A novel electrochemical chiral interface based on sandwich-structured molecularly imprinted SiO2/AuNPs/SiO2 for enantioselective recognition of cysteine isomers

Gold-silica hybrid nanolabels decorated with recognition and signaling bioreagents for enhanced electrochemical immunodetection of chemokine ligand-12 in colorectal cancer early diagnosis and monitoring

The use of gold-silica nanoconjugates (Au@SiO₂NCs) decorated with biotinylated detection antibodies (b-dAb) and horseradish peroxidase (HRP) is reported for the improved electrochemical immunosensing of chemokine ligand-12 (CXCL12), a relevant chemokine implicated in colorectal cancer (CRC) progression. Implemented on an amperometric sandwich immunoplatform the resulting nanobioconjugates provided significant signal amplification which is attributed to the high enzyme loading capacity and improved antibody orientation. The role played by each of the nanomaterials forming the nanohybrid was evaluated. Under optimized conditions, the developed immunoplatform exhibited a linear response ranging from 72 to 1000 pg mL-1, a 4 times higher sensitivity than the conventional labeling-based immunoplatform, a LOD of 22 pg mL-1, and a storage stability of 1 month. The immunoplatform was applied to the determination of CXCL12 in plasma from healthy individuals and CRC patients. The clinically relevant results obtained demonstrate the potential of plasma CXCL12 levels as a biomarker for both the early diagnosis of CRC and the monitoring of its progression.

A Molecularly Imprinted Chiral Sensor for Colorimetric Resolution of Cysteine Enantiomers Utilizing Oxidase Mimicking of Mn2O3 and Reducing Capacity of Cysteine

A surface molecularly imprinted chiral sensor is designed for colorimetric resolution of cysteine (Cys) enantiomers by utilizing oxidase mimicking of Mn2O3 and reducing capacity of Cys. As the templates, l-Cys is anchored to the Mn2O3 nanozymes through Mn-S bonds, and the resultant Mn2O3-l-Cys is coated by the rigid silicon dioxide (SiO2) imprinting layer. After the l-Cys templates are removed by calcination, molecularly imprinted SiO2@Mn2O3 (MI-SiO2@Mn2O3) is obtained. Owing to the oxidase mimicking of Mn2O3, colorless 3,3',5,5'-tetramethylbenzidine (TMB) can be converted into blue oxidized TMB (oxTMB) by the MI-SiO2@Mn2O3; while the blue colored oxTMB can be reduced to colorless TMB by the reductive Cys. Due to the higher affinity of MI-SiO2@Mn2O3 for l-Cys, more d-Cys is left in the solution after the Cys enantiomers are respectively incubated with the MI-SiO2@Mn2O3, which can make the fading of oxTMB easier. Therefore, colorimetric resolution of the Cys enantiomers can be achieved by the developed molecularly imprinted chiral sensor.

Dual-template rectangular nanotube molecularly imprinted polypyrrole for label-free impedimetric sensing of AFP and CEA as lung cancer biomarkers

A high-performance sensing layer based on dual-template molecularly imprinted polymer (DMIP) was fabricated and successfully applied for one-by-one detection of carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP) as lung cancer biomarkers. The plastic antibodies of AFP and CEA were created into the electropolymerized polypyrrole (PPy) on a fluorine-doped tin oxide (FTO) electrode. Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) tests were performed to pursue the formation and characterization of the sensing layer. Methyl orange (MO) increased the conductivity of PPy and induced the formation of MO doped PPy (PPy-MO) rectangular-shaped nanotubes. Using impedimetric detection, the rebinding of the template antigens was evaluated, the charge transfer resistance increased as the concentration of AFP and CEA increased. The linear dynamic ranges of 5-10⁴ and 10-10⁴ pg mL^-1 and detection limits of 1.6 and 3.3 pg mL^-1 were obtained for CEA and AFP, respectively. Given satisfactory results in the determination of AFP and CEA in the human serum samples, high sensitivity, and good stability of DMIP sensor made it a promising method for sensing of AFP and CEA in serum samples.

Recent advances of the ionic chiral selectors for chiral resolution by chromatography, spectroscopy and electrochemistry

Ionic chiral selectors have been received much attention in the field of asymmetric catalysis, chiral recognition, and preparative separation. It has been shown that the addition of ionic chiral selectors can enhance the recognition efficiency dramatically due to the presence of multiple intermolecular interactions, including hydrogen bond, π-π interaction, van der Waals force, electrostatic ion-pairing interaction, and ionic-hydrogen bond. In the initial research stage of the ionic chiral selectors, most of work center on the application in chromatographic separation (capillary electrophoresis, high-performance liquid chromatography, and gas chromatography). Differently, more and more attention has been paid on the spectroscopy (nuclear magnetic resonance, fluorescence, ultraviolet and visible absorption spectrum, and circular dichroism spectrum) and electrochemistry in recent years. In this tutorial review as regards the ionic chiral selectors, we discuss in detail the structural features, properties, and their application in chromatography, spectroscopy, and electrochemistry.

Enantioselective recognition of tryptophan isomers with molecularly imprinted overoxidized polypyrrole/poly(p-aminobenzene sulfonic acid) modified electrode

Poly(p-aminobenzene sulfonic acid) (pABSA) was electrodeposited onto the surface of a glassy carbon electrode (GCE), which was then used for the preconcentration of l-tryptophan (l-Trp) due to the electrostatic and π-π interactions between pABSA and l-Trp. Polypyrrole (PPy) was electrodeposited onto the surface of the l-Trp enriched pABSA, and then the l-Trp templates were removed, resulting in molecularly imprinted PPy/pABSA. To avoid the interference from the oxidation peak of PPy on the following electrochemical chiral recognition of Trp isomers, PPy was overoxidized by cyclic voltammetry (CV). The resultant molecularly imprinted overoxidized PPy (OPPy)/pABSA modified GCE exhibits higher affinity toward l-Trp than d-tryptophan (d-Trp); that is, the oxidation peak current of l-Trp is greatly higher than that of d-Trp at the molecularly imprinted OPPy/pABSA modified GCE.

Extraction of activated epimedium glycosides in vivo and in vitro by using bifunctional-monomer chitosan magnetic molecularly imprinted polymers and identification by UPLC-Q-TOF-MS

In this work, efficient, sensitive bifunctional-monomer chitosan magnetic molecularly imprinted polymers (BCMMIPs) were fabricated and successfully applied to concentrate the metabolites of Epimedium flavonoids in rat testis and bone that were later analyzed using UPLC-Q-TOF-MS. Using chitosan and methacrylic acid as co-functional monomers, BCMMIPs exhibited a large adsorption capacity (7.60 mg/g), fast kinetics (60 min), and good selectivity. Chitosan is bio-compatible and non-toxic, and methacrylic acid provides multiple hydrogen bond donors. The BCMMIPs were injected into rat testis to specifically enrich the total flavonoid metabolites in vivo and were used to extract metabolites from bone in vitro. The results showed that the BCMMIPs coupled with UPLC-Q-TOF-MS successfully identified 28 compounds from testis and 18 compounds from bone, including 19 new compounds. This study provided a reliable protocol for the concentration of metabolites from complex biological samples, and several new metabolites of Epimedium flavonoids were found in vivo and in vitro.

Early-stage cervical cancer diagnosis based on an ultra-sensitive electrochemical DNA nanobiosensor for HPV-18 detection in real samples

BACKGROUND

In several years ago, infection with human papillomaviruses (HPVs), have been prevalent in the worlds especially HPV type 18, can lead to cervical cancer. Therefore, rapid, accurate, and early diagnosis of HPV for successful treatment is essential. The present study describes the development of a selective and sensitive electrochemical biosensor base on DNA, for early detection of HPV-18. For this purpose, a nanocomposite of reduced graphene oxide (rGO) and multiwalled carbon nanotubes (MWCNTs) were electrodeposited on a screen-printed carbon electrode (SPCE). Then, Au nanoparticles (AuNPs) were dropped on a modified SPCE. Subsequently, single strand DNA (ssDNA) probe was immobilized on the modified electrode. The link attached between AuNPs and probe ssDNA provided by L-cysteine via functionalizing AuNPs (Cys-AuNPs). The differential pulse voltammetry (DPV) assay was also used to electrochemical measurement. The measurement was based on the oxidation signals of anthraquninone-2-sulfonic acid monohydrate sodium salt (AQMS) before and after hybridization between the probe and target DNA.

RESULTS

The calibration curve showed a linear range between 0.01 fM to 0.01 nM with a limit of detection 0.05 fM. The results showed that the optimum concentration for DNA probe was 5 µM. The good performance of the proposed biosensor was achieved through hybridization of DNA probe-modified SPCE with extracted DNA from clinical samples.

CONCLUSIONS

According to the investigated results, this biosensor can be introduced as a proprietary, accurate, sensitive, and rapid diagnostic method of HPV 18 in the polymerase chain reaction (PCR) of real samples.

Chiral Enantioselective Assemblies Induced from Achiral Porphyrin by l- and d-Lysine

π-Conjugated porphyrins have aroused particular attention for nanofabrication and biomimics; however, little attention has been paid to porphyrins-based chiral analysis owing to the achiral feature of porphyrins. Here, we demonstrated a chiral self-assembly of achiral porphyrin induced by l- and d-lysine (l- and d-Lys), and the resultant porphyrin 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 also investigated by using tryptophan (Trp) isomers as the model, and the results indicated that the developed chiral self-assembly showed significantly higher affinity toward l-Trp than d-Trp. 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).

Utilizing modules of different functions to construct a Janus-type membrane and derivative 3D Janus-type tube displaying synchronous trifunction of conductive aeolotropism, magnetism and luminescence

The microstructures and macrostructures play a crucial role in the properties and applications of multifunctional materials. Herein, microscopic partition and macroscopic partition are combined by devising and preparing different modules that can be elaborately devised to possess specific performances. A two-dimensional (2D) 3-module Janus-type membrane multifunctionalized by conductive aeolotropism, magnetism and luminescence (defined as 3M-CML Janus-type membrane) is constructed via electro-spinning. The modular structure of 3M-CML Janus-type membrane is obtained by devising and constructing three different modules, including luminescence module (denoted as L module), conductive aeolotropism-luminescence module (marked as C-L module) and magnetism-luminescence module (named as M-L module). The results prove that almost no mutual detrimental influences exist among different modules owing to the macroscopic modular structure and Janus-type structure, which effectively avoids the negative interactions among different materials. Tb(BA)₃phen/PVP nanofiber, [PMMA/Eu(BA)₃phen]//[PMMA/PANI] Janus-type nanoribbon and [PMMA/Tb(BA)₃phen]//[PMMA/Fe₃O₄] Janus-type nanoribbon are, respectively, selected as building units of the three modules, which further prevents the negative interactions among different materials and improves the versatility of 3M-CML Janus-type membrane. The luminescence, adjustable conductive aeolotropism and variable magnetism of 3M-CML Janus-type membrane are systematically discussed. Meanwhile, novel flexible four types of brand-new three-dimensional (3D) Janus-type tubes are obtained by rolling modularly devised 2D 3M-CML Janus-type membrane with different rolling schemes. As derivatives of the 2D 3M-CML Janus-type membranes, macroscopic 3D Janus-types tubes exhibit similar performances to 2D 3M-CML Janus-type membranes. The 2D Janus-type membrane and 3D Janus-type tube will have momentous applications in flexible electronics and nanodevices in the future.

Single-Template Molecularly Imprinted Chiral Sensor for Simultaneous Recognition of Alanine and Tyrosine Enantiomers

Chiral recognition of l-amino acids is of significant importance due to the crucial role of l-amino acids in life sciences and pharmaceutics. In this work, a chiral sensor with capability of probing two chiral amino acids by an attractive single-template molecular imprinting strategy is introduced and used in the simultaneous chiral recognition of d/l-alanine (d/l-Ala) and d/l-tyrosine (d/l-Tyr). The assay relies on the hydrolysis of l-alanyl-l-tyrosine dipeptide doped in silica/polypyrrole (SiO₂/PPy) under acidic conditions, resulting in l-Ala and l-Tyr coimprinted chiral sensor. This work opens up a new avenue for simultaneous chiral sensing of two or more chiral amino acids by incorporating only one template, circumventing the shortcomings encountered with multitemplate molecularly imprinted technology.

Perylene-functionalized graphene sheets modified with chitosan for voltammetric discrimination of tryptophan enantiomers

A composite was prepared from graphene functionalized with 3,4,9,10-perylene tetracarboxylic acid and chitosan (rGO-PTCA-chitosan) by a chemical method. It involves non-covalent functionalization of rGO with PTCA followed by amidation reaction with chitosan. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and electrochemical methods were used to characterize the composites. By combining the chiral features of chitosan and the excellent electrochemical behaviors of rGO-PTCA, a graphene-based material with enantioselectivity was constructed for electrochemical chiral recognition of tryptophan (Trp) enantiomers. A glassy carbon electrode (GCE) modified with rGO-PTCA-chitosan had a higher recognition capability for L-Trp than for D-Trp. Best operated at a working voltage near 0.78 V (vs. SCE), the enantioselectivity coefficient is 3.0. The sensor has a linear response in the 1 mM to 10 mM Trp concentration range and a 1.2 μM detection limit (at S/N = 3) for L-Trp, and of 3.0 μM to D-Trp. The sensor was successfully used to detect Trp enantiomers in real samples, and a recognition mechanism is presented. Graphical abstract Schematic presentation of a composoie prepared by graphene functionalized with 3,4,9,10-perylene tetracarboxylic acid and chitosan (rGO-PTCA-chitosan) via a chemical method. It involves non-covalent functionalization of rGO with PTCA followed by amidation reaction with chitosan and voltammetric determination of tryptophan enantiomers.

Efficient enantiorecognition of amino acids under a stimuli-responsive system: synthesis, characterization and application of electroactive rotaxane

An electroactive chiral rotaxane, consisting of a polymeric chiral ionic liquid as the flexible axle and 18-crown-6 as the wheel, is synthesized for efficient enantiorecognition of amino acids.

Chiral Sensing Platform Based on the Self-Assemblies of Diphenylalanine and Oxalic Acid

Molecular self-assemblies offer a promising strategy for the synthesis of advanced materials for the construction of novel chiral sensing systems, and latest innovations on such self-assemblies are focused on simple building blocks in biology such as nucleic acids, lipids, and peptides. Herein, the self-assemblies of diphenylalanine (FF) and oxalic acid (OA) were prepared as the chiral sensing device for the recognition of tryptophan (Trp) isomers. Interestingly, the self-assemblies composed of OA and FF with different charging states (neutral, positively charged, and negatively charged) exhibited quite different morphologies, resulting in significantly different chiral recognition ability toward the Trp isomers. Also, in this work, the temperature sensitivity and chiral selectivity of the proposed FF-OA self-assemblies were also studied. From a practical point of view, the FF-OA self-assemblies were finally applied for the determination of precise levels of d-Trp in the racemic mixture of Trp isomers.