Petar A. Atanasov

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 of a gold nanoparticle array on different substrates excited by a femtosecond laser

In this paper we present experimental and theoretical results on the properties of the electromagnetic field in the near-field zone of gold nanoparticles excited by an 800xa0nm ultrashort laser pulse. The near-field properties are studied for the case of a single isolated particle and 2D nanoparticle array case. Particles are deposited on different substrates: metal (Au), semiconductor (Si) and dielectric (SiO2). The calculations based on the finite difference time domain (FDTD) simulation technique predict that the field in the vicinity of the particles is enhanced as the magnitude of the field intensity depends on the substrate material and the interparticle distance for 2D array. For closely arrayed nanoparticles on the gold substrate, the maximal field intensity is more than two times lower than that of a single particle. With the increase of the distance between 200xa0nm diameter gold particles, the value of the field intensity increases up to a distance of about 800 nm. The theoretical prediction of the field enhancement on the substrate is confirmed experimentally. The irradiation of the nanoparticles deposited on the three different substrates with a single laser pulse of a Ti:sapphire laser results in a nanohole formation. Discussion on the observed properties is presented.

Pulsed laser deposited ZnO film on side-polished fiber as a gas sensing element

A simple sensor element consisting of a side-polished single-mode fiber and a planar metal oxide waveguide is described. The thin ZnO planar waveguide was produced on the polished fiber surface by pulsed laser deposition at optimized processing parameters. A measurement scheme for in situ control of the film thickness during the deposition process was developed and used. X-ray diffraction measurements and scanning electron microscopy were used to characterize the structure and the surface morphology of the planar waveguide, respectively. The numerical evaluation of the sensor sensitivity predicts the possibility to detect refractive index changes of less than 10(-4). Furthermore, preliminary gas sensor tests were performed by using a mixture of 1.5% butane diluted in N(2) and pure butane. A shift of the spectral position of the resonance points was observed from 3 to 5 s after gas exposure, which corresponds to refractive index changes of 3 x 10(-5) and 1.2 x 10(-3) for 1.5% butane and for pure butane, respectively.

Highly sensitive refractometers based on a side-polished single-mode fibre coupled with a metal oxide thin-film planar waveguide

Refractometric sensor elements were studied consisting of a side-polished single-mode optical fibre covered by a pulsed laser deposited ZnO thin film. A measurement scheme was used for in situ control of the film thickness during the deposition process. Highly sensitive sensors were produced based on the interaction with the zero- and first-order modes of the ZnO planar waveguide. The sensors applicability to the two spectral regions for communications, namely 800–1000 nm and 1300–1600 nm, was demonstrated. A high sensitivity of the order of 3000–6700 nm per refractive index unit change was obtained for sensor elements utilizing the interaction of the fibre mode with the TE0 or TM0 mode of the ZnO thin-film waveguide.

Fs-laser processing of polydimethylsiloxane

We present an experimental analysis on surface structuring of polydimethylsiloxane films with UV (263u2009nm) femtosecond laser pulses, in air. Laser processed areas are analyzed by optical microscopy, SEM, and μ-Raman spectroscopy. The laser-treated sample shows the formation of a randomly nanostructured surface morphology. μ-Raman spectra, carried out at both 514 and 785u2009nm excitation wavelengths, prior and after laser treatment allow evidencing the changes in the sample structure. The influence of the laser fluence on the surface morphology is studied. Finally, successful electro-less metallization of the laser-processed sample is achieved, even after several months from the laser-treatment contrary to previous observation with nanosecond pulses. Our findings address the effectiveness of fs-laser treatment and chemical metallization of polydimethylsiloxane films with perspective technological interest in micro-fabrication devices for MEMS and nano-electromechanical systems.

Plasmonic Nanometric Optical Tweezers in an Asymmetric Space of Gold Nanostructured Substrates

We present a plasmonic near-field tweezers in water with gold nanosphere pairs on various substrates. An enhanced near field localized in the nanometric gap space pumped with 800 nm femtosecond laser is to trap and kill small viruses. The maximal optical trapping force obtained is larger than 20 pN at an incident optical peak intensity of 1 mW/μm 2 . We also propose a new system consisting of a gold nanosphere and a gold nanoridge. In this system, the enhanced near field stems mainly from the image charge effect, exhibiting an optical trapping in an asymmetric space. The calculated trapping force is equivalent to the system of gold nanosphere pairs. The trapped viruses may easily be inactivated using a unfocused 800 nm femtosecond laser.

Femtosecond Laser Ablation of Crystalline Iron: Experimental Investigation and Molecular Dynamics Simulation

We report the ablation of crystalline iron (Fe) by a femtosecond laser examined both experimentally and theoretically. Laser ablation of Fe is investigated theoretically by a molecular dynamics (MD) simulation model. In the model, the electron system is taken into account. The dependence of the laser fluence on the ablation process is numerically simulated. The ablation rate achieved experimentally is well predicted at fluences just above the ablation threshold of 0.18 J/cm2. In addition, as a result of the X-ray diffraction (XRD) measurement of the ablated surface, the grain sizes of the surface become smaller. The heat-affected zone is experimentally observed even with lower fluence irradiation than the ablation threshold fluence of 0.18 J/cm2, while at higher laser fluences than the ablation threshold it is measured to be less than 1 µm.

Substrate nanomodification based on heating and near field properties of gold nanoparticles

Theoretical and experimental results on nanosized modifications of substrates placed in the near field zone of metal nanoparticles are demonstrated. Gold nanoparticles with diameter of 200 nm are deposited on different substrates (dielectric, semiconductor, and metal) and irradiated by ultrashort laser pulses at wavelength of 800 nm. Formation of surface modification under the nanoparticles is observed at laser fluences below the modification threshold of the bulk substrate. The mechanisms of the surface modifications are explained by the heating of the nanoparticles and by the local field enhancement in their vicinity. The heating of the nanoparticle is described by two-temperature diffusion model as the input optical properties of the nanoparticles are evaluated on the basis of the Mie theory. The near field distribution is obtained by finite difference time domain (FDTD) simulation. The influence of the incident irradiation properties and the dielectric properties of the substrates on the modification characteristics is discussed.

Au nanostructure fabrication by pulsed laser deposition in open air: Influence of the deposition geometry

We present a fast and flexible method for the fabrication of Au nanocolumns. Au nanostructures were produced by pulsed laser deposition in air at atmospheric pressure. No impurities or Au compounds were detected in the resulting samples. The nanoparticles and nanoaggregates produced in the ablated plasma at atmospheric pressure led to the formation of chain-like nanostructures on the substrate. The dependence of the surface morphology of the samples on the deposition geometry used in the experimental set up was studied. Nanocolumns of different size and density were produced by varying the angle between the plasma plume and the substrate. The electrical, optical, and hydrophobic properties of the samples were studied and discussed in relation to their morphology. All of the nanostructures were conductive, with conductivity increasing with the accumulation of ablated material on the substrate. The modification of the electrical properties of the nanostructures was demonstrated by irradiation by infrared light. The Au nanostructures fabricated by the proposed technology are difficult to prepare by other methods, which makes the simple implementation and realization in ambient conditions presented in this work more ideal for industrial applications.