Claus Jeppesen

Electromagnetically induced transparency in metamaterials at near-infrared frequency

We employ a planar metamaterial structure composed of a split-ring-resonator (SRR) and paired nano-rods to experimentally realize a spectral response at near-infrared frequencies resembling that of electromagnetically induced transparency. A narrow transparency window associated with low loss is produced, and the magnetic field enhancement at the center of the SRR is dramatically changed, due to the interference between the resonances with significantly different linewidths. The variation of the spectral response in terms of relative position of the bright and dark elements is evaluated with numerical simulations.

Uranyl salts as photochemical agents for cleavage of DNA and probing of protein-DNA contacts

Single‐strand DNA nicks are induced by uranyl nitrate or uranyl acetate in combination with long‐wavelength (λ ∼ 420 nm) ultraviolet irradiation. The nicks occur randomly with respect to the DNA sequence. Using the λ‐repressor/OR1 operator DNA system it is shown that uranyl salts can be used to photofootprint protein contacts with the DNA backbone.

Nearly zero transmission through periodically modulated ultrathin metal films

Transmission of light through an optically ultrathin metal film with a thickness comparable to its skin depth is significant. We demonstrate experimentally nearly-zero transmission of light through a film periodically modulated by a one-dimensional array of subwavelength slits. The suppressed optical transmission is due to the excitation of surface plasmon polaritons and the zero-transmission phenomenon is strongly dependent on the polarization of the incident wave.

Detection of intercalation-induced changes in DNA structure by reaction with diethyl pyrocarbonate or potassium permanganate Evidence against the induction of Hoogsteen base pairing by echinomycin

Binding of the bis‐intercalators echinomycin and N,N′‐di(9‐acridinyl)spermidine or the mono‐intercalators 9‐aminoacridine and ethidium to DNA induces hypersensitivity of adenines towards reaction with diethyl pyrocarbonate. It is proposed that this hyperreactivity is due to the DNA helix unwinding and extension induced by intercalation, thereby exposing N7 in the major groove, and not as previously suggested to the formation of Hoogsteen base pairing. Hypersensitivity of thymines towards oxidation with permanganate is also induced upon binding of these drugs (especially the bis‐intercalators) to DNA. This thymine hyperreactivity is both sequence‐ and intercalator‐dependent, thereby indicating the potential of KMnO4 as a useful probe for analysing the structure of intercalator‐DNA complexes in solution.

Nonlocal response in plasmonic waveguiding with extreme light confinement

Abstract We present a novel wave equation for linearized plasmonic response, obtained by combining the coupled real-space differential equations for the electric field and current density. Nonlocal dynamics are fully accounted for, and the formulation is very well suited for numerical implementation, allowing us to study waveguides with subnanometer cross-sections exhibiting extreme light confinement. We show that groove and wedge waveguides have a fundamental lower limit in their mode confinement, only captured by the nonlocal theory. The limitation translates into an upper limit for the corresponding Purcell factors, and thus has important implications for quantum plasmonics.

Human glucagon receptor antagonists with thiazole cores. A novel series with superior pharmacokinetic properties.

The aim of the work presented here was to design and synthesize potent human glucagon receptor antagonists with improved pharmacokinetic (PK) properties for development of pharmaceuticals for the treatment of type 2 diabetes. We describe the preparation of compounds with cyclic cores (5-aminothiazoles), their binding affinities for the human glucagon and GIP receptors, as well as affinities for rat, mouse, pig, dog, and monkey glucagon receptors. Generally, the compounds had slightly less glucagon receptor affinity compared to compounds of the previous series, but this was compensated for by much improved PK profiles in both rats and dogs with high oral bioavailabilities and sustained high plasma exposures. The compounds generally showed species selectivity for glucagon receptor binding with poor affinities for the rat, mouse, rabbit, and pig receptors. However, dog and monkey glucagon receptor affinities seem to reflect the human situation. One compound of this series, 18, was tested intravenously in an anesthetized glucagon-challenged monkey model of hyperglucagonaemia and hyperglycaemia and was shown dose-dependently to decrease glycaemia. Further, high plasma exposures and a long plasma half-life (5.2 h) were obtained.

Efficient Excitation of Channel Plasmons in Tailored,UV-Lithography-Defined V-Grooves

We demonstrate the highly efficient (>50%) conversion of freely propagating light to channel plasmon-polaritons (CPPs) in gold V-groove waveguides using compact 1.6 μm long waveguide-termination coupling mirrors. Our straightforward fabrication process, involving UV-lithography and crystallographic silicon etching, forms the coupling mirrors innately and ensures exceptional-quality, wafer-scale device production. We tailor the V-shaped profiles by thermal silicon oxidation in order to shift initially wedge-located modes downward into the V-grooves, resulting in well-confined CPPs suitable for nanophotonic applications.

The effect of Ti and ITO adhesion layers on gold split-ring resonators

Ultrathin adhesion layers serve a well-documented fabrication purpose while its influence on the optical properties of gold nanostructures is often neglected. Gold split-ring resonators are fabricated with two commonly used adhesion layers: titanium and indium tin oxide. When compared to all-gold reference samples, a spectral shift of the ground mode resonance is observed. For the titanium sample the spectral shift is accompanied by a resonance broadening, which is less profound for indium tin oxide. The mutual correlation between the shift and the broadening is shown to be qualitatively consistent with perturbative considerations.

Thin film Ag superlens towards lab-on-a-chip integration.

A thin metal film near-field superlens, as originally suggested by Pendry and realized by Fang et al. and Melville et al., is investigated with emphasis on materials suitable for integration on a lab-on-a-chip platform. A chemically resistant cyclo-olefin copolymer (COC), mr-I-T85 from microresist technology, is applied as dielectric matrix/spacer for an Ag thin film superlens. The superlens successfully resolves 80 nm half-pitch gratings when illuminated with UV radiation at a free space wavelength of 365 nm. The superlens design, fabrication and characterization is discussed.

Capacitance tuning of nanoscale split-ring resonators

We investigate the capacitance tuning of nanoscale split-ring resonators. Based on a simple inductor-capacitor circuit model, we derive an expression, where the inductance is proportional to the area while the capacitance reflects the aspect ratio of the slit. The resonance frequency may thus be tuned by the slit aspect ratio leaving the area, the lattice constant Λ, and nearest-neighbor coupling in periodic structures invariant. Experimental data follow the predictions of the simple LC-model.