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.

A research on the effect of plasma spectrum collection device on LIBS spectral intensity

Only a small amount of spectral information is collected because the collection solid angle of the optical fiber probe and lens is very limited when collecting spectral information.To overcome this limitation,this study presents a novel method for acquiring plasma spectral information from various spatial directions.A parabolic-shaped plasma spectral collection device(PSCD)is employed to effectively collect more spectral information into the spectrometer,thereby enhancing the overall spectral intensity.The research objects in this study were soil samples containing different concentrations of heavy metals Pb,Cr,and Cd.The results indicate that the PSCD significantly enhances the spectral signal,with an enhancement rate of up to 45%.Moreover,the signal-to-noise ratio also increases by as much as 36%.Simultaneously,when compared to the absence of a device,it is found that there is no significant variation in plasma temperature when the PSCD is utilized.This observation eliminates the impact of the spatial effect caused by the PSCD on the spectral intensity.Consequently,a concentrationspectral intensity relationship curve is established under the PSCD.The results revealed that the linear fitting R^(2)for Pb,Cr,and Cd increased by 0.011,0.001,and 0.054,respectively.Additionally,the limit of detection(LOD)decreased by 0.361 ppm,0.901 ppm,and 0.602 ppm,respectively.These findings indicate that the spectral enhancement rate elevates with the increase in heavy metal concentration.Hence,the PSCD can effectively enhance the spectral intensity and reduce the detection limit of heavy metals in soil.

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.

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.

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.

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.

Determination of Iron in Water Solution by Time-Resolved Femtosecond Laser-Induced Breakdown Spectroscopy

The influence of the energy of femtosecond laser pulses on the intensity of Fe I （371.99 nm） emission line and the continuous spectrum of the plasma generated on the surface of Fe^3＋ water solution by a Ti： sapphire laser radiation with pulse duration 〈45 fs and energies up to 7 mJ is determined. A calibration curve was obtained for Fe3＋ concentration range from 0.5 g/L to the limit of detection in water solution, and its saturation was detected for concentrations above 0.25 g/L, which is ascribed to self-absorption. The 3σ- limit of detection obtained for Fe in water solution is 2.6 mg/L in the case of 7 mJ laser pulse energy. It is found that an increase of laser pulse energy insignificantly affects on LOD in the time-resolved LIBS and leads to a slight improvement of the limit of detection.

Determination of Aluminum in Nickel-Based Superalloys by Using Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy （LIBS） was developed to detect aluminum in nickel-based superalloys （K417, GH4033, DZ125L, З ∏742y） using a non-intensified, non-gated, low-cost detection system. The precision of LIBS depends strongly on the experimental conditions. The calibration curves of Al（I）394.4 nm and Al（I）396.2 nm under the optimum experimental parameters are presented. Finally the limit of detection （LOD） for aluminum is calculated from the experimental data, which is in the range of 0.09% to 0.1% by weight.

Methods of Data Processing for Trace Elements Analysis Using Laser Induced Breakdown Spectroscopy

With the development of Laser Induced Breakdown Spectroscopy （LIBS）, increasing numbers of researchers have begun to focus on problems of the application. We are not just satisfied with analyzing what kinds of elements are in the samples but are also eager to accomplish quantitative detection with LIBS. There are several means to improve the limit of detection and stability, which are important to quantitative detection, especially of trace elements, increasing the laser energy and the resolution of spectrometer, using dual pulse setup, vacuuming the ablation environment etc. All of these methods are about to update the hardware system, which is effective but expensive. So we establish the following spectrum data processing methods to improve the trace elements analysis in this paper： spectrum sifting, noise filtering, and peak fitting. There are small algorithms in these three method groups, which we will introduce in detail. Finally, we discuss how these methods affect the results of trace elements detection in an experiment to analyze the lead content in Chinese cabbage.

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.

Effect of the distance between focusing lens and target surface on quantitative analysis of Mn element in aluminum alloys by using filament-induced breakdown spectroscopy

Ultrafast laser filament-induced breakdown spectroscopy(FIBS)is a potential technique for quantitative analysis of trace elements.In this work,we investigate the effect of the distance between focusing lens and target surface on the FIBS quantitative analysis of Mn element in aluminum alloys,and several major parameters are calculated such as the linear correlation coefficient(R^2),limits of detection(LOD),relative standard deviation(RSD),and root-mean-square error of cross-validations(RMSECV).The results show that the quantitative analysis parameter values before and after filament position are different.The optimal value can be obtained at the filament region,the average values of total 23 positions of R^2,LOD,RSD,and RMAECV were 99.45%,1.41 mg/kg,7.12%,and 0.56%,respectively.Besides,the spatial distributions of quantitative analysis parameter values in filament region are noticeable,and this is essentially due to intensity clamping effect in a filament.

Recent advances in photoelectrochemical sensors for detection of ions in water

Over the last 50 years,the explosive adoption of modern agricultural practices has led to an enormous increase in the emission of non-biodegradable and highly biotoxic ions into the hydrosphere.Excess intake of such ions,even essential trace elements such as Cu^(2+)and F^(-),can have serious consequences on human health.Therefore,to ensure safe drinking water and regulate wastewater discharge,photoelectrochemical(PEC)online sensors were developed,with advantages such as low energy consumption,inherent miniaturization,simple instrumentation,and fast response.However,there is no publicly available systematic review of the recent advances in PEC ion sensors available in the literature since January 2017.Thus,this review covers the various strategies that have been used to enhance the sensitivity,selectivity,and limit of detection for PEC ion sensors.The photoelectrochemically active materials,conductive substrates,electronic transfer,and performance of various PEC sensors are discussed in detail and divided into sections based on the measurement principle and detected ion species.We conclude this review by highlighting the challenges and potential future avenues of research associated with the development of novel high-performance PEC sensors.

Rapid Detection of Sildenafil Drugs in Liquid Nutraceuticals Based on Surface-Enhanced Raman Spectroscopy Technology

In this study, surface-enhanced Raman Spectroscopy （SERS） technology was used to rapidly detect illegally added sildenafil drugs. A detailed attribution analysis by density functional theory （DFT） was used to guide specific experiments. The Raman signals were obtained from a silver colloid （Ag col） substrate, and they increased in the presence of the mineral salt, potassium iodide （KI）. These methods detected sildenafil in aqueous solutions as low as 1 μg/mL with high signal uniformity （RSD=3.77%）. Prior to this study, traditional Raman techniques detected substances in solid samples only. Here, Raman technology detected low contents of sildenaful drugs in liquid nutraceuticals. Therefore, SERS technology has great potential for on-site and real-time detection of illegal drugs in water and in liquid nutraceuticals.

Integrated silicon-based suspended racetrack micro-resonator for biological solution sensing with high-order mode

A biological sensing structure with a high-order mode(E^(y)_(21))is designed,which is composed of a suspended racetrack micro-resonator(SRTMR)and a microfluidic channel.The mode characteristics,coupling properties,and sensing performances are simulated by using the finite element method(FEM).To analyze the mode confinement property,the confinement factors in the core and cladding of the suspended waveguide for the E^(x)_(11),E^(y)_(11),and E^(y)_(21) are calculated.The simulation results show that the refractive index(RI)sensitivity of the proposed sensing structure can be improved by using the high-order mode(Ey 21).The RI sensitivity for the E^(y)_(21) mode is~201 nm/RIU,which is twice to thrice higher than those for the E^(x)_(11) mode and the E^(y)_(11) mode.Considering a commercial spectrometer,the proposed sensing structure based on the SRTMR achieves a limit of detection(LOD)of -4.7×10^(-6) RIU.Combined with the microfluidic channel,the SRTMR can possess wide applications in the clinical diagnostic assays and biochemical detections.

Novel Palladium （II） Selective Membrane Electrode Based on Phenyl Disulfide

PVC （a poly vinyl chloride） membrane was prepared by using phenyl disulfide as a carrier for selective determination of Pd （II） ion. The membrane can be worked well over a wide concentration range （1.0 × 106-1.0 × 10-1） M with a slope 29.53 mV/decade and a limit of detection （1.77× 10-7） M. The measured of response time was 9 s. It was found to be selective and useable within the pH range （3.0-7.0）. The lifetime of membrane sensor prepared could be used for at least 4 months. The electrode was successfully used as an indicator electrode in potentiometric titration of palladium ion with EDTA.

Nanoparticles Modified Electrodes: Synthesis, Modification, and Characterization—A Review

Nanoparticles offer unique features such as a larger surface area and enhanced electrochemical performance compared to their contemporary matters. These properties make them suitable to be considered in bridging the lacunae associated with the use of bare electrodes in electrochemical sensors. Nanomaterials enhance the redox reversibility on the electrodes’ surfaces, hence, improving the reproducibility, sensitivity, and limit of detection of the electrodes/sensors. Their methods of synthesis (top-to-bottom and bottom-to-to-top) are tailored toward manipulating their sizes, shapes, and preventing their agglomeration. This review paper provides a synopsis on research done in synthesizing nanoparticles, modifying electrodes, and pinpointing the improved performances of the modified electrodes via known characteristic techniques, namely: cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. In addition, a perspective is given in terms of increasing the lifespan of the working electrodes and the need for non-faradaic sensors.

Determination of organophosphorus pesticide residues in vegetables by an enzyme inhibition method using α-naphthyl acetate esterase extracted from wheat flour

The widespread use of organophosphorus pesticides(OPs) poses a great threat to human health and has made the detection of OP residues in food an important task,especially in view of the fact that easy and rapid detection methods are needed.Because OPs have inhibitory effects on the activity of α-naphthyl acetate esterase(ANAE) in plants,in this work we evaluated the possibility of detecting OPs in vegetables with ANAE extracted from commercial flour.The limits of detection(LODs) obtained for methamidophos,dichlorvos,phoxim,dimethoate,and malathion in lettuce samples with crude ANAE were 0.17,0.11,0.11,0.96,and 1.70 mg/kg,respectively.Based on the maximum residue limits(MRLs) for OPs in food stipulated by Chinese laws which are 0.05,0.20,0.05,1.00,and 8.00 mg/kg for methamidophos,dichlorvos,phoxim,dimethoate,and malathion,respectively,the esterase inhibition method with crude ANAE had sufficient sensitivity to detect the residues of dichlorvos,dimethoate,and malathion in lettuce,but it could not be used to guarantee the safety of the same samples if methamidophos or phoxim residue was present.The sensitivity of the method was improved by the use of esterase purified by ammonium sulfate salting-out.The LODs obtained for methamidophos and phoxim with purified esterase were lower than the MRLs for these OPs in food.This is a very promising method for the detection of OP residues in vegetables using crude or purified esterase because of its cheapness,sensitivity,and convenience.

Biomimetic synthesis of all-inclusive organic-inorganic nanospheres for enhanced electrochemical immunoassay

A friendly biomimetic process was adopted for the mild preparation of"all-inclusive"organic-inorganic nanospheres,which effectively integrate biorecognition function and signal amplification function.The resulted Ca3(PO4)2-Ab2-BSA nanospheres were employed as signal labels for enhancing detection of nuclear matrix protein 22(NMP 22).The fabricated electrochemical immunosensor exhibited a linear range(0.08-77.00 U/mL)and an ultralow limit of detection(0.01 U/mL)towards NMP 22,which can be taken as a promising tool for clinical diagnosis of bladder cancer.

Cyanobacterial toxin biosensors for environmental monitoring and protection

Cyanobacterial toxins are primarily monitored using a variety of commercially available techniques,such as enzyme-linked immunosorbent assay(ELISA)and liquid chromatography–mass spectrometry(LC-MS).Indeed,official protocols created and utilized by regulatory bodies have these methodologies ingrained into the technical documentation.However,biosensor technology has been advancing for decades and are positioned to replace many existing methods.The requirements of biosensors include,but are not limited to,real time diagnostics,ease of use(reducing requirements for trained personnel),lower costs,high sensitivity,robust platforms,and good reproducibility.In contrast,laboratory techniques like ELISA require immobile equipment and the use of certified standards for toxin quantification.The use of biosensors may reduce the overall burden of materials and associated costs of production.Given the regulatory limits for toxins in drinking water and recreation,a wide array of biosensor platforms(graphene-based,optical,immunological,etc.)reported in the literature have sufficient sensitivity to comply with these guidelines,however,currently no biosensor has been approved for use in the same manner or accepted as a suitable alternative.In many cases,biosensors have been compared in a limited capacity to established technologies such as the previously mentioned ELISA,LC-MS,and HPLC(High Performance Liquid Chromatography)and would serve as good tools to be used as proxy screening methods.Biosensors examined in this review are evaluated on four criterion:(1)feasibility for point-of-care(POC)use,(2)assay time(time from sample collection to receipt of data),(3)variation between measurements(reported coefficient of variation values),and(4)dynamic range and/or limit of detection(LOD)to obtain a measure of a given technique’s suitability to be used for toxin quantification and detection.