Angela Longo

Imidazole-stabilized gold nanoparticles induce neuronal apoptosis: an in vitro and in vivo study.

Gold nanoparticles are increasingly being employed in innovative biological applications thanks to their advantages of material- and size-dependent physics and chemical interactions with the cellular systems. On the other hand, growing concern has emerged on the toxicity which would render gold-based nanoparticles harmful to cell cultures, animals, and humans. Emerging attention is focused on the interaction of gold nanoparticles with nervous system, especially regarding the ability to overcome the blood-brain barrier (BBB) which represents the major impediment to the delivery of therapeutics into the brain. We synthesized highly stable 2-mercapto-1-methylimidazole-stabilized gold-nanoparticles (AuNPs)-mmi to investigate their entry, accumulation, and toxicity in vitro (SH-SY5Y human neuroblastoma cells) and in vivo (brain of C57BL/6 mice) through optical and electron microscopy. After incubation in the cell culture medium at the lowest dose of 0.1 mg/mL the (AuNPs)-mmi nanoparticles were found compacted and recruited into endosome/lysosomes (1 h) before their fusion (2 h) and the onset of neuronal death by apoptosis (4 h) as proved by terminal-transferase-mediated dUTP nick end labeling assay and caspase-3 immunoreactivity. The ability of (AuNPs)-mmi to cross the BBB was assessed by injection in the caudal vein of C57BL/6 mice. Among different brain regions, the nanoparticles were found in the CaudatoPutamen area, mainly in the striatal neurons 4 h after injection. These neurons showed the typical hallmarks of apoptosis. Our findings provide, for the first time, the dynamic of 2-mercapto-1-methylimidazole nanogold uptake. The molecular mechanism which underlies the nanogold-driven apoptotic event is analyzed and discussed in order to take into account when designing nanomaterials to interface with biological structures.

Holographic patterning of graphene-oxide films by light-driven reduction

We report on the patterning and reduction of graphene-oxide films by holographic lithography. Light reduction can be used to engineer low-cost graphene-based devices by performing a local conversion of insulating oxide into the conductive graphene. In this work, computer-generated holograms have been exploited to realize complex graphene patterns in a single shot, different from serial laser writing or mask-based photolithographic processes. The technique has been further improved by achieving speckle noise reduction: submicron and diffraction-limited features have been obtained. In addition we have also demonstrated that the gray-scale lithography capability can be used to obtain different reduction levels in a single exposure.

Optical limiters based on silver nanoparticles embedded in amorphous polystyrene

Abstract A simple technique to prepare plastic color-filters based on the surface plasmon resonance (SPR) of silver nanoparticles has been developed. In particular, silver/polystyrene nanocomposites have been prepared by dissolving silver acetylacetonate in amorphous polystyrene and heating the obtained solid solution at a convenient temperature (ca. 200°C). When the metal precursor decomposes, the produced silver atoms diffuse into the polymeric matrix and clusterize, leading to the formation of a contact-free dispersion of hyperfine silver phase. The obtained films have been characterized by UV-VIS spectroscopy and the optical extinction spectra have been fitted by the Mie’s theory, introducing the limitation of the mean free path due to the collisions of conduction electrons with the boundary of the nanoparticles.

Tuned linear optical properties of gold-polymer nanocomposites

The linear optical properties of gold-polystyrene nanocomposites, obtained by thermal decomposition of gold dodecyl-mercaptide into polystyrene matrix, can be significantly manipulated in the visible range, from absorption to emission at specific wavelengths as a function of nanocluster size, by the sensitive and reliable control of the annealing parameters (temperature and time). The performed optical investigation shows that these composites combine the peculiar optical properties of the metallic nanophase (strong surface plasmon absorption/strong and stable photoluminescence in the visible range) with the outstanding transparent polymer characteristic, for advanced applications in optical sensors, frequency converters, anti-counterfeiting tags, etc.

Molecular responses of cells to 2-mercapto-1-methylimidazole gold nanoparticles (AuNPs)-mmi: investigations of histone methylation changes

While nanomedicine has an enormous potential to improve the precision of specific therapy, the ability to efficiently deliver these materials to regions of disease in vivo remains limited. In this study, we describe analyses of (AuNPs)-mmi cellular intake via fluorescence microscopy and its effects on H3K4 and H3K9 histone dimethylation. Specifically, we studied the level of H3K4 dimethylation in serving the role of an epigenetic marker of euchromatin, and of H3K9 dimethylation as a marker of transcriptional repression in four different cell lines. We analyzed histone di-methyl-H3K4 and di-methyl-H3K9 using either variable concentrations of nanoparticles or variable time points after cellular uptake. The observed methylation effects decreased consistently with decreasing (AuNPs)-mmi concentrations. Fluorescent microscopy and a binarization algorithm based on a thresholding process with RGB input images demonstrated the continued presence of (AuNPs)-mmi in cells at the lowest concentration used. Furthermore, our results show that the treated cell line used is able to rescue the untreated cell phenotype.

Graphene–polymer coating for the realization of strain sensors

In this work we present a novel route to produce a graphene-based film on a polymer substrate. A transparent graphite colloidal suspension was applied to a slat of poly(methyl methacrylate) (PMMA). The good adhesion to the PMMA surface, combined with the shear stress, allows a uniform and continuous spreading of the graphite nanocrystals, resulting in a very uniform graphene multilayer coating on the substrate surface. The fabrication process is simple and yields thin coatings characterized by high optical transparency and large electrical piezoresitivity. Such properties envisage potential applications of this polymer-supported coating for use in strain sensing. The electrical and mechanical properties of these PMMA/graphene coatings were characterized by bending tests. The electrical transport was investigated as a function of the applied stress. The structural and strain properties of the polymer composite material were studied under stress by infrared thermography and micro-Raman spectroscopy.

Microstructures of carbon nanoscrolls characterized by polarized micro-Raman spectroscopy

Abstract Carbon nanoscrolls (CNSs) are produced by rolling up the graphite layer in graphite nanoplatelets on a nanofibrous bi-axially oriented polypropylene surface by a shear-friction mechanism. Microstructures of the CNSs are characterized by optical and scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and micro-Raman spectroscopy. Results indicate that the CNSs have a long tubular and fusiform structure with a hollow core surrounded by few graphene layers. The orientation of the graphite lattice with respect to the scroll axis is accurately determined from the split of the vibrational G mode by polarized micro-Raman spectroscopy. Morphological changes produced by the rolling are also described.

Optical and electrical characterizations of graphene nanoplatelet coatings on low density polyethylene

Coatings of graphene nanoplatelets (GNPs) were deposited on a low density polyethylene (LDPE) substrate by a micromechanical method based on rubbing graphite platelets against the surface of the polymer. Transmission electron microscopy measurements reveal that the coatings were composed of nanoplatelets containing 13–30 graphene layers. Thermal gravimetric analysis shows that the investigated GNP coatings on LDPE (GNP/LDPE) samples are thermally stable up to 250 °C. Optical spectra of these samples, compared to those of pristine LDPE in the ultraviolet-visible-near-infrared range, indicate an increase in both reflectance and absorptance. On the other hand, the coating is able to markedly improve the surface conductivity of the polymeric substrate, indeed in the case of electrical contacts in the coplanar configuration (1 cm long and spaced 1 mm), the resistance of LDPE is 1015 Ω, while that of GNP/LDPE is 670 Ω. Electrical measurements under white light illumination point out a decrease in the conductance and a linear behavior of the photoconductance as a function of the optical power density. GNP/LDPE materials can be used for their optical, electrical, thermal, and flexibility properties in large area plastic electronics and optoelectronics.Coatings of graphene nanoplatelets (GNPs) were deposited on a low density polyethylene (LDPE) substrate by a micromechanical method based on rubbing graphite platelets against the surface of the polymer. Transmission electron microscopy measurements reveal that the coatings were composed of nanoplatelets containing 13–30 graphene layers. Thermal gravimetric analysis shows that the investigated GNP coatings on LDPE (GNP/LDPE) samples are thermally stable up to 250 °C. Optical spectra of these samples, compared to those of pristine LDPE in the ultraviolet-visible-near-infrared range, indicate an increase in both reflectance and absorptance. On the other hand, the coating is able to markedly improve the surface conductivity of the polymeric substrate, indeed in the case of electrical contacts in the coplanar configuration (1 cm long and spaced 1 mm), the resistance of LDPE is 1015 Ω, while that of GNP/LDPE is 670 Ω. Electrical measurements under white light illumination point out a decrease in the conductanc...

Graphene oxide reduction by microwave heating

The possibility to prepare thermal reduced graphene oxide (Tr-GO) colloidal suspensions by microwave heating of graphene oxide (GO) suspensions in N-methyl-2-pyrrolidone (NMP) has been investigated. According to transmission electron microscopy (TEM) and absorption and emission spectroscopy characterization, such a type of thermal reduction does not lead to graphene quantum dots formation because only mono-functional oxygen-containing groups are removed.

Synthesis of luminescent gold nano-clusters coated by N-acetyl-L-cysteine

New high luminescent thiolate-protected gold nano-clusters have been obtained by using a natural thiol, i.e. N-acetyl-L-cysteine (NALC). These gold nano-clusters were obtained by reacting HAuCl4 with N-acetyl-L-cysteine in ethanol and NH4OH was used to obtain a alckaline pH. Morphological and structural properties of this class of gold nano-clusters have been investigated by Transmission Electron Microscopy (TEM) and X Ray Diffraction (XRD). Optical properties have been studied by UV-visible spectroscopy and spectrofluorimetry.