We experimentally demonstrate a three-dimensional chiral optical metamaterial that exhibits an asymmetric transmission for forwardly and backwardly propagating linearly polarized light. The observation of this novel effect requires a metamaterial composed of three-dimensional chiral metaatoms without any rotational symmetry. Our analysis is supported by a systematic investigation of the transmission matrices for arbitrarily complex, lossy media that allows deriving a simple criterion for asymmetric transmission in an arbitrary polarization base. Contrary to physical intuition, in general the polarization eigenstates in such three-dimensional and low-symmetry metamaterials do not obey fixed relations and the associated transmission matrices cannot be symmetrized.PACS numbers: XX.XX.XX During the past several years optical metamaterials (MMs) have attracted an enormous interest since they promise to allow for a manipulation of light propagation to a seemingly arbitrary extent. MMs are usually obtained by assembling sub-wavelength unit cell structures called metaatoms. Initial studies on MMs were based on rather simple and highly symmetric metaatoms [1][2][3]. Recently, more and more sophisticated structures were explored in order to achieve customized functionalities like, e.g. a negative refractive index due to chirality [4-6]. Also, a large variety of plasmonic metaatoms were investigated that evoke a huge polarization rotation like gammadions, omega shaped particles or helices [7][8][9]. Studying the characteristics of light propagation in such low-symmetry MMs also revealed unexpected phenomena like asymmetric transmission for circularly polarized light [10][11][12]. Although at first sight this effect of nonreciprocal transmission, to date not observed for linearly polarized light, is counterintuitive, it does not violate Lorentz' reciprocity theorem. This asymmetric transmission of circularly polarized light was demonstrated at so-called planar chiral MMs. Such MMs are composed of metaatoms without structural variation in the principal propagation direction. They preserve symmetry in this direction and are only chiral in the two-dimensional space [13]; thus, strictly speaking, they are intrinsically achiral in three dimensions since the mirror image of a structure is congruent with the structure itself if operated from the backside. The remaining mirroring plane is perpendicular to the propagation direction.In this Letter we theoretically and experimentally demonstrate a novel MM design which breaks the latter symmetry. For the first time our approach reveals that the very structures exhibit asymmetric transmission for linearly polarized light. We emphasize that also in this case the reciprocity theorem is not violated since only reciprocal materials are involved.Prior to any further considerations we concisely discuss the effect of a potential MM substrate that is, after all, in most cases required for fabricating planar MMs. Generally speaking, just this supporting substrate breaks the mirror symmetry for ...

The structure of protein, lipid and water molecules in the crystals represents the functional entity of bR in the purple membrane of the bacteria at atomic resolution. Proton translocation from the Schiff base to the extracellular medium is mediated by a hydrogen-bond network that involves charged residues and water molecules.

By relying on an advanced Jones calculus we analyze the polarization properties of light upon propagation through metamaterial slabs in a comprehensive manner. Based on symmetry considerations, we show that all periodic metamaterials may be divided into five different classes only. It is shown that each class differently affects the polarization of the transmitted light and sustains different eigenmodes. We show how to deduce these five classes from symmetry considerations and provide a simple algorithm that can be applied to decide by measuring transmitted intensities to which class a given metamaterial is belonging to only.

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We show for the first time that a planar metamaterial, an array of coupled metal split-ring resonators with a unit cell lacking mirror symmetry, exhibits asymmetric transmission of terahertz radiation (0.25-2.5 THz) propagating through it in opposite directions. This intriguing effect, that is compatible with Lorentz reciprocity and time-reversal, depends on a directional difference in conversion efficiency of the incident circularly polarized wave into one of opposite handedness, that is only possible in lossy low-symmetry planar chiral metamaterials. We show that asymmetric transmission is linked to excitation of enantiomerically sensitive plasmons, these are induced charge-field excitations that depend on the mutual handedness of incident wave and metamaterial pattern. Various bands of positive, negative and zero phase and group velocities have been identified indicating the opportunity to develop polarization sensitive negative index and slow light media based on such metamaterials.In contrast to three-dimensionally chiral structures (e.g. helices), planar chiral patterns (e.g. flat spirals) have the intriguing property that their sense of twist is reversed for observation from opposite sides. Not only human observers, but also circularly polarized waves incident on opposite sides of a planar chiral structure, see materials of opposite handedness. It has recently been discovered that planar chiral metamaterial patterns can show different levels of total transmission for circularly polarized waves of the same handedness propagating in opposite directions. The effect, which has been detected in microwave [1,2,3,4] and photonic [5,6] metamaterials and plasmonic nanostructures [7], is known as asymmetric transmission. Such asymmetric transmission phenomenon has not yet been observed for terahertz radiation. The terahertz spectral region has tremendous technological importance since many biological materials and substances have molecular vibration frequencies in this regime, making it highly attractive for sensing, material characterization, spectroscopy and biomedical imaging. In spite of intense research activity in this domain over the past decade terahertz radiation has proved to be extremely challenging to detect, measure, propagate and manipulate since electronic and magnetic responses of natural materials die out at these frequencies, thus earning the name of the socalled "terahertz gap". Recently, terahertz metamaterials [8,9,10,11,12,13,14,15,16,17,18] have shown potential for use in the terahertz gap with their fascinating novel properties but the region still suffers from a severe shortage of devices needed for fully exploiting the attractive potential applications of terahertz radiation.In this Letter we report the first experimental observation of asymmetric transmission in the terahertz do- main. We demonstrate a new type of polarization sensitive terahertz metamaterial device showing directionally asymmetric transmission of circularly polarized waves between 0.25 and 2.5 THz. The phenomenon resembl...

The human Plasma Proteome Project pilot phase aims to analyze serum and plasma specimens to elucidate specimen characteristics by various proteomic techniques to ensure sufficient sample quality for the HUPO main phase. We used our proprietary peptidomics technologies to analyze the samples distributed by HUPO. Peptidomics summarizes technologies for visualization, quantitation, and identification of the low-molecular-weight proteome (<15 kDa), the "peptidome." We analyzed all four HUPO specimens (EDTA plasma, citrate plasma, heparin plasma, and serum) from African- and Asian-American donors and compared them to in-house collected Caucasian specimens. One main finding focuses on the most suitable method of plasma specimen collection. Gentle platelet removal from plasma samples is beneficial for improved specificity. Platelet contamination or activation of platelets by low temperature prior to their removal leads to distinct and multiple peptide signals in plasma samples. Two different specimen collection protocols for platelet-poor plasma are recommended. Further emphasis is placed on the differences between plasma and serum on a peptidomic level. A large number of peptides, many of them in rather high abundance, are only present in serum and not detectable in plasma. This ex vivo generation of multiple peptides hampers discovery efforts and is caused by a variety of factors: the release of platelet-derived peptides, other peptides derived from cellular components or the clot, enzymatic activities of coagulation cascades, and other proteases. We conclude that specimen collection is a crucial step for successful peptide biomarker discovery in human blood samples. For analysis of the low-molecular-weight proteome, we recommend the use of platelet-depleted EDTA or citrate plasma.

Quantitative or comparative proteome analysis was initially performed with 2-dimensional gel electrophoresis with the inherent disadvantages of being biased towards certain proteins and being labor intensive. Alternative mass spectrometry-based approaches in conjunction with gel-free protein/peptide separation have been developed in recent years using various stable isotope labeling techniques. Common to all these techniques is the incorporation, biosynthetically or chemically, of a labeling moiety having either a natural isotope distribution of hydrogen, carbon, oxygen, or nitrogen (light form) or being enriched with heavy isotopes like deuterium, 13 C, 18 O, or 15 N, respectively. By mixing equal amounts of a control sample possessing for instance the light form of the label with a heavy-labeled case sample, differentially labeled peptides are detected by mass spectrometric methods and their intensities serve as a means for direct relative protein quantification. While each of the different labeling methods has its advantages and disadvantages, the endoprotease 16 O-to-18 O catalyzed oxygen exchange at the C-terminal carboxylic acid is extremely promising because of the specificity assured by the enzymatic reaction and the labeling of essentially every proteasederived peptide. We show here that this methodology is applicable to complex biological samples such as a subfraction of human plasma. Furthermore, despite the relatively small mass difference of 4 Da between the two labeled forms, corresponding to the exchange of two oxygen atoms by two 18 O isotopes, it is possible to quantify differentially labeled proteins on an ion trap mass spectrometer with a mass resolution of about 2000 in automated data dependent LC-MS/MS acquisition mode. Post column sample deposition on a MALDI target parallel to on-line ESI-MS/MS enables the analysis of the same compounds by means of ESIand MALDI-MS/MS. This has the potential to increase the confidence in the quantification results as well as to increase the sequence coverage of potentially interesting proteins by complementary peptide ionization techniques. Additionally the paired y-ion signals in tandem mass spectra of 16 O/ 18 O-labeled peptide pairs provide a means to confirm automatic protein identification results or even to assist de novo sequencing of yet unknown proteins. (J Am Soc Mass Spectrom 2003, 14, 704 -718)