The lack of symmetry between electric and magnetic charges, a fundamental consequence of the small value of the fine-structure constant, is directly related to the weakness of magnetic effects in optical materials. Properly tailored plasmonic nanoclusters have been proposed recently to induce artificial optical magnetism based on the principle that magnetic effects are indistinguishable from specific forms of spatial dispersion of permittivity at optical frequencies. In a different context, plasmonic Fano resonances have generated a great deal of interest, particularly for use in sensing applications that benefit from sharp spectral features and extreme field localization. In the absence of natural magnetism, optical Fano resonances have so far been based on purely electric effects. In this Letter, we demonstrate that a subwavelength plasmonic metamolecule consisting of four closely spaced gold nanoparticles supports a strong magnetic response coupled to a broad electric resonance. Small structural asymmetries in the assembled nanoring enable the interaction between electric and magnetic modes, leading to the first observation of a magnetic-based Fano scattering resonance at optical frequencies. Our findings are supported by excellent agreement with simulations and analytical calculations, and represent an important step towards the quest for artificial magnetism and negative refractive index metamaterials at optical frequencies.

Using atomically smooth epitaxial silver films, new optical permittivity highlighting significant loss reduction in the visible frequency range is extracted. Largely enhanced propagation distances of surface plasmon polaritons are measured, confirming the low intrinsic loss in silver. The new permittivity is free of extrinsic spectral features associated with grain boundaries and localized plasmons inevitably present in thermally deposited films.

Metasurfaces, the two-dimensional equivalent of metamaterials, are periodic arrays of sub-wavelength engineered inclusions that can locally manipulate and enhance wave–matter interactions, thus providing unprecedented possibilities to realize exotic wave phenomena over a sub-wavelength thickness. In this review, we summarize recent advances in the theoretical modeling, realization and application of optical metasurfaces, outlining their impact on integrated and free-space flatland nanophotonic components. We describe recent developments on the homogenization of periodic metasurfaces with arbitrary inclusion shape and geometry and, on the basis of this description, we revisit recent developments in this area of research, especially focusing on their optical applications for radiation control, lensing, beam shaping and optical communications.

The authors have realized that the calculation shown in the inset of Figure 2c plotted electric fi eld decay, while they had used intensity decay to defi ne propagation distance for the experimental data in the rest of the manuscript. The calculation plot is corrected here to refl ect intensity decay. In the inset of Figure 2c, the graph is replotted with semilog predictions. A plot of the predicted propagation distances using the JC data is also added. The predicted propagation distances at 632nm from all three predictions are now labelled. Some of the values quoted in the text that were based on this calculation were incorrect as a result of this. These values are also corrected here. As the graph in the inset of Figure 2c is also part of the table of contents image, the table of contents image is also corrected. The corrected ToC image -On page 6108; right column; line 7: "intensity" should be added before "propagation distances". CONTENTS

A study of a new amino acid analysis method using 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate as a precolumn derivatization reagent for the analysis of food and feed is described. All amino acids, including methionine sulfone and cysteic acid, were well separated on a liquid chromatographic system using the optimized chromatographic conditions. Salts in food and feed interfered very slightly with the derivatization yields of all amino acids. Several typical agricultural products and animal feeds, including 2 AOAC test samples, were analyzed with the method. The results agreed well with the data generated by using the classical postcolumn method with ion-exchange chromatography. The average relative standard deviations for corn and broiler starter feed were 0.74 and 0.70%, respectively. Good recoveries of all amino acids were demonstrated (average, 101%), even for a sample with a very complex matrix.