Study on Metal Detection with an Electromagnetic Induction Probe Utilizing a Rotating Magnetic Field

The present paper describes an investigation conducted on metal detectors installed with a scanning probe.The authors applied a rotating magnetic field probe to metal detection.The rotating magnetic field probe is comprised of two vertically placed rectangular exciting coils and a circular detecting coil.The experimental results confirmed that the probe can detect metal objects and provide more information about their shape,direction,and electromagnetic characteristics than conventional metal detector probes.A two-dimensional signal display shows a low-resolution image of the metal object and the signal phase indicates the object’s direction and electromagnetic characteristics.The experimental results show that excellent reconstruction of the surface shapes of metal objects can be obtained for both magnetic and nonmagnetic metals under present conditions.There is also the potential for the approximate shape of a metal object to be estimated from the reconstructed image.

Detection and quantification of Pb and Cr in oysters using laser-induced breakdown spectroscopy

The quantitative determination of heavy metals in aquatic products is of great importance for food security issues.Laser-induced breakdown spectroscopy(LIBS)has been used in a variety of foodstuff analysis,but is still limited by its low sensitivity when targeting trace heavy metals.In this work,we compare three sample enrichment methods,namely drying,carbonization,and ashing,for increasing detection sensitivity by LIBS analysis for Pb and Cr in oyster samples.The results demonstrate that carbonization can remove a significant amount of the contributions of organic elements C,H,N and O;meanwhile,the signals of the metallic elements such as Cu,Pb,Sr,Ca,Cr and Mg are enhanced by3–6 times after carbonization,and further enhanced by 5–9 times after ashing.Such enhancement is not only due to the more concentrated metallic elements in the sample compared to the dried ones,but also the unifying of the matter in carbonized and ashed samples from which higher plasma temperature and electron density are observed.This condition favors the detection of trace elements.According to the calibration curves with univariate and multivariate analysis,the ashing method is considered to be the best choice.The limits of detection of the ashing method are 0.52 mg kg-1 for Pb and0.08 mg kg-1 for Cr,which can detect the presence of heavy metals in the oysters exceeding the maximum limits of Pb and Cr required by the Chinese national standard.This method provides a promising application for the heavy metal contamination monitoring in the aquatic product industry.

Hydroxylated graphene quantum dots as fluorescent probes for sensitive detection of metal ions

Highly sensitive methods are important for monitoring the concentration of metal ions in industrial wastewater.Here,we developed a new probe for the determination of metal ions by fluorescence quenching.The probe consists of hydroxylated graphene quantum dots(H-GQDs),prepared from GQDs by electrochemical method followed by surface hydroxylation.It is a non-reactive indicator with high sensitivity and detection limits of 0.01μM for Cu2+,0.005μM for Al3+,0.04μM for Fe3+,and 0.02μM for Cr3+.In addition,the low biotoxicity and excellent solubility of H-GQDs make them promising for application in wastewater metal ion detection.

THE STUDY ON NOVEL MICROELECTRODE ARRAY CHIPS FOR THE DETECTION OF HEAVY METALS IN WATER POLLUTION

Qualitative and quantitative analysis of trace heavy metals in aqueous environment are rapidly assuming significance along with the rapid development of industry.In this paper,gold microelectrode array(MEA)plated with mercury film was used for simultaneous voltammetric detection of zinc,cadmium,lead and copper ions in water.The electrochemical behavior and the actual surface area of the MEA were investigated by cyclic voltammetry in K_(3)[Fe(CN)_(6)].Electrochemical impedance spectrum(EIS)was utilized to examine the deposition of mercury on the electrode surface.Based on anodic stripping voltammetry,mercury film
Au MEA was applied to the detection of heavy metals in artificial analyte,where good calibrate linearity was obtained for cadmium,lead and copper ions,but with zinc exhibiting poor linearity.

Sign Response Mechanism of TCA Self-assembled Fluorescence Probe for Cu^2＋ Detection： FRET Evidence by DFT

A new type of self-assembled molecule ON-OFF fluorescence probe for toxic transition metal ions, made up of thiacalix[4]arene, micelle and fluorescence group, has been studied by DFT/TDDFT method combined with experiment spectra. Since the mechanism of the optical quenching signal response of such self-assembled micelle probe has always been a controversial issue of uncertainty, the spatial construction and geometric structures of the functional units of probe in the Cu2＋ ion detecting process were calculated and the mechanism was investigated by the molecular transition orbital pairs method to explore the origination of ON-OFF fluorescence sign response. The results presented that the signal response mechanism of the micelle probe is ascribed to F？rster resonance energy transfer（FRET） which provides new sights different from most of the conclusions by the related research work reported.

Nanopore-Based Metal Ion Detection and Metal Ion-Mediated Nanopore Sensing

With the continuous development of nanotechnology,single-molecule nanopore detection has become a popular research topic.In this review,we summarize the application of biological nanopores for metal ions detection as well as overview the function of metal ions in the ion-mediated nanopore detection of different analytes in recent decades.According to the previous reports,biological nanopores utilize two strategies to detect metal ions.First,the specific binding sites are engineered in the nanopore to slow down the translocation rate of metal ions,resulting in the diverse specific current blockage signals.Secondly,the external molecule probes are added in the detection system to interact with metal ions,leading to the characteristic changes in the signals.At the same time,the external addition of metal ions into the nanopore detection systems enhances the sensitivity and selectivity through the changes of pore charges,the coordination with analytes or indirect detection.This review provides a summary on the role of metal ions in the application of nanopore detection technology.

Research on Electromagnetic Acoustic Emission Signal Recognition Based on Local Mean Decomposition and Least Squares Support Vector Machine

Electromagnetic acoustic emission technology is one of nondestructive testing, which can be used for defect detection of metal specimens. In this study, round and cracked metal specimens, round metal specimens, and intact metal specimens were prepared. And the electromagnetic acoustic emission signals of the three specimens were collected. In addition, the local mean decomposition(LMD), Autoregressive model(AR model) and least squares support vector machine (LSSVM) algorithms were combined to identify the eletromagnetic acoustic emission signals of round and cracked, round, and intact specimens. According to the algorithm recognition results, the recognition accuracy of can reach above 97.5%, which has a higher recognition rate compared with SVM and BP neural network. The results of the study show that the algorithm is able to identify quickly and accurately crack defect in metal specimens.

Fluorogenic detection of mercury ion in aqueous environment using hydrogel-based AIE sensing films

A“turn-on”fluorescent sensing strategy was developed for ultrasensitive detection of heavy metal mercury ion(Hg2+)directly in water.It utilized an aqueous soluble aggregation-induced emission(AIE)-active probe,named 1,1,2,2-tetrakis(4-(1Htetrazol-5-yl)phenyl)ethene(TPE-4TA),composing of a luminescent tetraphenylene core and multiple anionic tetrazolate spawns.The probe retained dark when molecularly dissolved in water.However,mercury ions can ligate with multiple tetrazolate groups to form infinite coordination polymer particles spontaneously,thus inducing a fluorogenic AIE response for in situ analysis.Moreover,by embedding this AIE sensing molecules in a hydrophilic polyvinyl alcohol substrate,the resulting hydrogel film allowed in situ detection of Hg^(2+)on a laser-induced fluorescence analysis setup in aqueous environment.This strategy worked effectively in common aqueous environments with pH from 4 to 7.5 and showed high sensitivity(limit of detection down to 0.38 ppb/1.9 nM),good selectivity and a wide linearity range for quantification.This work may lead to a reliable and promising platform for on-site environmental water analysis.

A portable and low-cost parallel-plate capacitor sensor for alkali and heavy metal ions detection

A portable and low-cost design of parallel-plate capacitor sensor is proposed and investigated for detection of heavy and alkali metal ions concentration in liquid solution.The application of a thin and long-sided parallel PCB plate allows one to measure the dielectric response of each sample through capacitive sensing technique.The measurements were based on the peak output voltage corresponding to the capacitance of the output measured by an oscilloscope with metal ions concentration of the solution varying from 0 to 10 ppm and input frequency ranging from 1 kHz to 10 MHz.The ICF of Li,Na and K in chloride solution was 2.4,2.1 and 1.9 MHz,respectively.The ICF of Na and K in hydroxide solution was 1.5 MHz and 1.1 MHz,respectively,while the ICF of Pb(NO_(3))_(2)was 490 kHz.The detected ICF was applied to further construct the portable sensor system,which is simple in design,low-cost in fabrication and easy to operate.The finding of ICF of each chemical element is necessary to solve the selectivity challenge of the capacitance-based sensor,which will be appropriate for chemical,environmental and engineering applications.

A multiple-function fluorescent pillar[5]arene:Fe^(3+)/Ag^(+)detection and light-harvesting system

A novel pillar[5]arene(P5DPB)that includes a classicalπ-conjugated molecule,4,4'-(1,4-phenylenedi-2,1-ethenediyl)bis-pyridine(DPB),was designed and synthesized as a substituent.Because of this modification,P5DPB exhibits several unique properties that differ from those of common pillar[5]arenes.The P5DPB neutral pyridine shows good selectivity for Ag^(+)and Fe^(3+).The presence of Ag^(+)ions cause a blue shift(from yellow-green to green)and a decrease in the intensity of the P5DPB emission,while the addition of Fe^(3+)significantly quenches the P5DPB fluorescence.In addition,P5DPB satisfies the conditions for the construction of an energy transfer system with the commonly used Rhodamine B dye and shows great potential for the development of artificial light-harvesting systems.This work provides a new approach for the construction of energy transfer systems and a new reference for metal detection based on derivatized pillar[n]arenes,greatly enriching the applications of these systems.

Synthesis of β-cyclodextrin functionalized gold nanoparticles for the selective detection of Pb2＋ ions from aqueous solution

In the present study we carried out the synthesis of β-cyclodextrin （β-CD） functionalized gold nanoparticles （AuNPs） using a microwave assisted heating method in alkaline media. Stable dispersion of β-CD stabilized AuNPs was obtained at an optimized pH of 10,5. At this pH value the deprotonated secondary hydroxyl group of β-CD shows the highest chelating affinity toward Pb2＋ ions thereby inducing AuNP aggregation. The Pb2＋ induced aggregation in β-CD-AuNP solution is monitored by both colorimetric response and UV-Vis spectroscopy. TEM, DLS and FTIR analyses were carried out to confirm the Pb2＋ ion induced aggregation behaviour of β-CD-AuNPs under alkaline conditions. Furthermore at the experimental pH the response of the β-CD-AuNP system towards Pb2＋ ions is selective when compared with other interfering metal cations.

A review on foreign object detection for magnetic coupling-based electric vehicle wireless charging

With the rapid development and widespread application of electric vehicles(EVs)around the world,the wireless power transfer(WPT)technology is also accelerating for commercial applications in EV wireless charging(EV-WPT)because of its high reliability,safety,and convenience,especially high suitability for the future self-driving scenario.Foreign object detection(FOD),mainly including metal object detection and living object detection,is required urgently and timely for the practical application of EV-WPT technology to ensure electromagnetic safety.In the last decade,especially in the past three years,many pieces of research on FOD have been reported.This article reviews FOD state-of-the-art technology for EV-WPT and compares the pros and cons of different approaches in terms of sensitivity,reliability,adaptability,complexity,and cost.Future challenges for research and development are also discussed to encourage commercialisation of EV-WPT technique.

A green path to extract carbon quantum dots by coconut water:Another fluorescent probe towards Fe^(3+) ions

In recent years,carbon quantum dots(CQDs)have been of great enthrallment in the fluorescent probe field.Carbon precursors with interesting physicochemical properties may be derived from natural sources.In this research,for the first time,coconut water has been used as a source of carbon to prepare blue fluorescent CQDs without any modification and functionalization.The preparation of CQDs is very simple and cost-effective,when compared with other conventional techniques.The reaction parameters temperature and pH were varied to obtain monodispersed spherical CQDs with an average grain size of ∼5 nm.The CQDs exhibit blue emission with a wavelength of 487 nm with an excitation wavelength of 390 nm and are used for Fe^(3+) ions detection.Fe^(3+) ions have been observed to quench the fluorescence intensity of the CQDs than other heavy metals.In the presence of Fe^(3+) ions,the fluorescent CQDs are quenched due to the interaction of CQDs and Fe^(3+) ions.A spectroscopic result shows that Fe^(3+) ions can be observed within a concentration of 0-700μM,as well as the detection limit is 0.30μM.The CQDs provide a unique pathway for potential application in the environmental monitoring of heavy metal ions.

Formation mechanism and application potential of carbon dots synthesized from palm kernel shell via microwave assisted method

The present study systematically investigated the influence of synthesis conditions(duration,reaction medium,and doping concentration)and formation mechanism of carbon dots(CDs)derived from low-cost and abundant biomass palm kernel shell(PKS).Surprisingly,the dopant(urea)did not enhance the photoluminescence of CDs as expected,which could be attributed to the low reactivity between the dopant and PKS macromolecules.Variation of synthesis duration from 30 to 120 s clearly indicated the formation mechanism of CDs,involving the stages of dehydration,carbonization,and nucleation.The CDs with the highest photoluminescent intensity and quantum yield was obtained at synthesis duration of 90 s,aligned well with the perfect spherical shape of CDs and the synergistic effects of both surface and carbogenic core conditions.Understanding the formation mechanism could be used to optimize the synthesis of CDs,and hence linked to quantum yield and fluorescent intensity.In terms of application potential,the CDs illuminated well as fluorescent ink and in bacteria cells imaging.The potential of CDs as sensing material has also been proven with the quenching of fluorescence in the presence of metal ions.The linear range for detection of Cu2+ions was 0.1–0.5 mM with a detection limit as low as 0.05 mM.This signifies the potential of CDs fabricated from PKS as a low-cost and easily available material for Cu2+ions detection in aqueous solution.The CDs possessed reasonable photo stability as indicated by its consistent fluorescence level even after exposure to UV radiation for a prolonged period of 180 minutes.Overall,a simple,straightforward,and fast method is developed to synthesis strong blue emissive CDs from green PKS that are potentially suitable for Cu2+ions sensing in real application.