Optical force decoration of 3D microstructures with plasmonic particles.

Optical forces are used to push and aggregate gold nanorods onto several substrates creating surface-enhanced Raman scattering (SERS) active hot spots for Raman-based identification of proteins. By monitoring the increase of the protein SERS signal, we observe different aggregation times for different curvatures of the substrates. The slower aggregation dynamics on curved surfaces is justified by a simple geometrical model. In particular, this technique is used to decorate three-dimensional microstructures and to quickly realize hybrid micro/nanosensors for highly sensitive detection of biological material directly in a liquid environment.

Optical trapping and optical force positioning of two-dimensional materials.

In recent years, considerable effort has been devoted to the synthesis and characterization of two-dimensional materials. Liquid phase exfoliation (LPE) represents a simple, large-scale method to exfoliate layered materials down to mono- and few-layer flakes. In this context, the contactless trapping, characterization, and manipulation of individual nanosheets hold perspectives for increased accuracy in flake metrology and the assembly of novel functional materials. Here, we use optical forces for high-resolution structural characterization and precise mechanical positioning of nanosheets of hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide obtained by LPE. Weakly optically absorbing nanosheets of boron nitride are trapped in optical tweezers. The analysis of the thermal fluctuations allows a direct measurement of optical forces and the mean flake size in a liquid environment. Measured optical trapping constants are compared with T-matrix light scattering calculations to show a quadratic size scaling for small size, as expected for a bidimensional system. In contrast, strongly absorbing nanosheets of molybdenum disulfide and tungsten disulfide are not stably trapped due to the dominance of radiation pressure over the optical trapping force. Thus, optical forces are used to pattern a substrate by selectively depositing nanosheets in short times (minutes) and without any preparation of the surface. This study will be useful for improving ink-jet printing and for a better engineering of optoelectronic devices based on two-dimensional materials.

Light-induced rotations of chiral birefringent microparticles in optical tweezers.

We study the rotational dynamics of solid chiral and birefringent microparticles induced by elliptically polarized laser light in optical tweezers. We find that both reflection of left circularly polarized light and residual linear retardance affect the particle dynamics. The degree of ellipticity of laser light needed to induce rotations is found. The experimental results are compared with analytical calculations of the transfer of angular moment from elliptically polarized light to chiral birefringent particles.

Optical trapping of silver nanoplatelets.

Optical trapping of silver nanoplatelets obtained with a simple room temperature chemical synthesis technique is reported. Trap spring constants are measured for platelets with different diameters to investigate the size-scaling behaviour. Experimental data are compared with models of optical forces based on the dipole approximation and on electromagnetic scattering within a T-matrix framework. Finally, we discuss applications of these nanoplatelets for surface-enhanced Raman spectroscopy.

Polarization-dependent optomechanics mediated by chiral microresonators.

Chirality is one of the most prominent and intriguing aspects of nature, from spiral galaxies down to aminoacids. Despite the wide range of living and non-living, natural and artificial chiral systems at different scales, the origin of chirality-induced phenomena is often puzzling. Here we assess the onset of chiral optomechanics, exploiting the control of the interaction between chiral entities. We perform an experimental and theoretical investigation of the simultaneous optical trapping and rotation of spherulite-like chiral microparticles. Due to their shell structure (Bragg dielectric resonator), the microparticles function as omnidirectional chiral mirrors yielding highly polarization-dependent optomechanical effects. The coupling of linear and angular momentum, mediated by the optical polarization and the microparticles chiral reflectance, allows for fine tuning of chirality-induced optical forces and torques. This offers tools for optomechanics, optical sorting and sensing and optofluidics.

Mid-range structure of niobium-sodium-phosphate electro-optic glasses.

The mid-range structure of glasses of the glass-forming system xNb(2)O(5)-(60 - x)P(2)O(5)-40Na(2)O, with x varying from 0 to 40, has been investigated by Raman spectroscopy and electro-optical Kerr measurements. It was found that the mid-range inhomogeneities in the glasses under study vary with x and their compositions and structures dramatically differ from the gross glass composition. It is shown that inhomogeneities with the 8NaNbO(3) + (Nb(2)O(5)·P(2)O(5)) composition are responsible for the electro-optical sensitivity of the glasses. The electro-optical structural elements of the inhomogeneities of this type are assumed to be fragments of the quasicubic lattice of crystalline NaNbO(3) demonstrating a rather high electro-optic Kerr coefficient. The obtained results are discussed in terms of the concepts of constant stoichiometric groupings and crystal motifs.

Optical trapping of nanotubes with cylindrical vector beams.

We use laser beams with radial and azimuthal polarization to optically trap carbon nanotubes. We measure force constants and trap parameters as a function of power showing improved axial trapping efficiency with respect to linearly polarized beams. The analysis of the thermal fluctuations highlights a significant change in the optical trapping potential when using cylindrical vector beams. This enables the use of polarization states to shape optical traps according to the particle geometry, as well as paving the way to nanoprobe-based photonic force microscopy with increased performance compared to a standard linearly polarized configuration.

Influence of carbon source and Fe-catalyst support on the growth of multi-walled carbon nanotubes.

Catalytic activity of iron based catalysts in the production of multi-walled carbon nanotubes (MWCNTs) has been investigated. The effect of the carbon source (ethane or isobutane), catalyst support (Al2O3 or SiO2), iron loading, catalyst reduction temperature and reaction temperature on yield and quality of carbon products has been examined. The structural and morphological properties of catalyst and carbon products obtained have been analyzed by means of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD). The iron-based catalysts supported on alumina seem to be efficient systems for the production of carbon nanotubes from chemical vapor deposition (CVD) of isobutane with very interesting yields. The opportune calibration of reaction parameters, such as iron loading and reaction temperature, can in fact drive the synthesis toward the formation of high quality CNTs.

The determination of non-steroidal antiinflammatory drugs in pharmaceuticals by capillary zone electrophoresis and micellar electrokinetic capillary chromatography.

Ibuprofen, indomethacin, ketoprofen, piroxicam and diclofenac have been quantified in dragees, suspension, suppositories, capsules, injection solutions and tablets by capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MEKC). The experiments were performed without specific sample pretreatment. The reproducibility of the method was investigated. Good quantitation was obtained in short analysis times. CE and MEKC are found to offer a good alternative to conventional HPLC methods.

Capillary zone electrophoresis and micellar electrokinetic capillary chromatography of some non-steroidal antiinflammatory drugs (NSAIDs).

The possibilities of capillary electrophoresis (CE) and micellar electrokinetic capillary chromatography (MEKC) were investigated for the qualitative analysis of some non-steroidal antiinflammatory drugs. In CE the influence of the pH of the buffer and its ionic strength were investigated for a test mixture of six compounds. Also the influence of organic modifiers was studied. The best conditions were applied to the separation of 15 drugs. In MEKC the influence of the concentration of SDS in buffers with pH ranges of 8.0-9.0 was investigated. The influence of an organic modifier, namely acetonitrile was discussed, whereby an interesting phenomenon of change in retention behaviour was noted. A combination of CE and MEKC allows the separation of the 15 above-mentioned compounds and forms an interesting alternative to HPLC.