Construction Of A Novel Electrochemical Sensor For The Detection Of Heavy Metal Lead In Foods

Lead ions(Pb²⁺)are well-known toxic heavy metal elements that are difficult to degrade by microorganisms in the environment.They accumulate in animals and plants through the biological chain and eventually enter the human body,posing a serious threat to human health.Therefore,constructing sensitive and reliable Pb²⁺detection methods is of great significance for the safety of the ecological environment and human health.In this paper,three electrochemical biosensors have been designed for the highly sensitive detection of Pb²⁺by using fast response electrochemical sensors,metal nanomaterials with good conductivity and specific target recognition of aptamers and nuclease,as well as DNA Walker,hybrid chain reaction,catalytic hairpin assembly reaction and other signal amplification technologies.The specific research content and related results are as follows:1.An impedance electrochemical aptamer sensor for detecting Pb²⁺was constructed by using the high conductivity of gold Nanoflower（Au NFs）and the signal amplification technology initiated by the combination of HCR and Y-DNA nanostructures.Among them,the electroactive surface area of gold Nanoflower（Au NFs）modified electrode is 2 times that of gold nanoparticles（Au NPs）modified electrode,and the peak current value increases by 1.6times,indicating that Au NFs can significantly enhance the conductivity of the sensor.Due to the positive charge of Au NFs,their electrostatic adsorption capacity with DNA strands is stronger than that of Au NPs with negative charges.The high affinity between Pb²⁺and its Aptamer transforms Aptamer from a flexible single stranded structure to a highly stable G-quadruplex structure and detaches from the sensor.The combination of HCR and Y-DNA nanostructures reduces the electron transfer rate on the electrode surface.Within the concentration range of 0.5 to 1000 nmol/L,ΔRct has a good linear relationship with Lg C_Pb²⁺,with a detection limit of 0.38 nmol/L.2.A multi-stage assisted signal amplification strategy based electrochemical biosensor for rapid detection of Pb²⁺in food was designed using DNA Walker-CHA cascade assisted signal amplification mediated by Pb²⁺-DNAzyme and Au NPs/Zr MOF nanocomposite loaded MB as signal probes.The Pb²⁺-DNAzyme chain is fixed on magnetic beads（MBs）through the strong binding force between biotin（Bio）-Streptavidin（SA）.The Pb²⁺-DNAzyme structure in the form of DNA Walker triggers the primary signal amplification,and the CHA cycle fixes the signal tag on the electrode to achieve the secondary signal amplification.Porous Au NPs/Zr MOFs have high stability and signal molecule loading ability,ultimately generating stable current signals.The multi-level signal amplification strategy used in this experiment achieves trace detection of Pb²⁺with a detection limit of 4.65 pmol/L,which has certain application value.3.A high-efficiency fluorescence/electrochemical dual-mode biosensor based on DNAzyme cycle was developed by combining Pb²⁺-DNAzyme assisted signal amplification.The Pb²⁺-DNAzyme structure is immobilized on the surface of MBs through the binding force of Bio-SA,and the detection of Pb²⁺is achieved using fluorescent group FAM and electrochemical signal label MB as fluorescence and electrochemical response signals,respectively.Compared to sensors with a single signal,sensors with dual response signals undergo cross validation to avoid false positive reactions,while signal amplification strategies can further improve the sensitivity of the sensor.The detection limit for electrochemical mode（EC）is 4 pmol/L,and for fluorescence mode（FL）is 10 pmol/L.In addition,the designed dual mode biosensor performs well in four aspects:anti-interference ability,reproducibility,repeatability,and stability.The recovery rates of various actual samples are between 93.1%-104.0%（EC）and 95.7%-107.7%（FL）,respectively,with RSD less than 15%,indicating that it has great potential for application in the detection of Pb²⁺.