Vapor-Phase Contribution to Laser-Induced Plasma Emission of Magnesium in Liquid Aluminum.

Liquid aluminum containing the important alloying element magnesium in varying concentrations was analyzed using in-situ laser-induced breakdown spectroscopy (LIBS). Magnesium emission shows an exponential dependence on melt temperature that correlates well with the expected partial pressure of magnesium above the aluminum melt. Furthermore, comparison with LIBS measurements on corresponding solid samples supports the conclusion that a significant part of Mg emission from liquid metal samples originates from the vapor phase above the metal surface.

SERS Imaging of Mesenchymal Stromal Cell Differentiation.

Understanding the process of mesenchymal stromal cell (MSC) osteogenic differentiation is essential for a wide range of medical applications. However, these primary cells vary significantly from donor to donor, making it difficult to fully exploit their therapeutic potential. Although osteogenic differentiation has been studied extensively, there is still a shortage of standardized methods for the evaluation of the degree of differentiation.

Molecular Structure and Interactions of Lipids in the Outer Membrane of Living Cells Based on Surface-Enhanced Raman Scattering and Liposome Models.

The distribution and interaction of lipids determine the structure and function of the cellular membrane. Surface-enhanced Raman scattering (SERS) is used for selective molecular probing of the cell membrane of living fibroblast cells grown adherently on gold nanoisland substrates across their whole contact areas with the substrate, enabling mapping of the membrane's composition and interaction. From the SERS data, the localization and distribution of different lipids and their interactions, together with proteins in the outer cell membrane, are inferred.

Gold nanoisland substrates for SERS characterization of cultured cells.

We demonstrate a simple approach for fabricating cell-compatible SERS substrates, using repeated gold deposition and thermal annealing. The substrates exhibit SERS enhancement up to six orders of magnitude and high uniformity. We have carried out Raman imaging of fixed mesenchymal stromal cells cultured directly on the substrates.

Innovative in vitro method to study ventilator induced lung injury.

Mechanical ventilation (MV) is a life-saving therapy for critically ill patients, alleviating the work of breathing and supporting adequate gas exchange. However, MV can cause ventilator induced lung injury (VILI) by baro/volu- and atelectrauma, even lead to acute respiratory distress syndrome (ARDS), and substantially augment mortality. There is a need for specific biomarkers and novel research platforms for VILI/ARDS research to study these detrimental disorders and seek ways to avoid or prevent them.

Polarization state generation and measurement with a single metasurface.

The constituent elements of metasurfaces may be designed with explicit polarization dependence, making metasurfaces a fascinating platform for new polarization optics. In this work we show that a metasurface grating can be designed to produce arbitrarily specified polarization states on a set of defined diffraction orders given that the polarization of the incident beam is known. We also demonstrate that, when used in a reverse configuration, the same grating may be used as a parallel snapshot polarimeter, requiring a minimum of bulk polarization optics.

Microgels and apparatus for PAGE of nucleic acids in one or two dimensions.

We describe a system for horizontal 1D or 2D PAGE comprising an apparatus and microgels. There is no buffer outside the gel, making handling and sample loading easy. Specially designed electrodes on all four sides allow 2D electrophoresis without gel rotation.

Efficient interfacing photonic and long-range dielectric-loaded plasmonic waveguides.

Long-range dielectric-loaded surface plasmon-polariton waveguides (LR-DLSPPWs) operating at telecom wavelengths are efficiently (end-fire) interfaced with photonic waveguides by taking advantage of very similar lateral mode field profiles in these waveguide configurations. The LR-DLSPPWs are formed by 1-μm-high and 1-μm-wide polymer ridges fabricated atop 15-nm-thin and 500-nm-wide gold stripes supported by a 289-nm-thick ormoclear polymer deposited on a low-index (1.34) layer of cytop, whereas gold stripes are absent in the photonic waveguide configuration that is identical to the plasmonic one in all other respects.

Data transmission in long-range dielectric-loaded surface plasmon polariton waveguides.

We demonstrate the data transmission of 10 Gbit/s on-off keying modulated 1550 nm signal through a long-range dielectric-loaded surface plasmon polariton waveguide structure with negligible signal degradation. In the experiment the bit error rate penalties do not exceed 0.6 dB over the 15 nm wavelength range and received optical power between -7 and 3 dBm.

Polarization-selective coupling to long-range surface plasmon polariton waveguides.

We demonstrate polarization-selective coupling from an optical fiber to long-range surface plasmon polariton waveguide modes using plasmonic antenna arrays. The arrays allow the sorting of two distinct (not necessarily orthogonal) polarizations to counter-propagating waveguide modes. The polarization-selective behavior of the devices is described by a compact formalism based on Stokes vectors that offers a clear graphical representation of the response.

Real-time optical pH measurement in a standard microfluidic cell culture system.

The rapid growth of microfluidic cell culturing in biological and biomedical research and industry calls for fast, non-invasive and reliable methods of evaluating conditions such as pH inside a microfluidic system. We show that by careful calibration it is possible to measure pH within microfluidic chambers with high accuracy and precision, using a direct single-pass measurement of light absorption in a commercially available phenol-red-containing cell culture medium. The measurement is carried out using a standard laboratory microscope and, contrary to previously reported methods, requires no modification of the microfluidic device design.

Directional coupling in long-range dielectric-loaded plasmonic waveguides.

Directional couplers (DCs) based on long-range dielectric-loaded surface plasmon-polariton waveguides (LR-DLSPPWs) operating at telecom wavelengths are studied both numerically and experimentally. The investigated LR-DLSPPWs are formed by ~1.2-µm-high and 1-µm-wide polymer ridges fabricated atop of 15-nm-thick and 500-nm-wide gold stripes supported by a 288-nm-thick Ormoclear polymer deposited on a low-index (n(s) ≈1.

Tetraphenylporphyrin tethered chitosan based carriers for photochemical transfection.

Water-soluble amphiphilic chitosan nanocarriers tethered with the photosensitizer meso-tetraphenylporphyrin were synthesized in a seven-step procedure, starting from 3,6-di-O-tert-butyldimethylsilyl-chitosan and 5-(p-aminophenyl)-10,15,20-triphenylporphyrin. The lipophilic photosensitizer could be introduced in a quantitative and reproducible reaction to give either 0.1 or 0.

Comparing resonant photon tunneling via cavity modes and Tamm plasmon polariton modes in metal-coated Bragg mirrors.

Resonant photon tunneling was investigated experimentally in multilayer structures containing a high-contrast (TiO(2)/SiO(2)) Bragg mirror capped with a semitransparent gold film. Transmission via a fundamental cavity resonance was compared with transmission via the Tamm plasmon polariton resonance that appears at the interface between a metal film and a one-dimensional photonic bandgap structure. The Tamm-plasmon-mediated transmission exhibits a smaller dependence on the angle and polarization of the incident light for similar values of peak transmission, resonance wavelength, and finesse.

On-chip modulation of evanescent illumination and live-cell imaging with polymer waveguides.

Imaging of live cells was carried out using evanescent-wave excitation on a polymer waveguide chip. Integrated waveguide-based interferometric light modulators were fabricated in order to demonstrate on-chip control of excitation light, e.g.

Long-range dielectric-loaded surface plasmon polariton waveguides operating at telecommunication wavelengths.

We report on the realization of long-range dielectric-loaded surface plasmon polariton waveguides (LR-DLSPPWs) consisting of straight and bent subwavelength dielectric ridges deposited on thin and narrow metal stripes supported by a dielectric buffer layer covering a low-index substrate. Using imaging with a near-field optical microscope and end-fire coupling with a tapered fiber connected to a tunable laser at telecommunication wavelengths (1425-1545 nm), we demonstrate low-loss (propagation length ∼500 μm) and well-confined (mode width ∼1 μm) LR-DLSPPW mode guiding and determine the propagation and bend loss.

High index contrast polymer waveguide platform for integrated biophotonics.

We present detailed characterization of a unique high-index-contrast integrated optical polymer waveguide platform where the index of the cladding material is closely matched to that of water. Single-mode waveguides designed to operate across a large part of the visible spectrum have been fabricated and waveguide properties, including mode size, bend loss and evanescent coupling have been modeled using effective-index approximation, finite-element and finite-difference time domain methods. Integrated components such as directional couplers for wavelength splitting and ring resonators for refractive-index or temperature sensing have been modeled, fabricated and characterized.

Surface enhanced Raman imaging: periodic arrays and individual metal nanoparticles.

Surface enhanced Raman scattering (SERS) from Rhodamine 6G homogenously adsorbed on both periodic arrays of and individual gold nanoparticles is investigated using high-resolution Raman imaging with polarized excitation. Rectangular 50-nm-high nanoparticles of different sizes chosen to ensure the presence of localized surface plasmon resonances close to the 532-nm excitation wavelength are fabricated with electron-beam lithography on the surface of a smooth gold film and arranged both individually (i.e.

Evanescent-wave fluorescence microscopy using symmetric planar waveguides.

We describe a new evanescent-wave fluorescence excitation method, ideally suited for imaging of biological samples. The excitation light propagates in a planar optical waveguide, consisting of a thin waveguide core sandwiched between a sample in an aqueous solution and a polymer with a matching refractive index, forming a symmetric cladding environment. This configuration offers clear advantages over other waveguide-excitation methods, such as superior image quality, wide tunability of the evanescent field penetration depth and compatibility with optical fibers.

Compact plasmonic variable optical attenuator.

We demonstrate plasmonic nanowire-based thermo-optic variable optical attenuators operating in the 1525-1625 nm wavelength range. The devices have a footprint as low as 1 mm, extinction ratio exceeding 40 dB, driving voltage below 3 V, and full modulation bandwidth of 1 kHz. The polarization dependent loss is shown to be critically dependent on the nanowire geometry but devices with polarization-dependent loss as low as +/-2.

Observation of propagation of surface plasmon polaritons along line defects in a periodically corrugated metal surface.

Propagation of surface plasmon polaritons (SPPs) excited in the wavelength range 720-830 nm at a corrugated gold-film surface with areas of 150-nm-wide and 45-nm-high scatterers arranged in a 380-nm-period triangular lattice containing line defects is investigated by use of near-field optical microscopy. We demonstrate that the SPP at 740-750 nm propagates along 2.2-microm -wide and 16-microm -long line defects with ~50% loss, whereas its propagation along narrower line defects is strongly damped and in periodically corrugated areas is inhibited.

Long-range surface plasmon polariton nanowire waveguides for device applications.

We report an experimental study of long-range surface plasmon polaritons propagating along metallic wires of sub-micrometer rectangular cross-sections (nanowires) embedded in a dielectric. At telecom wavelengths, optical signals are shown to propagate up to several millimeters along such nanowires. As the wires approach a square cross-section, the guided mode becomes more symmetric and can, for example, be tuned to match closely the mode of a standard single-mode optical fiber.

Compact Z-add-drop wavelength filters for long-range surface plasmon polaritons.

We design, fabricate and investigate compact Z-add-drop (ZAD) filters for long-range surface plasmon polaritons (LR-SPPs) at telecom wavelengths. The ZAD filter for LR-SPPs consists of two ridge gratings formed by periodic gold thickness modulation at the intersections of three zigzag-crossed gold stripes embedded in polymer. We investigate influence of the grating length and crossing angle on the filter characteristics and demonstrate a 10 masculine- ZAD filter based on 80-microm-long gratings that exhibit a 15-dB dip (centered at ~ 1.

Near-field imaging of surface plasmon-polariton guiding in band gap structures at telecom wavelengths.

Using a collection near-field microscope, we image interaction of surface plasmon-polaritons (SPPs) excited locally at telecom wavelengths with periodic triangular arrays of gold bumps placed on gold film surfaces. We observe the inhibition of SPP propagation into the arrays within a certain wavelength range depending on their period and orientation, i.e.

Experimental studies of surface plasmon polariton band gap effect.

Surface plasmon polaritons (SPPs) propagation at a gold film surface covered by periodic arrays of approximately 40-nm-high scatterers arranged in a triangular lattice of different periods containing straight line defects is studied using collection scanning near-field optical microscopy. The results reveal the dependence of the SPP band gap (SPPBG) effect manifested via the SPP reflection and guiding (along line defects) on the parameters of the surface structures (period, filling factor and lattice orientation). We find that the SPPBG effect is stronger along GammaK direction for all investigated periodic structures.