Fabrication Of Electrochemical Chiral Sensors Based On Magnetic Field Induced Assembly For The Enantioselective Recognition Of Aromatic Amino Acids

Electrochemical sensors based on various chemically modified electrodes have attracted wide attention in the field of the discrimination and determination of enantiomers due to the advantages including the ease of operation,fast response and low cost.The key step for the fabrication of a chiral electrochemical sensor is to synthesis of novel chiral nanomaterials to improve the selectivity and sensitivity of the modified electrodes.More than 60%of the drugs in use are chiral.The two enantiomers of a chiral drug may have substantially different biological effects in terms of pharmacological activity,metabolic behavior and toxicity.Therefore,the development of chiral recognition and determination is of great importance in practical applications.As a novel assembly approach,the magnetic field induced assembly provides a unique quick strategy in the design and fabrication of electrochemical sensors with highly uniform and orderly organized magnetic nanoparticles by external magnetic field.To improving the sensitivity and selectivity of chiral discrimination,our work focuses on the synthesis of chiral selector-functionalized nanoparticles,the construction of chiral sensing films,and the evaluation of chiral aromatic amino acids,etc.The details are categorized as following:1.Electrochemical chiral sensor based on magnetic field induced assembly for the enantiorecognition of tyrosineChiral selector-functionalized magnetic nanoparticles were achieved by self-assembly anchoring L-cysteine（L-Cys）on the surface of the Au/Fe₃O₄nanocomposites,which was synthesized via a facile in-situ reduction process.The as-prepared L-Cys-Au/Fe₃O₄magnetic nanoparticles（MNPs）were characterized by ultraviolet-visible spectroscopy,Fourier-transform infrared spectroscopy and circular dichroism spectroscopy.Scanning electron microscopy was used to observe the surface morphology and microstructure of the modified electrode.Cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）were used to evaluate the electron transfer rate,electrode reaction process and the conductivity of the chiral sensor using[Fe（CN）₆]^3-/^4-as redox probe.Based on magnetic field induced assembly,a novel magnetic electrochemical chiral sensor（MECS）was constructed by MNPs for the discrimination and determination of tyrosine（Tyr）enantiomers.The mechanism of the chiral recognition was further verified by circular dichroism spectroscopy.The results showed that the sensing interface exhibited higher affinity for L-Tyr than D-Tyr.The oxidation peak current ratio of L-Tyr to D-Tyr（I_L/I_D）and the difference between the peak potential of the two enantiomers（?E_p=E_D–E_L）was observed to be 1.85 and 84 m V according to square wave voltammetry（SWV）.A linear relationship between the peak current and the concentration of the two enantiomers was obtained over the range of 1-125μM,with the limit of detection of0.021μM and 0.084μM for L-and D-Tyr,respectively.Furthermore,the sensitive MECS has been successfully used for the practical determination of L-or D-enantiomer in the Tyr mixture solutions by continuously increasing the concentration of one isomer,showing the consistent and reproducible results.The average recoveries were 98.93%-102.11%with RSD lower than 1.45%.2.Magnetic carbon nanotube sensing film based onβ-cyclodextrin for the electrochemical recognition of tryptophaneMagnetic multi-walled carbon nanotube composites（MMWCNTs）were in-situ synthesized by a co-precipitation method in the presence of chitosan-multi-walled carbon nanotube composites,which was prepared under ultrasonication by dispersion of multi-walled carbon nanotubes in chitosan solution.Thenβ-cyclodextrin was cross-linked on MMWCNTs via glutaraldehyde to form theβ-cyclodextrin functionalized magnetic multi-walled carbon nanotube composites（β-CD/MMWCNTs）.The chiral sensing film was constructed by drop-coatingβ-CD/MMWCNTs onto the surface of magnetic glass carbon electrode.Cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）were used to evaluate the electrochemical properties of sensing film.In addition,square wave voltammetry（SWV）was used to investigate the stereoselectivity of Trp enantiomers.The oxidation peak current ratio of L-Trp to D-Trp（I_L/I_D）and the difference between the peak potential of the two enantiomers（E_p=E_D–E_L）were observed to be 1.96 and76 m V.Under the optimum conditions,the chiral sensor exhibited a good linear response to Trp enantiomers in a linear range of 0.5-100μM.The limit of detection of L-Trp and D-Trp were 0.043μM and 0.071μM（based on S/N=3）,respectively.