Liju Guo

The application of thionine–graphene nanocomposite in chiral sensing for Tryptophan enantiomers

The thionine-graphene (THi-GR, positively charged) nanocomposite was successfully synthesized as a good biocompatible matrix for ds-DNA which acted as a chiral selector to construct an electrochemical chiral biosensor for Tryptophan (Trp) enantiomers sensing with the assistance of Cu(II). The nano-bionic interface was constructed as follows: Firstly, the nanocomposite was dropped on the surface of glassy carbon electrode (GCE), and then ds-DNA (negatively charged) was immobilized onto the nanocomposite film via the opposite-charged adsorption techniques. This biofunctionalized nanocomposite was characterized with scanning electron microscopy (SEM), ultraviolet-visible (UV-vis) spectrometry and cyclic voltammetry (CV). The chiral biosensor was employed to study the recognition effect between ds-DNA and Trp enantiomers by CV. The results show that larger electrochemical response was obtained from l-Trp when Cu(II) was present, indicating this strategy could be employed to enantioselectively recognize Trp enantiomers. Under optimum conditions, the chiral biosensor exhibited a good linear response to Trp enantiomers in the range of the concentration of [Cu(II)(Trp)2] from 5.0 × 10(-4) to 2.5mM with a low limit of detection of 0.17 μM (S/N=3). The binding constant was calculated to be 2.97 × 10(3)M(-1) for [Cu(II)(l-Trp)2] and 2.50 × 10(2)M(-1) for [Cu(II)(d-Trp)2].

A reagentless enantioselective sensor for tryptophan enantiomers via nanohybrid matrices

A reagentless method for the selective electrochemical discrimination of tryptophan (Trp) enantiomers has been developed by means of adsorbing human serum albumin (HSA) onto a methylene blue–multi-wall carbon nanotubes nanohybrid (MB–MWNTs) modified glassy carbon electrode (HSA/MB–MWNT/GCE). Cyclic voltammetry (CV) was employed to monitor the immobilization processes and the electrochemical behavior of the Trp enantiomers on the HSA/MB–MWNT/GCE. It was found that the newly developed electrode exhibited different interactions toward the Trp enantiomers, with a stronger binding effect obtained between HSA and L-Trp. The linear range of the biosensor was investigated from 1.0 × 10−1 to 1.0 × 10−8 mol L−1 with a detection limit of 3.3 × 10−9 mol L−1. In addition, the values of the enantioselectivity coefficient (α) and the association constant (k) were calculated. This work appears to provide a reference for the development of a reagentless electrochemical chiral biosensor and improves understanding of the high selectivity between biological molecules and chiral amino acids.

Chiral sensing for electrochemical impedance spectroscopy recognition of lysine enantiomers based on a nanostructured composite

A simple and reliable chiral sensing platform for enantioselective recognition of lysine (Lys) enantiomers based on a nanostructured composite (NC) via the electrochemical impedance spectroscopy (EIS) technique was described. The NC has been successfully synthesized through covalent linkage among the semiconductor 3,4,9,10-perylenetetracarboxylic acid (PTCA), thionine (Thi) and chiral selector L-N-tert-butoxycarbonyl-O-benzylserine (L-BBSer). The stepwise synthesis process of the NC was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and EIS. The enantioselective interaction assay between NC modified glassy carbon electrode and lysine enantiomers relied on EIS technology. As a prototype example, good recognition results were obtained from the difference of electron transfer resistance (ΔRet), where ΔRetD was larger than ΔRetL and linear responses in ΔRet were found for Lys enantiomers ranging from 100 nM to 10 mM with a detection limit of 33 nM (S/N = 3). In addition, the results of analyzing another four amino acids revealed the specificity of the proposed sensor. The developed sensor with the advantages of simple preparation, long-term stability, good sensitivity and commendable selectivity, holds great potential application for the nanostructured composite adulterated with a chiral selector in chiral bio-electroanalysis.

Enantioselective recognition of penicillamine enantiomers on bovine serum albumin-modified glassy carbon electrode

As a natural chiral selector, bovine serum albumin (BSA) has been used to recognize penicillamine (Pen) enantiomers through electrochemical methods. The recognition and assay rely on the stereoselectivity of BSA embedded in ultrathin Al2O3 sol–gel film coated on the surface of glassy carbon electrode (BSA/GCE). The enantioselective interaction between Pen enantiomers and BSA was monitored by cyclic voltammetry and electrochemical impedance spectroscopy measurements, from which larger response signals were obtained from d-Pen. The factors influencing the performance of the modified biosensor were also investigated. The association constant (K) was calculated to be 1.93 × 104 L mol−1 for d-Pen and 1.20 × 103 L mol−1 for l-Pen. A good linear response was exhibited with the concentration of Pen enantiomers by BSA/GCE over the range of 1 × 10−8–1 × 10−1 mol L−1 with a detection limit of 3.31 × 10−9 mol L−1.

DNA-based nanocomposite as electrochemical chiral sensing platform for the enantioselective interaction with quinine and quinidine

A novel chiral sensing platform, employing a biomolecule-based nanocomposite prepared by calf thymus double stranded DNA, methylene blue and multiwall carbon nanotubes (DNA–MB–MWNTs), was utilized for the discrimination of quinine (QN) and quinidine (QD). The DNA-based nanocomposite, which could be used as an electrochemical sensing unit and chiral probe, was characterized by transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis) and cyclic voltammetry (CV). After the proposed sensing platform interacted with QN and QD, a larger electrochemical signal was obtained from QD. The comparative experiments indicated that the proposed strategy not only simplified the fabrication processes but also enhanced the enantioselective interaction in chiral analysis. In addition, experimental factors such as acidity, interaction time and the concentration of enantiomers were investigated in regards to the effect on enantioselective interaction.

Chiral recognition of penicillamine enantiomers based on a vancomycin membrane electrode

An enantioselective membrane electrode based on vancomycin (Van) was proposed for the assay of penicillamine enantiomers. Cyclic voltammetry, electrochemical impedance spectroscopy, atomic force microscopy and UV-Vis spectra were employed to investigate the chiral recognition phenomenon. The results exhibited that the binding effect between D-penicillamine (D-Pen) and the proposed Van membrane electrode was obviously stronger than that of L-penicillamine (L-Pen). In addition, the amount of Van, the pH of the supporting electrolyte solution and the concentration of Pen enantiomers were systematically investigated and optimized. The association constant (K) was calculated to be 1.05 × 104 L mol−1 for D-Pen and 1.40 × 102 L mol−1 for L-Pen. The enantioselective concentration range of the proposed membrane electrode is 10−7 to 10−2 mol L−1. The results suggested that the chiral selective membrane has the potential to discriminate and determine chiral drugs in the pharmaceutical application of electrochemical analysis.

Stereoselective interaction between hemoglobin and penicillamine enantiomers modified chiral surfaces

Chiral surfaces were obtained based on self-assembled monolayers of penicillamine enantiomers (L- or D-Pen) onto gold electrodes, and the enantioselective behavior was investigated by adsorbing hemoglobin (Hb) on the different chiral surfaces. Electrochemical methods, UV-vis and atomic force microscopy were adopted to monitor the protein adsorption. The properties of Hb adhesion on different chiral surfaces were further demonstrated by electrocatalytic responding to H2O2. The results showed that L-Pen had a higher dense adsorption to Hb than that of D-Pen. The Michaelis–Menten constants of the Hb/L-Pen/Au and Hb/D-Pen/Au sensors were first calculated to appeal to chiral recognition, the results showed that Hb/L-Pen/Au had a stronger catalytic ability, and further certified that Hb could adsorb on L-Pen assembled surfaces more easily. This work provided a promising reference for the investigation of chiral molecules.

The selective interaction between N-isobutyryl-cysteine enantiomers and L-methotrexate

Simple and sensitive chiral interfaces were constructed by assembling L- or D-N-isobutyryl-cysteine (NIBC) on a gold electrode surface through an Au–S bond, and the two chiral interfaces were utilized to interact with L-methotrexate (L-Mtx). The surface characteristics and the process of interaction were explored via cyclic voltammetry (CV). The difference in peak current after L- and D-NIBC interacted with L-Mtx reached 525.3 μA, and a larger current difference was obtained from the L-NIBC interface, suggesting a stereoselective effect between L-Mtx and NIBC enantiomers. Therefore, the chiral NIBC interfaces could not only enhance the electron transfer of L-Mtx, but could also discriminate between NIBC enantiomers.