N.N. Nedyalkov

Transplacental clastogenic and epigenetic effects of gold nanoparticles in mice.

The broad application of nanotechnology in medicine, biology, and pharmacology is leading to a dramatic increase of the risk of direct contact of nanoproducts, among which gold nanoparticles (AuNP), with the human organism. The present study aimed at evaluating in vivo the genotoxicity of AuNPs with average size of 40 nm and 100 nm. A single intraperitoneal treatment of adult male and female Swiss mice (strain H) with AuNPs, at a dose of 3.3 mg/kg body weight, had no effect on the frequency of micronucleated polychromatic erythrocytes (MN PCEs) in bone marrow. Conversely, the transplacental treatment with AuNP-100 nm, but not with AuNP-40 nm, applied intraperitoneally at a dose of 3.3 mg/kg to pregnant mice on days 10, 12, 14, and 17 of gestation, resulted in a significant increase in the frequency of MN PCEs in both liver and peripheral blood of mouse fetuses. In parallel, the same treatment with AuNP-100 nm, but not with AuNP-40 nm, produced significant changes in microRNA expression. In particular, out of 1281 mouse microRNAs analyzed, 28 were dys-regulated more than two-fold and to a statistically significant extent in fetus lung, and 5 were up-regulated in fetal liver. Let-7a and miR-183 were significantly up-regulated in both organs. The data presented herein demonstrate for the first time the transplacental size-dependent clastogenic and epigenetic effects of AuNPs in mouse fetus, thus highlighting new aspects concerning the putative genotoxicity of AuNPs during a vulnerable period of life.

Surface enhanced Raman scattering properties using Au-coated ZnO nanorods grown by two-step, off-axis pulsed laser deposition

ZnO nanorod arrays on Si (1 0 0) substrate were grown by the pulsed laser deposition (PLD) method, and then coated with Au. Two samples of Au-coated nanorod arrays with different average diameters of 150 and 400 nm were prepared to investigate the size dependence of the surface enhanced Raman scattering (SERS). The diameter of the nanorods was controllable by the substrate position during PLD. High SERS enhancement was observed from both Au-coated ZnO nanorod arrays. The Raman spectra of rhodamine 6G (R6G) as low as 1 nM were measured with an average diameter of 400 nm at an excitation wavelength of 532 nm. The SERS was explained by the field enhancement effect induced by surface plasmon polaritons of Au-coated nanorods (nanoshells).

Near field properties in the vicinity of gold nanoparticles placed on various substrates for precise nanostructuring

We present theoretical results on the near field distribution in the vicinity of gold particles excited by laser radiation and placed on various substrate materials. The study is directed towards the precise nanostructuring of different material surfaces. The calculations are performed on the basis of the FDTD simulation technique. Metal (Au), semiconductor (Si) and dielectric (SiO2) substrate materials are investigated. Experimental results are shown to confirm the validity of the obtained FDTD simulation results. The results show that the field in the vicinity of the point of contact is enhanced, and the enhancement factor depends on the substrate material, particle size and the wavelength of the incident optical radiation. The characteristic size of the field enhanced area is found to be several times smaller than the gold particle size: for the case of the smallest particle diameter of 40 nm it is about 10 nm. The enhancement factor of the electric field on the substrate surface is highest when the substrate is gold metal and it decreases about two orders of magnitude when dielectric SiO2 substrate is used. The characteristic penetration depth of the enhanced field is within several tens of nanometres and the depth weakly depends on the substrate material and the laser excitation wavelength. The dependence of the gold particle size on the field enhancement factor is investigated as well. The present results can be used to predict and design precise nanostructuring on different materials with gold nanoparticles excited by a femtosecond laser pulse.

Near field distribution in two dimensionally arrayed gold nanoparticles on platinum substrate

Theoretical and experimental results for near field properties in the vicinity of two dimensionally aligned gold nanoparticles are presented. The numerical analysis is based on finite difference time domain simulation code. The simulated system consists of gold particles with a radius of 100nm, deposited on platinum substrate. The near field distribution on the substrate surface and its magnitude are found to depend on the interparticle distance. The experimental results obtained confirm the theoretical findings and demonstrate that the produced near field can result in a permanent substrate surface nanomodification and selective nanoparticle removal.

Plasmonic and Mie scattering control of far-field interference for regular ripple formation on various material substrates

We present experimental and theoretical results on plasmonic control of far-field interference for regular ripple formation on semiconductor and metal. Experimental observation of interference ripple pattern on Si substrate originating from the gold nanosphere irradiated by femtosecond laser is presented. Gold nanosphere is found to be an origin for ripple formation. Arbitrary intensity ripple patterns are theoretically controllable by depositing desired plasmonic and Mie scattering far-field pattern generators. The plasmonic far-field generation is demonstrated not only by metallic nanostructures but also by the controlled surface structures such as ridge and trench structures on various material substrates.

Friction characteristics of submicrometre-structured surfaces fabricated by particle-assisted near-field enhancement with femtosecond laser

We present friction characteristics of sliding textured silicon surfaces at the submicrometre scale. A two-dimensional submicrometre dimple array on the Si surface is fabricated by femtosecond laser processing. Direct femtosecond laser nano-structuring of the Si (1?0?0) substrate by polystyrene particle-assisted near-field enhancement is used. In the investigated hole diameter domain from 229 to 548?nm, an increase in the friction coefficient with the decrease in the hole size is found experimentally. The fabricated submicrometre dimples act evidently as lubricant reservoirs to supply lubricants and traps to capture wear debris. The fluctuation of the friction coefficient is also increased by reducing the dimple size. The lowest friction coefficient of 1.41 ? 10?2 is achieved with the dimple array having a diameter of about 550?nm. This value is 2.6 times lower than that of non-structured substrates.

Direct observation of surface plasmon far field for regular surface ripple formation by femtosecond laser pulse irradiation of gold nanostructures on silicon substrates

We have directly observed the interference ripple pattern between surface plasmon far field by gold nanosphere and the incident laser on silicon substrate. We explained the ripple formation using three-dimensional finite-difference time-domain simulation method. Nanosphere is an origin for regular ripple formation due to Mie scattering. We present a new method to control the plasmonic far-field pattern using an arbitrary gold nanostructure on the silicon substrate. Previously, the formed ripples were not regular but wavy because they were formed incoherently through the self organization process originating from the random surface roughness. The ripple structure was well controlled coherently.

Near-field interaction of two-dimensional high-permittivity spherical particle arrays on substrate in the Mie resonance scattering domain

We describe theoretical and experimental results on near-field interaction of two-dimensionally (2D) arrayed, high-permittivity spherical particles on a substrate in the Mie resonance scattering domain for surface nano-patterning processing. When a touching particle pair of Mie resonance particles on the substrate is considered, an electromagnetic mode different from the single particle mode is excited inside the particles, resulting in an intensity enhancement in a gap between two hotspots at particle-substrate contact points. As for 2D hexagonal close-packed particle arrays on the substrate, the refractive index of particle exhibiting a maximal enhancement factor for the 2D particle arrays is found to be shifted from the Mie resonance conditions for the single particle system.

Ultrafast laser ablation of gold thin film targets

Ultrafast laser ablation of a gold thin film is studied and compared with that of a bulk target, with particular emphasis given to the process of nanoparticles generation. The process is carried out in a condition where a single laser shot removes all the irradiated film spot. The experimental results evidence interesting differences and, in particular, a reduction of the nanoparticles size, and a narrowing of a factor two of their size distribution in the case of ablation of a thin film target, a feature which we relate to a more uniform heating of the target material. We thus show that ultrashort laser ablation of thin films provides a promising way of controlling plume features and nanoparticles size.

Positive and negative nanohole-fabrication on glass surface by femtosecond laser with template of polystyrene particle array

We demonstrate a new nano-processing technique using the near- electromagnetic field around a small transparent particle irradiated by an 820 nm femtosecond laser pulse. We fabricate a 2D nanohole array with negative and positive patterns on a soda lime glass surface by irradiating a monolayer of 790 nm diameter polystyrene (PS) particles, arranged in a close-packed hexagonal lattice, with a femtosecond laser pulse. At the lower laser fluence domain, PS particles act as focusing lenses and/or near-field enhancers due to Mie scattering; it enables nanohole processing just under the particle (positive patterning). Nanoholes with diameters ranging from 84 to 170 nm are fabricated in this regime. At the higher fluence domain, the PS particle acts as a mask; while the positive nanohole formation disappears, then it enables nano-patterning of the surface in gap areas corresponding to the region between particles (negative patterning). Nanoholes with diameters ranging from 65 to 110 nm are fabricated in this case. The switching of negative and positive nano-patterning by simply controlling the incident laser fluence is experimentally demonstrated for the first time to our knowledge. A simple theoretical explanation for the switching of the positive and negative patterning is presented by FDTD simulation of the near-field distribution.