Oxidative stress plays a key role in the pathogenesis of diabetic myopathy. Celastrol provides a wide range of health benefits, including antioxidant, anti-inflammatory and antitumor effects. We hypothesized that celastrol may exert an antioxidant effect in the skeletal muscle of diabetic rats. In the present study, MnSOD activity was determined by spectrophotometry. The protein levels were evaluated by western blot analysis and mRNA content was quantified by RT-qPCR. We firstly found that the levels of AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor coactivator 1α (PGC1α), silent mating-type information regulation 2 homolog 3 (SIRT3) and manganese superoxide dismutase (MnSOD) were all decreased in the skeletal muscle of diabetic patients. Male rats with diabetes were also treated with the vehicle or with celastrol at 1, 3 and 6 mg/kg/day for 8 weeks. The administration of celastrol at 3 and 6 mg/kg attenuated the deterioration of skeletal muscle, as shown by histological analysis, decreased the malondialdehyde (MDA) level and increased the glutathione (GSH) level assayed by enzyme-linked immunosorbent assay (ELISA) method. It also enhanced the enzyme activity and increased the expression of MnSOD, and increased the AMPK phosphorylation level, as well as PGC1α and Sirt3 expression. The findings of our study suggest that the expression of AMPK, PGC1α, SIRT3 and MnSOD are decreased in the skeletal muscle of diabetic patients. Celastrol exerted antioxidant effects on skeletal muscle partly by regulating the AMPK-PGC1α-SIRT3 signaling pathway.

Two types of plasmonic metamaterial absorbers (PMAs) formed from patterned all-dielectric resonators are designed and demonstrated experimentally in the terahertz (THz) range. Both PMAs use a simple grating design on highly N-doped silicon. The first shows broadband absorption with near-perfect peak absorbance at 1.45 THz and a bandwidth of 1.05 THz for 90% absorbance, while the second is a dual-band absorber. Experiments show that the second absorber has two distinct absorption peaks at 0.96 and 1.92 THz with absorption rates of 99.7 and 99.9%, respectively. A fundamental cavity mode coupled to coaxial surface plasmon polaritons is responsible for the characteristics of both PMAs. Additionally, the optically tunable responses of these all-dielectric absorbers demonstrate that the absorption behavior can be modified. The quality factor (Q) values of the dual-band resonances are 4.6 and 7.8 times larger than those of the broadband PMAs, respectively, which leads to a better sensing performance. As an example, the two proposed PMAs act as high-sensitivity sensors and demonstrate considerable potential for chlorpyrifos detection. These results show that these PMAs can be used as sensors that can detect the presence of trace pesticides in adsorption analyses, among other practical applications.

With the rapid advances in functional optoelectronics, the research on carbon-based materials and devices has become increasingly important at the terahertz frequency range owing to their advantages in terms of weight, cost, and freely bendable flexibility. Here, we report an effective material and device design for a terahertz plasmonic metasurface sensor (PMS) based on carbon nanotubes (CNTs). CNT metasurfaces based on silicon wafers have been prepared and obvious resonant transmission peaks are observed experimentally. The enhanced resonant peaks of transmission spectra are attributed to the surface plasmon polariton resonance, and the transmission peaks are further well explained by the Fano model. Furthermore, the different concentration gradients of pesticides (2,4-dichlorophenoxyacetic and chlorpyrifos solutions) have been detected by the designed PMSs, showing the lowest detection mass of 10 ng and the sensitivities of 1.38 × 10–2/ppm and 2.0 × 10–3/ppm, respectively. Good linear relationships between transmission amplitude and pesticide concentration and acceptable reliability and stability have been obtained. These materials and device strategies provide opportunities for novel terahertz functional devices such as sensors, detectors, and wearable terahertz imagers.

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Perfect metasurface absorbers play a significant role in imaging, detecting, and manipulating terahertz radiation. We utilize all-dielectric gratings to demonstrate tunable multi-band absorption in the terahertz region. Simulation reveals quad-band and tri-band absorption from 0.2 to 2.5 THz for different grating depths. Coupled-mode theory can explain the absorption phenomenon. The absorption amplitude can be precisely controlled by changing the pump beam fluence. Furthermore, the resonant frequency is sensitive to the medium’s refractive index, suggesting the absorber may be of great potential in the sensor detection field. The experimental results exhibit a high detectivity of pesticides.