Measuring Binding Constants of Cucurbituril-Based Host-Guest Interactions at the Single-Molecule Level with Nanopores

Supramolecular host-guest nanosystems for overcoming cancer drug resistance

Cancer drug resistance has become one of the main challenges for the failure of chemotherapy, greatly limiting the selection and use of anticancer drugs and dashing the hopes of cancer patients. The emergence of supramolecular host-guest nanosystems has brought the field of supramolecular chemistry into the nanoworld, providing a potential solution to this challenge. Compared with conventional chemotherapeutic platforms, supramolecular host-guest nanosystems can reverse cancer drug resistance by increasing drug uptake, reducing drug efflux, activating drugs, and inhibiting DNA repair. Herein, we summarize the research progress of supramolecular host-guest nanosystems for overcoming cancer drug resistance and discuss the future research direction in this field. It is hoped that this review will provide more positive references for overcoming cancer drug resistance and promoting the development of supramolecular host-guest nanosystems.

Highly sensitive determination of L-glutamic acid in pig serum with an enzyme-free molecularly imprinted polymer on a carbon-nanotube modified electrode

Through electrochemical polymerization using L-glutamic acid (L-Glu) as a template and 4,6-diaminoresorcinol as a functional monomer, an enzyme-free molecularly imprinted polymer (MIP) based L-Glu sensor with multi-walled carbon nanotubes (MWCNTs) decorated on a glassy carbon electrode (GCE), namely G-MIP/MWCNTs/GCE, was developed in this work. The reaction conditions were optimized as follows: electrochemical polymerization of 23 cycles, pH of 3.0, molar ratio of template/monomer of 1 : 4, volume ratio of elution reagents of acetonitrile/formic acid of 1 : 1, and elution time of 2 min. The prepared materials and molecularly imprinted polymer were characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) as well as electrochemical methods. The electrochemical properties of different electrodes were investigated via differential pulse voltammetry (DPV), showing that the electrode of G-MIP/MWCNTs/GCE exhibited excellent catalytic oxidation activity towards L-Glu. A good linear relationship between peak-currents and L-Glu concentrations in a range from 1.00 × 10-8 to 1.00 × 10-5 mol L-1 was observed, with a detection limit of 5.13 × 10-9 mol L-1 (S/N = 3). The imprinted sensor possesses excellent selectivity, high sensitivity, and good stability, which have been successfully applied for the detection of L-Glu in pig serum samples with a recovery rate of 97.4-105.5%, being comparable to commercial high-performance liquid chromatography, demonstrating a simple, rapid, and accurate way for the determination of L-Glu in the fields of animal nutrition and biomedical engineering.

Recognition Receptor for Methylated Arginine at the Single Molecular Level

Among the various types of post-translational modifications (PTMs), methylation is the simple functionalized one that regulates the functions of proteins and affects interactions of protein-protein and protein-DNA/RNA, which will further influence diverse cellular processes. The methylation modification has only a slight effect on the size and hydrophobicity of proteins or peptides, and it cannot change their net charges at all, so the methods for recognizing methylated protein are still limited. Here, we designed a recognition receptor consisting of a α-hemolysin (α-HL) nanopore and polyamine decorated γ-cyclodextrin (am₈γ-CD) to differentiate the methylation of peptide derived from a heterogeneous nuclear ribonucleoprotein at the single molecule level. The results indicate that the modification of a methyl group enhances the interaction between the peptide and the recognition receptor. The results of molecular simulations were consistent with the experiments; the methylated peptide interacts with the receptor strongly due to the more formation of hydrogen bonds. This proposed strategy also can be used to detect PTM in real biological samples and possesses the advantages of low-cost and high sensitivity and is label-free. Furthermore, the success in the construction of this recognition receptor will greatly facilitate the investigation of pathogenesis related to methylated arginine.

Chemistry solutions to facilitate nanopore detection and analysis

Characteristic ionic current modulations will be produced in a single molecule manner during the communication of individual molecules with a nanopore. Hence, the information regarding the length, composition, and structure of a molecule can be extracted from deciphering the electrical message. However, until now, achieving a satisfactory resolution for observation and quantification of a target analyte in a complex system remains a nontrivial task. In this review, we summarize the progress and especially the recent advance in utilizing chemistry solutions to facilitate nanopore detection and analysis. The discussed chemistry solutions are classified into several major categories, including covalent/non-covalent chemistry, redox chemistry, displacement chemistry, back titration chemistry, chelation chemistry, hydrolysis-chemistry, and click chemistry. Considering the significant success of using chemical reaction-assisted nanopore sensing strategies to improve sensor sensitivity & selectivity and to study various topics, other non-chemistry based methodologies can undoubtedly be employed by nanopore sensors to explore new applications in the interdisciplinary area of chemistry, biology, materials, and nanotechnology.

Current Simultaneous Discrimination of Mismatched MicroRNAs Using Base-Flipping within the α-Hemolysin Latch

The simultaneous discrimination of let-7 microRNAs (miRNAs) would greatly facilitate the early diagnosis and prognosis monitoring of diseases. In this work, a molecular beacon DNA probe was designed to be able to flip out its mismatched cytosine base within the α-hemolysin (α-HL) latch and generate completely separated blocking currents to identify the single-base difference. As a result, the characteristic blocking current of fully matched MB/let-7a and single-base mismatched MB/let-7f was 84.30 ± 0.92 and 87.05 ± 0.86% (confidence level P 95%), respectively. Let-7 miRNA family let-7a and let-7f were completely simultaneously discriminated, which could be attributed to the following strengths. (1) The statistic distribution of blocking current is extremely concentrated with a small relative standard deviation (RSD) of less than 1% and a narrow distribution range. (2) Complete separation is achieved with a high separation resolution of 1.54. (3) The cytosine base flipping out within the α-HL latch provides a universal labeling-free strategy to simultaneously discriminate the single-base mismatch. Overall, the target let-7f sequences were detected with a linear range from 0.001 to 10 pM in human serum samples containing 200 nM let-7a. Great potential has been demonstrated for precise detection, early diagnosis, and prognosis monitoring of diseases related to single-base difference.

Multiplex quantitative detection of SARS-CoV-2 specific IgG and IgM antibodies based on DNA-assisted nanopore sensing

The coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread into a global pandemic. Early and accurate diagnosis and quarantine remain the most effective mitigation strategy. Although reverse transcriptase polymerase chain reaction (RT-qPCR) is the gold standard for COVID-19 diagnosis, recent studies suggest that nucleic acids were undetectable in a significant number of cases with clinical features of COVID-19. Serologic assays that detect human antibodies to SARS-CoV-2 serve as a complementary method to diagnose these cases, as well as to identify asymptomatic cases and qualified convalescent serum donors. However, commercially available enzyme-linked immunosorbent assays (ELISA) are laborious and non-quantitative, while point-of-care assays suffer from low detection accuracy. To provide a serologic assay with high performance and portability for potential point-of-care applications, we developed DNA-assisted nanopore sensing for quantification of SARS-CoV-2 related antibodies in human serum. Different DNA structures were used as detection reporters for multiplex quantification of immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies against the nucleocapsid protein of SARS-CoV-2 in serum specimens from patients with conformed or suspected infection. Comparing to a clinically used point-of-care assay and an ELISA assay, our technology can reliably quantify SARS-CoV-2 antibodies with higher accuracy, large dynamic range, and potential for assay automation.

Cucurbiturils in nucleic acids research

During the past ten years, the importance of cucurbiturils (CB[n]) as macrocyclic hosts in supramolecular assemblies with various types of natural and synthetic nucleic acids (NAs) has increased explosively. As a component of such systems, CB[n] macrocycles can play a wide spectrum of roles from drug and gene delivery vehicles to catalysts/inhibitors of biochemical reactions and even building blocks for NA-based materials. The aim of this highlight article is to describe the development of the CB[n] applications in nucleic acids research and to outline the current situation and perspectives of this fascinating synergistic combination of supramolecular chemistry of CB[n] and NAs.

Teaching indicators to unravel the kinetic features of host–guest inclusion complexes

Three new, practically convenient methods are introduced for measuring kinetic parameters of supramolecular host–guest and protein–ligand complexes. Combined with thermodynamic data, this allows for an in-depth of the binding mechanism.

Highly sensitive determination of L-tyrosine in pig serum based on ultrathin CuS nanosheets composite electrode

Nanometer-sized copper sulfide has remarkable properties such as metal like electrical conductivity and electrocatalytic activity. In this work, ultrathin copper sulfide nanosheets (CuS NS) were synthesized and employed to modify on surface of glassy carbon electrode (GCE) combining with chitosan (CS) and acidified multi-walled carbon nanotubes (F-MWCNTs). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the shape of CuS NS was hexagon with side length of 13.33 ± 0.67 nm and thickness of 4.50 ± 0.58 nm. The electrochemical characteristics of different nanocomposite modified electrodes were examined by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), indicating that the modified electrode of CuS NS-CS/F-MWCNTs/GCE possessed good electrocatalytic activity towards oxidation of L-tyrosine (L-Tyr). Under the optimal condition, the modified electrode exhibited a wide linear response range for L-Tyr (0.08-1.0 μM) with a detection limit of 4.9 nM. No obvious interferences from coexisted two-fold of L-tryptophan and 50-fold of other amino acids could be observed, indicating its relatively good selectivity. The electrode also had good repeatability, reproducibility and stability. Compared with a commercial instrument analytical method, HPLC, the electrode can be successfully applied to the determination of L-Tyr in pig serums with a recovery rate of 95.7%-102.6%, and its test results are in good agreement with that of HPLC, showing its promising application value.

Visible-light-promoted organic dye-catalyzed sulfidation and phosphorylation of arylhydrazines toward aromatic sulfides and diarylphosphoryl hydrazides

Visible-light-promoted sulfidation and phosphorylation of arylhydrazines for the synthesis of aromatic sulfides and diarylphosphoryl hydrazides were developed using the organic dyes rose bengal and Na₂-eosin Y as photocatalysts, respectively.

Silver-mediated radical phosphorylation/cyclization of N-allylbenzamides to access phosphoryl-substituted dihydroisoquinolones

A silver-mediated phosphorylation/cyclization of N-allylbenzamides with phosphine oxides for the synthesis of phosphoryl-substituted dihydroisoquinolones was developed.