Search

As a candidate for a rapid detection of biomaterials, terahertz (THz) spectroscopy system can be considered with some advantage in non-destructive, label-free, and non-contact manner. Because protein-ligand binding energy is in the THz range, especially, most important conformational information in molecular interactions can be captured by THz electromagnetic wave. Based on the THz time-domain spectroscopy system, THz nano-metamaterial sensing chips were prepared for great enhancing of detection sensitivity. A metamaterial sensing chip was designed for increasing of absorption cross section of the target sample, related to the transmitted THz near field enhancement via the composition of metamaterial. The measured THz optical properties were then analyzed in terms of refractive index and absorption coefficient, and compared with simulation results. Also, virus quantification regarding various concentrations of the viruses was performed, showing a clear linearity. The proposed sensitive and selective THz detection method can provide abundant information of detected biomaterials to help deep understanding of fundamental optical characteristics of them, suggesting rapid diagnosis way especially useful for such dangerous and time-sensitive target biomaterials.

We report an optically patternable metamaterial (OPM) for ultraviolet nanolithography below the diffraction limit. The OPM features monolayered silver nanoislands embedded within a photosensitive polymer by using spin-coating of an ultrathin polymer, oblique angle deposition, and solid-state embedment of silver nanoislands. This unique configuration simultaneously exhibits both negative effective permittivity and high image contrast in the ultraviolet range, which enables the surface plasmon excitation for the clear photolithographic definition of minimum feature size of 70 nm (≲ λ/5) beyond the near-field zone. This new metamaterial provides a new class of photoresist for ultraviolet nanolithography below the diffraction limit.

Nanostructured copper sulfides, promising earth-abundant p-type semiconductors, have found applications in a wide range of fields due to their versatility, tunable low bandgap, and environmental sustainability. The synthesis of hexagonal Cu 7 S 4 @Au 2 S@Au nanorings exhibiting plasmon enhanced emissions at the direct bandgap is reported. The synthesized Cu 7 S 4 @Au 2 S@Au nanorings show greatly enhanced absorption and emission by local plasmons compared to pure copper sulfide nanoparticles., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Molecular recognition and discrimination of carbohydrates are important because carbohydrates perform essential roles in most living organisms for energy metabolism and cell-to-cell communication. Nevertheless, it is difficult to identify or distinguish various carbohydrate molecules owing to the lack of a significant distinction in the physical or chemical characteristics. Although there has been considerable effort to develop a sensing platform for individual carbohydrates selectively using chemical receptors or an ensemble array, their detection and discrimination limits have been as high in the millimolar concentration range. Here we show a highly sensitive and selective detection method for the discrimination of carbohydrate molecules using nano-slot-antenna array-based sensing chips which operate in the terahertz (THz) frequency range (0.5-2.5 THz). This THz metamaterial sensing tool recognizes various types of carbohydrate molecules over a wide range of molecular concentrations. Strongly localized and enhanced terahertz transmission by nano-antennas can effectively increase the molecular absorption cross sections, thereby enabling the detection of these molecules even at low concentrations. We verified the performance of nano-antenna sensing chip by both THz spectra and images of transmittance. Screening and identification of various carbohydrates can be applied to test even real market beverages with a high sensitivity and selectivity.

The Purcell effect explains the modification of the spontaneous decay rate of quantum emitters in a resonant cavity. For quantum emitters such as chiral molecules, however, the cavity modification of the spontaneous decay rate has been little known. Here we extend Purcell's work to the chiral light-matter interaction in optical resonators and find the differential spontaneous decay rate of chiral molecules coupled to left and right circularly polarized resonator modes. We determine the chiral Purcell factor, which characterizes the ability of optical resonators to enhance chiroptical signals, by the quality factor and the chiral mode volume of a resonator, representing, respectively, the temporal confinement of light and the spatial confinement of the helicity of light. We show that the chiral Purcell effect can be applied to chiroptical spectroscopy. Specifically, we propose a realistic scheme to achieve resonator enhanced chiroptical spectroscopy that uses the double fishnet structure as a nanoscale cuvette supporting the chiral Purcell effect.

Sensing and manipulating targets hidden under scattering media are universal problems that take place in applications ranging from deep-tissue optical imaging to laser surgery. A major issue in these applications is the shallow light penetration caused by multiple scattering that reflects most of incident light. Although advances have been made to eliminate image distortion by a scattering medium, dealing with the light reflection has remained unchallenged. Here we present a method to minimize reflected intensity by finding and coupling light into the anti-reflection modes of a scattering medium. In doing so, we achieved more than a factor of 3 increase in light penetration. Our method of controlling reflected waves makes it readily applicable to in vivo applications in which detector sensors can only be positioned at the same side of illumination and will therefore lay the foundation of advancing the working depth of many existing optical imaging and treatment technologies.

Metals can transmit light by tunnelling when they possess skin-depth thickness. Tunnelling can be resonantly enhanced if resonators are added to each side of a metal film, such as additional dielectric layers or periodic structures on a metal surface. Here we show that, even with no additional resonators, tunnelling resonance can arise if the metal film is confined and fractionally thin. In a slit waveguide filled with a negative permittivity metallic slab of thickness L, resonance is shown to arise at fractional thicknesses (L = Const./m; m = 1,2,3,…) by the excitation of 'vortex plasmons'. We experimentally demonstrate fractional tunnelling resonance and vortex plasmons using microwave and negative permittivity metamaterials. The measured spectral peaks of the fractional tunnelling resonance and modes of the vortex plasmons agree with theoretical predictions. Fractional tunnelling resonance and vortex plasmons open new perspectives in resonance physics and promise potential applications in nanotechnology.

Reducing unwanted reflections through impedance matching, called anti-reflection, has long been an important challenge in optics and electrical engineering. Beyond trial and error optimization, however, a systematic way to realize anti-reflection is still absent. Here, we report the discovery of an analytic solution to this long standing problem. For electromagnetic waves, we find the graded permittivity and permeability that completely remove any given impedance mismatch. We demonstrate that perfect broadband anti-reflection is possible when a dispersive, graded refractive index medium is used for the impedance-matching layer. We also present a design rule for the ultra-thin anti-reflection coating which we confirm experimentally by showing the anti-reflection behavior of an exemplary λ/25-thick coating made of metamaterials. This work opens a new path to anti-reflection applications in optoelectronic device, transmission line and stealth technologies.

Fabricating well-defined and highly reproducible platforms for surface-enhanced Raman scattering (SERS) is very important in developing practical SERS sensors. We report a novel SERS platform composed of a single metallic nanowire (NW) on a metallic film. Optical excitation of this novel sandwich nanostructure provides a line of SERS hot spots (a SERS hot line) at the gap between the NW and the film. This single nanowire on a film (SNOF) architecture can be easily fabricated, and the position of hot spots can be conveniently located in situ by using an optical microscope during the SERS measurement. We show that high-quality SERS spectra from benzenethiol, brilliant cresyl blue, and single-stranded DNA can be obtained on a SNOF with reliable reproducibility, good time stability, and excellent sensitivity, and thus, SNOFs can potentially be employed as effective SERS sensors for label-free biomolecule detection. We also report detailed studies of polarization- and material-dependent SERS enhancement of the SNOF structure.