A novel electrode for simultaneous detection of multiple heavy metal ions without pre-enrichment in food samples.

Integrating a pre-enrichment step into electrochemical detection methodologies has traditionally been employed to enhance the performance of heavy metal detection. However, this augmentation also introduces a degree of intricacy into the sensing process and increases energy consumption. In this work, Mo-doped WO3 is grown in situ on carbon cloth by one-step electrodeposition. The electrode detect multiple heavy metal ions simultaneously in the range of 0.1-100.0 µM with LODs ranging from 11.2 to 17.1 nM. The electrode successfully detected heavy metal ions in diverse food samples. This pioneering detection strategy realized the direct and simultaneous detection of multiple heavy metal ions by utilizing the valence property of WO3 and oxygen vacancies generated by molybdenum doping. The Mo-WO3/CC pre-enrichment-free detection electrode boasts straightforward preparation, a streamlined detection procedure, swift response kinetics, and superior performance relative to previously reported electrodes, which makes it possible to develop a portable heavy metal ion detection device.

Sensitive Electrochemical Detection of Ammonia Nitrogen via a Platinum-Zinc Alloy Nanoflower-Modified Carbon Cloth Electrode.

As a common water pollutant, ammonia nitrogen poses a serious risk to human health and the ecological environment. Therefore, it is important to develop a simple and efficient sensing scheme to achieve accurate detection of ammonia nitrogen. Here, we report a simple fabrication electrode for the electrochemical synthesis of platinum-zinc alloy nanoflowers (PtZn NFs) on the surface of carbon cloth. The obtained PtZn NFs/CC electrode was applied to the electrochemical detection of ammonia nitrogen by differential pulse voltammetry (DPV). The enhanced electrocatalytic activity of PtZn NFs and the larger electrochemical active area of the self-supported PtZn NFs/CC electrode are conducive to improving the ammonia nitrogen detection performance of the sensitive electrode. Under optimized conditions, the PtZn NFs/CC electrode exhibits excellent electrochemical performance with a wide linear range from 1 to 1000 µM, a sensitivity of 21.5 µA µM-1 (from 1 µM to 100 µM) and a lower detection limit of 27.81 nM, respectively. PtZn NFs/CC electrodes show excellent stability and anti-interference. In addition, the fabricated electrochemical sensor can be used to detect ammonia nitrogen in tap water and lake water samples.

Enhanced Sensitivity of Electrochemical Sensors for Ammonia-Nitrogen via In-Situ Synthesis PtNi Nanoleaves on Carbon Cloth.

Pt-based electrochemical ammonia-nitrogen sensors played a significance role in real-time monitoring the ammonia-nitrogen concentration. The alloying of Pt and transition metals was one of the effective ways to increase the detectability of the sensitive electrode. In this paper, a self-supported electrochemical electrode for the detection of ammonia nitrogen was obtained by the electrodeposition of PtNi alloy nanoleaves on a carbon cloth (PtNi-CC). Experimental results showed that the PtNi-CC electrode exhibited enhanced detection performance with a wide linear range from 0.5 to 500 µM, high sensitivity (7.83 µA µM-1 cm-2 from 0.5 to 150 µM and 0.945 µA µM-1 cm-2 from 150 to 500 µM) and lower detection limit (24 nM). The synergistic effect between Pt and Ni and the smaller lattice spacing of the PtNi alloy were the main reasons for the excellent performance of the electrode. This work showed the great potential of Pt-based alloy electrodes for the detection of ammonia-nitrogen.

Electrocardiogram-Based Biometric Identification Using Mixed Feature Extraction and Sparse Representation.

(1) Background: The ability to recognize identities is an essential component of security. Electrocardiogram (ECG) signals have gained popularity for identity recognition because of their universal, unique, stable, and measurable characteristics. To ensure accurate identification of ECG signals, this paper proposes an approach which involves mixed feature sampling, sparse representation, and recognition. (2) Methods: This paper introduces a new method of identifying individuals through their ECG signals. This technique combines the extraction of fixed ECG features and specific frequency features to improve accuracy in ECG identity recognition. This approach uses the wavelet transform to extract frequency bands which contain personal information features from the ECG signals. These bands are reconstructed, and the single R-peak localization determines the ECG window. The signals are segmented and standardized based on the located windows. A sparse dictionary is created using the standardized ECG signals, and the KSVD (K-Orthogonal Matching Pursuit) algorithm is employed to project ECG target signals into a sparse vector-matrix representation. To extract the final representation of the target signals for identification, the sparse coefficient vectors in the signals are maximally pooled. For recognition, the co-dimensional bundle search method is used in this paper. (3) Results: This paper utilizes the publicly available European ST-T database for our study. Specifically, this paper selects ECG signals from 20, 50 and 70 subjects, each with 30 testing segments. The method proposed in this paper achieved recognition rates of 99.14%, 99.09%, and 99.05%, respectively. (4) Conclusion: The experiments indicate that the method proposed in this paper can accurately capture, represent and identify ECG signals.

In-situ growth of porous rod-like tungsten oxide for electrochemical determination of cupric ion.

Preconcentration can effectively enhance the detection performance of electrodes in the electrochemical detection of heavy metal ions, but it also presents challenges for real-time monitoring. Several attempts have been made to optimize preconcentration by improving the adsorption capacity or detection mechanism of the electrode. The valence transfer of tungsten oxide between W5+/W6+ can participate in the reduction between the electrode material and heavy metal ions, playing a role in preconcentration to some extent. Therefore, we developed a WO3/SSM electrochemical sensor for the detection of Cu(II) that utilizes the valence variation property of WO3. The crystallinity and microstructure of the WO3/SSM electrode can be regulated by controlling the deposition parameters, and we prepared three types of WO3/SSM with different morphologies to identify the influence of the electrochemical effective surface area. The proposed electrode shows high performance as a Cu(II) sensor under short preconcentration time (60 s), with an excellent sensitivity of 14.113 µA µM-1 cm-2 for 0.1-10.0 µM and 4.7356 µA µM-1 cm-2 for 10.0-20.0 µM. Overall, the combined effect of morphology and valence transfers shortens the preconcentration time and optimizes preconcentration while ensuring excellent electrode performance. This WO3/SSM electrode is expected to drive great advances in the application of tungsten oxide in the electrochemical detection of heavy metal ions.

A near-infrared light triggered fluormetric biosensor for sensitive detection of acetylcholinesterase activity based on NaErF4: 0.5 % Ho3+@NaYF4 upconversion nano-probe.

Acetylcholinesterase (AChE), as an important neurotransmitter, is widely present in the peripheral and central nervous systems. The aberrant expression of AChE could cause diverse neurodegenerative diseases. Herein, we developed a facile and interference-free fluorimetric biosensing platform for highly sensitive AChE activity determination based on a NaErF4: 0.5 % Ho3+@NaYF4 nano-probe. This nano-probe exhibits a unique property of emitting bright monochromic red (650 nm) upconversion (UC) emission under multiband (~808, ~980, and ~1530 nm) near-infrared (NIR) excitations. The principle of this detection relies on the quenching of the strong monochromic red UC emission by oxidization products of 3,3',5,5'-tetramethylbenzidine generated through AChE-modulated cascade reactions. This system shows a great sensing performance with a detection limit (LOD) of 0.0019 mU mL- 1 for AChE, as well as good specificity and stability. Furthermore, we validated the potential of the nano-probe in biological samples by determination of AChE in whole blood with a LOD of 0.0027 mU mL-1, indicating the potential application of our proposed platform for monitoring the progression of AChE-related disease.

Fabrication of ZnO/Carbon Quantum Dots Composite Sensor for Detecting NO Gas.

ZnO and carbon quantum dots (CQDs) were synthesized by a hydrothermal method, and CQDs were doped into ZnO by a grinding method to fabricate a ZnO/CQDs composite. The X-ray diffraction and the scanning electron microscope revealed that the as-prepared ZnO has a structure of wurtzite hexagonal ZnO and a morphology of a flower-like microsphere which can provide more surface areas to adsorbed gases. The ZnO/CQDs composite has a higher gas sensitivity response to NO gas than ZnO microspheres. A gas sensitivity test of the ZnO/CQDs composite showed that the sensor had a high NO response (238 for 100 ppm NO) and NO selectivity. The detection limit of the ZnO/CQDs composite to NO was 100 ppb and the response and recovery times were 34 and 36 s, respectively. The active functional group provided by CQDs has a significant effect on NO gas sensitivity, and the gas sensitivity mechanism of the ZnO/CQDs composite is discussed.

In situ synthesis of hierarchical platinum nanosheets-polyaniline array on carbon cloth for electrochemical detection of ammonia.

In this work, a self-supported electrode has been designed and fabricated based on carbon cloth-supported polyaniline array and Pt nanosheets (Pt-PANI-CC). PANI array was firstly loaded on the surface of CC via chronoamperometry technique, and then, Pt nanosheets were deposited on the per-grown PANI array through amperometric measurement. The hierarchical structure of Pt-PANI-CC electrode and unique sheet-like Pt nanoparticles offered large specific surface and response centers. The electrochemical sensor based on Pt-PANI-CC electrode has been successfully constructed for detection of ammonia. The experiment results demonstrated that Pt-PANI-CC displayed great catalytic activity for electro-oxidation of ammonia and exhibited acceptable performances for sensing ammonia with low detection limit of 77.2 nM and wide linear range from 0.5 µM to 550 µM. Moreover, the anti-interference ability, reusability, reproducibility and stability of sensor have been investigated and showed great performances. This work provides a promising way for designing self-supported sensing electrode toward a wide electrochemical detection.

Synthesis of three-dimensional hierarchical furball-like tungsten trioxide microspheres for high performance supercapacitor electrodes.

A hierarchical furball-like WO3 electrode material, based on stainless-steel mesh, was successfully synthesized via a simple in situ hydrothermal method. The electrode materials obtained are made from a self-assembled nanorod core and a connected/quasi-connected nano-thorn network shell, and could help utilize all the surface or near-surface regions for faradaic reaction. Furthermore, the furball-like WO3 special microstructure provides a more effective charge storage area, exhibiting a high specific capacitance of 8.35 F cm-2 and excellent cycling stability (93.4% of its initial value after 10 000 cycles). These performances indicate this furball-like WO3 material would be a promising candidate for high performance supercapacitors.

[Source and spatio-temporal variation characteristics of dissolved inorganic carbon in Wanfenghu Reservoir, China].

The flux and form of dissolved inorganic carbon (DIC), an important part of carbon budget, play a key role in the biogeochemistry of aquatic ecosystem. By analyzing physicochemical parameters and water DIC and δ13CDIC characteristics in Wanfenghu Reservoir, we examined the behavior and source of DIC. In the epilimnion, water pH in the entire reservoir was conservative, being weakly alkaline. Nitrate (NO3--N) had the maximum coefficient of variation and a high spatio-temporal variation. Due to the dilution effect, the lowest values of electrical conductivity (EC), partial pressure of carbon dioxide (pCO2) and DIC appeared during the summer high flow phase. On the water column in summer, redox potential (Eh) and NO3--N did not change with water depth, while other indicators changed significantly, with greatest variation in the thermocline. Water temperature (T), pH and Eh all decreased with increasing water depth in both seasons, while pCO2 showed an opposite trend. Water EC, total alkalinity (TA), and DIC decreased with increa-sing water depth in summer, but with a smaller gradient of change in winter. The DIC in water was negatively correlated with water pH and Eh, while positively correlated with EC and pCO2 in both seasons. 2) The concentration of DIC was 2.66-4.9 mmol·L-1 in summer and 3.38-4.52 mmol·L-1 in winter. During the period of thermal stratification, the variation gradients of DIC and δ13CDIC in the thermocline were most significant. DIC was positively correlated with δ13CDIC of epilimnion in summer. DIC was negatively correlated with δ13CDIC in epilimnion in winter and on water column in both summer and winter. However, the variation of DIC and δ13CDIC with water depth was not obvious in winter. 3) In summer, δ13CDIC was -7.71‰- -1.38‰, indicating that the dissolution of carbonate minerals was dominant. In winter, δ13CDIC was -16.93‰- -9.44‰, signifi-cantly lower than that in summer but with a wider range, indicating biological input of CO2 and mineralization of organic matter were the main sources. The δ13CDIC varied significantly in different seasons and water depths because of differences in carbon sources and changes in the relative contribution proportion of carbon sources.

An efficient colorimetric high-throughput screening method for synthetic activity of tyrosine phenol-lyase.

Tyrosine phenol-lyase (TPL) naturally catalyzes the reversible ß-elimination of l-tyrosine to phenol, pyruvate and ammonium. With its reverse reaction (synthetic activity), l-tyrosine and its derivatives could be synthesized with high atom economy, which are widely used in pharmaceutical industries. In this study, a high-throughput screening method for synthetic activity of TPL was developed. One of the substrate, sodium pyruvate was found to react with salicylaldehyde under alkali condition, forming a yellow color compound. The concentration of sodium pyruvate can be quantified according to the absorbance of the colorimetric compound at wavelength of 465 nm and the activity of TPL could be screened according to the decrease of the absorbance. After optimization of the colorimetric reaction conditions, the established high-throughput screening method was successfully used for screening of TPL with enhanced activity for l-DOPA synthesis. The confirmed sensitivity and accuracy demonstrated the feasibility and application potential of this screening method.

Process development for efficient biosynthesis of L-DOPA with recombinant Escherichia coli harboring tyrosine phenol lyase from Fusobacterium nucleatum.

The tyrosine phenol lyase (TPL) catalyzed synthesis of L-DOPA was regarded as one of the most economic route for L-DOPA synthesis. In our previous study, a novel TPL from Fusobacterium nucleatum (Fn-TPL) was exploited for efficient biosynthesis of L-DOPA. However, the catalytic efficiency decreased when the reaction system expanded from 100 mL to 1 L. As such, the bioprocess for scale-up production of L-DOPA was developed in this study. To increase the stability of substrate and product, as well as decrease the by-product formation, the optimum temperature and pH were determined to be 15 °C and pH 8.0, respectively. The initial concentration of pyrocatechol, pyruvate and ammonium acetate was fixed at 8, 5 and 77 g/L and a fed-batch approach was applied with sodium pyruvate, pyrocatechol and ammonium acetate fed in a concentration of 5, 5 and 3.5 g/L, respectively. In addition, L-DOPA crystals were exogenously added to inhibit cell encapsulation by the precipitated product. The final L-DOPA concentration reached higher than 120 g/L with pyrocatechol conversion more than 96% in a 15-L stirred tank, demonstrating the great potential of Fn-TPL for industrial production of L-DOPA.

Biochemical characterization of a novel tyrosine phenol-lyase from Fusobacterium nucleatum for highly efficient biosynthesis of l-DOPA.

Tyrosine phenol-lyase (TPL) catalyzes the reversible cleavage of l-tyrosine to phenol, pyruvate and ammonia. When pyrocatechol is substituted for phenol, l-dihydroxyphenylalanine (l-DOPA) is produced. The TPL-catalyzed route was regarded as the most economic process for l-DOPA production. In this study, a novel TPL from Fusobacterium nucleatum (Fn-TPL) was successfully overexpressed in Escherichia coli and screened for l-DOPA synthesis with a specific activity of 2.69Umg-1. Fn-TPL was found to be a tetramer, and the optimal temperature and pH for α, ß-elimination of l-tyrosine was 60°C and pH 8.5, respectively. The enzyme showed broad substrate specificity toward natural and synthetic l-amino acids. Kinetic analysis suggested that the kcat/Km value for l-tyrosine decomposition was much higher than that for l-DOPA decomposition, while Fn-TPL exhibited similar catalytic efficiency for synthesis of l-tyrosine and l-DOPA. With whole cells of recombinant E. coli as biocatalyst, l-DOPA yield reached 110gL-1 with a pyrocatechol conversion of 95%, which was comparable to the reported highest level. The results demonstrated the great potential of Fn-TPL for industrial production of l-DOPA.

Construction of leaf-like CuO-Cu2O nanocomposites on copper foam for high-performance supercapacitors.

Leaf-like CuO-Cu2O nanosheets have been prepared on copper foam by a one-step simple anodization method, which can be used as an advanced binder-free supercapacitor electrode. The performance of the CuO-Cu2O/Cu foam electrode was optimized through controlling and restraining the current density and reaction time. The prepared electrode exhibits a very high specific capacitance (1.954 F cm-2 at a scan rate of 2 mV s-1), excellent durability (120% retention after 5000 cycles), remarkable rate capability (91.8% retention upon increasing the current density by 10 times) and good coulombic efficiency (78.2% at a current density of 2 mA cm-2). The facile and cost-effective fabrication process is also suitable for large scale practical production. These results indicate the leaf-like CuO-Cu2O/Cu foam electrode would be a promising electrode for high-performance supercapacitor applications.

A high-performance supercapacitor electrode based on tremella-like NiC2O4@NiO core/shell hierarchical nanostructures on nickel foam.

Tremella-like nickel oxalate@nickel oxide (NiC2O4@NiO) core/shell hierarchical nanostructures have been successfully synthesized on nickel foam, using Ni foam as a current collector, a Ni source and a three-dimensional (3D) substrate, through a facile hydrothermal method followed by an electrochemical activation process. The prepared samples can be directly used as binder-free electrodes for supercapacitors. The tremella-like morphology, together with the NiC2O4 nanoblocks on 3D Ni foam, significantly increases the amount of active sites for redox reactions and the conductivity of the electrode material, shortens the diffusion pathway for ions, facilitates the effective penetration of the electrolyte, and lowers the intrinsic equivalent series resistance, demonstrating good potential for energy storage application. This material has a high specific capacitance of 2287.09 F g-1 at 1 A g-1, a good cycling stability (remaining 95% after 10 000 cycles) and a good rate capability (83.2% retention upon increasing the current density by 10 times).

Yunicella, a new genus in the Empoasca-complex of the Empoascini (Hemiptera: Cicadellidae: Typhlocybinae) from China and Thailand.

A new leafhopper genus, Yunicella gen. nov., based on the type species, Yunicella rotunda, sp. nov., is described from Yunnan (southwest China) and Thailand, and placed in the Empoasca-complex of the tribe Empoascini. Habitus photos and illustrations of male genitalia of this new species are given. Differences between this new genus and related genera are also discussed.

Revision of the genus Ficiana Ghauri and its relationship to other genera in Empoascini (Hemiptera, Cicadellidae, Typhlocybinae).

The empoascine genus Ficiana Ghauri is reviewed based on specimens from China. One new Ficiana species, Ficiana aurantia sp. n. is described from Guangxi in south China. An identification key to all species in this genus is provided. The morphological characters of Ficiana and related genera in this tribe are discussed.

Computational simulation and preparation of fluorescent magnetic molecularly imprinted silica nanospheres for ciprofloxacin or norfloxacin sensing.

A magnetic molecularly imprinted fluorescent sensor for the sensitive and convenient determination of ciprofloxacin or norfloxacin in human urine was synthesized and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, ultraviolet/visible spectroscopy, and fluorescence spectroscopy. Both cadmium telluride quantum dots and ferroferric oxide nanoparticles are introduced into the polymer for the rapid separation and detection of the target molecules. The synthesized molecularly imprinted polymers were applied to detect ciprofloxacin or its structural analog norfloxacin in human urine with the detection limit 130 ng/mL. A computational study was developed to evaluate the template-monomer geometry and interaction energy in the polymerization mixture to determine the reaction molar ratio of the template and monomer molecules.

[Transfer calibration for alcohol determination using temperature-induced shortwave near infrared spectra].

The authors studied the temperature influence on short-wave near-infrared spectra of ethanol aquatic solution and utilized four methods to establish the transfer partial least squares (PLS) calibration model: direct transfer calibration, global calibration, orthogonal signal correction (OSC) and generalized least squares weighting (GLSW). The PLS models were built at four temperatures: 15, 25, 35 and 40 degrees C. The results showed that direct calibration provided high prediction bias: significantly high positive prediction bias for a temperature lower than calibration temperature and negative bias for higher temperatures. By using the global correction, OSC and GLSW, the systematic errors could be reduced. However, the global correction needed more calibration samples and built a more complex model. The OSC and GLSW methods provided better predictions using fewer latent variables. By using the GLSW method, prediction bias less than 0.1% and RMSEP less than 0.9% were obtained. The absolute prediction error of GLSW method was less than 1.5%. Additionally, the GLSW provided smaller prediction error at every researched temperature using fewer latent variables than OSC. Thus, GLSW was superior to OSC and could establish more robust transfer calibration model.

Short-wave near-infrared spectrometer for alcohol determination and temperature correction.

A multichannel short-wave near-infrared (SW-NIR) spectrometer module based on charge-coupled device (CCD) detection was designed. The design relied on a tungsten lamp enhanced by light emitting diodes, a fixed grating monochromator and a linear CCD array. The main advantages were high optical resolution and an optimized signal-to-noise ratio (0.24 nm and 500, resp.) in the whole wavelength range of 650 to 1100 nm. An application to alcohol determination using partial least squares calibration and the temperature correction was presented. It was found that the direct transfer method had significant systematic prediction errors due to temperature effect. Generalized least squares weighting (GLSW) method was utilized for temperature correction. After recalibration, the RMSEP found for the 25°C model was 0.53% v/v and errors of the same order of magnitude were obtained at other temperatures (15, 35 and 40°C). And an r(2) better than 0.99 was achieved for each validation set. The possibility and accuracy of using the miniature SW-NIR spectrometer and GLSW transfer calibration method for alcohol determination at different temperatures were proven. And the analysis procedure was simple and fast, allowing a strict control of alcohol content in the wine industry.