Plasmon hybridization in stacked double gold nanorings with reduced symmetry

Uniform Gold Nanostructure Formation via Weakly Adsorbed Gold Films and Thermal Annealing for Reliable Localized Surface Plasmon Resonance-Based Detection of DNase-I

Deoxyribonuclease-I (DNase-I), a representative endonuclease, is an important biomarker for the diagnosis of infectious diseases and cancer progression. However, enzymatic activity decreases rapidly ex vivo, which highlights the need for precise on-site detection of DNase-I. Here, a localized surface plasmon resonance (LSPR) biosensor that enables the simple and rapid detection of DNase-I is reported. Moreover, a novel technique named electrochemical deposition and mild thermal annealing (EDMIT) is applied to overcome signal variations. By taking advantage of the low adhesion of gold clusters on indium tin oxide substrates, both the uniformity and sphericity of gold nanoparticles are increased under mild thermal annealing conditions via coalescence and Ostwald ripening. This ultimately results in an approximately 15-fold decrease in LSPR signal variations. The linear range of the fabricated sensor is 20-1000 ng mL-1 with a limit of detection (LOD) of 127.25 pg mL-1 , as demonstrated by spectral absorbance analyses. The fabricated LSPR sensor stably measured DNase-I concentrations from samples collected from both an inflammatory bowel disease (IBD) mouse model, as well as human patients with severe COVID-19 symptoms. Therefore, the proposed LSPR sensor fabricated via the EDMIT method can be used for early diagnosis of other infectious diseases.

Advancements in fractal plasmonics: structures, optical properties, and applications

Fractal nanostructures exhibit optical properties that span the visible to far-infrared and are emerging as exciting structures for plasmon-mediated applications.

Periodic arrays of metal nanorings and nanocrescents fabricated by a scalable colloidal templating approach

Here, we report a scalable bottom-up approach for fabricating periodic arrays of metal nanorings and nanocrescents. Wafer-scale monolayer silica colloidal crystals with an unusual non-close-packed structure prepared by a simple and rapid spin-coating technology are used as both etching and shadowing masks to create nanoring-shaped trenches in between templated polymer posts and sacrificial nanoholes. Directional deposition of metals in the trenches followed by liftoff of the polymer posts and the sacrificial nanoholes results in forming ordered metal nanorings. The inner and outer radii of the final nanorings are determined by the sizes of the templated polymer posts and the silica microspheres which can be easily adjusted by tuning the spin-coating and templating conditions. Most importantly, by simply controlling the tilt angle of the substrate toward the directional metal beams, continuous geometric transition from concentric nanorings to eccentric nanorings to nanocrescents can be achieved. This new colloidal templating approach is compatible with standard semiconductor microfabrication, promising for mass-production and on-chip integration of periodic nanorings and nanocrescents for a wide spectrum of technological applications ranging from nanooptical devices and ultrasensitive biosensing to magnetic memories and logic circuits.

Symmetry breaking and optical negative index of closed nanorings

Metamaterials have extraordinary abilities, such as imaging beyond the diffraction limit and invisibility. Many metamaterials are based on split-ring structures, however, like atomic orbital currents, it has long been believed that closed rings cannot produce negative refractive index. Here we report a low-loss and polarization-independent negative-index metamaterial made solely of closed metallic nanorings. Using symmetry breaking that negatively couples the discrete nanorings, we measured negative phase delay in our composite 'chess metamaterial'. The formation of an ultra-broad Fano-resonance-induced optical negative-index band, spanning wavelengths from 1.3 to 2.3 μm, is experimentally observed in this structure. This discrete and mono-particle negative-index approach opens exciting avenues towards symmetry-controlled topological nanophotonics with on-demand linear and nonlinear responses.

Colloidal self-assembly meets nanofabrication: from two-dimensional colloidal crystals to nanostructure arrays

Self-assembly of colloidal microspheres or nanospheres is an effective strategy for fabrication of ordered nanostructures. By combination of colloidal self-assembly with nanofabrication techniques, two-dimensional (2D) colloidal crystals have been employed as masks or templates for evaporation, deposition, etching, and imprinting, etc. These methods are defined as "colloidal lithography", which is now recognized as a facile, inexpensive, and repeatable nanofabrication technique. This paper presents an overview of 2D colloidal crystals and nanostructure arrays fabricated by colloidal lithography. First, different methods for fabricating self-assembled 2D colloidal crystals and complex 2D colloidal crystal structures are summarized. After that, according to the nanofabrication strategy employed in colloidal lithography, related works are reviewed as colloidal-crystal-assisted evaporation, deposition, etching, imprinting, and dewetting, respectively.

High sensitivity and large field enhancement of symmetry broken Au nanorings: effect of multipolar plasmon resonance and propagation

The multipolar plasmon resonance and propagation of Au nanorings with symmetry broken were analyzed by using DDA and FDTD methods. Based on the multipolar plasmon resonance and propagation, we proposed ring-nanosensors with high sensitivities and optical ringnanoantennas with large local field enhancements. We revealed that the refractive index sensitivities of split nanorings are about 100% larger than those of perfect nanorings with same size; the local field intensity enhancement of split nanoring with three gaps has increased by 37% than that of dipole antennas.