Research On The Key Techniques For Heavy Metals Detection In Farmland Soil And Irrigation Water

With the development of industry and agriculture in China,an increasing number of industries have involved in heavy metals for their productions.Due to the illegal discharge of sewage by some enterprises,sewage irrigation and the excessive use of chemical fertilizers and pesticides containing heavy metals,the soil,and water environment has been contaminated by these heavy metal pollutants,which causes the contents of heavy metals in farmland and irrigation water are much higher than the background value.The heavy metals in farmland and irrigation water are easily absorbed by the crops,and then eat by the organisms that can affect their health.Therefore,it is of great significance to develop a method for the rapid detection of heavy metals in the agricultural environment.The traditional methods using spectrometries have high accuracy and good repeatability for the detection of heavy metals.However,these methods require a complicated operation,expensive equipment,and skilled workers,which limits the application.The electrochemical method has many advantages,such as high detection speed,high sensitivity,good selectivity,low price,and portable device.It can be used together with different sensors to realize the simultaneous detection of multiple heavy metals and is very suitable for the farmland environment.On-site inspection analysis.At present,this method has become a hot spot in the field of heavy metal detection research.This thesis is aimed at the technical difficulties existed in the rapid detection of heavy metals by the electrochemical method,including poor specificity,low sensitivity,and high cost.Explored new nanomaterials and biomaterials synthesis and modification technology,carry out low-cost heavy metal detection electrochemical sensors and biosensors research,improve the detection of heavy metal detection sensor selectivity and sensitivity.The sensors/biosensors combined with the portable electrochemical workstation is to quickly and accurately obtain the qualitativity and quantitativity of heavy metals in farmland and irrigation waters under a complex agricultural environment.1.To trace the concentrations of Cd(?)and Pb(?),we have developed an electrochemical inexpensive,sensitive and selective sensor using disposable screen-printed carbon electrode(SPE)immobilized with a composite film of reduced graphene oxide/carboxylation multi-walled carbon nanotubes/gold nanoparticle hybrid(RGO-MWNT-AuNP)through ?-? bind.This high conductive nanocomposite layer,"RGO-MWNT-AuNP",was characterized by scanning electron microscopy,UV-visible spectrometer,cyclic voltammetry,and electrochemical impedance spectroscopy.Square wave stripping voltammetry was applied to RGO-MWNT-AuNP/SPE to electroplate bismuth film and monitor the heavy metal ions in the tested solution simultaneously.To obtain high current responses,the detecting parameters were optimized.Under optimized conditions,the linear detection range of the sensor was 1.0?80.0 ?g/L for lead and cadmium.The linear regression equation was I(?A)= 0.3001 +0.4413C(?g/L))and I(?A)=0.6285 + 0.4893C(?g/L)for cadmium and lead with a detection limit of 0.7 ?g/L and 0.3 ?g/L,respectively.Finally,the prepared electrode was further employed to detect Cd(?)and Pb(?)in soil samples with satisfactory results.2.The article describes a reusable biosensor for Pb(II)ions.A duplex DNA with a terminal amino group,which contained a G-quadruplex(G4)aptamer,was covalently conjugated to single-walled carbon nanotubes on a field effect transistor(FET).The detection scheme is based on the despiralization of the DNA duplex because Pb(?)can induce the G4 aptamer to form a stabilizing G4/Pb(?)complex.This structural change affects the electrical conductivity of SWNTs which serves as the analytical signal.The biosensor was characterized via scanning electron microscopy,Raman,UV-vis,and voltage-current profiles.Under optimized conditions,the relative resistance at 0.02 V increases linearly with the logarithm of the Pb(?)concentration in the range from 1 ng/L to 100 ?g/L.The linear regression equation was y=10.104 log[CPb(?)]+ 5.8656 and the limit of detection is 0.39 ng/L.Compared to other sensors,the sensor demonstrates superior simplicity,sensitivity,and selectivity even in mixtures of heavy metal ions.It was applied to the determination of Pb(?)in(spiked)water and soil samples and gave good results.3.Mercury(Hg)and its compounds,originating from a variety of nature and anthropogenic source,are ubiquitous in the natural environment,which cause severe environmental contamination and pose irreversible harm to human health.Fast and accurate sensing approach is of significant importance for mercury detection.Here,a label-free biosensor using Hg(?)-induced cleavage of phosphorothioate(PS)modified RNA was exploited.We designed a specific single-stranded DNA embedded four PS-modified RNA(Hg-DPR)to improve the cleavage reaction yield,and then Hg-DPR was covalently linked with single-walled carbon nanotube field effect transistor(SWNTs/FET)via a peptide bond.The Hg-DPR can be efficiently cleaved after exposed to Hg(?),which further causes the conductivity of the SWNTs to change.Using the relative resistance change,the Hg-DPR/SWNTs/FET successfully obtained the calibration curves were linear in the range of 50 pmol/L to 100 nmol/L and 100 nmol/L to 10 ?mol/L.The linear regression equation was y1=0.957 + 5.461 log[CHg(?)]and y2=-135.67 +32.3131og[CHg(?)],which the limit of detection was 10 pmol/L.Our work suggests that DPR/SWNTs/FET are promising for low-cost,portable,real-time,heavy metal ion detectors.Additionally,DPR/SWNTs/FET exhibited excellent sensitivity,portability and low-cost for Hg(?)detection.4.Silver is a very common heavy metal,and its detection is of significant analytical importance.In this article,we report a label-free field-effect transistor(FET)biosensor using single-walled carbon nanotubes(SWNTs)functionalized with a silver ion(Ag(?))specific RNA-cleaving DNAzyme for ultrasensitive detection of silver ions(Ag(?)).The complementary strand DNA(CS-DNA)is covalently immobilized on the surface of SWNTs through amide bond formation and then combine with Agzyme.The properties of DNAzyme/SWNT/FET were investigated using different spectroscopy and electrochemical methods.The RNA-base on the CS-DNA can be cleaved at RNA site efficiently when Agzyme specific binding with Ag(?).The structure of duplex DNA on the SWNTs changes,which further induces a remarkable changing electrical conductivity of the SWNTs.This proposed biosensor is much more convenient and efficient than that of the previously reported biosensor based on cytosine-Ag-cytosine.After the detecting parameters were optimized,the biosensor presented a high sensitivity and selectivity towards Ag(?)at unprecedentedly low concentrations 5 pmol/L with a wide linear range from 10 pmol/L to 107 pmol/L.The linear regression equation was y = 7.0744 + 12.007 log[CAg(1)].Additionally,the prepared biosensor was applied to measure the Ag(1)in the water sample with good performance.5.Research on portable heavy metal device.Aiming at the different detecting signals required by the electrochemical sensors and biosensors developed in the paper,a portable heavy metal device was designed that can provide multiple detection methods.The device used an ultra-low-power mixed signal processor MSP430 MCU,integrates power supply module,communication module,I/V conversion module,potentiostat,I/V conversion circuit,filter circuit and other peripheral auxiliary circuits.The voltage generation and current signal acquisition during the heavy metal detection process.The upper computer software developed using C#language can output square wave anodic stripping voltammetry and linear sweep voltammetry,which was suitable to different sensors.