Synthesis And Application Of (Ultrathin) Layered Double Hydroxide Nanosheets Composite Film Electrochemical Sensor In Detection Of Isomers

The isomers containing the same functional groups,such as phenolic isomers and chiral enantiomers of amino acids,have highly similar molecular structures and very similar physical and chemical properties.Therefore,rapid and sensitive identification and detection of these isomers are still a huge challenge.Traditional detection methods such as chromatography and spectroscopy cannot meet the needs of online monitoring and rapid determination due to some factors such as high instrument cost,high professional skills,cumbersome sample pretreatment,time-consuming and other factors that are limited in practical applications.However,the electrochemical method has the advantages of simplicity,economy,simple operation,short test time,high sensitivity,and fast on-site analysis.It has been widely used in the determination of phenolic compounds and chiral isomers.One of the important factors affecting the performance of electrochemical sensors is the preparation of electrode modification materials.Nanocomposite modified electrodes with excellent properties improve current response,stability and sensitivity.In this paper,three Co-Al layered double hydroxide composite film modified electrodes are prepared to realize the simultaneous detection of NAP isomers and the chiral detection of D-/L-methionine（D-/L-Met）enantiomers.（1）After preparing ultrathin Co-Al layered double hydroxide nanosheets（The following is represented by LDH）by"one-step"method,Co-Al LDH@ZIF-67nanomaterials were obtained by in-situ synthesis of ZIF-67 with cobalt in LDH as Co²⁺source by RDF.Reaction diffusion can ensure the in-situ growth of ZIF-67 crystals on the LDH substrate in a vertical gradient way,which not only retains the characteristics of large surface area of LDH,but also prevents the aggregation between them.To a certain extent,the size controlled preparation of the mixed materials can be realized.Therefore,LDH@ZIF-67 can provide more adsorption and electrocatalysis sites for NAP isomers by integrating the organic ligand part and the inorganic nanosheet,and the oxidation peak current can be greatly increased,realizing the simultaneous detection ofα-NAP andβ-NAP.Under the optimal experimental conditions,the NAP isomers were quantitatively analyzed by differential pulse voltammetry（DPV）.The results show that the sensor has a good linear relationship in the range of 0.2～120 m M.The detection limits ofα-NAP andβ-NAP are 54 nM and 82 nM,respectively.（2）After preparing ultrathin Co-Al layered double hydroxide nanosheets by"one-step"method,AuCl₄^-and carboxymethyl-β-cyclodextrin（CMCD）are adsorbed by electrostatic adsorption,and then reduced with sodium borohydride to obtain LDH@AuNCs/CMCD composite material.As a chiral reagent,CMCD can form a special host-guest coating structure with D-/L-Met,and has different binding affinity with D-/L-Met.The combination of AuNCs and LDHs with good biocompatibility and a large number of active sites improved the electrical conductivity of the material,provided a large number of active sites,and gave full play to the synergistic effect of the three components to achieve the detection of D-/L-Met.Under the optimal conditions,quantitative determination of D-/L-Met was performed using DPV.The linear range of L-Met was 0.02～20μM,and the detection limit was 10 nM.The D-Met showed a good linear relationship in the range of 0.2～20μM,and the detection limit was 61 nM.（3）Ti₃C₂T_xMXene was prepared by fluoride etching method.After in situ growth of Co-Al LDH on the surface of MXene,carboxymethyl-β-cyclodextrin was modified to the surface of MXene@LDH by electrostatic adsorption to obtainMXene@LDH/CMCD nanocomposite material.The difference in binding affinity of CMCD for amino acid enantiomers makes it possible to identify and detect D-/L-Met.The MXene@LDH material not only offsets the defects of CMCD in electron transport,but also provides more attachment sites for CMCD.And the MXene@LDH/CMCD composite material has a high degree of asymmetry,giving full play to the synergy between different materials and realizing the qualitative and quantitative detection of D-/L-Met.For L-Met,the linear range was 0.02～25μM with a detection limit of 9.6nM,and for D-Met,the linear range was 0.1～25μM with a detection limit of 39 nM.