Studies On Electrochemical Chiral Sensors Based On Graphene-Based Nanocomposites

The characteristic of misalignment between the mirror image of a molecule and itself is called chirality. Chirality is one of the significant features of a life, and research on it have important application value in the fields of medicine, life science, food science and materials science. A couple of enantiomers present distinguished difference in metabolic fate, pharmacological activity and toxicity, even opposite effects. Therefore, it is significant to develop methods for chiral recognition which are simple, fast, sensitive and low cost in theory and practice. So far, a lot of means for recognition have achieved some progress. Particularly, electrochemical approaches, due to the merits of easy operation, fast detection, higher sensitivity and lower cost, have become attractive for analytical researchers. Nanomaterials and nanocomposites possessing a multitude of advantages, which can be applicatied in electrochemical chiral recognition, undoubtedly opens up a new perspective for electroanalytical chemistry. To achieve the goal of signals amplification and improved sensitivity, graphene-based nanocomposites were employed to construct electrochemical chiral sensors. The main research work contains three fractions as follows:i. The thionine-graphene (THi-GR) nanocomposite was successfully synthesized and modified on the surface of glassy carbon electrode (GCE), then ds-DNA was immobilized to construct a chiral interface via the opposite-charged adsorption techniques, then it was used for Tryptophan (Trp) enantiomers sensing with the assistance of the electrostaic interaction between ds-DNA and Cu(Ⅱ) complexes. The surface morphology and structure of this chiral interface were characterized with scanning electron microscopy (SEM) and ultraviolet-visible (UV-vis) spectrometry; The interactions between ds-DNA and Trp enantiomers in the presence and absence of Cu(II) were investigated by cyclic voltammetry (CV) and Cu(Ⅱ) played an important role in chiral recognition:The influence of concentration of target analyte, pH of base solution and incubation time on chiral recognition were studied, and the binding constants were calculated after the information of adduct profiles between the chiral interface and Cu(II) complexes of Trp enantiomers. The results implied stronger response was obtained from [Cu(Ⅱ)(L-Trp)2] and the chiral sensor can recognize Trp enantiomers in the presence of Cu(II). Not only could the THi-GR nanocomposite act as redox probe producing signal and enhance electron transfer but also could retain the activity of ds-DNA. Meanwhile, the adduct profiles might play a role of conducting, speeding up the process of chiral recognition and improving the sensitivity. Hence, a novel model for recognition of other chiral molecules and chiral drugs and some useful information for design of new DNA targeted drugs are very expected.2. The novel nanosheets of Toluidin blue O functionalized reduced graphene oxide (TBO@rGO) were synthesized as a nano-interface to modify with BSA on GCE and a reagentless chiral-sensor for the recognition of a chiral drug, naproxen (Nap) was fabricated. The synergy of the prominent properties from TBO such as outstanding electroactivity and water solubility as well as positive charge and rGO such as large surface area, accelerating electron transfer and biocompatible properties gave rise to the nanosheets with double function, which not only acted as redox probe and amplified signal, but also immobilized BSA as much as possible via opposite-charged adsorption techniques and retained its activity. SEM and UV-vis spectrometry were performed to characterize the surface morphologies and structure of the BSA biofunctionalized rGO nanosheets; CV was employed to study and explore the electrochemical properties and kinetic parameters of the chiral interface; The interactions between BSA and Nap enantiomers were investigated by CV and quartz crystal microbalance (QCM); The influence of concentration of target analyte, pH of base solution and incubation time on chiral recognition were inspected. The results indicated larger electrochemical response was assigned to R-Nap. Owing to the electrochemical merits, TBO@rGO nanosheets have much potential application in electrochemistry and sensor devices.3. Gold nanoparticles/graphene (Au NPs/GNs) nanohybrids were synthesized with "all in one" strategy. Together with the join of chiral selector (β-cyclodextrin,β-CD) and chitosan (CS), the chiral nanohybrids (CS//β-CD/Au NPs/GNs) with recognition function were prepared by an easy mixing method. The chiral-responsive nano-platform towards chiral drug, Nap was constructed via the easy coating of the nanohybrids on GCE. The chiral nanohybrids were characterized with UV-vis, fourier transform infrared (FT-IR) spectrometry, SEM, Transmission Electron Microscopy (TEM) etc; Using [Fe(CN)6]4-/3-as redox probe, CV and differential pulse voltammetry (DPV) were utilized to inspect the interactions between the chiral interface and Nap enantiomers, and the effects derived from different interfaces were compared; Some factors such as concentration of target analyte, pH of solution and incubation time on chiral recognition were investigated. The result indicated the chiral interface underwent stronger interaction with S-Nap. This chiral nanohybrids and chiral sensor are easily prepared, consistent with "Green Chemistry" and also provide some reference for the application of GNs and design of novel chiral-sensors.