Conical versus Gaussian terahertz emission from two-color laser-induced air plasma filaments.

In this Letter, we demonstrate that the far-field terahertz (THz) beam generated from a Ti:Sapphire two-color laser-induced filament can exhibit a conical or Gaussian distribution, depending on the filtering experimental conditions. Using both an incoherent Golay cell detector and a two-dimensional coherent electro-optic detection covering the 0.2-2.

Surface plasmon polariton excitation by second harmonic generation in single organic nanofibers.

Coherent local excitation of surface plasmon polaritons (SPPs) by second-harmonic generation (SHG) in individual aligned crystalline organic functionalized para-phenylene nanofibers deposited on a thin silver film is demonstrated. The SH-SPP generation is considered theoretically and investigated experimentally with angular-resolved leakage radiation spectroscopy for normal incidence of the excitation beam. Both measurements and simulations show asymmetric excitation of left- and right-propagating SH-SPPs, which is explained as an effect of fiber molecules being oriented at an angle relative to the silver film surface.

Study of the tryptophan-terbium FRET pair coupled to silver nanoprisms for biosensing applications.

Plasmonic coupling between fluorophores and metal surfaces has become a focal point of optical research during the last two decades, however, the interactions of FRET couples with metal surfaces remain relatively unexplored. In this study, interactions of the tryptophan-Tb(3+) FRET pair with silver nanoprisms for potential biosensor development have been investigated. For this purpose an engineered lanthanide binding peptide (LBTtrp) containing tryptophan as the sensitizer for bound lanthanide ions (Tb(3+)) as well as a trypsin cleavage site was synthesized.

Near-field electrospinning of dielectric-loaded surface plasmon polariton waveguides.

Dielectric-loaded surface plasmon polariton waveguides (DLSPPWs) are typically made using nanolithography fabrication methods. In this paper we demonstrate that near-field electrospinning of polymer nanofibers directly onto a gold coated substrate can be used as an alternative method for rapid prototype fabrication of DLSPPWs. Surface plasmon polaritons (SPPs) have been excited directly inside the electrospun fibers using a prism in the Kretschmann-Raether configuration.

Pore size dependence of diffuse light scattering from anodized aluminum solar cell backside reflectors.

The development of backside reflectors (BSRs) is crucial for the efficiency of future low cost thin-film silicon solar cells. In this work, the scattering efficiency of bare aluminum BSRs with different pore sizes and ordering of surface microstructures are investigated. The BSRs were fabricated by utilizing the process of self-ordering anodic oxidation on aluminum foils resulting in regions with an approximately hexagonally periodic surface microstructure.

Immobilization of biomolecules onto surfaces according to ultraviolet light diffraction patterns.

We developed a method for immobilization of biomolecules onto thiol functionalized surfaces according to UV diffraction patterns. UV light-assisted molecular immobilization proceeds through the formation of free, reactive thiol groups that can bind covalently to thiol reactive surfaces. We demonstrate that, by shaping the pattern of the UV light used to induce molecular immobilization, one can control the pattern of immobilized molecules onto the surface.

Biophysical properties of phenyl succinic acid derivatised hyaluronic acid.

Modification of hyaluronic acid (HA) with aryl succinic anhydrides results in new biomedical properties of HA as compared to non-modified HA, such as more efficient skin penetration, stronger binding to the skin, and the ability to blend with hydrophobic materials. In the present study, hyaluronic acid has been derivatised with the anhydride form of phenyl succinic acid (PheSA). The fluorescence of PheSA was efficiently quenched by the HA matrix.

Immobilizing biomolecules near the diffraction limit.

Our group has previously shown that biomolecules containing disulfide bridges in close proximity to aromatic residues can be immobilized, through covalent bonds, onto thiol derivatized surfaces upon UV excitation of the aromatic residue(s). We have also previously shown that our new technology can be used to print arrays of biomolecules and to immobilize biomolecules according to any specific pattern on a planar substrates with micrometer scale resolution. In this paper we show that we can immobilize proteins according to diffraction patterns of UV light.

Photonic immobilization of high-density protein arrays using Fourier optics.

The technique of UV-light-assisted immobilization of disulfide containing proteins has been combined with the Fourier-transforming properties of lenses as well as with a simple millimeter scale feature size spatial mask. The result is a new simple and inexpensive way of creating high-density protein arrays with feature sizes down to a few hundred nanometers, which represents an improvement of tenfold over existing commercially available high-density protein arraying methods.

Flash photolysis of cutinase: identification and decay kinetics of transient intermediates formed upon UV excitation of aromatic residues.

Aromatic amino acids play an important role in ultraviolet (UV)-induced photochemical reactions in proteins. In this work, we aim at gaining insight into the photochemical reactions induced by near-UV light excitation of aromatic residues that lead to breakage of disulfide bridges in our model enzyme, Fusarium solani pisi cutinase, a lipolytic enzyme. With this purpose, we acquired transient absorption data of cutinase, with supplemental experimental data on tryptophan (Trp) and lysozyme as reference molecules.

Printing novel molecular architectures with micrometer resolution using light.

In this paper we present a new photonic technology and demonstrate that it allows for precise immobilisation of proteins to sensor surfaces. The new technology secures spatially controlled molecular immobilisation since the immobilisation of each molecule to a support surface can be limited to the focal point of the UV laser beam, with dimensions as small as a few micrometers. We have demonstrated that we are not limited to immobilising molecules according to conventional patterns like microarrays.

Light-induced immobilisation of biomolecules as an attractive alternative to microdroplet dispensing-based arraying technologies.

The present work shows how UV 'light-induced molecular immobilisation' (LIMI) of biomolecules onto thiol reactive surfaces can be used to make biosensors, without the need for traditional microdispensing technologies. Using 'LIMI,' arrays of biomolecules can be created with a high degree of reproducibility. This technology can be used to circumvent the need for often expensive nano/microdispensing technologies.

Optical detection of singlet oxygen from single cells.

The lowest excited electronic state of molecular oxygen, singlet molecular oxygen, O(2)(a (1)Delta(g)), is a reactive species involved in many chemical and biological processes. To better understand the roles played by singlet oxygen in biological systems, particularly at the sub-cellular level, optical tools have been developed to create and directly detect this transient state in time- and spatially-resolved experiments from single cells. Data obtained indicate that, contrary to common perception, this reactive species can be quite long-lived in a cell and, as such, can diffuse over appreciable distances including across the cell membrane into the extracellular environment.

Lifetime and diffusion of singlet oxygen in a cell.

In time- and spatially resolved experiments, singlet molecular oxygen, O(2)(a(1)Delta(g)), was created in a single nerve cell upon irradiation of a sensitizer incorporated in the cell nucleus using a focused laser beam. The singlet oxygen thus produced was detected by its infrared phosphorescence. Data obtained indicate that, contrary to common perception, this reactive species can be quite long-lived in a cell and, as such, can diffuse over appreciable distances including across the cell membrane into the extra-cellular environment.

Two-photon singlet oxygen microscopy: the challenges of working with single cells.

A microscope is described in which singlet molecular oxygen, O2(a1deltag), is produced in a femtoliter focal volume via a nonlinear two-photon photosensitized process, and the 1270 nm phosphorescence from this population of O2(a1deltag) is detected in a photon counting experiment. Although two-photon excitation of a sensitizer is less efficient than excitation by a one-photon process, nonlinear excitation has several distinct advantages with respect to the spatial resolution accessible. Pertinent aspects of this two-photon O2(a1deltag) microscope were characterized using bulk solutions of photosensitizers.

Subcellular, time-resolved studies of singlet oxygen in single cells.

In time-resolved and spatially resolved experiments, singlet molecular oxygen, O2(a1Deltag), was created in a single nerve cell upon irradiation of a sensitizer incorporated in the cell using a focused laser beam. The singlet oxygen thus produced was detected by its infrared phosphorescence. Data obtained indicate that in both the cytoplasm and the nucleus of the cell, this reactive species is approximately 1-2 orders of magnitude longer-lived than previously believed.

Two-photon photosensitized production of singlet oxygen in water.

Singlet molecular oxygen (a(1)Delta(g)) has been produced and optically detected in time-resolved experiments upon nonlinear two-photon excitation of a photosensitizer dissolved in water. For a given sensitizer, specific functional groups that impart water solubility and that give rise to larger two-photon absorption cross sections are, in many cases, not conducive to the production of singlet oxygen in high yield. This issue involves the competing influence of intramolecular charge transfer that can be pronounced in aqueous systems; more charge transfer in the chromophore facilitates two-photon absorption but decreases the singlet oxygen yield.

Singlet oxygen microscope: from phase-separated polymers to single biological cells.

The lowest excited electronic state of molecular oxygen, singlet molecular oxygen (a1Deltag), is an intermediate in many chemical and biological processes. Tools and methods have been developed to create singlet-oxygen-based optical images of heterogeneous samples that range from phase-separated polymers to biological cells. Such images provide unique insight into a variety of oxygen-dependent phenomena, including the photoinitiated death of cells.

Quantum state tomography of dissociating molecules.

Using tomographic reconstruction we determine the complete internuclear quantum state, represented by the Wigner function, of a dissociating I2 molecule based on femtosecond time resolved position and momentum distributions of the atomic fragments. The experimental data are recorded by timed ionization of the photofragments with an intense 20 fs laser pulse. Our reconstruction method, which relies on Jaynes's maximum entropy principle, will also be applicable to time resolved position or momentum data obtained with other experimental techniques.

Imaging and control of interfering wave packets in a dissociating molecule.

Using two identical 110 femtosecond (fs) optical pulses separated by 310 fs, we launch two dissociative wave packets in I2. We measure the square of the wave function as a function of both the internuclear separation, /Psi(R)/(2), and of the internuclear velocity, /Psi(v(R))/(2), by ionizing the dissociating molecule with an intense 20 fs probe pulse. Strong interference is observed in both /Psi(R)/(2) and in /Psi(v(R))/(2).