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Current sensor devices for the detection of methane or natural gas emission are either expensive and have high power requirements or fail to provide a rapid response. This report describes an electrochemical methane sensor utilizing a non-volatile and conductive pyrrolidinium-based ionic liquid (IL) electrolyte and an innovative internal standard method for methane and oxygen dual-gas detection with high sensitivity, selectivity, and stability. At a platinum electrode in bis(trifluoromethylsulfonyl)imide (NTf2)-based ILs, methane is electro-oxidized to produce CO2 and water when an oxygen reduction process is included. The in situ generated CO2 arising from methane oxidation was shown to provide an excellent internal standard for quantification of the electrochemical oxygen sensor signal. The simultaneous quantification of both methane and oxygen in real time strengthens the reliability of the measurements by cross-validation of two ambient gases occurring within a single sample matrix and allows for the elimination of several types of random and systematic errors in the detection. We have also validated this IL-based methane sensor employing both conventional solid macroelectrodes and flexible microfabricated electrodes using single- and double-potential step chronoamperometry.

A 20-point laser Doppler vibrometer with single photodetector is presented for noncontact dynamic measurement. A 5×4 beam array with various frequency shifts is generated by a 1.55 μm distributed feedback laser and four acousto-optic devices, and illuminating different points on vibrating objects. The reflected beams are coupled into a single-mode fiber by a pigtailed collimator and interfere with a reference beam. The signal output from a high-speed photodetector is amplified and then digitized by a high-speed analog-to-digital converter with a sampling rate of 1 gigasample per second (1 GS/s). Several methods are introduced to avoid the cross talk among different frequencies and extract the vibration information of 20 points from a one-dimensional signal. Two signal processing algorithms based on Fourier transform and windowed Fourier transform are illustrated to extract the vibration signals at different points. The experimental results are compared with that from a commercial single-point laser vibrometer. The results show simultaneous vibration measurement can be realized on multiple points using a single laser source and a single photodetector.

A laser Doppler vibrometer with single photodetector is introduced to measure the vibration on multiple points of target simultaneously. A 2 x 5 beam array with various frequency shifts is generated by three acousto-optic devices, illuminating different points on a vibrating object. The reflected beams interfere with a reference beam on a high-speed photodetector, and the signal is amplified and digitized with a rate of 500 megasamples/s. To extract vibration information of different points, the carrier frequencies of each beam are elaborately designed so that they can be separated from cross-talk regions in the spectrum. The experimental results are compared with that from a commercial single-point vibrometer, and the comparison shows that it is possible to do a precise measurement on multiple points simultaneously using a single photodetector.

We demonstrate a highly sensitive and stable fiber-optic Fabry-Perot cantilever microphone based on fast demodulated white-light interferometry. The cavity length of the low-finesse Fabry-Perot interferometry is absolutely measured by realizing a high-speed demodulation method utilizing a full spectrum, with the advantages of both high resolution and large dynamic range. An acoustic test demonstrates high sensitivities and linear responsivities at frequencies below 2 kHz. The pressure responsivity and the noise-limited minimum detectable acoustic pressure level are measured to be 211.2 nm/Pa and 5  μPa/Hz, respectively, at the frequency of 1 kHz. Comparative experimental results show that the signal-to-noise ratio is over 10 times higher than a reference condenser microphone.

Background and Aims The widespread use of Rare Earth Elements (REEs) has resulted in localized soil pollution. Phytolacca americana L. has potential for REE phyto-extraction, but the related mechanism is not clear. Methods In this study, the uptake and fractionation of REEs, and the influence of REEs on biomass production was investigated in hydroponically grown plants. Furthermore, the effects of Ca 2+ and Al 3+ on REE uptake, and the role of organic acids in REE translocation were also examined. Results Results showed that biomass and accumulation of REEs in P. americana were enhanced at low REE concentrations, but inhibited at higher concentrations in solution. Significant heavy REE (HREE) enrichment was observed during the stem-to-leaf transport, with a quotient of ∑LREE/∑HREE decreasing from 0.75 to 0.23. Ca 2+ and Al 3+ treatments diminished REE accumulation. The ∑LREE/∑HREE ratio decreased from 0.84 to 0.62 with increasing input of Ca 2+ , but increased from 0.83 to 0.92 with higher Al addition. Conclusions LREEs appear to enter into the root of P. americana through Ca 2+ ion channels, whereas HREEs may share pathways with Al 3+. Finally, citrate plays an important role in the translocation of REEs in P. americana.

We present a method to identify and quantify methane using a hydrophobic ionic liquid (IL)-electrified metal electrode interface by electrochemical impedance spectroscopy. We investigated the mechanisms of the responses of the IL-electrified electrode interface to the exposure of methane and other interfering gases (H 2 , C 6 H 12 , SO 2 , NO, NO 2 , CO 2 , O 2 , H 2 O). Our results show that at low frequency the IL-electrified electrode interface shows a predominantly capacitive response. The IL-electrode double layer (EDL) was found to be the primary response layer while the transition zone and bulk region of the IL-electrode interface contribute little to the overall signal change. For recognition and quantification of methane using the Langmuir adsorption model and measurement of differential capacitance change, an optimum EDL interface structure was found to form at a specific DC bias potential. The cumulative results shown in this work suggest that an ideal IL-electrode interface can be formed by varying IL structure and applied DC bias electrode potential for a specific analyte and that the semi-ordered structure of IL-electrified interface can act as a recognition element for the sensitive and selective adsorption and detection of gaseous molecules.Due to their unique properties and increasing availability, room temperature ionic liquids (ILs) have received great interests in electrochemistry, catalysis, electronics, and energy conversion as well as interdisciplinary investigations on both fundamental and practical applications. 1-5 For example, ILs as solvent free and ion-coupled material exhibit strong benefits as non-aqueous electrolytes for enhancing the safety and robustness for sensor and transistor devices. 6-12 However, the low intrinsic conductivity of the ILs correlates with their high viscosity, which limits the response time and sensitivity of detection methods such as those based on amperometry and potentiometry. [13][14][15][16][17] Methane, which has been considered as a clean energy source and one of the most important greenhouse gases, has attracted significant interest to the characterization of its adsorption on surfaces and its quantification in atmosphere as well. Since methane is relative chemically and electrochemically inert, current methods for methane detection are either relatively high-cost (e.g. optical), which prevents widespread deployment, or lack the selectivity (e.g. catalytic bead) 18 demanded by various applications. Many methane sensors also need improvement regarding their size, power consumption and the ease of use. [19][20][21] Current results show that the potential-dependent interface of an IL and metal electrode is very sensitive to surface conditions on the electrode, such as the proton adsorption on an oxide electric interface 22 and the adsorption of CO on a metal electrode 23 . As shown in Figure 1, the molecular selectivity of an IL-electrode interface comes from the ordering of the electric double layer (EDL) as well as molecular interactions between the IL...

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