Bruno Torre

Simple and effective graphene laser processing for neuron patterning application

A straightforward fabrication technique to obtain patterned substrates promoting ordered neuron growth is presented. Chemical vapor deposition (CVD) single layer graphene (SLG) was machined by means of single pulse UV laser ablation technique at the lowest effective laser fluence in order to minimize laser damage effects. Patterned substrates were then coated with poly-D-lysine by means of a simple immersion in solution. Primary embryonic hippocampal neurons were cultured on our substrate, demonstrating an ordered interconnected neuron pattern mimicking the pattern design. Surprisingly, the functionalization is more effective on the SLG, resulting in notably higher alignment for neuron adhesion and growth. Therefore the proposed technique should be considered a valuable candidate to realize a new generation of highly specialized biosensors.

Nanoscale reduction of graphene oxide thin films and its characterization.

In this paper, we report on a method to reduce thin films of graphene oxide (GO) to a spatial resolution better than 100 nm over several tens of micrometers by means of an electrochemical scanning probe based lithography. In situ tip-current measurements show that an edged drop in electrical resistance characterizes the reduced areas, and that the reduction process is, to a good approximation, proportional to the applied bias between the onset voltage and the saturation thresholds. An atomic force microscope (AFM) quantifies the drop of the surface height for the reduced profile due to the loss of oxygen. Complementarily, lateral force microscopy reveals a homogeneous friction coefficient of the reduced regions that is remarkably lower than that of native graphene oxide, confirming a chemical change in the patterned region. Micro Raman spectroscopy, which provides access to insights into the chemical process, allows one to quantify the restoration and de-oxidation of the graphitic network driven by the electrochemical reduction and to determine characteristic length scales. It also confirms the homogeneity of the process over wide areas. The results shown were obtained from accurate analysis of the shift, intensity and width of Raman peaks for the main vibrational bands of GO and reduced graphene oxide (rGO) mapped over large areas. Concerning multilayered GO thin films obtained by drop-casting we have demonstrated an unprecedented lateral resolution in ambient conditions as well as an improved control, characterization and understanding of the reduction process occurring in GO randomly folded multilayers, useful for large-scale processing of graphene-based material.

The structure of DNA by direct imaging.

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.

Nanocomposite Pattern-Mediated Magnetic Interactions for Localized Deposition of Nanomaterials

We present a method to create, align, and locate magnetic wires throughout and on the surface of patterned polymer matrices, following the magnetophoretic transport and self-assembly of ferromagnetic nanoparticles under a static magnetic field during laser photopolymerization of monomer/nanoparticle casted solutions. The resulting films have the ability to attract and immobilize small quantities of magnetic nanomaterials locally on the ferromagnetic wires, as proved by a detailed topography study. Magnetic studies on the films before and after the spontaneous deposition, demonstrate that the deposited nanomaterials alter significantly the magnetic character of the system, making thus possible their macroscopic identification. This offers the possibility to realize sensing devices based on hybrid materials with magnetic properties.

Magnetic Force Microscopy and Energy Loss Imaging of Superparamagnetic Iron Oxide Nanoparticles

We present quantitative, high spatially resolved magnetic force microscopy imaging of samples based on 11 nm diameter superparamagnetic iron oxide nanoparticles in air at room temperature. By a proper combination of the cantilever resonance frequency shift, oscillation amplitude and phase lag we obtain the tip-sample interaction maps in terms of force gradient and energy dissipation. These physical quantities are evaluated in the frame of a tip-particle magnetic interaction model also including the tip oscillation amplitude. Magnetic nanoparticles are characterized both in bare form, after deposition on a flat substrate, and as magnetically assembled fillers in a polymer matrix, in the form of nanowires. The latter approach makes it possible to reveal the magnetic texture in a composite sample independently of the surface topography.

Microfluidic device for continuous single cells analysis via Raman spectroscopy enhanced by integrated plasmonic nanodimers

In this work a Raman flow cytometer is presented. It consists of a microfluidic device that takes advantages of the basic principles of Raman spectroscopy and flow cytometry. The microfluidic device integrates calibrated microfluidic channels- where the cells can flow one-by-one -, allowing single cell Raman analysis. The microfluidic channel integrates plasmonic nanodimers in a fluidic trapping region. In this way it is possible to perform Enhanced Raman Spectroscopy on single cell. These allow a label-free analysis, providing information about the biochemical content of membrane and cytoplasm of the each cell. Experiments are performed on red blood cells (RBCs), peripheral blood lymphocytes (PBLs) and myelogenous leukemia tumor cells (K562).

Oxidative and carbonaceous patterning of Si surface in an organic media by scanning probe lithography

A simple top-down fabrication technique that involves scanning probe lithography on Si is presented. The writing procedure consists of a chemically selective patterning in mesitylene. Operating in an organic media is possible to perform local oxidation or solvent decomposition during the same pass by tuning the applied bias. The layer deposited with a positively biased tip with sub-100-nm lateral resolution consists of nanocrystalline graphite, as verified by Raman spectroscopy. The oxide pattern obtained in opposite polarization is later used as a mask for dry etching, showing a remarkable selectivity in SF6 plasma, to produce Si nanofeatured molds.

Formation and microscopic investigation of iron oxide aligned nanowires into polymeric nanocomposite films

We present a microscopic investigation of nanocomposite films of iron oxide (γ‐Fe2O3) magnetic nanowires (NWs) aligned into polymers, formed upon evaporation of solutions of acrylate polymer/magnetic nanoparticles under magnetic field (MF). The field causes the assembly of the γ‐Fe2O3 nanoparticles along the direction of the MF lines, resulting in magnetic NWs embedded throughout the entire volume of the polymer film. The scanning electron microscopy and the transmission electron microscopy studies show that the cylindrical‐shaped NWs have ∼15‐μm average length and are isotropically distributed throughout the film. The study with the MF microscopy technique not only proves that the composed NWs are magnetic but also makes possible the magnetic study of each individual NW in a nondestructive way. In this way it becomes possible for the localized study of the magnetic properties alteration after the binding of various molecules onto individual NWs, opening up the way of using these films in sensor devices applied in various fields ranging from biology to environmental purposes. Microsc. Res. Tech. 73:952–958, 2010.

Rod-shaped nanostructures based on superparamagnetic nanocrystals as viscosity sensors in liquid

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.

Scanning probe oxidation of SiC, fabrication possibilities and kinetics considerations

We report the outcome of atomic force microscopy local anodic oxidation experiments on 6H-SiC in air. Oxide thickness can be easily tuned by varying applied voltage and pulse duration. The height and the aspect ratio of single dots produced by single DC pulses are remarkably higher than what was reported previously, with self limiting heights exceeding 100 nm. We propose that the diminished density and the change in chemical composition of the oxide grown on SiC with respect to oxide grown under similar condition on Si cause a drop in the activation energy of oxanions diffusion within the newly formed oxide layer.