VIS-NIR TMOKE enhanced dielectric-metal hybrid structure for high performance dual-channel sensing.

Magneto-plasmon sensors based on the transverse magneto-optical Kerr effect (TMOKE) have been extensively studied in recent years. In this paper, we theoretically propose a hybrid structure composed of a one-dimensional bismuth iron garnet: yttrium iron garnet (BIG: YIG) nanowire arrays and thin film stack, which is grown on an infinite thick silicon wafer. The thin film stack, from top to bottom, consists of the following layers: BIG: YIG, SiO2, and Au. By exciting the magnetic dipole resonance mode between the cylindrical nanowires and the SPP mode on the surface of the Au film, dual-channel sensing has been achieved in both visible and infrared spectra. The results demonstrate that the TMOKE response spectrum of the structure supports ultra-narrow linewidths of 0.03 nm in the visible light range and 1.54 nm in the infrared range. By changing the refractive index of the analyte, the detected sensitivity of the sensor system in visible and infrared bands is 553 nm RIU-1 and 285 nm RIU-1, and the Figure of merit (FOM) can reach up to 69125 RIU-1 and 303 RIU-1, respectively. This work provides a theoretical basis and a feasible approach for the design of dual channel gas sensors.

Large-scale plasmonic nanodisk array as a biosensing platform fabricated by transfer nanoprinting.

Surface plasmon resonance based on nanostructures has been a powerful analytical tool in rapid detection and analysis of biomolecules. However, the fabrication of nanostructure sensors, such as electron beam lithography and focused ion beam milling, has inherent defects as manufacturing cost, complex process flow, and small fabrication area. In this paper, using the transfer nanoprinting approach based on an ultrathin anodic aluminum oxide membrane, a centimeter-scale ordered periodic Ag-ZnS bilayer nanodisk on Au film with a low cost and simple process is fabricated. A surface plasmon polariton Bloch mode from nanodisk arrays is experimentally demonstrated at normal incident of light. The plasmonic platform exhibits an ideal refractive index bulk sensitivity of up to 438 nm/RIU. Furthermore, by using a polyelectrolyte bilayer with well-defined thickness, the surface sensitivity of the biosensing platform is also investigated. The large-scale plasmonic bilayer nanoparticle biosensing platform has broad application prospects in development of low-cost and high-performance biosensing chips.

Enhancement of PPARα-Inhibited Leucine Metabolism-Stimulated ß-Casein Synthesis and Fatty Acid Synthesis in Primary Bovine Mammary Epithelial Cells.

Leucine, a kind of branched-chain amino acid, plays a regulatory role in the milk production of mammalian mammary glands, but its regulatory functions and underlying molecular mechanisms remain unknown. This work showed that a leucine-enriched mixture (LEUem) supplementation increased the levels of milk protein and milk fat synthesis in primary bovine mammary epithelial cells (BMECs). RNA-seq of leucine-treated BMECs indicated alterations in lipid metabolism, translation, ribosomal structure and biogenesis, and inflammatory response signaling pathways. Meanwhile, the supplementation of leucine resulted in mTOR activation and increased the expression of BCKDHA, FASN, ACC, and SCD1. Interestingly, the expression of PPARα was independently correlated with the leucine-supplemented dose. PPARα activated by WY-14643 caused significant suppression of lipogenic genes expression. Furthermore, WY-14643 attenuated leucine-induced ß-casein synthesis and enhanced the level of BCKDHA expression. Moreover, promoter analysis revealed a peroxisome-proliferator-response element (PPRE) site in the bovine BCKDHA promoter, and WY-14643 promoted the recruitment of PPARα onto the BCKDHA promoter. Together, the present data indicate that leucine promotes the synthesis of ß-casein and fatty acid and that PPARα-involved leucine catabolism is the key target.

Merging bound states in the continuum in all-dielectric metasurfaces for ultrahigh-Q resonances.

The concept of symmetry-protected bound states in the continuum (BICs) offers a simple approach to engineer metasurfaces with high-quality (Q) factors. However, traditional designs driven by symmetry-protected BICs require an extremely small perturbation parameter to obtain very large Q factors, complicating fabrication and limiting practical applications. Here, we demonstrate a BIC-driven structure composed of two coupled all-dielectric metasurfaces that enables ultrahigh-Q resonances even at large perturbations. The underlying mechanism enabling this is to merge the symmetry-protected BIC and Fabry-Pérot BIC in the parameter space by tuning the distance between the two metasurfaces, thereby altering the intrinsic radiation behavior of the isolated symmetry-protected BIC. It is found that this simple strategy results in Q factors that are three orders of magnitude higher than those with isolated-BIC configurations. Our approach provides a promising route for designing high-Q BIC nanostructures promising in exciting device applications as sensors and filters.

Self-hybridized exciton-polaritons in thin films of transition metal dichalcogenides for narrowband perfect absorption.

Monolayer direct-band gap transition metal dichalcogenides (TMDCs) have been extensively investigated in the context of light-matter interactions. To reach strong coupling, these studies make use of external optical cavities supporting well-defined resonant modes. However, use of an external cavity might limit the scope of possible applications of such systems. Here, we demonstrate that thin films of TMDCs can themselves serve as high-quality-factor cavities due to the guided optical modes they sustain in the visible and near-infrared ranges. Making use of the prism coupling, we achieve the strong coupling between excitons and guided-mode resonances lying below the light line, and show that the thickness of TMDC membranes can be used to tune and promote photon-exciton interactions within the strong-coupling regime. Additionally, we demonstrate narrowband perfect absorption in thin TMDC films through critical coupling with guided-mode resonances. Our work not only provides a simple and intuitive picture to tame interaction of light and matter in thin TMDC films, but also suggests that these simple systems are a promising platform for realizing polaritonic and optoelectronic devices.

Wedged Fiber Optic Surface Plasmon Resonance Sensor for High-Sensitivity Refractive Index and Temperature Measurements.

Here, we experimentally demonstrate a wedged fiber optic surface plasmon resonance (SPR) sensor enabling high-sensitivity temperature detection. The sensing probe has a geometry with two asymmetrical bevels, with one inclined surface coated with an optically thin film supporting propagating plasmons and the other coated with a reflecting metal film. The angle of incident light can be readily tuned through modifying the beveled angles of the fiber tip, which has a remarkable impact on the refractive index sensitivity of SPR sensors. As a result, we measure a high refractive index sensitivity as large as 8161 nm/RIU in a wide refractive index range of 1.333-1.404 for the optimized sensor. Furthermore, we carry out a temperature-sensitivity measurement by packaging the SPR probe into a capillary filled with n-butanol. This showed a temperature sensitivity reaching up to -3.35 nm/°C in a wide temperature range of 20 °C-100 °C. These experimental results are well in agreement with those obtained from simulations, thus suggesting that our work may be of significance in designing reflective fiber optic SPR sensing probes with modified geometries.

Enhanced light-matter interactions in ultrathin transition-metal-dichalcogenide metasurfaces by magnetic and toroidal dipole bound states in the continuum.

Nonradiating states of light have recently received a lot of attention in nanophotonics owing to their ability to confine and enhance the electromagnetic fields at the nanoscale. Such optical states not only offer a promising way to overcome the problem of losses associated with plasmonic materials, but also constitute an efficient platform for interaction of light and matter. Here, we report the radiationless states in compact, ultrathin transition-metal-dichalcogenide metasurfaces, namely bound states in the continuum (BICs). Through applying the multipole analysis to the BIC-based metasurfaces, we demonstrate that the BICs can be classified as magnetic dipole (MD) and electric toroidal dipole (TD) modes, both of which correspond to the Γ-point symmetry-protected BIC. Due to the large field confinement inside the nanoresonators originating from the BICs, the strong coupling is realized between quasi-BICs and the exciton resonance, showing that the Rabi splitting energy can be up to 134 meV and 162 meV for the MD and TD quasi-BIC, respectively. We reveal that reduction of the effective mode volume is highly responsible for the enhancement of coupling strength. Furthermore, it is demonstrated that a large mode volume can lead to increase of the field leakage, which enables our metasurfaces to find applications in, for instance, label-free sensing based on refractometric detection.

Plasmonic crystals fabricated by nanosphere lithography for advanced biosensing.

Plasmonic nanostructures have attracted wide attention in the past few years for their promising applications such as surface-enhanced spectroscopies, chemical or biosensing, and so on. However, the fabrication of plasmonic nanostructures relies on traditional photolithography methods such as electron beam lithography and focused ion beam lithography, which have inherent shortcomings, such as high fabrication cost and being time-consuming. Here, using the nanosphere lithography approach, we fabricate large-area long-range ordered periodic Au nanohole arrays on an opaque Au substrate. The structure supports spectral-isolation and well-defined plasmonic resonances favorable to spectral monitoring at normal incidence of light. The bulk sensitivity of up to 403 nm/RIU is measured for the plasmon modes. Furthermore, we assess the surface-sensing performance of the system and obtain a near-field decay length of about 240 nm, meaning that it is desirable to detect the biological protein molecules. The suggested plasmonic-sensing platform has broad application prospects in the development of low-cost and high-throughput biosensor chips.

Bound states in the continuum in all-van der Waals photonic crystals: a route enabling electromagnetically induced transparency.

Recent studies have demonstrated that multilayer transition metal dichalcogenides can serve as promising building blocks for creating new kinds of resonant optical nanostructures due to their very high refractive indices. However, most of such studies have focused on excitonic regimes of light-material interaction, while there are few on the low-loss region below the bandgap. Here, we conceptually propose all-van der Waals photonic crystals made of electronically bulk MoS2 and h-BN, designed to operate in the telecom wavelengths. And we demonstrate that, due to extremely low absorption loss and destructive interaction between symmetry-protected and resonance-trapped bound states in the continuum, high-quality factor transmission peaks associated with electromagnetically induced transparency (EIT) are observed, thus rendering our proposed structures highly useful for applications like slow light and optical sensing. Furthermore, EIT-like effects are demonstrated in well-engineered MoS2 nanostructures with broken symmetry. We argue that this work is not only of significance for light harvesting in nanostructured van der Waals materials, but provides also a simple path of constructing classical analogues of EIT using dielectric photonic crystals.

FADS1 overexpression promotes fatty acid synthesis and triacylglycerol accumulation via inhibiting the AMPK/SREBP1 pathway in goat mammary epithelial cells.

Delta-5 desaturase (D5D), encoded by the fatty acid desaturase 1 (FADS1) gene, is a rate-limiting enzyme in polyunsaturated fatty acid (PUFA) synthesis that influences the PUFA levels in milk fat. However, the function and molecular mechanism of FADS1 in milk fat metabolism remain largely unknown. The FADS1 overexpression increased the triglyceride content, lipid droplet size, and expression of genes related to fatty acid de novo synthesis (SREBP1 and ACC), intracellular fatty acid transporters (FABP3 and FABP4) and triacylglycerol synthesis gene (DGAT2). It also significantly promoted the SREBP1 nuclear translocation by inhibiting the AMPK activation. In addition, FADS1 overexpression inhibited cell proliferation and arrested cell cycle at the G1 phase. These findings reveal a novel FADS1-AMPK-SREBP1 pathway regulating milk fat production in the goat mammary gland.

Photonic bound states in the continuum in nanostructured transition metal dichalcogenides for strong photon-exciton coupling.

Optical cavities supporting the optical bound states in the continuum (BICs) with infinite radiative lifetime have recently been widely reported. Here, we theoretically investigate BICs in an ultrathin photonic structure consisting of a multilayer, nanostructured transition metal dichalcogenide (TMD). Using finite element simulations, we demonstrate two distinct groups of BICs, namely symmetry-protected BICs and interference-based BICs, in the photonic system. Under normal incidence, their dispersion can be mediated by altering the grating pitch, which makes it possible to explore the strong coupling of these two photonic modes with the TMD exciton band in the same structure. This work expands not only the library of traditional nanophotonic approaches, but also provides more possibilities for optoelectronic devices toward miniaturization.

Liquid crystal filled dual-channel self-calibration optical-fiber surface plasmon resonance thermometer.

In this paper, we propose and demonstrate a dual-channel self-calibration multimode optical-fiber surface plasmon resonance thermometer. The structure of this thermometer is mainly composed by dual sensing channels, in which one channel is coated with a gold layer surrounded by liquid crystal (LC), and the other is prepared with bilayers of silver and thin indium tin oxide (ITO) layer. The gold channel is the main channel, and the channel of the ITO layer with high refractive index is viewed as a configuration of self-calibration. The experimental results of the system show that the temperature sensitivities are 1.006 nm/°C in the range of 20°C-34°C and 0.058 nm/°C in the range of 35°C-80°C. In particular, at the phase transition temperature 34.5°C of changing from the nematic to the isotropic phase of the LC, the temperature sensitivity shows a step increase of 6.8 nm with a unit temperature change. This structure can be highly advantageous for temperature controlling and alarming in laboratory monitoring and industrial production.

Self-assembly plasmonic metamaterials based on templated annealing for advanced biosensing.

In this paper, we introduce a novel method for the fabrication of self-assembly plasmonic metamaterials by exploiting fluid instabilities of optical thin films. Due to interplay between template reflow and spinodal dewetting, two metal nanoparticles of different sizes are generated on the top mesas of free-standing porous anodic aluminum oxide (AAO) template, which results in the apprearance of double resonant peaks in the extinction spectrum. These two resonant peaks possess refractive index resolution 3.27 × 10-4 and 2.53 × 10-4 RIU, respectively. This optical intensity modulation based plasmonic nanoplatform shows a dramatically surface sensing performance with outstanding detection capacity of biomolecules, because of the very small decay length of electric field at dual-modes. The detection ability for concanavalin A (Con A) demonstrats that the limit of detection of dual-modes reaches as small as 68 and 79 nM, respectively.