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Platinum-palladium (PtPd) alloy catalysts with high durability are viable substituents to commercial Pt/C for proton exchange membrane fuel cells (PEMFCs). Herein, a facile approach for gram-scale preparation of Pt

By combining the excellent surface-enhanced Raman scattering (SERS) activity of Ag nanoparticles (AgNPs), the well-separated pyramid arrays of the pyramidal silicon (PSi) and unique physical/chemical properties of molybdenum disulfide (MoS2), the MoS2@AgNPs@PSi substrate shows high performance in terms of sensitivity, uniformity, reproducibility and stability. By using rhodamine 6G (R6G) as probe molecule, the SERS results indicate that the MoS2@AgNPs@PSi substrate is superior to the AgNPs@PSi, AgA@PSi (the second annealing of the AgNPs@PSi) and the MoS2@AgNPs@flat-Si substrate. The MoS2@AgNPs@PSi substrate also shows the reasonable linear response between the Raman intensity and R6G concentration. The maximum deviations of SERS intensities from 20 positions on a same MoS2@AgNPs@PSi substrate and 10 MoS2@AgNPs@PSi substrates in different batches are less than 7.6% and 9%, respectively, revealing the excellent uniformity and reproducibility of the substrate. Besides, the SERS substrate has a good stability, the Raman intensity of the MoS2@AgNPs@PSi substrate only drop by 15% in a month. The corresponding experimental and theoretical results suggest that our proposed MoS2@AgNPs@PSi substrate is expected to offer a new and practical way to accelerate the development of label-free SERS detection.

In this work, we demonstrated facile and low-cost fabrication of highly sensitive SERS substrates via replacement reaction by immersing Cu foils into a AgNO 3 solution. Different morphologies of Ag nanostructures were observed on the substrate surface by controlling the reaction time. The growth mechanism of Ag nanostructures on the Cu substrates was also analyzed based on the nanostructure evolution. The Ag-Cu substrates showed optimum SERS enhancement at certain reaction time, and the minimum detected concentration of Rhodamine 6G is as low as 10 −13 M. The easy and low-cost fabrication makes the Ag-Cu SERS substrates promising for rapid, sensitive detection of targeted analytes, such as biomolecules, pollutants, and explosives in the environment.

In the experiment of combined navigation filtering using wavelet neural network, the initial parameters of the network have the influence of randomness on network convergence and navigation accuracy. A combined navigation filtering method based on wavelet neural network optimized by mind evolution algorithm is proposed. Firstly, the efficient global search ability of the mind evolution algorithm was used to quickly and accurately obtain the initial parameters of the appropriate wavelet neural network, and then the optimized wavelet neural network was applied to directly predict the position and velocity error data. This method is different from the traditional filtering method, while avoiding the drawbacks of the neural network. The simulation experiments with wavelet neural network and GA-wavelet network were carried out. The results show that the proposed method can effectively improve the accuracy of the integrated navigation system and provide a feasible path for combined navigation filtering.

An evanescent wave absorption (EWA) sensor based tapered plastic optical fiber (TPOF) coated with monolayer graphene film for ethanol molecules detection is demonstrated in this study. The continuous and monolayer graphene films were grown on a Cu foil by using chemical vapor deposition (CVD) technology. Polymethyl methacrylate (PMMA) was used as the carrier to support the transfer of graphene from Cu foil to the skinless tapered optical fiber core. The accuracy of the TPOF sensor with graphene (G-TPOF sensor) is much higher than that without graphene (TPOF sensor), which can be attributed to the molecules enriched on the surface of graphene. The absorbance (A) and the concentrations of ethanol solution show an excellent proportional relationship in a range of 0–100%. The dynamic response of the G-TPOF sensor has shown strong reversibility, repeatability and stability at room temperature. The response time and recovery time of the G-TPOF sensor for different concentrations are all less than 30 s. Beyond that, we selected the Chinese liquor as the analyte, and the results are consistent with the concentration-list obtained in the experiment.

An evanescent wave absorption (EWA) sensor based on tapered multimode fiber (TMMF) coated with monolayer graphene film for the detection of double-stranded DNA (DS-DNA) is investigated in this work. The TMMF is a silica multimode fiber (nominally at 62.5 μm), which was tapered to symmetric taper with waist diameters of ~30 μm and total length of ~3 mm. Monolayer graphene film was grown on a copper foil via chemical vapor deposition (CVD) technology and transferred onto skinless tapered fiber core via dry transfer technology. All the components of the sensor are coupled together by fusion splicer in order to eliminate the external disturbance. DS-DNA is created by the assembly of two relatively complemented oligonucleotides. The measurements are obtained by using a spectrometer in the optical wavelength range of 400–900 nm. With the increase of DS-DNA concentration, the output light intensity (OPLI) arisen an obvious attenuation. Importantly, the absorbance (A) and the DS-DNA concentrations shown a reasonable linear variation in a wide range of 5–400 μM. Through a series of comparison, the accuracy of TMMF sensor with graphene (G-TMMF) is much better than that without graphene (TMMF), which can be attributed to the molecular enrichment of graphene by π–π stacking.

A facile fabrication of high-quality and large-area tungsten disulfide (WS2) layers is demonstrated using a thermal decomposition of tetrathiotungstates ((NH4)2WS4) with two annealing process. During synthesis, the first annealing step is utilized to achieve lateral epitaxial growth of the WS2 and create seamless and large-area WS2 film. The second annealing step can offer an S-rich and high temperature condition, which is beneficial for the high quality of the WS2 film. Scanning electron microscopy, Raman spectroscopy and atomic force microscopy confirm the presence of large-area and high-quality WS2 film. The crucial role of the S, H2 and the effect of the temperature during the experiment are also investigated. Furthermore, the potential application of the prepared WS2 as a substrate for Raman enhancement is first discussed using R6G molecules as probe molecule.

In this work, we present a novel optical fiber SERS (OF-SERS) sensor based on a sandwich structure of GO/AgNPs/rGO. Rhodamine 6G (R6G) was selected as the probe molecule to compare the SERS ability of different films composed of the bare optical fiber, GO, AgNPs, rGO/AgNPs, GO/AgNPs and GO/AgNPs/rGO. Raman spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were performed to characterize the sandwich structure hybrid films. Besides, the stability of GO/AgNPs and GO/AgNPs/rGO was compared on the optical fiber end face. The OF-SERS sensor based GO/AgNPs/rGO hybrid films had stable SERS performance even when exposed to ambient conditions for a prolonged time of 30 days. This work may provide a new strategy for an efficient stable OF-SERS sensor due to its simplicity, low-cost and long-term stability.

In this paper, we designed a 2D distance and rotation angle plasmon ruler based on Fano resonance of a trimer nanostructure, which consists of a concentric square nanoring–disk and an outside nanorod (CSRDR). The Fano dip energy and depth are fairly sensitive to the nanometer-scale displacements and rotations, when the nanodisk moves in all direction and rotates around its center. When the symmetry of the nanoring is broken, we can identify the moving and rotating direction of the nanodisk more accurately. We use the CSRDR nanostructure which supports a narrow line-width as a 2D plasmon ruler, which can enhance the sensitivity of a plasmon ruler significantly.

Combining transition metal phosphides (TMPs) with carbon nanotubes (CNTs) is a promising and proven approach to enhance their performance in the electrochemical hydrogen evolution reaction (HER), due to the excellent conductivity and stability of CNTs. Generally, the deep oxidation of CNTs to form oxygen-containing groups on their surface is indispensable before combining them with TMPs. However, such approaches inevitably introduce a large number of defects to CNTs and apparently decrease their stability and electrical conductivity. Hence, fabricating TMP-CNT composites which does not come at the expense of CNTs' high electrical conductivity is quite desirable. In this work, alkylated CNTs (named as ACNT) functionalized via the Birch reaction are used to prepare the pearl necklace-like NiCo

We present a novel surface-enhanced Raman spectroscopy (SERS) substrate based on a double-deck hybrid system assembled by monolayer graphene and Cu nanoparticle layer. The monolayer graphene film was grown by chemical vapor deposition (CVD) technology. The Cu nanoparticles with a uniform distribution were synthesized by liquor-phase reduction synthesis (LPRS) method on the SiO2 (3 cm × 3 cm) substrate. By transferring graphene onto the Cu nanoparticle layer, we fabricated graphene/Cu nanoparticle hybrids (G/CuNPs) SERS substrate. The hybrid SERS substrate showed excellent Raman enhancement effect for adenosine. A reasonable linear response between the SERS intensity and adenosine concentration was obtained in the concentrations of 10−2–10−6 M. This work provided amazing potential for sensitive label-free detection of biomolecular.

In this study, a novel tapered plastic optical fiber sensor based on the single-layer graphene film is demonstrated. A single-layer graphene film was grown on copper foil by chemical vapor deposition (CVD) and transferred to the cone area of the optical fiber by wetting transfer technology. The tapered plastic optical fiber was fabricated with waist diameters of 1 mm and total lengths of 5 cm. In order to increase the stability of the sensor, the taper regions were coated with a single-layer graphene with length of 1.5 cm. By using this platform, the glucose solution as the analyte was measured. The output light intensity and glucose concentration shows a reasonable linear relationship in the range of 1%∼40%

In our work, we directly synthesized few layer MoS2 on a pyramid-Si substrate to fabricate a surface-enhanced Raman scattering (SERS) substrate via thermally decomposing the precursor of ammonium thiomolybdate ((NH4)2MoS4). Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectra are employed to characterize the as-grown MoS2 layers. Adenosine and cytidine were selected as the probe molecules to investigate the SERS ability of the MoS2-pyramid-Si substrate, and have shown that the MoS2-pyramid-Si substrate can prominently suppress photobleaching and fluorescence of the probe molecule. Compared with the MoS2-flat-Si substrate (MoS2 layers synthesized on flat-Si substrate), the MoS2-pyramid-Si substrate has more significant SERS ability. The minimum detected concentration of both adenosine and cytidine on the MoS2-pyramid-Si substrate can reach 10−6 M. Importantly, the linear relationship between the Raman intensity and the concentration of adenosine or cytidine can apply to the bimolecular detection. This work may provide a new opportunity for the study of the chemistry mechanism (CM) and novel SERS substrate fabrication.

Aiming at the problem that the satellite navigation and positioning system can not cover the whole area and that the positioning accuracy of the existing ground-based reinforcement system decreases with the increase of the distance between the target and the ground station, a method for optimizing the positioning system of mobile ground station based on whale optimization algorithm is proposed. Based on the mobile ground station, the method identifies the positioning target with the optimal whale individual and the mobile ground station with other whale individuals, realizes that the position of the ground station varies with the position of the target point, and ensures the high precision positioning of the target in area with weak signals or without satellite navigation and without the support of the enhanced system. The feasibility of this method is proved by MATLAB, which provides a new way of thinking for solving the problem of regional target location.

Aiming at the problems of the difficulty to establish the model and the large data dimension for the traditional integrated navigation method, a method of using the wavelet neural network to directly predict the position and velocity error information is proposed. Get rid of the mathematical model establishment, void introducing new errors in the model establishment, and adopt multiple parallel networks to reduce the dimensionality of the data, which greatly reduces the amount of calculation. The Kalman filter is used as a reference for simulation experiment. The results show that the proposed method can effectively improve the accuracy and real-time performance of the integrated navigation system, and provides a new feasible path for combined navigation filtering.

In this work, we presented a novel evanescent wave absorption sensor based on U-bent tapered multimode fiber covered by molybdenum disulfide (MoS2) film (MoS2@TU fiber EWA sensor). The multimode fiber was manufactured by the fused tapered fiber machine, and then heated using a butane candle flame and bent into a U-bent structure. MoS2 was grown on the fiber directly by thermally decomposing the precursor of (NH4)2MoS4. We have demonstrated that the MoS2 can be applied in the filed of EWA sensor, and the EWA sensor based on U-bent tapered multimode fiber (TU fiber) possessed higher sensitivity than that based on U-bent fiber. The sensitivity (ΔA/ΔC) of the developed EWA sensor is 0.34 in detection of ethanol solution. It shows good sensitivity, linearity, repeatability and stability in detection. And the developed EWA sensor also shows good performance in detection of the adenosine solution, this work shows that the developed EWA sensor may have promising applications in biosensing.

In this work, we have presented a novel local surface plasmon resonance (LSPR) sensor based on the U-bent plastic optical fibre (U-POF). Firstly, a layer of discontinuous silver (Ag) thin film was deposited on the U-POF and then the Ag film was covered by a layer of cladding synthesized by polyvinyl alcohol (PVA), graphene and silver nanoparticles forming the PVA/G/AgNPs@Ag film. The normalized transmittance spectrum of the LSPR sensor have been collected in a range of the refractive index (RI) from 1.330 to 1.3657 in ethanol solution, and 700.3 nm/RIU sensitivity of the developed LSPR sensor has been demonstrated. By experiments, we demonstrated that the graphene could improve the sensitivity of the LSPR sensor and delay the oxidation process of the AgNPs effectively to keep the stability of the LSPR sensor. The LSPR sensor also exhibited good sensitivity and linearity in the detection of glucose solutions. This work shows that the developed LSPR sensor may have promising applications in biosensing.