 protein to form amyloid fibrils. By a combined experimental with the molecular dynamics simulations, the conformational polymorphism of these amyloid fibrils were characterized. The study provided a feasible procedure to optimize the amyloid fibrils formation and characterizations of other types of proteins in future studies., Zhang et al present an integrated real-time imaging and flow field control platform based on water droplet evaporation on super-hydrophobic substrate (SHS) to enable amyloid fibril aggregation. They apply this methodology to observe structural polymorphism in PHF6 peptide and full length Tau441.

In this work, micro-fabrication, super-hydrophobic properties and a physiologically compatible preparation step are combined and tailored to obtain background free biological samples to be investigated by Transmission Electron Microscopy (TEM) diffraction technique. The validation was performed evaluating a well-known parameter such as the DNA interbases value. The diffraction spacing measured is in good agreement with those obtained by HRTEM direct metrology and by traditional X-Ray diffraction. This approach addresses single molecule studies in a simplified and reproducible straightforward way with respect to more conventional and widely used techniques. In addition, it overcomes the need of long and elaborated samples preparations: the sample is in its physiological environment and the HRTEM data acquisition occurs without any background interference, coating, staining or additional manipulation. The congruence in the results reported in this paper makes the application of this approach extremely promising towards those molecules for which crystallization remains a hurdle, such as cell membrane proteins and fibrillar proteins.

This review looks at the different approaches, techniques, and materials devoted to DNA studies. In the past few decades, DNA nanotechnology, micro-fabrication, imaging, and spectroscopies have been tailored and combined for a broad range of medical-oriented applications. The continuous advancements in miniaturization of the devices, as well as the continuous need to study biological material structures and interactions, down to single molecules, have increase the interdisciplinarity of emerging technologies. In the following paragraphs, we will focus on recent sensing approaches, with a particular effort attributed to cutting-edge techniques for structural and mechanical studies of nucleic acids.

In bio-imaging by electron microscopy, damage of the sample and limited contrast are the two main hurdles for reaching high image quality. We extend a new preparation method based on nanofabrication and super-hydrophobicity to the imaging and structural studies of nucleic acids, nucleic acid–protein complexes (DNA/Rad51 repair protein complex) and neuronal ion channels (gap-junction, K+ and GABAA channels) as paradigms of biological significance and increasing complexity. The preparation method is based on the liquid phase and is compatible with physiological conditions. Only in the very last stage, samples are dried for TEM analysis. Conventional TEM and high-resolution TEM (HRTEM) were used to achieve a resolution of 3.3 and 1.5 Å, respectively. The EM dataset quality allows the determination of relevant structural and metrological information on the DNA structure, DNA–protein interactions and ion channels, allowing the identification of specific macromolecules and their structure.

A long-standing goal of neuroscience is a theory that explains the formation of the minicolumns in the cerebral cortex. Minicolumns are the elementary computational units of the mature neocortex. Here, we use zinc oxide nanowires with controlled topography as substrates for neural-cell growth. We observe that neuronal cells form networks where the networks characteristics exhibit a high sensitivity to the topography of the nanowires. For certain values of nanowires density and fractal dimension, neuronal networks express small world attributes, with enhanced information flows. We observe that neurons in these networks congregate in superclusters of approximately 200 neurons. We demonstrate that this number is not coincidental: the maximum number of cells in a supercluster is limited by the competition between the binding energy between cells, adhesion to the substrate, and the kinetic energy of the system. Since cortical minicolumns have similar size, similar anatomical and topological characteristics of neuronal superclusters on nanowires surfaces, we conjecture that the formation of cortical minicolumns is likewise guided by the interplay between energy minimization, information optimization and topology. For the first time, we provide a clear account of the mechanisms of formation of the minicolumns in the brain.

A new concept based setup for Tip Enhanced Raman Scattering measurement assisted by gold nanostructure is presented, that can provide a platform for gap-mode enhancement of the signal at the single molecule level conjugated with controlled spatial localization of the molecule under investigation and a method to determine the diffraction limit properties of the tip. In essence, this effect is obtained illuminating a gold coated AFM tip which is raster scanned over a nanostructured gold substrate, after chemisorption of a Raman active molecule. We expect that the near-field Raman enhancement would be given by the gap-mode effect of the two facing nano-features. Thanks to the nanostructured substrate, we verify that the resolution of the Raman mapping signal is well below the diffraction limit given by the combination of the optics geometry and the laser wavelength. We show that the gap-mode TERS can generate an estimated field- enhancement ( g ) of ~20 in localized areas of the sample and we demonstrate the ability to spatially define the molecule position (by Raman mapping) at the tens of nanometers scale.

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In this paper, we propose the use of a standing nanowires array, constituted by plasmonic active gold wires grown on iron disks, and partially immersed in a supporting alumina matrix, for surface-enhanced Raman spectroscopy applications. The galvanic process was used to fabricate nanowires in pores of anodized alumina template, making this device cost-effective. This fabrication method allows for the selection of size, diameter, and spatial arrangement of nanowires. The proposed device, thanks to a detailed design analysis, demonstrates a broadband plasmonic enhancement effect useful for many standard excitation wavelengths in the visible and NIR. The trigonal pores arrangement gives an efficiency weakly dependent on polarization. The devices, tested with 633 and 830 nm laser lines, show a significant Raman enhancement factor, up to around 6 × 104, with respect to the flat gold surface, used as a reference for the measurements of the investigated molecules.

Super-hydrophobic micro-patterned surfaces are ideal substrates for the controlled self-assembly and substrate-free characterization of biological molecules. In this device, the tailored surface supports a micro-volume drop containing the molecules of interest. While the quasi-spherical drop is evaporating under controlled conditions, its de-wetting direction is guided by the pillared microstructure on top of the device, leading to the formation of threads between the neighboring pillars. This effect has been exploited here to elucidate the mechanism triggering the formation of amyloid fibers and oligomers in tau related neurodegenerative diseases. By using Raman spectroscopy, we demonstrate that the fiber bridging the pillars contains β-sheets, a characteristic feature of amyloid aggregation. We propose that the combination of laminar flow, shear stress and molecular crowding taking place while the drop is evaporating on the SHMS, induces the reorganization of the tau protein secondary structure and we suggest that this effect could in fact closely mimic the actual mechanism occurring in the human brain environment. Such a straightforward technique opens up new possibilities in the field of self-assembly of biomolecules and their characterization by different methods (SEM, AFM, Raman spectroscopy, TEM), in a single device.

Display Omitted Photolithography and micromolding techniques for fabrication of 3D polymeric pillared scaffolds.Micro scale features characterized by the same length scale of fibrous proteins constituents of the extracellular matrix.Employment of biocompatible, bioresorbable long term degradation polymer for biomedical application. Material science, cell biology, and engineering are all part of the research field of tissue engineering. It is the application of knowledge, methods and instrumentations of engineering and life science to the development of biocompatible solutions for repair and/or replace tissues and damaged organs.Last generation microfabrication technologies utilizing natural and synthetic biomaterials allow the realization of scaffolds resembling tissue-like structures as skin, brain, bones, muscles, cartilage and blood vessels.In this work we describe an effective and simple micromolding fabrication process allowing the realization of 3D polycaprolactone (PCL) scaffold for human neural stem cells (hNSC) culture. Scanning Electron Microscopy has been used to investigate the micro and nano features characterizing the surface of the device. Immunofluorescence analysis showed how, after seeding cells onto the substrate, healthy astrocytes grew up in a well-organized 3D network. Thus, we proposed this effective fabrication method for the production of nanopatterned PCL pillared scaffold providing a biomimetic environment for the growth of hNSC, a promising and efficient means for future applications in tissue engineering and regenerative medicine.

The shear flow generated at the rim of a drop evaporating on a micro-fabricated super-hydrophobic surface has been used to suspend and orient single/few lysozyme amyloid fibrils between two pillars for substrate-free characterization. Micro Raman spectroscopy performed on extended fibers evidenced a shift of the Amide I band main peak to the value attributed to β-sheet secondary structure, characteristic of the amyloid fibers. In addition, given the orientation sensitivity of the anisotropic molecule, the Raman signal of the main secondary structure was nicely enhanced for a fiber alignment parallel to the polarization direction of the laser. The substrate-free sample generated by this suspending technique is suitable for other structural analysis methods, where fiber crystals are investigated. It could be further employed for generation of arrays and patterns in a controllable fashion, where bio-compatible material is needed.

The A- and B-form are two of the most common structural conformations of double strand DNA present in nature and they can interchange on the basis of the helices hydration [1,2]. Herein we demonstrate that the use of non-destructive techniques such as Raman spectroscopy coupled with the use of a super-hydrophobic device, allows the clear identification of the DNA hydration state, of the backbone (phosphate+deoxyribose sugar) conformation and of the nucleotides. There is a wide prospect for an increase of knowledge in biomolecules using this combined approach resulting in a significant impact in the study of more complex supramolecular assemblies and of fine chemical variation along the genomic loci undergoing to epigenetic variations. Display Omitted Non-destructive Raman spectroscopy technique coupled with super-hydrophobic devices for biological fibers investigationSuper-hydrophobic surfaces comprising micro-pillars for DNA localizationDiscrimination between A- and B-form of dsDNA suspended between micro-pillars by means of Raman analysis.Electron Microscopy preliminary investigation of suspended dsDNA molecules

In this paper graphene over SiO2/Si substrate was used as a building base to fabricate SERS device. A thin film of silver was deposited over graphene and annealed at 250°C. The substrate was examined after chemisorption of two molecules; rhodamine 6G which is a fluorescent dye, and 3-mercaptobenzoic acid, a thiol molecule. SERS enhancement factor for the proposed device is estimated to be 2.1 × 106 with respect to the flat silver substrate deposited over Si. The experimental results were compared in two ways: a) by using electromagnetic field calculation and b) quantum mechanical calculation derived from density function theory. The experimental findings were consistent with the theoretical observations.

The spectral dependence of the two-photon absorption in CdSe/CdS core/shell nanocrystal heterorods has been studied via two-photon-induced luminescence excitation spectroscopy. We verified that the two-photon absorption in these samples is a purely nonlinear phenomenon, excluding the contribution from multistep linear absorption mediated by defect states. A large absorption cross section was observed for CdSe/CdS core/shell quantum rods, in the range of 10(5) GM (1 GM = 10(-50) cm(4) s phot(-1)), scaling with the total nanocrystal volume and thus independent of the core emission wavelength. In the two-photon luminescence excitation spectra, peaks are strongly blue-shifted with respect to the one-photon absorption peaks, for both core and shell transitions. The experimental results are confirmed by k·p calculations, which attribute the shift to both different parity selection rules that apply to one-photon and two-photon transitions and a low oscillator strength for two-photon transitions close to the ground-state one-photon absorption. In contrast with lead chalcogenide quantum dots, we found no evidence of a breakdown of the optical selection rules, despite the presence of band anisotropy, via the anisotropic hole masses, and the explicitly induced reduction of the electron wave function symmetry via the rod shape of the shell. The anisotropy does lead to an unexpected splitting of the electron P-states in the case of a large CdSe core encapsulated in a thin CdS shell. Hence, tuning of the core and shell dimensions and the concurrent transition from type I to quasi-type II carrier localization enables unprecedented control over the band-edge two-photon absorption.

Three dimensional optical data storage is one of the most promising tools to respond to the always growing demand for high data storage capacity. Here, we focused a femtosecond laser source by means of a confocal microscope onto different transparent recording media. The purpose of the study is to probe the capability of the system to independently address different data layers within the storage medium achieving thus three dimensional data storage. We demonstrated the possibility to write superposed independent layers of data due to either multiphoton excitation or to local optical breakdown and the performances observed in the different types of media used are compared.

We present a method of spatial and dimensional controlled formation of CdS quantum dots into polymer matrices by light irradiation. The initial samples consist of Cd thiolate precursors doped in TOPAS polymer matrix. Under pulsed UV laser irradiation the precursors are photolysed driving to the nucleation of CdS nanocrystals, with increasing size and concentration, related to the number of UV pulses. The formed quantum dots are localized in the irradiated area, while the host polymer remains macroscopically unaffected by the UV irradiation. In this study we investigate how the formation of the nanocrystals (size, dimensions, and concentration) is affected by the use of different irradiation conditions (wavelength, number of pulses), revealing information about the different pathways followed during the formation. The change of the size of the dots results in the change of the peak of their emission due to the quantum size effect, which is studied by fluorescence measurements. The results are reinforced by TEM microscopy and by XRD measurements. The main advantages of the presented method are the size tuning of the produced dots and their spatial confinement inside the host matrix, not possible by the other methods used until now (thermal annealing, mixing etc.).

Optical excitation of surface plasmons in wet-chemically grown monocrystalline silver nanowires ( approximately 100 nm diameter and up to a few tens of micrometers length) is studied by broadband imaging spectroscopy. Surface plasmons excited by an incident light beam in the so-called Kretschmann-Raether configuration give optical interference phenomena in the spectral domain. These spectral oscillations are interpreted in terms of Fabry-Perot cavity modes for surface plasmons in silver nanowires and allow for a direct experimental determination of the surface plasmon group velocity and cavity losses.

In order to develop surfaces with improved cell culture biocompatibility, we optimized a solvent-casting and particulate-leaching fabrication technique to create porous three-dimensional polycaprolactone scaffolds. These biocompatible porous surfaces were realized by means of NaCl particles as porogen; salt leaching by immersion in distilled water created porosity and pore interconnectivity in the material. Scanning electron microscopy and mercury intrusion porosimetry were used for the measurement of porosity, pore size distribution, permeability and compressibility. To evaluate scaffold biocompatibility, fibroblasts were cultured on the porous surfaces and confocal immunofluorescence characterization indicated that they were effective for in vitro cell culture and practical tissue engineering applications.

The DNA helix and its internal structures were directly imaged; characteristic lengths and inner components were measured and reported., The structure of DNA was determined in 1953 by x-ray fiber diffraction. Several attempts have been made to obtain a direct image of DNA with alternative techniques. The direct image is intended to allow a quantitative evaluation of all relevant characteristic lengths present in a molecule. A direct image of DNA, which is different from diffraction in the reciprocal space, is difficult to obtain for two main reasons: the intrinsic very low contrast of the elements that form the molecule and the difficulty of preparing the sample while preserving its pristine shape and size. We show that through a preparation procedure compatible with the DNA physiological conditions, a direct image of a single suspended DNA molecule can be obtained. In the image, all relevant lengths of A-form DNA are measurable. A high-resolution transmission electron microscope that operates at 80 keV with an ultimate resolution of 1.5 Å was used for this experiment. Direct imaging of a single molecule can be used as a method to address biological problems that require knowledge at the single-molecule level, given that the average information obtained by x-ray diffraction of crystals or fibers is not sufficient for detailed structure determination, or when crystals cannot be obtained from biological molecules or are not sufficient in understanding multiple protein configurations.

In this work we review novel strategies and new physical effects to achieve compositional and structural recognition at single molecule level. This chapter is divided in two main parts. The first one introduces the strategies currently adopted to investigate matter at few molecules level. Exploiting the capability of surface plasmon polaritons to deliver optical excitation at nanoscale, we introduce a technique relying on a new transport phenomenon with chemical sensitivity and nanometer spatial resolution. The second part describes how micro and nanostructured superhydrofobic textures can concentrate and localize a small number of molecules into a well-defined region, even when only an extremely diluted solution is available. Several applications of these devices as micro- and nano-systems for high-resolution imaging techniques, cell cultures and tissue engineering applications are also discussed.

In this work we use nonlinear optical properties of Ga nanoparticles monolayers of different average sizes embedded in dielectric matrices to investigate the liquid-solid phase transitions in these materials. Ga nanoparticles, formed by exploiting the partial wetting of liquid Ga over a SiOx surface are irradiated with fs laser pulses from a Ti:sapphire source. The resulting Second Harmonic (SH) generated in the reflection and transmission directions is measured along the phase transitions by cooling the sample from 320 K down to liquid nitrogen temperature. Hysteresis cycles are observed in the nonlinear transmission, which exhibit a strong amplification from the solid to liquid values as compared to the linear optical results. A simple model for SH generation, based on Mie scattering calculations which includes the effect of surface plasmon resonance provides a fair key for the interpretation of the observed effects.

This paper presents details on a new experimental apparatus implementing the hot electron nanoscopy (HENs) technique introduced for advanced spectroscopies on structure and chemistry in few molecules and interface problems. A detailed description of the architecture used for the laser excitation of surface plasmons at an atomic force microscope (AFM) tip is provided. The photogenerated current from the tip to the sample is detected during the AFM scan. The technique is applied to innovative semiconductors for applications in electronics: 2D MoS2 single crystal and a p-type SnO layer. Results are supported by complementary scanning Kelvin probe microscopy, traditional conductive AFM, and Raman measurements. New features highlighted by HEN technique reveal details of local complexity in MoS2 and polycrystalline structure of SnO at nanometric scale otherwise undetected. The technique set in this paper is promising for future studies in nanojunctions and innovative multilayered materials, with new insight on interfaces.

Superhydrophobicity refers to surfaces on which drops assume a quasi-spherical shape and a high contact angle (more than 150°). This well-known phenomenon occurs in nature and we can take advantage of this principle fabricating bio-inspired superhydrophobic surfaces constituted of ordinate arrays of silicon micro-pillars.

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.

We report on second-harmonic generation from Ga nanoparticle monolayers embedded in a dielectric transparent matrix for different average radii and at different temperatures. The nanoparticles are produced in the liquid phase by means of a self-organized process in ultra high vacuum (Vollmer–Weber mode). The measurements show a strong size dependence of the second-harmonic signal. A wide hysteresis cycle appears in correspondence of the melting–solidification process. The experimental results have been analyzed through a nonlinear Mie scattering model and explained in terms of the coupling of SH radiation with surface plasma oscillations in the nanoparticles.

In this work, we demonstrate that the photoluminescence emission of CdSe/CdS spherical core/rod like shell nanorods can be completely inhibited by using low-energy femtosecond laser pulses at 720 nm. A combined analysis of optical confocal microscopy images and transmission electron microscope micrographs reveals the presence of different power regimes in the nanocrystals photodegradation process. The photoluminescence inhibition of the nanorods is found to start at a power range in which no apparent structural damage occurs to the nanorods after irradiation. This suggests the presence of a photochemical transformation of the nanocrystals that is of potential interest for application in optical data storage. This is because in recording systems based on photochemical processes the photoexcited volume can be effectively confined within the diffraction-limited laser focus. We indeed demonstrate that the recorded mark can be scaled down to a few nanorods, or even to a single nanorod, without crosstalk betwee...

The future of optical data storage and the search for next generation high-density technologies have become a topic of lively debate. Three dimensional (3D) optical data storage, a relatively new technique which enables hundreds-layer data recording in a hard memory, seems a viable candidate for this role. In this work, we report on 3D optical data storage in photochromic compounds. The recording medium used in the experiments was a photochromic diarylethenes derivative embedded in different host polymers. Multi-photon processes capability of triggering photochemical reactions and physical changes with micrometer-sized resolution in three dimensions offers a well-suited means to achieve volumetric storage densities. A commercial microscope coupled to pulsed NIR and CW lasers have been used to write, read and erase data in our prototype memories. Information was recorded within the volume of the media via a multi-photon process achieving high localized photoconversion and the fluorescence emission from the photoconverted molecules when excited by a 405 nm laser diode was the readout signal. It is also shown that data recorded in such a medium can be selectively erased by irradiating with 514 nm CW laser light giving the chance to write new data in the formerly used memory space. These storage media, thus, have good potentials to achieve volumetric storage of data although they certainly deserve further optimization work to achieve high number of superposed layers and to assure durability of the written data under readout conditions.

Diarylethenes were proposed as very promising candidates for optical memory applications due to their thermal stability and fatigue resistance. The latter property of two photochromic molecules of the diarylethene family embedded in polymer films was investigated in this work. The obtained results demonstrate a noticeable influence of the polymer matrix and possible photochemical damage on the fatigue resistance of the photochromic materials.

International audience; Ga-Pb alloys with 15 at% Pb mean concentration have been prepared at the nanoscale by means of evaporation-condensation technique in ultra high vacuum conditions. Transmission electron microscope images indicate that at room temperature, the system is a two-components breath figure composed of liquid Ga nanodrops containing Pb nanocrystals. Some thermodynamic properties of this nano-alloy are investigated for different temperatures and particle sizes. The results obtained put in evidence a large modification of the Ga-Pb bulk phase diagram: a decrease of the melting temperatures of the two components as well as the ones of the miscibility gap. Changes in the microscopic structure of the system as a function of temperature have been investigated and a full wetting transition from a dry to a completely wet state has been put in evidence.

Adiabatic compression plays a fundamental role in the realization of localized enhanced electromagnetic field hot spots, it provides the possibility to focus at nanoscale optical excitation. It differs from the well-known lightning rod effect since it is based on the lossless propagation of surface plasmon polaritons (SPPs) up to a nano-sized metal tip where the energy density is largely enhanced. Here we discuss two important applications of adiabatic compression: Raman and hot electron spectroscopy at nanometric resolution. The underlying phenomena are the conversion of SPPs into photons or hot electrons. New scanning probe spectroscopy techniques along with experimental results are discussed. We foresee that these techniques will play a key role in relating the functional and structural properties of matter at the nanoscale.

We report on the generation of second-harmonic signals by irradiating monolayers of high purity Ga nanoparticles, embedded in a ${\mathrm{S}\mathrm{i}\mathrm{O}}_{x}$ matrix, with femtosecond laser pulses at 800 nm. A remarkable melting-induced enhancement of the second-harmonic generation is observed in correspondence of the phase transition. In addition, the hysteresis cycle of nonlinear transmittance is shown to be amplified a factor of 80--100 with respect to the linear response and interpreted in the framework of a nonlinear effective-medium model.

A quantitative demonstration of reversible stiffness upon appropriate light stimulus in a spiropyran-polymeric composite is presented. The polymeric films containing 3% wt. of the photochromic spiropyran were irradiated with alternating ultraviolet and visible light and the storage modulus was measured. A reversible change in modulus of about 7% was observed. The modulus change was attributed to an interaction of the polar merocyanine with the polymeric chains and/or to a variation of effective free volume induced by merocyanine aggregates formed in the polymer upon ultraviolet irradiation. The effect is fully reversed when the merocyanine isomers turn back to the spiropyran state after visible irradiation.

The following article appeared in Journal of Applied Physics 110.6 (2011): 064907 and may be found at http://scitation.aip.org/content/aip/journal/jap/110/6/10.1063/1.3638695, Superparamagnetic nanostructures are becoming increasingly important as tools for biological and medical applications. We report the study of the movement of rod-shaped assemblies of superparamagnetic nanocrystals under the action of a rotating magnetic field. The dynamic was characterized by means of light scattering detection at different frequencies and for different values of the intensity of the applied external field. The possibility to correlate the motion to the viscosity of the medium is used to monitor viscosity changes inside the liquid. We propose this technique as a valuable tool to monitor viscosity at microscale for application in biological studies., This work was partially supported by the European project Magnifyco (Contract NMP4-SL-2009-228622).