Fluorescence lifetime microscopy unveils the supramolecular organization of liposomal Doxorubicin.

The supramolecular organization of Doxorubicin (DOX) within the standard Doxoves® liposomal formulation (DOX®) is investigated using visible light and phasor approach to fluorescence lifetime imaging (phasor-FLIM). First, the phasor-FLIM signature of DOX® is resolved into the contribution of three co-existing fluorescent species, each with its characteristic mono-exponential lifetime, namely: crystallized DOX (DOXc, 0.2 ns), free DOX (DOXf, 1.0 ns), and DOX bound to the liposomal membrane (DOXb, 4.5 ns). Then, the exact molar fractions of the three species are determined by combining phasor-FLIM with quantitative absorption/fluorescence spectroscopy on DOXc, DOXf, and DOXb pure standards. The final picture on DOX® comprises most of the drug in the crystallized form (∼98%), with the remaining fractions divided between free (∼1.4%) and membrane-bound drug (∼0.7%). Finally, phasor-FLIM in the presence of a DOX dynamic quencher allows us to suggest that DOXf is both encapsulated and non-encapsulated, and that DOXb is present on both liposome-membrane leaflets. We argue that the present experimental protocol can be applied to the investigation of the supramolecular organization of encapsulated luminescent drugs/molecules all the way from the production phase to their state within living matter.

Biopolymer Gels as a Cleaning System for Differently Featured Wooden Surfaces.

The cleaning of some wooden artefacts can be challenging due to peculiar surface roughness and/or particular finishing treatments that favour the deposition of dirt and contaminants. The most common cleaning system used by conservators is agar gel, characterized by its rigidity and brittleness, which challenges the cleaning of rough and irregular surfaces typical of most wooden artefacts. In this work, alginate crosslinked with calcium (CA) and konjac glucomannan crosslinked with borax (KGB) gels were proposed to solve this issue. They were prepared and applied to smooth- and rough-surfaced mock-ups replicating wooden musical instruments' surfaces that had been subsequently covered by artificial soiling and sweat contaminants. The mechanical properties of CA and KGB gels, including their stability over a 60-day storage time, were evaluated by a texture analyzer, while cleaning efficacy was analytically evaluated by non-invasive X-ray fluorescence mapping and profilometric investigation. CA gel appeared to have a higher tensile strength and elongation at break. KGB gel was shown to be soft and resilient, indicating its suitability for cleaning rough surfaces. After repeating the cleaning application three times on the rough-surfaced mock-ups, both the CA and KGB gels were shown to have cleaning efficacy. The results obtained with CA and KGB were compared with those from the Agar application.

Large-Area Oxidized Phosphorene Nanoflakes Obtained by Electrospray for Energy-Harvesting Applications.

Bidimensional (2D) materials are nowadays being developed as outstanding candidates for electronic and optoelectronic components and devices. Targeted applications include sensing, energy conversion, and storage. Phosphorene is one of the most promising systems in this context, but its high reactivity under atmospheric conditions and its small-area/lab-scale deposition techniques have hampered the introduction of this material in real-world applications so far. However, phosphorene oxides in the form of low-dimensional structures (2D PO x ) should behave as an electroresponsive material according to recent theoretical studies. In the present work, we introduce electrospraying for the deposition of stoichiometric and large-area 2D PO x nanoflakes starting from a suspension of liquid-phase-exfoliated phosphorene. We obtained 2D PO x nanostructures with a mean surface area two orders of magnitude larger than phosphorene structures obtained with standard mechanical and liquid exfoliation techniques. X-ray spectroscopy and high-resolution electron microscopy confirmed the P2O5-like crystallographic structure of the electrosprayed flakes. Finally, we experimentally demonstrated for the first time the electromechanical responsivity of the 2D P2O5 nanoflakes, through piezoresponse force microscopy (PFM). This work sheds light on the possible implementation of phosphorus oxide-based 2D nanomaterials in the value chain of fabrication and engineering of devices, which might be easily scaled up for energy-harvesting/conversion applications.

Scanning Probe Spectroscopy of WS2/Graphene Van Der Waals Heterostructures.

In this paper, we present a study of tungsten disulfide (WS2) two-dimensional (2D) crystals, grown on epitaxial Graphene. In particular, we have employed scanning electron microscopy (SEM) and µRaman spectroscopy combined with multifunctional scanning probe microscopy (SPM), operating in peak force-quantitative nano mechanical (PF-QNM), ultrasonic force microscopy (UFM) and electrostatic force microscopy (EFM) modes. This comparative approach provides a wealth of useful complementary information and allows one to cross-analyze on the nanoscale the morphological, mechanical, and electrostatic properties of the 2D heterostructures analyzed. Herein, we show that PF-QNM can accurately map surface properties, such as morphology and adhesion, and that UFM is exceptionally sensitive to a broader range of elastic properties, helping to uncover subsurface features located at the buried interfaces. All these data can be correlated with the local electrostatic properties obtained via EFM mapping of the surface potential, through the cantilever response at the first harmonic, and the dielectric permittivity, through the cantilever response at the second harmonic. In conclusion, we show that combining multi-parametric SPM with SEM and µRaman spectroscopy helps to identify single features of the WS2/Graphene/SiC heterostructures analyzed, demonstrating that this is a powerful tool-set for the investigation of 2D materials stacks, a building block for new advanced nano-devices.

Optical and mechanical properties of streptavidin-conjugated gold nanospheres through data mining techniques.

The thermo-mechanical properties of streptavidin-conjugated gold nanospheres, adhered to a surface via complex molecular chains, are investigated by two-color infrared asynchronous optical sampling pump-probe spectroscopy. Nanospheres with different surface densities have been deposited and exposed to a plasma treatment to modify their polymer binding chains. The aim is to monitor their optical response in complex chemical environments that may be experienced in, e.g., photothermal therapy or drug delivery applications. By applying unsupervised learning techniques to the spectroscopic traces, we identify their thermo-mechanical response variation. This variation discriminates nanospheres in different chemical environments or different surface densities. Such discrimination is not evident based on a standard analysis of the spectroscopic traces. This kind of analysis is important, given the widespread application of conjugated gold nanospheres in medicine and biology.

Seedless Hydrothermal Growth of ZnO Nanorods as a Promising Route for Flexible Tactile Sensors.

Hydrothermal growth of ZnO nanorods has been widely used for the development of tactile sensors, with the aid of ZnO seed layers, favoring the growth of dense and vertically aligned nanorods. However, seed layers represent an additional fabrication step in the sensor design. In this study, a seedless hydrothermal growth of ZnO nanorods was carried out on Au-coated Si and polyimide substrates. The effects of both the Au morphology and the growth temperature on the characteristics of the nanorods were investigated, finding that smaller Au grains produced tilted rods, while larger grains provided vertical rods. Highly dense and high-aspect-ratio nanorods with hexagonal prismatic shape were obtained at 75 °C and 85 °C, while pyramid-like rods were grown when the temperature was set to 95 °C. Finite-element simulations demonstrated that prismatic rods produce higher voltage responses than the pyramid-shaped ones. A tactile sensor, with an active area of 1 cm2, was fabricated on flexible polyimide substrate and embedding the nanorods forest in a polydimethylsiloxane matrix as a separation layer between the bottom and the top Au electrodes. The prototype showed clear responses upon applied loads of 2-4 N and vibrations over frequencies in the range of 20-800 Hz.

Novel Ultrathin Films Based on a Blend of PEG-b-PCL and PLLA and Doped with ZnO Nanoparticles.

In this paper, a novel nanofilm type is proposed based on a blend of poly(ethylene glycol)-block-poly(ε-caprolactone) methyl ether (PEG-b-PCL) and poly(l-lactic acid), doped with zinc oxide nanoparticles (ZnO NPs) at different concentrations (0.1, 1, and 10 mg/mL). All nanofilm types were featured by a thickness value of ∼500 nm. Increasing ZnO NP concentrations implied larger roughness values (∼22 nm for the bare nanofilm and ∼67 nm for the films with 10 mg/mL of NPs), larger piezoelectricity (average d33 coefficient for the film up to ∼1.98 pm/V), and elastic modulus: the nanofilms doped with 1 and 10 mg/mL of NPs were much stiffer than the nondoped controls and nanofilms doped with 0.1 mg/mL of NPs. The ZnO NP content was also directly proportional to the material melting point and crystallinity and inversely proportional to the material degradation rate, thus highlighting the stabilization role of ZnO particles. In vitro tests were carried out with cells of the musculoskeletal apparatus (fibroblasts, osteoblasts, chondrocytes, and myoblasts). All cell types showed good adhesion and viability on all substrate formulations. Interestingly, a higher content of ZnO NPs in the matrix demonstrated higher bioactivity, boosting the metabolic activity of fibroblasts, myoblasts, and chondrocytes and enhancing the osteogenic and myogenic differentiation. These findings demonstrated the potential of these nanocomposite matrices for regenerative medicine applications, such as tissue engineering.

Ag@TiO2 nanogranular films by gas phase synthesis as hybrid SERS platforms.

The synthesis of hybrid metallic-dielectric substrates as reliable SERS platforms relies on core-shell nanoparticles, obtained by wet chemistry, with an outer dielectric shell composed of SiO2 or TiO2. Apart from the shell composition, the nanoparticle density and aggregation type strongly affect the surface-enhanced SERS. Going beyond a single layer by building random aggregates of hybrid NPs would result in a step forward in the production of reliable hybrid SERS platforms. Here we achieve the fabrication of a 3D nanogranular film of Ag metallic cores not fully enclosed in a TiO2 capping layer, defined as a Ag@TiO2 quasi-shell-isolated Raman substrate (Ag@TiO2 QuaSIRS) by an environmentally friendly gas phase synthesis technique (SCBD). The Ag core drives the electromagnetic enhancement with plasmonic hotspots while the TiO2 shell passivates it and leads to different possible surface functionalization. The SERS capabilities of the Ag@TiO2 QuaSIRS peak at a film thickness of 60 nm providing a detection limit of 10-9 M concentration for Methylene Blue at 632.81 nm. The importance of the nanogranular 3D morphology is evidenced by the very good detection of analytes dispersed in aqueous solutions, since the liquid can penetrate the pores hence exploiting most of the plasmonic hotspots present in the film. The versatility of SCBD to deposit such reliable hybrid SERS platforms by a single step at room temperature over different substrates provides an opportunity to design a new generation of hybrid SERS-active substrates based on hybrid nanoparticles.

Small-caliber vascular grafts based on a piezoelectric nanocomposite elastomer: Mechanical properties and biocompatibility.

The development of small-caliber grafts still represents a challenge in the field of vascular prostheses. Among other factors, the mechanical properties mismatch between natural vessels and artificial devices limits the efficacy of state-of-the-art materials. In this paper, a novel nanocomposite graft with an internal diameter of 6 mm is proposed. The device is obtained through spray deposition using a semi-interpenetrating polymeric network combining poly(ether)urethane and polydimethilsyloxane. The inclusion of BaTiO3 nanoparticles endows the scaffold with piezoelectric properties, which may be exploited in the future to trigger beneficial biological effects. Graft characterization demonstrated a good nanoparticle dispersion and an overall porosity that was not influenced by the presence of nanoparticles. Graft mechanical properties resembled (or even ameliorated) the ones of natural vessels: both doped and non-doped samples showed a Young's modulus of ∼700 kPa in the radial direction and ∼900 kPa in the longitudinal direction, an ultimate tensile strength of ∼1 MPa, a strain to failure of ∼700%, a suture retention force of ∼1.7 N and a flexural rigidity of ∼2.5 × 10-5 N m2. The two grafts differed in terms of burst strength that resulted ∼800 kPa for the control non-doped samples and ∼1100 kPa for the doped ones. The graft doped with BaTiO3 nanoparticles showed a d33 coefficient of 1.91 pm/V, almost double than the non-doped control. The device resulted highly stable, with a mass loss smaller than 2% over 3 months and an excellent biocompatibility.

Assessment of occupational exposure to engineered nanomaterials in research laboratories using personal monitors.

Exposure assessment is a key stage in the risk assessment/management of engineered nanomaterials. Although different sampling strategies and instruments have been used to define the occupational exposure to nano-scale materials, currently there is no international consensus regarding measurement strategy, metrics and limit values. In fact, the assessment of individual exposure to engineered nanomaterials remains a critical issue despite recent innovative developments in personal monitors and samplers. Hence, we used several of these instruments to evaluate the workers' personal exposure in a large research laboratory where engineered nanomaterials are produced, handled, and characterized in order to provide input data for nanomaterial exposure assessment strategies and future epidemiological studies. The results obtained using personal monitors showed that the workplace concentrations of engineered nanomaterials (lung deposited surface area and particle number concentrations) were quite low in all the different workplaces monitored, with short spikes during the execution of some specific job tasks. The sampling strategy was been adopted on the basis of an Organisation for Economic Cooperation and Development (OECD) suggestion for a tiered approach and was found to be suitable for determining the individual exposure and for identifying possible sources of emission, even those with very low emission rates. The use of these instruments may lead to a significant improvement not only in the exposure assessment stage but, more generally, in the entire risk assessment and management process.

Workers' Exposure to Nano-Objects with Different Dimensionalities in R&D Laboratories: Measurement Strategy and Field Studies.

With the increasing interest in the potential benefits of nanotechnologies, concern is still growing that they may present emerging risks for workers. Various strategies have been developed to assess the exposure to nano-objects and their agglomerates and aggregates (NOAA) in the workplace, integrating different aerosol measurement instruments and taking into account multiple parameters that may influence NOAA toxicity. The present study proposes a multi-metric approach for measuring and sampling NOAA in the workplace, applied to three case studies in laboratories each dedicated to materials with different shapes and dimensionalities: graphene, nanowires, and nanoparticles. The study is part of a larger project with the aim of improving risk management tools in nanomaterials research laboratories. The harmonized methodology proposed by the Organization for Economic Cooperation and Development (OECD) has been applied, including information gathering about materials and processes, measurements with easy-to-use and hand-held real-time devices, air sampling with personal samplers, and off-line analysis using scanning electron microscopy. Significant values beyond which an emission can be attributed to the NOAA production process were identified by comparison of the particle number concentration (PNC) time series and the corresponding background levels in the three laboratories. We explored the relations between background PNC and microclimatic parameters. Morphological and elemental analysis of sampled filters was done to identify possible emission sources of NOAA during the production processes: rare particles, spherical, with average diameter similar to the produced NOAA were identified in the nanoparticles laboratory, so further investigation is recommended to confirm the potential for worker exposure. In conclusion, the information obtained should provide a valuable basis for improving risk management strategies in the laboratory at work.

Local anodic oxidation on hydrogen-intercalated graphene layers: oxide composition analysis and role of the silicon carbide substrate.

We investigate nanoscale local anodic oxidation (LAO) on hydrogen-intercalated graphene grown by controlled sublimation of silicon carbide (SiC). Scanning probe microscopy was used as a lithographic and characterization tool in order to investigate the local properties of the nanofabricated structures. The anomalous thickness observed after the graphene oxidation process is linked to the impact of LAO on the substrate. Micro-Raman (µ-Raman) spectroscopy was employed to demonstrate the presence of two oxidation regimes depending on the applied bias. We show that partial and total etching of monolayer graphene can be achieved by tuning the bias voltage during LAO. Finally, a complete compositional characterization was achieved by scanning electron microscopy and energy dispersive spectroscopy.

Subsurface imaging of two-dimensional materials at the nanoscale.

Scanning probe microscopy (SPM) represents a powerful tool that, in the past 30 years, has allowed for the investigation of material surfaces in unprecedented ways at the nanoscale level. However, SPM has shown very little capability for depth penetration, which several nanotechnology applications require. Subsurface imaging has been achieved only in a few cases, when subsurface features influence the physical properties of the surface, such as the electronic states or the heat transfer. Ultrasonic force microscopy (UFM), an adaption of the contact mode atomic force microscopy, can dynamically measure the stiffness of the elastic contact between the probing tip and the sample surface. In particular, UFM has proven highly sensitive to the near-surface elastic field in non-homogeneous samples. In this paper, we present an investigation of two-dimensional (2D) materials, namely flakes of graphite and molybdenum disulphide placed on structured polymeric substrates. We show that UFM can non-destructively distinguish suspended and supported areas and localise defects, such as buckling or delamination of adjacent monolayers, generated by residual stress. Specifically, UFM can probe small variations in the local indentation induced by the mechanical interaction between the tip and the sample. Therefore, any change in the elastic modulus within the volume perturbed by the applied load or the flexural bending of the suspended areas can be detected and imaged. These investigation capabilities are very promising in order to study the buried interfaces of nanostructured 2D materials such as in graphene-based devices.

Nanostructured ultra-thin patches for ultrasound-modulated delivery of anti-restenotic drug.

This work aims to demonstrate the possibility to fabricate ultra-thin polymeric films loaded with an anti-restenotic drug and capable of tunable drug release kinetics for the local treatment of restenosis. Vascular nanopatches are composed of a poly(lactic acid) supporting membrane (thickness: ~250 nm) on which 20 polyelectrolyte bilayers (overall thickness: ~70 nm) are alternatively deposited. The anti-restenotic drug is embedded in the middle of the polyelectrolyte structure, and released by diffusion mechanisms. Nanofilm fabrication procedure and detailed morphological characterization are reported here. Barium titanate nanoparticles (showing piezoelectric properties) are included in the polymeric support and their role is investigated in terms of influence on nanofilm morphology, drug release kinetics, and cell response. Results show an efficient drug release from the polyelectrolyte structure in phosphate-buffered saline, and a clear antiproliferative effect on human smooth muscle cells, which are responsible for restenosis. In addition, preliminary evidences of ultrasound-mediated modulation of drug release kinetics are reported, thus evaluating the influence of barium titanate nanoparticles on the release mechanism. Such data were integrated with quantitative piezoelectric and thermal measurements. These results open new avenues for a fine control of local therapies based on smart responsive materials.

Nanoscale rippling on polymer surfaces induced by AFM manipulation.

Nanoscale rippling induced by an atomic force microscope (AFM) tip can be observed after performing one or many scans over the same area on a range of materials, namely ionic salts, metals, and semiconductors. However, it is for the case of polymer films that this phenomenon has been widely explored and studied. Due to the possibility of varying and controlling various parameters, this phenomenon has recently gained a great interest for some technological applications. The advent of AFM cantilevers with integrated heaters has promoted further advances in the field. An alternative method to heating up the tip is based on solvent-assisted viscoplastic deformations, where the ripples develop upon the application of a relatively low force to a solvent-rich film. An ensemble of AFM-based procedures can thus produce nanoripples on polymeric surfaces quickly, efficiently, and with an unprecedented order and control. However, even if nanorippling has been observed in various distinct modes and many theoretical models have been since proposed, a full understanding of this phenomenon is still far from being achieved. This review aims at summarizing the current state of the art in the perspective of achieving control over the rippling process on polymers at a nanoscale level.

Terahertz confocal microscopy with a quantum cascade laser source.

We report on the implementation of a confocal microscopy system based on a 2.9 THz quantum cascade laser source. Lateral and axial resolutions better than 70 µm and 400 µm, respectively, are achieved, with a large contrast enhancement compared to the non-confocal arrangement. The capability of resolving overlapping objects lying on different longitudinal planes is also clearly demonstrated.

Ordered rippling of polymer surfaces by nanolithography: influence of scan pattern and boundary effects.

We demonstrate how AFM nanolithography, with a proper choice of scan pattern, can induce an exceptionally ordered alignment of ripples on the surface of polymer films on the first scan. By analogy with the manipulation of nanoparticles, the orientation of the ripples is determined by the material flow, which is ultimately fixed by the direction of motion of the probing tip. This makes a raster scan pattern the best choice for orienting the ripples, as opposed to the zigzag scan pattern commonly adopted by most AFM setups. Our hypothesis is substantiated by a series of measurements on a solvent-enriched ultrathin film of PET, which allowed ripple formation on the first scan. We also show how the ripple orientation is significantly modified by the boundary conditions appearing when nanolithography is performed on circular, triangular and L-shaped areas on the polymer surface.

High-resolution poly(ethylene terephthalate) (PET) hot embossing at low temperature: thermal, mechanical, and optical analysis of nanopatterned films.

In this work we present controlled, low-damage nanotopographic surface modification of poly(ethylene terephthalate) (PET). High-resolution nanopatterning over macroscopic areas was performed by " low-temperature" hot embossing lithography (HEL). While for standard HEL the temperature is typically raised up to many tens of Celsius degrees above the polymer glass transition temperature (Tg), we demonstrate optimal results at a temperature very close to the bulk Tg of PET (72 degrees C). Nanopits and nanobarcodes were transferred onto the surface of PET commercial sheets, demonstrating reliable sub-100 nm resolution over macroscopic areas. Sample optical, mechanical, and thermal characteristics were systematically analyzed before and after embossing at low (75 degrees C) and high (150 degrees C) temperature by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, tensile tests, and differential scanning calorimetry (DSC). We show that, while conventional high-temperature HEL can lead to dramatic degradation of the polymer in terms of transparency, flexibility, and crystallinity content, our low-temperature process fully maintains original surface and bulk substrate properties.

Influence of a reduced mobility layer on the structural relaxation dynamics of aluminum capped ultrathin films of poly(ethylene terephthalate).

The structural dynamics of ultrathin polymer films of poly(ethylene terephthalate) capped between aluminum electrodes have been investigated by dielectric relaxation spectroscopy. A deviation from bulk behavior, appearing as an increase of the relaxation time at a fixed temperature, is observed for films of thickness below 35 nm. The slowing down acts as a constant shift factor independent from the temperature, and the fragility is constant. The interfacial energy between aluminum and poly(ethylene terephthalate) is calculated to be 3 mJ/m2, confirming a strong interaction between polymer and substrate, which leads to the presence of a layer characterized by a reduced mobility at their interfaces. We proposed a mathematical schematization of a multylayer model that allowed qualitative reproduction of the observed thickness dependences of the static and dynamic properties. In terms of such a model, the upper limit for the thickness of the reduced mobility layer was estimated as 20 nm. The conditions to extend the proposed model to different observables are finally suggested.