Electrical detection of trace zinc ions with an extended gate-AlGaN/GaN high electron mobility sensor.

In this report, we have developed a high sensitivity zinc ion (Zn2+) detection method based on a Schiff base functionalized extended gate (EG)-AlGaN/GaN high electron mobility (HEMT) sensor. The complexation reaction between the Schiff base and the zinc ions would cause surface potential change on the extended gate, and achieve the purpose of zinc ion detection. Compared with conventional methods, the Schiff base functionalized EG-AlGaN/GaN high electron mobility sensor showed a rapid response (less than 10 seconds) and the limit of detection (LOD) was 1 fM. At the same time, the real-time detection of zinc ion concentration ranging from 1 fM to 1 µM showed good linearity (R2 = 0.9962). These results indicated that it provides a promising real-time detection method for trace-free zinc ion trace detection.

Observation of terahertz plasmon and plasmon-polariton splitting in a grating-coupled AlGaN/GaN heterostructure.

Plasmon in two-dimensional electron gas (2DEG) has long been considered as a promising active medium for terahertz emitters and detectors. However, the efficiency of terahertz plasmonic devices is severely limited by the high damping rate of plasma wave in solid state. In addition to the enhancement of plasmon lifetime by using 2DEGs with higher carrier mobility, engineering on the boundary condition and electromagnetic environment of plasmon cavity helps to preserve the plasmon states. Here we report on terahertz reflection spectroscopy of plasmon states in a grating-coupled AlGaN/GaN-2DEG plasmonic device at 7 K in equilibrium with ambient blackbody irradiation. Localized plasmon states and plasmon-polariton states were observed when the core plasmonic device is integrated with a silicon lens and when it is embedded in a terahertz Fabry-Pérot cavity, respectively. Simulation results including the reflection spectra and total reflection power agree well with the measured results. The Rabi splitting is found to be inversely proportional to the resonance frequency, and follows a linear relation with the square root of the sheet electron density. A normalized coupling ratio, ΩRω0≈0.13, is achieved between the Rabi splitting ΩR and the resonance frequency ω0. The coupling ratio could be further increased to allow for ultrastrong coupling between terahertz photons and plasmons.

Molecular gated-AlGaN/GaN high electron mobility transistor for pH detection.

A molecular gated-AlGaN/GaN high electron mobility transistor has been developed for pH detection. The sensing surface of the sensor was modified with 3-aminopropyltriethoxysilane to provide amphoteric amine groups, which would play the role of receptors for pH detection. On modification with 3-aminopropyltriethoxysilane, the transistor exhibits good chemical stability in hydrochloric acid solution and is sensitive for pH detection. Thus, our molecular gated-AlGaN/GaN high electron mobility transistor acheived good electrical performances such as chemical stability (remained stable in hydrochloric acid solution), good sensitivity (37.17 µA/pH) and low hysteresis. The results indicate a promising future for high-quality sensors for pH detection.

Microlens array expander with an improved light intensity distribution throughperiodic submicro-scale filling for near-eye displays.

A type of microlens array (MLA) expander with an improved light intensity distribution (LID) is designed and fabricated through submicro-scale filling, which could be applied to near-eye displays. Through the reflection of a 0.8-µm-wide metal filling, the light field is split and superimposed only through the microlens. The bright spot at the center of the LID is effectively eliminated. The results demonstrate that the expanded numerical aperture (NA) and focal length are about 0.38 and 19 µm, respectively, and the error in the radius of curvature is within 5% between the experimental and designed values. An improved image quality with an 80% brightness uniformity for an area of 22×22 mm2 is realized through the MLA. Compared with the MLA based on thermal reflow, the largest NA is obtained with the smallest focal length and gap. The experimental LID is consistent with that obtained by a theoretical simulation.

Synthesis and Properties of two CuI Complexes Involving Tetrathia-fulvalene-Fused Phenanthroline Ligand.

Two CuI complexes based on the π-conjugated tetrathiafulvalene-annulated phenanthroline ligands (TTF-Phen, L1 and L2), [CuI(Xantphos)(L1)]BF4 (1, Xantphos = 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene) and [CuI(Binap)(L2)]BF4 (2, Binap = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl), have been synthesized. They have been fully characterized, and their photophysical and electrochemical properties are reported together with those of L1 and L2 for comparison. Both CuI complexes show metal-to-ligand charge transfer (MLCT) absorption bands, whereas the 3MLCT luminescence is strongly quenched.

Preoperative Detection and Intraoperative Visualization of Brain Tumors for More Precise Surgery: A New Dual-Modality MRI and NIR Nanoprobe.

In clinical practice, it is difficult to identify tumor margins during brain surgery due to its inherent infiltrative character. Herein, a unique dual-modality nanoprobe (Gd-DOTA-Ag2S QDs, referred as Gd-Ag2S nanoprobe) is reported, which integrates advantages of the deep tissue penetration of enhanced magnetic resonance (MR) imaging of Gd and the high signal-to-noise ratio and high spatiotemporal resolution of fluorescence imaging in the second near-infrared window (NIR-II) of Ag2S quantum dots (QDs). Due to the abundant tumor angiogenesis and the enhanced permeability and retention effect in the tumor, a brain tumor (U87MG) in a mouse model is clearly delineated in situ with the help of the Gd assisted T1 MR imaging and the intraoperative resection of the tumor is precisely accomplished under the guidance of NIR-II fluorescence imaging of Ag2S QDs after intravenous injection of Gd-Ag2S nanoprobe. Additionally, no histologic changes are observed in the main organs of the mouse after administration of Gd-Ag2S nanoprobe for 1 month, indicating the high biocompatibility of the nanoprobe. We expect that such a novel "Detection and Operation" strategy based on Gd-Ag2S nanoprobe is promising in future clinical applications.

Resolution enhancement of random adsorbed single-molecule localization based on surface plasmon resonance illumination.

Single-molecule localization (SML) is a powerful tool to overcome the diffraction limit in optical imaging, because the fluorescence emitted by single molecules can be observed with nanometer accuracy when the optical background and associated noise are made sufficiently small. Random adsorbed SML has been successfully demonstrated for superresolution imaging on metal surfaces. To optimize the random adsorbed SML, we developed a new illumination method based on surface plasmon resonance (SPR). The enhancement of the fluorescence signal and the reduction of background noise were achieved simultaneously. A high localization resolution of 15 nm was demonstrated with this new SPR illumination system.

A Self-Powered Transparent Photodetector Based on Detached Vertical (In,Ga)N Nanowires with 360° Omnidirectional Detection for Underwater Wireless Optical Communication.

Underwater wireless optical communication (UWOC) is a wireless communication technology using visible light to transmit data in an underwater environment, which has wide applications. Based on lift-off (In,Ga)N nanowires, this work has proposed and successfully demonstrated a self-powered photoelectrochemical (PEC) photodetector (PD) with excellent transmissivity. The transparent functionality of the PD is critical for 360° omnidirectional underwater detection, which was realized by detaching the (In,Ga)N nanowires from the opaque epitaxial substrates to the indium tin oxide (ITO)/glass. It was also found that the insulating SiO2 layer can enhance the photocurrent by about 12 times. The core-shell structure of the nanowires is beneficial for generating carriers and contributing to the photocurrent. Furthermore, a communication system with ASCII code is set to demonstrate the PD detection in underwater communication. This work paves an effective way to develop 360° omnidirectional PDs for the wide applications in UWOC system and underwater photodetection.

Dual-wavelength visible photodetector based on vertical (In,Ga)N nanowires grown by molecular beam epitaxy.

Due to the wide applications of blue and red photodetectors, dual-wavelength (blue/red) photodetectors are promising for future markets. In this work, a dual-wavelength photodetector based on vertical (In,Ga)N nanowires and graphene has been fabricated successfully. By using the transparent graphene, both blue and red responses can be clearly detected. The rise time of response can reach 3.5 ms. Furthermore, the underlying mechanism of double responses has also been analyzed. The main reason contributing to the dual-wavelength response could be the different diameters of nanowires, leading to different In components within (In,Ga)N sections.

Highly sensitive AlGaN/GaN HEMT biosensors using an ethanolamine modification strategy for bioassay applications.

In this paper, we propose a highly efficient surface modification strategy on an AlGaN/GaN high electron mobility transistor (HEMT), where ethanolamine (EA) was utilized to functionalize the surface of GaN and provided amphoteric amine groups for probe molecular immobilization for bioassay application. The molecular gated-AlGaN/GaN HEMT was utilized for pH and prostate-specific antigen (PSA) detection to verify its performance as a biosensor. Benefitting from the high coating quality on the GaN surface, the performance of our biosensor is drastically improved compared to other AlGaN/GaN HEMT based pH and PSA biosensors reported before. Our molecular gated-AlGaN/GaN HEMT biosensor has achieved good static electrical performance for pH sensing, such as high sensitivity, good linearity and chemical stability. Moreover, after further immobilization of PSA antibody onto the EA aminated GaN surface, the limit of detection (LOD) for PSA detection is as low as 1 fg mL-1 in PBS buffer, which has reached an at least two orders of magnitude decrease compared to any other AlGaN/GaN HEMT based PSA biosensor reported before. And the sensitivity of our PSA biosensor has achieved a substantial increase, reaching up to 2.04% for 100 ng mL-1. The measurements of pH and PSA utilizing the EA modified AlGaN/GaN HEMT biosensor indicate that the surface modification strategy on the GaN proposed in this paper can effectively improve the performance of the AlGaN/GaN HEMT based biosensor, which demonstrates a promising application prospect in the AlGaN/GaN HEMT based biological detection field.

New Iridium Complex Coordinated with Tetrathiafulvalene Substituted Triazole-pyridine Ligand: Synthesis, Photophysical and Electrochemical Properties.

A new iridium(III) complex based on the triazole-pyridine ligand with tetrathiafulvalene unit, [Ir(ppy)2(L)]PF6 (1), has been synthesized and structurally characterized. The absorption spectra, luminescent spectra and electrochemical behaviors of L and 1 have been investigated. Complex 1 is found to be emissive at room temperature with maxima at 481 and 510 nm. The broad and structured emission bands are suggested a mixing of 3LC (3π-π*) and 3CT (3MLCT) excited states. The influence of iridium ion coordination on the redox properties of the TTF has also been investigated by cyclic voltammetry.

Pancharatnam-Berry Phase Induced Spin-Selective Transmission in Herringbone Dielectric Metamaterials.

A dielectric metamaterial approach for achieving spin-selective transmission of electromagnetic waves is proposed. The design is based on spin-controlled constructive or destructive interference between propagating phase and Pancharatnam-Berry phase. The dielectric metamaterial, consisting of monolithic silicon herringbone structures, exhibits a broadband operation in the terahertz regime.

Charge gradient-induced on-surface growth of ultralarge single-crystalline Ag nanomembranes for long surface plasmon propagation.

A facile strategy for the fabrication of ultralarge (edge length >50 µm), single-crystalline Ag nanomembranes is reported in this work. The Ag nanomembrane with an atomically smooth surface demonstrates a much longer surface plasmonic propagation length as compared to vacuum-deposited polycrystalline Ag film, representing superior plasmonic properties.

In vivo real-time visualization of tissue blood flow and angiogenesis using Ag2S quantum dots in the NIR-II window.

Improving the tissue penetration depth and spatial resolution of fluorescence-based optical nanoprobes remains a grand challenge for their practical applications in in vivo imaging, due to the scattering and absorption and endogenous autofluorescence of living tissues. Here, we present that Ag2S quantum dots (QDs), containing no toxic ions, exhibiting long circulation time and high stability, act as a new kind of fluorescent probes in the second near-infrared window (NIR-II, 1000-1350 nm) which enable in vivo monitoring of lymphatic drainage and vascular networks with deep tissue penetration and high spatial and temporal resolution. In addition, NIR-II fluorescence imaging with Ag2S QDs provide ultrahigh spatial resolution (~40 µm) that permits us to track angiogenesis mediated by a tiny tumor (2-3 mm in diameter) in vivo. Our results indicate that Ag2S QDs are promising NIR-II fluorescent nanoprobes that could be useful in surgical treatments such as sentinel lymph node (SLN) dissection as well in assessment of blood supply in tissues and organs and screening of anti-angiogenic drugs.

Super-resolution imaging by random adsorbed molecule probes.

Single molecule localization (SML) is a powerful tool to measure the position and trajectory of molecules in numerous systems, with nanometer accuracy. This technique has been recently utilized to overcome the diffraction limit in optical imaging. So far, super-resolution imaging by SML was demonstrated using photoactivable or photoswitchable fluorophores, as well as diffusive fluorophore probes in solution. All these methods, however, rely on special fluorophore or object properties. In this Letter, we propose and demonstrate a new super-resolution technique attainable for a bio/dielectric structure on a metal substrate. A sub-diffraction-limited image is obtained by randomly adsorbed fluorescent probe molecules on a liquid-solid interface, while the metal substrate, quenching the unwanted fluorescent signal, provides a significantly enhanced imaging contrast. As this approach does not use specific stain techniques, it can be readily applied to general dielectric objects, such as nanopatterned photoresist, inorganic nanowires, subcellular structures, etc.