Estimation of multivariate detection limits of four quality parameters in licorice using MEMS–NIR spectrometry coupled with two sampling accessories

In this work,multivariate detection limits(MDL)estimator was obtained based on the microelectro-mechanical systems–near infrared(MEMS–NIR)technology coupled with two sampling accessories to assess the detection capability of four quality parameters(glycyrrhizic acid,liquiritin,liquiritigenin and isoliquiritin)in licorice from di®erent geographical regions.112 licorice samples were divided into two parts(calibration set and prediction set)using Kennard–Stone(KS)method.Four quality parameters were measured using high-performance liquid chromatography(HPLC)method according to Chinese pharmacopoeia and previous studies.The MEMS–NIR spectra were acquired from¯ber optic probe(FOP)and integrating sphere,then the partial least squares(PLS)model was obtained using the optimum processing method.Chemometrics indicators have been utilized to assess the PLS model performance.Model assessment using chemometrics indicators is based on relative mean prediction error of all concentration levels,which indicated relatively low sensitivity for low-content analytes(below 1000 parts per million(ppm)).Therefore,MDL estimator was introduced with alpha error and beta error based on good prediction characteristic of low concentration levels.The result suggested that MEMS–NIR technology coupled with fiber optic probe(FOP)and integrating sphere was able to detect minor analytes.The result further demonstrated that integrating sphere mode(i.e.,MDL0:05;0:05,0.22%)was more robust than FOP mode(i.e.,MDL0:05;0:05,0.48%).In conclusion,this research proposed that MDL method was helpful to determine the detection capabilities of low-content analytes using MEMS–NIR technology and successful to compare two sampling accessories.

Ultralow detection limit of giant magnetoresistance biosensor using Fe3O4–graphene composite nanoparticle label

A special Fe3O4nanoparticles–graphene（Fe3O4–GN） composite as a magnetic label was employed for biodetection using giant magnetoresistance（GMR） sensors with a Wheatstone bridge. The Fe3O4–GN composite exhibits a strong ferromagnetic behavior with the saturation magnetization MS of approximately 48 emu/g, coercivity HC of 200 Oe, and remanence Mr of 8.3 emu/g, leading to a large magnetic fringing field. However, the Fe3O4 nanoparticles do not aggregate together, which can be attributed to the pinning and separating effects of graphene sheet to the magnetic particles. The Fe3O4–GN composite is especially suitable for biodetection as a promising magnetic label since it combines two advantages of large fringing field and no aggregation. As a result, the concentration x dependence of voltage difference ｜？V｜ between detecting and reference sensors undergoes the relationship of ｜？V｜ = 240.5 lgx ＋ 515.2 with an ultralow detection limit of 10 ng/mL（very close to the calculated limit of 7 ng/mL） and a wide detection range of 4 orders.

DISCUSSION ON DECISION LIMIT AND DETECTION LIMIT IN SPECTROSCOPY

Based on fundamental arguments, the expressions for the decision limit and the detection limit both in the count domain and in the count rate domain are derived.These expressions are found to be different from those shown in the existing literature.

Achieving Ultra-Low Detection Limit Using Nanofiber Labels for Rapid Disease Detection

Early diagnosis of diseases is critical in its effective management. Traditional disease detection methods require specialized equipment and trained personnel. With the introduction of rapid diagnostic test kits (RDTs), disease detection has become easier and faster. However, these RDTs have failed to compete with the specialized laboratory equipment due to their high detection limits and false alarm rates. This paper presents a novel method of using carbon nanofibers (CNFs) grown on glass microballoons (NMBs) to achieve ultra-low detection limits in RDTs. The NMBs have millions of nanosized CNFs grown on each microballoon, with each CNF having a strong bonding affinity for antibodies. The NMBs conjugated with secondary antibodies have therefore a significantly higher probability of capturing minute antigen concentrations in solution. Furthermore, the dark color formation at the capture zone makes visual disease detection possible. Human Immunoglobulin G (IgG) was selected as the model analyte to study the performance of NMBs using a sandwich immunoassay protocol. Ultra-low electrical detection limit of (4 pg/ml) and rapid re- sponse (~1 minute) was achieved using this method.

Theoretical and experimental assessment of a novel method to establish the complete measurement range of the calorimeter and its limit of detection and quantification

For determining the accuracy of a calorimeter over the instrument’s entire measuring range,a novel method has been established.For this new approach,(a)benzoic acid(C_(6)H_(5)CO_(2)H) as a certified reference material(CRM),(b)SiO_(2) and(c)a mixture of CRM benzoic acid and SiO_(2) have been used.To illustrate the essential difference between 1)the novel analytical method for control of the entire measurement range and 2)the calorimeter calibration,both applications of benzoic acid(BA)have been demonstrated.An experimental result showed that BA was successfully used to check the whole calorimeter measurement range.The results also showed that the same new method was successfully applied to determine the limit of detection and quantification.A new instrument testing process and a new measurement technique have thus been established.In this way,the cost of using CRM to control the accuracy of measuring the entire measuring range of the calorimeter,as shown in this paper,is minimized.The requirements of the ISO/IEC 17025:2017 standard are satisfied.ISO/IEC 17025:2017,together with ISO 9001:2015(quality management systems),ISO 14001:2015(relate to environmental protection)and ISO45001:2018(occupational safety),constitute an integrated quality system by which a testing laboratory may also accredit.

Using a Surface Plasmon Resonance Biosensor for Rapid Detection of Salmonella Typhimurium in Chicken Carcass

Chicken is one of the most popular meat products in the world. Salmonella Typhimurium is a common foodbome pathogens associated with the processing of poultry. An optical Surface Plasmon Resonance （SPR） biosensor was sensitive to the presence of Salmonella Typhimurium in chicken carcass. The Spreeta biosensor kits were used to detect Salmonella Typhimurium on chicken carcass successfully. A taste sensor like electronic tongue or biosensors was used to basically ＂taste＂ the object and differentiated one object from the other with different taste sensor signatures. The surface plasmon resonance biosensor has potential for use in rapid, real-time detection and identification of bacteria, and to study the interaction of organisms with dif- ferent antisera or other molecular species. The selectivity of the SPR biosensor was assayed using a series of antibody con- centrations and dilution series of the organism. The SPR biosensor showed promising to detect the existence of Salmonella Typhimurium at 1 x 106 CFU/ml. Initial results show that the SPR biosensor has the potential for its application in pathogenic bacteria monitoring. However, more tests need to be done to confirm the detection limitation.

Ultrasensitive and stable X-ray detection using zero-dimensional lead-free perovskites

Sensitive and reliable X-ray detectors are essential for medical radiography,industrial inspection and security screening.Lowering the radiation dose allows reduced health risks and increased frequency and fidelity of diagnostic technologies for earlier detection of disease and its recurrence.Three-dimensional(3 D)organic-inorganic hybrid lead halide perovskites are promising for direct X-ray detection-they show improved sensitivity compared to conventional X-ray detectors.However,their high and unstable dark current,caused by ion migration and high dark carrier concentration in the 3 D hybrid perovskites,limits their performance and long-term operation stability.Here we report ultrasensitive,stable X-ray detectors made using zero-dimensional(0 D)methylammonium bismuth iodide perovskite(MA3Bi2I9)single crystals.The 0 D crystal structure leads to a high activation energy(Ea)for ion migration(0.46 e V)and is also accompanied by a low dark carrier concentration(~10^6 cm^-3).The X-ray detectors exhibit sensitivity of 10,620μC Gy-1 air cm-2,a limit of detection(Lo D)of 0.62 nG yairs-1,and stable operation even under high applied biases;no deterioration in detection performance was observed following sensing of an integrated X-ray irradiation dose of^23,800 m Gyair,equivalent to>200,000 times the dose required for a single commercial X-ray chest radiograph.Regulating the ion migration channels and decreasing the dark carrier concentration in perovskites provide routes for stable and ultrasensitive X-ray detectors.

Heavy Metal Detection in Soils by Laser Induced Breakdown Spectroscopy Using Hemispherical Spatial Confinement

Spatial confinement has great potential for Laser Induced Breakdown Spectroscopy （LIBS） instruments after it has been proven that it has the ability to enhance the LIBS signal strength and repeatability. In order to achieve in-situ measurement of heavy metals in farmland soils by LIBS, a hemispherical spatial confinement device is designed and used to collect plasma spectra, in which the optical fibers directly collect the breakdown spectroscopy of the soil samples. This device could effectively increase the stability of the spectrum intensity of soil. It also has other advantages, such as ease of installation, and its small and compact size. The relationship between the spectrum intensity and the laser pulse energy is studied for this device. It is found that the breakdown threshold is 160 cm-2, and when the laser fluence increases to 250 J/cm2, the spectrum intensity reaches its maximum. Four different kinds of laser pulse energy were set up and in each case the limits of detection of Cd, Cu, Ni, Pb and Zn were calculated. The results show that when the laser pulse fluence was 2.12 GW/cm2, we obtained the smallest limits of detection of these heavy metals, which are all under 10 mg/kg. This device can satisfy the needs of heavy metal in-situ detection, and in the next step it will be integrated into a portable LIBS instrument.

Hydrogen sulphide detection using near-infrared diode laser and compact dense-pattern multipass cell

Sub-ppmv level detection of hydrogen sulphide(H2 S) using a 1.578-μm distributed feedback tunable diode laser combining with wavelength modulation spectroscopy and second harmonic detection scheme is reported. A home-developed novel compact dense-pattern multipass gas cell with an effective optical path length of 29.37 m is used to improve sensitivity and reduce sample volume. Detection parameters are optimized, including modulation frequency and amplitude. The analysis of Allan variance shows that a minimum detectable concentration 60 ppbv is obtained with a lock-in time constant of 10 ms, and a detection limit of 13 ppbv can be achieved by average in 300 s. The demonstrated H2 S sensor has a strong penitential application in natural gas process for regulating and controlling H2 S concentration.

LIBS Detection of Heavy Metal Elements in Liquid Solutions by Using Wood Pellet as Sample Matrix

Laser-induced breakdown spectroscopy （LIBS） has been applied to the analysis of heavy metals in liquid samples. A new approach was presented to lower the limit of detection （LOD） and minimize the sample matrix effects, in which dried wood pellets absorbed the given amounts of Cr standard solutions and then were baked because they have stronger and rapid absorption properties for liquid samples as well as simple elemental compositions. In this work, we have taken a typical heavy metal Cr element as an example, and investigated the spectral feasibility of Cr solutions and dried wood pellets before and after absorbing Cr solutions at the same experimental conditions. The results were demonstrated to successfully produce a superior analytical response for heavy metal elements by using wood pellet as sample matrix according to the obtained LOD of 0.07 ppm for Cr element in solutions.

Development and evaluation of a DNA microarray assay for the simultaneous detection of nine harmful algal species in ship ballast and seaport waters

Rapid,high-throughput and reliable methods are urgently required to accurately detect and monitor harmful algae,which are responsible for algal blooms,such as red and green tides. In this study,we successfully developed a multiplex PCR-based DNA microarray method capable of detecting nine harmful algal species simultaneously,namely A lexandrium tamarense,Gyrodinium instriatum,Heterosigma akashiwo,Karenia mikimotoi,Prorocentrum donghaiense,Prorocentrum minimum,Ulva compressa,Ulva ohnoi and Ulva prolifera. This method achieved a limit of detection(LOD) of 0.5 ng of genomic DNA(orders of magnitude of the deci-nanogram range) in the tested algae cultures. Altogether,230 field samples from ship ballast waters and seaport waters were used to evaluate the DNA microarray. The clinical sensitivity and specificity of the DNA microarray assay in detecting field samples were 96.4% and 90.9%,respectively,relative to conventional morphological methods. This indicated that this high-throughput,automatic,and specific method is well suited for the detection of algae in water samples.

Improved sensitivity on detection of Cu and Cr in liquids using glow discharge technology assisted with LIBS

Laser-induced breakdown spectroscopy-assisted glow discharge(LIBS-GD)for analysis of elements in liquid was proposed,and it was applied to detect heavy metals in highly sensitive mixed solutions of Cu and Cr.During the experiments of GD and LIBS-GD,the experimental parameters have been optimized and the optimal voltage is 450 V,laser energy is 60 mJ,and the delay time is 4000 ns.Furthermore,the calibration curves of Cu and Cr under GD and LIBS-GD experiments have been established,and the limits of detection(LODs)of Cu and Cr were obtained with the method of GD and LIBS-GD,respectively.The LOD of Cu decreased from3.37(GD)to 0.16 mg l(LIBS-GD),and Cr decreased from 3.15 to 0.34 mg l.The results prove that the capability of elemental detection under LIBS-GD has improved compared with the GD method.Therefore,LIBS-GD is expected to be developed into a highly sensitive method for sewage detection.

Lead-free perovskite Cs_(2)AgBiBr_(6)/Cs_(3)Bi_(2)Br_(9)single-crystalline heterojunction X-ray detector with enhanced sensitivity and ultra-low detection limit

Lead-halide perovskite single crystal(SC)heterojunctions have attracted significant attention for X-raydetection owing to their unique combination of high sensitivity,resolution,stability and low detection limit.However,the toxicity of lead in those perovskite heterojunctions limitstheir practical applications.Herein,we report the constructionof the first all-inorganic lead-free Cs_(2)AgBiBr_(6)/Cs_(3)Bi_(2)Br_(9)SCheterojunctions with an area of 20×20 mm^(2)via a facile liquidphase epitaxial method through temperature-lowering crystallization.The epitaxial crystallization of the three-dimensional(3D)Cs_(2)AgBiBr_(6)SC film on a 2D Cs_(3)Bi_(2)Br_(9)SCsubstrate requires a large driving force for transitioning fromthe Volmer–Weber mode to the layer-by-layer growth modeunder a rapid cooling rate.The Cs_(2)AgBiBr_(6)/Cs_(3)Bi_(2)Br_(9)SCheterojunction detector achieves a high sensitivity of1390μC Gy_(air)^(−1)cm^(−2)for 100 keV hard X-ray detection atroom temperature,which is enhanced to 2075μC Gy_(air)^(−1)cm^(−2)at 75℃,demonstrating impressive high-temperature stability.Moreover,the detector achieves a detection limit of37.48 nG_(yair)s^(−1)and excellent stability for 90 days without anyencapsulation.This work demonstrates the feasibility of usingthe epitaxial mechanism of perovskite formation on a highsurface-energy substrate for the controllable construction of a3D/2D heterojunction that significantly enhances X-ray detection performance.

基于序贯贝叶斯方法的核素快速检测方法研究

适当的放射性核素快速检测方法对于具有流量大和计数率水平低特征的海关放射性安检等场景是必要的。相较于传统不确定性分析方法,贝叶斯方法和序贯概率比检验可充分利用测量物理量的全部信息而所需的样本量较少,基于此提出了一种新型序贯贝叶斯核素快速检测方法,分别在低辐射本底环境和自然辐射本底环境,使用一套LaBr3(Ce)探测系统和一组标准点源对该方法的可行性、检测性能和普适性开展了实验研究,并探究了方法的关键参数中第一类错误概率α、第二类错误概率β和时间间隔下限τmin对检测性能的影响。在本底计数率分别为59.3 s^(-1)和165.9 s^(-1)的两类本底环境中,α和β分别不超过0.1和0.01的条件下,实验结果显示:在无源情况下,该方法对本底辐射的平均检出时间分别为24.08 s和10.54 s,平均检出样本量分别为1427和1742,且发生误报后均可快速自适应消除并做出有效判决;在有源情况下,实验测量检测灵敏度下限分别约为8.2%和6.1%,对应的平均检出时间分别为8.59 s和6.61 s,实验测量漏报率均为0,平均检出时间只与全谱净计数率有关,平均检出样本量只与放射源信号的计数率信噪比有关,检测灵敏度下限可理论计算且与实验结果相吻合;参数τ_(min)的减小会增大检测灵敏度下限和减小检出时间,参数α和β可决定实验测量误报率和漏报率。研究表明本方法非常适用于低水平放射性核素的快速检测。

基于GaN肖特基二极管的大功率微波限幅技术研究

随着高功率微波技术的发展,超宽带、高功率等强电磁技术对电子化设备威胁越来越大,使用高功率微波摧毁电子信息装备成为了干扰通信系统的重要方式。对高功率微波的防护主要分为前门防护和后门防护,限幅器作为前门防护的重要微波器件也面临越来越高的要求。本文首先介绍了GaN材料及肖特基二极管的器件特点和性能优势,然后论文介绍了以半导体器件为基础的限幅器原理及电路结构,并对以GaN肖特基二极管为基础的新一代大功率微波限幅技术研究进展进行论述。

Detection of Nonlinear Behavior Induced by Hard Limiting in Voltage Source Converters in Wind Farms Based on Higher-order Spectral Analysis

In recent years, sub-synchronous oscillation accidents caused by wind power integration have received extensive attention. The recorded constant-amplitude waveforms can be induced by either linear or nonlinear oscillation mechanisms. Hence, the nonlinear behavior needs to be distinguished prior to choosing the analysis method. Since the 1960s, the higher-order statistics(HOS) theory has become a powerful tool for the detection of nonlinear behavior(DNB) in production quality control wherein it has mainly been applied to mechanical condition monitoring and fault diagnosis. This study focuses on the hard limiters of the voltage source converter(VSC) control systems in the wind farms and attempts to detect the nonlinear behavior caused by bi-or uni-lateral saturation hard limiting using the HOS analysis. First, the conventional describing function is extended to obtain the detailed frequency domain information on the bi-and uni-lateral saturation hard limiting. Furthermore, the bi-and tri-spectra are introduced as the HOS, which are extended into bi-and tri-coherence spectra to eliminate the effects of the linear parts on the harmonic characteristics of hard limiting in the VSC control system, respectively. The effectiveness of the HOS in the DNB and the classification of the hard-limiting types is proven, and its detailed derivation and estimation procedure is presented. Finally, the quadratic and cubic phase coupling in the signals is illustrated, and the performance of the proposed method is evaluated and discussed.

Assessment of Different Instruments and Methods for Detecting Pollution Share Rate of Heavy Metals in Water Samples

[ Objective ] This study aimed to investigate the impacts of different instruments and methods on detection of water samples and evaluate the detection results and pollution share rate. [ Method] Concentrations of six heavy metals in three surface water samples and three underground water samples were detected by AAS and ICP-AES to analyze the differences in detection results and calculate the pollution share rate of heavy metals. [Result] As a result, the pollution share rate of six heavy metals varied significantly. Calculation results of comprehensive pollution share rate based on the lower pollution index of the same heavy metal in the same water sample detected by two methods were different from the results using either method. Due to different detection limits of instruments, detection results of heavy metals in the same water sample were different, which affected the accuracy of environmental quality assessment. [ Conclusion ] The detected pollution share rate varies with different detection limits. Therefore, instruments and methods with lower detection limit should be used. To be specific, AAS is suitable for detection of Pb and Cd, while ICP is suitable for detection of Cu, Zn, Fe and Mn.

The Number and Distributions of Limit Cycles of a Cubic Hamiltonian System with Z_2-symmetry Perturbation

This paper is concerned with the number and distributions of limit cycles of a cubic Z2-symmetry Hamiltonian system under quintic perturbation.By using qualitative analysis of differential equation,bifurcation theory of dynamical systems and the method of detection function,we obtain that this system exists at least 14 limit cycles with the distribution C91 [C11 ＋ 2（C32 2C12）].

Confidence Interval Estimation of the Correlation in the Presence of Non-Detects

This article deals with correlating two variables that have values that fall below the known limit of detection (LOD) of the measuring device;these values are known as non-detects (NDs). We use simulation to compare several methods for estimating the association between two such variables. The most commonly used method, simple substitution, consists of replacing each ND with some representative value such as LOD/2. Spearman’s correlation, in which all NDs are assumed to be tied at some value just smaller than the LOD, is also used. We evaluate each method under several scenarios, including small to moderate sample size, moderate to large censoring proportions, extreme imbalance in censoring proportions, and non-bivariate normal (BVN) data. In this article, we focus on the coverage probability of 95% confidence intervals obtained using each method. Confidence intervals using a maximum likelihood approach based on the assumption of BVN data have acceptable performance under most scenarios, even with non-BVN data. Intervals based on Spearman’s coefficient also perform well under many conditions. The methods are illustrated using real data taken from the biomarker literature.

Dispersion Limit for IM/DD Fiberoptic Transmission Systems

A general formula for the dispersion limit of single-mode-fiber IM/DD (Intensity Modulation /Direct Detection) systems is derived for arbitrary given normalized pulse width P, eye opening penalty X and source linewidth enchancement factor α. From the comparison with published theoretical results, computer simulation and experimental data, its validity and convenience in system design and evaluation are shown. Using this simple and general formula, one can easily obtain the dispersion limit of various fiber types under different working conditions in IM/DD systems.