Daniel Rytz

Harmonic nanocrystals for biolabeling: a survey of optical properties and biocompatibility.

Nonlinear optical nanocrystals have been recently introduced as a promising alternative to fluorescent probes for multiphoton microscopy. We present for the first time a complete survey of the properties of five nanomaterials (KNbO(3), LiNbO(3), BaTiO(3), KTP, and ZnO), describing their preparation and stabilization and providing quantitative estimations of their nonlinear optical response. In the light of their prospective use as biological and clinical markers, we assess their biocompatibility on human healthy and cancerous cell lines. Finally, we demonstrate the great potential for cell imaging of these inherently nonlinear probes in terms of optical contrast, wavelength flexibility, and signal photostability.

Investigation of the structure of barium titanate thin films by Raman spectroscopy

Raman spectroscopy was used to examine the structure of barium titanium oxide thin films grown by metal‐organic chemical vapor deposition (MOCVD) and laser‐assisted deposition. The spectra were compared with the spectra of a ceramic specimen and a single crystal. Raman peaks specific to the tetragonal ferroelectric phase of BaTiO3 were seen in the spectra of several films. Other Raman peaks were ascribed to impurity (non‐BaTiO3) phases in the films or to the substrates (fused quartz, MgO). Some of the Raman peaks showed a strong polarization dependence. The MOCVD films were also characterized by x‐ray diffraction, energy‐dispersive x‐ray spectroscopy, and transmission electron microscopy. The film‐to‐film variation of the strength of BaTiO3 features in the Raman spectrum, relative to impurity‐phase features, was qualitatively consistent with the x‐ray diffraction and electron microscopy results. Spatially resolved Raman measurements showed that the structure of the laser‐deposited film varies significantl...

Raman spectroscopy of (K,Na)NbO3 and (K,Na)1−xLixNbO3

We report Raman spectroscopy in all four phases of a (K0.5+δNa0.5−δ)NbO3 (δ∼0.03) crystal and ((K0.5+δNa0.5−δ)1−xLix)NbO3 for x=0.02 and 0.03. The phase transitions in the Li-free crystal are homogeneous and hysteretic, with no mixed-phase region between the rhombohedral and orthorhombic phases. Raman spectra in the lowest-temperature phase in the Li-doped material differ significantly from those at x=0 and suggest a structural phase boundary at a Li concentration of less than 2%.

Structural origins of relaxor behavior in a 0.96(Bi1/2Na1/2)TiO3―0.04BaTiO3 single crystal under electric field

Diffuse x-ray scattering intensities from a single crystal of 0.96(Bi1/2Na1/2TiO3)–0.04(BaTiO3) have been collected at room temperature with and without application of an electric field along the [100] direction. Distinct features in the diffuse scattering intensities indicate correlations on a nanometer length scale. It is shown that locally correlated planar-like structures and octahedral tilt-domains within the room temperature rhombohedral R3c phase are both electrically active and are irreversibly affected by application of an electric field of 4.3 kV/mm. The field dependence of these nanoscale structures is correlated with the relaxor behavior of the material by macroscopic permittivity measurements.

Large and stable thickness coupling coefficients of [001]c-oriented KNbO3 and Li-modified (K,Na)NbO3 single crystals

Large thickness coupling factors kT⩽0.7 are measured in both [001]C-oriented (45° cut in the orthorhombic ac plane), monodomain and [001]C-poled, domain-engineered single crystals of KNbO3. kT is extremely stable over a large temperature range, remaining high (⩾0.65) even upon heating and cooling through the orthorhombic-tetragonal phase transition. This is likely related to another finding that spontaneously high kT values (⩽0.68) are observed in as-grown (unpoled), [001]C-cut, polydomain KNbO3 crystals. kT is also stable upon thinning to thicknesses below 60μm, as required for high-frequency applications. Finally, large kT values (⩽0.7) are reported in [001]C-poled, polydomain, Li-doped (K0.5Na0.5)NbO3.

Photorefractive and domain gratings in barium titanate

We present concrete evidence for the formation of ferroelectric domain gratings induced by photorefractive space‐charge electric fields in top‐seeded solution‐grown barium titanate crystals. These domain gratings are not destroyed by light and, by applying a field, can be reconverted into photorefractive gratings that diffract much more light than the photorefractive gratings that create them, as much as 67% of an incident beam.

Anisotropy of ferroelectric behavior of (1 − x)Bi1/2Na1/2TiO3–xBaTiO3 single crystals across the morphotropic phase boundary

(1 − x)(Bi1/2Na1/2)TiO3-xBaTiO3 (BNT-100xBT) single crystals with three different compositions of xu2009=u20090.036, 0.065, and 0.088, covering the rhombohedral to predominantly tetragonal region of the phase diagram and encompassing the morphotropic phase boundary (MPB), were grown by top-seeded solution growth. Dielectric and ferroelectric measurements were performed on samples with different orientations with respect to the crystallographic axes. While the results complied with the current understanding of the crystallographic structure, no enhancement of electromechanical properties based on transient polarization rotation was observed. This clearly sets BNT-100xBT apart from other relaxor ferroelectric systems with a rhombohedral-tetragonal MPB such as (1 − x) Pb(Mg1/3Nb2/3)O3-xPbTiO3. An anomaly was observed in the poling behavior of the strain in 〈001〉 oriented BNT-100xBT in the immediate vicinity of the MPB with xu2009=u20090.065, resulting in a giant small-signal piezoelectric coefficient d 33 of 4600u2009pm/V. This effect is hypothesized to be due to an irreversible phase change from rhombohedral polar nanoregions to tetragonal ferroelectric microdomains.

Nonlinear optical and magnetic properties of BiFeO3 harmonic nanoparticles

Second Harmonic Generation (SHG) from BiFeO3 nanocrystals is investigated for the first time to determine their potential as biomarkers for multiphoton imaging. Nanocrystals are produced by an auto-combustion method with 2-amino-2-hydroxymethyl-propane-1,3-diol as a fuel. Stable colloidal suspensions with mean particle diameters in the range 100–120u2009nm are then obtained after wet-milling and sonication steps. SHG properties are determined using two complementary experimental techniques, Hyper Rayleigh Scattering and nonlinear polarization microscopy. BiFeO3 shows a very high second harmonic efficiency with an averaged 〈d〉 coefficient of 79u2009±u200912u2009pm/V. From the nonlinear polarization response of individual nanocrystals, relative values of the independent dij coefficients are also determined and compared with recent theoretical and experimental studies. Additionally, the particles show a moderate magnetic response, which is attributed to γ-Fe2O3 impurities. A combination of high nonlinear optical efficiency and magnetic response within the same particle is of great interest for future bio-imaging and diagnostic applications.

Low‐temperature annealing of ion‐implanted KNbO3 waveguides for second‐harmonic generation

Results on annealing experiments of He+ ion‐implanted KNbO3 planar and channel waveguides are reported. Annealing at 150u2009°C for several hours leads to a reduction of the waveguide attenuation constant by more than 5 dBu2009cm−1 at a wavelength of 457 nm without significant change of the profile of the mode confining barrier. A minimum waveguide attenuation constant of 1.3 dBu2009cm−1 in planar and 2.2 dBu2009cm−1 in channel waveguides at 515 nm was achieved. Second‐harmonic generation measurements in the waveguides showed that the conversion efficiency can be improved by more than a factor of 2 by the annealing process.

Cellular uptake and biocompatibility of bismuth ferrite harmonic advanced nanoparticles

UNLABELLEDnBismuth Ferrite (BFO) nanoparticles (BFO-NP) display interesting optical (nonlinear response) and magnetic properties which make them amenable for bio-oriented diagnostic applications as intra- and extra membrane contrast agents. Due to the relatively recent availability of this material in well dispersed nanometric form, its biocompatibility was not known to date. In this study, we present a thorough assessment of the effects of in vitro exposure of human adenocarcinoma (A549), lung squamous carcinoma (NCI-H520), and acute monocytic leukemia (THP-1) cell lines to uncoated and poly(ethylene glycol)-coated BFO-NP in the form of cytotoxicity, haemolytic response and biocompatibility. Our results support the attractiveness of the functional-BFO towards biomedical applications focused on advanced diagnostic imaging.nnnFROM THE CLINICAL EDITORnBismuth Ferrite nanoparticles (BFO-NP) have been recently successfully introduced as photodynamic tools and imaging probes. However, how these nanoparticles interact with various cells at the cellular level remains poorly understood. In this study, the authors performed in vitro experiments to assess the effects of uncoated and PEG-coated BFO-NP in the form of cytotoxicity, haemolytic response and biocompatibility.