An Electrochemical Chiral Sensor That Can Be Used To Identify Optical Isomers Of Amino Acids

Electrochemical chiral sensors stand out among many chiral analytical technologies because they can convert chiral molecular recognition events to discernible changes in electrochemical signals.In recent years,construction of electrochemical chiral sensors for chiral recognition of amino acid enantiomers has received extensive attention.In this thesis,tetra（4-carboxyphenyl）-porphyrin（TCPP）and precious metal nanoparticles were used to prepare electrochemical chiral sensors for the chiral discrimination of the isomers of several amino acids.This thesis is divided into three parts.In this chapter,we demonstrated a chiral self-assembly of achiral porphyrin induced by L-and D-lysine（L-and D-Lys）,and the resultant self-assembly exhibited alterable morphologies depending on the inducer used（L-or D-Lys）.The supramolecular chirality of the self-assembly was characterized by circular dichroism（CD）spectra,confirming successful transfer of molecular chirality from L-and D-Lys to the self-assembly.The enantioselective property of the chiral self-assembly was investigated by using tryptophan（Trp）isomers as the model.Also in this work,the L-/D-Lys-induced chiral self-assembly of porphyrin and the supramolecular interaction between the self-assembly and L-/D-Trp were also studied by density functional theory（DFT）.In this chapter,β-cyclodextrin（β-CD）modified silver nanoparticles（Ag NPs）,denoted asβ-CD/Ag NPs,were prepared by a simple one-pot method.Due to the inherent chirality ofβ-CD,the developedβ-CD/Ag NPs exhibited higher affinity toward L-tyrosine（L-Tyr）than D-tyrosine（D-Tyr）,leading to higher peak currents of L-Tyr on the differential pulse voltammograms（DPVs）.In addition,the differences in the electrochemical signals could be further amplified in the presence of Ag NPs,which could be applied for the electrochemical chiral discrimination of the Tyr isomers.Other chiral amino acids including tryptophan and phenylalanine could also be successfully discriminated with theβ-CD/Ag NPs,suggesting high universality of the developed chiral sensor.In this chapter,core-shell structured gold-silver nanoparticles（Au@Ag NPS）were synthesized and used to construct an ultrasensitive electrochemical chiral sensor.The results of CD indicated that the optical activity of Au@Ag NPs was consistent with that of D-Trp but opposite to that of L-Trp,and thus the Au@Ag NPs could selectively combine with D-Trp.Because the charge transfer ability of D-Trp was greatly weaker than that of Au@Ag NPs,the charge transfer resistance(R_ct)of Au@Ag NPs and D-Trp complex（Au@Ag NPs/D-Trp）on the electrochemical impedance spectroscopy（EIS）was significantly increased compared with those of Au@Ag NPs and Au@Ag NPs and L-Trp complex（Au@Ag NPs/L-Trp）.Therefore,ultrasensitive chiral discrimination of Trp isomers at the extremely low concentration（0.1 n M）could be achieved based on the difference in R_ct.Finally,the electrochemical chiral sensor was successfully applied to the accurate determination of D-Trp at low concentrations.The detection limit and the linear range was 58 p M and 100 p M～10μM,respectively.The results demonstrated that the electrochemical chiral sensor based on the Au@Ag NPS can be used not only for ultrasensitive discrimination of Trp isomers,but also for ultrasensitive detection of D-Trp.