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.

A Comparative Analysis of Prehospital Emergency Treatments: Midazolam Intramuscularly, Diazepam Enema, and Chloral Hydrate Enema for Pediatric Convulsions.

Objective: This study aimed to compare the effectiveness of prehospital emergency treatments using midazolam (MDL) intramuscularly, diazepam (DZP) enema, and chloral hydrate (CH) enema in managing pediatric convulsions. Methods: A comparative observational study was conducted, and a total of 140 children with acute convulsions treated with prehospital anti-convulsions at Qinhuangdao First Hospital's emergency department between June 2015 and May 2019 were included in this study. The children were categorized based on the prehospital anti-convulsion measures received: group M (n = 48) received MDL intramuscularly, group D (n = 46) received DZP enema, and group C (n = 46) received CH enema. The emergency effects of the three treatment groups were compared. Results: 1. Group M showed significantly shorter treatment preparation time and total rescue time compared to groups C and D (both P < .05); no significant difference was observed between groups C and D (both P > .05), including convulsion control time in the effective cases (45 in group M, 42 in group C, and 43 in group D) (all P > .05 Group M had effective rates of 93.75%, while group C and group D had rates of 91.3% and 93.48%, respectively (all P > .05); Group M had more controlled cases at 1 min, 3 min, 5 min, and 10 min than group C and group D (all P > .05). Group M had significantly fewer relapses, cases requiring intravenous maintenance treatment, and faster convulsion control after intravenous maintenance compared to groups C and D (P < .05), with no significant differences between groups C and D in time to recovery of consciousness and length of hospitalization (P > .05). 4. Systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), respiratory (R) frequency, and peripheral oxygen saturation (SpO2) showed no significant differences before and 10 minutes after medication in all three groups (P > .05); SBP and DBP levels fluctuated within the normal range, while HR decreased, R frequency decreased, and SpO2 increased significantly 10 minutes after medication compared to before treatment (P < .05). 5. No significant adverse effects were observed in the three patient groups. Conclusions: MDL intramuscular injection, DZP enema, and CH enema were effective prehospital treatments for pediatric acute convulsions. MDL intramuscular injection demonstrated advantages such as fast onset, reliable efficacy, ease of use, and high safety, making it more suitable for the prehospital treatment of pediatric convulsions.

Preparation and Stability of Monodisperse Amorphous CaCO3 Microspheres of High Hardness and Sphericity.

Using amorphous CaCO3 (ACC) to biomimic the crustacean exoskeleton and optimize the physical and chemical properties of the polymeric phase of ACC holds great promise. Controlling the ACC morphology and stability is key in this process. For this article, monodisperse ACC microspheres, with a high sphericity of 0.973 ± 0.001 and a hardness of 0.6755 GPa, were prepared using the gas diffusion method in the presence of Mg2+. Their hardness is 3.58-16 times greater than that ever reported before for ACC microspheres. The stability of ACC is strongly affected by environmental conditions. The liquid phase and high temperature are not conducive to its stability, but ACC microspheres do have high stability under ambient conditions. After 100 days under such conditions, only a small amount of crystallization occurs, and their spherical shape survives intact. This article provides guidance for the preparation of ACC biomimetic composites, sheds light on the biological function of ACC in crustacean exoskeletons, and improves the theoretical understanding of the mechanism of biomineralization.

Biomimetic Molecular Clamp Nanopores for Simultaneous Quantifications of NAD+ and NADH.

NADH/NAD+ is pivotal to fundamental biochemistry research and molecular diagnosis, but recognition and detection for them are a big challenge at the single-molecule level. Inspired by the biological system, here, we designed and synthesized a biomimetic NAD+/NADH molecular clamp (MC), octakis-(6-amino-6-deoxy)-γ-cyclomaltooctaose, and harbored in the engineered α-HL(M113R)7 nanopore, forming a novel single-molecule biosensor. The single-molecule measurement possesses high selectivity and a high signal-to-noise ratio, allowing to simultaneously recognize and detect for sensing NADH/NAD+ and their transformations.

Crowding-Induced DNA Translocation through a Protein Nanopore.

A crowded cellular environment is highly associated with many significant biological processes. However, the effect of molecular crowding on the translocation behavior of DNA through a pore has not been explored. Here, we use nanopore single-molecule analytical technique to quantify the thermodynamics and kinetics of DNA transport under heterogeneous cosolute PEGs. The results demonstrate that the frequency of the translocation event exhibits a nonmonotonic dependence on the crowding agent size, while both the event frequency and translocation time increase monotonically with increasing crowder concentration. In the presence of PEGs, the rate of DNA capture into the nanopore elevates 118.27-fold, and at the same time the translocation velocity decreases from 20 to 120 µs/base. Interestingly, the impact of PEG 4k on the DNA-nanopore interaction is the most notable, with up to ΔΔG = 16.27 kJ mol-1 change in free energy and 764.50-fold increase in the binding constant at concentration of 40% (w/v). The molecular crowding effect will has broad applications in nanopore biosensing and nanopore DNA sequencing in which the strategy to capture analyte and to control the transport is urgently required.

Nanopore Single-Molecule Analysis of Metal Ion-Chelator Chemical Reaction.

Metal ions play critical roles in wide range of biochemical and physiological processes, but they can cause toxicity if excessive ingestion or misregulation. Chelating agents offer an efficient mean for metal ions intoxication and therapeutics of diseases. Studies on metal ion-chelator interactions are important for understanding the reaction mechanism and developing new specific metal chelator drugs. However, it remains a significant challenge to detect the metal ion-chelator interactions at the molecular level. Here, we report a label-free nanopore sensing approach that enables single-molecule investigation of the complexation process. We demonstrate that the chemical reaction between Cu2+ and carboxymethyl-ß-cyclodextrin (CMßCD) in a nanoreactor is completely different from in the bulk solution. The formation constant (Kf = 4.70 × 104 M-1) increases 14 417-fold in the nanopore than that in the bulk solution (Kf = 3.26 M-1). The bioavailable CMßCD as a natural derivative with higher affinity for Cu2+ could be used in the safe medicinal removal of toxic metal. On the basis of the different ionic current signatures across an α-hemolysin (α-HL) mutant (M113N)7 nanopore lodged with a CMßCD adaptor in the presence and absence of Cu2+, the reversible molecular binding events to CMßCD can be in situ recorded and the single-molecule thermodynamic and kinetic information can be obtained. Interestly, we found that the Cu2+ binding leads to the increase of the channel current, rather than the blocking as usual nanopore experiment. The uncommon (on/off) characteristic could be very useful for fabricating the nanodevice. Furthermore, the unique nanopore sensor can provide a highly sensitive approach for detecting metal ions.

Metal-organic complex-functionalized protein nanopore sensor for aromatic amino acids chiral recognition.

Chiral recognition at single-molecule level for small active molecules is important, as exhibited by many nanostructures and molecular assemblies in biological systems, but it presents a significant challenge. We report a simple and rapid sensing strategy to discriminate all enantiomers of natural aromatic amino acids (AAA) using a metal-organic complex-functionalized protein nanopore, in which a chiral recognition element and a chiral recognition valve were equipped. A trifunctional molecule, heptakis-(6-deoxy-6-amino)-ß-cyclodextrin (am7ßCD), was non-covalently lodged within the nanopore of an α-hemolysin (αHL) mutant, (M113R)7-αHL. Copper(ii) ion reversibly bonds to the amino group of am7ßCD to form an am7ßCD-CuII complex, which allowed chiral recognition for each enantiomer in the mixture of AAA by distinct current signals. The CuII plugging valve plays a crucial rule that holds chiral molecules in the nanocavity for a sufficient registering time. Importantly, six enantiomers of all nature AAA could be simultaneously recognized at one time. Enantiomeric excess (ee) could also be accurately detected by this approach. It should be possible to generalize this approach for sensing of other chiral molecules.

Tetramethylammonium-filled protein nanopore for single-molecule analysis.

Nanopore technology, as the simplest and most inexpensive single-molecule tool, is being intensively developed. In nanopore stochastic sensing, KCl and NaCl have traditionally been employed as pore-filled electrolytes for recording the change of ion conductance in nanopores triggered by analyte translocation through the pore. However, some challenges limit its further advance. Here we used tetramethylammonium (TMA) chloride, instead of KCl, as a novel analysis system for nanopores. Some unique nanopore characteristics were observed: (1) The stability of the planar lipid bilayer for embedding the protein pores was elevated at least 6 times. (2) The TMA-Cl system could effectively reduce the noise of single-channel recording. (3) It was easy to control the insertion of protein pores into the lipid bilayer, and the formed single nanopore could last for a sufficiently long time. (4) TMA-Cl could be used as a DNA speed bump in the nanopore to slow DNA translocation speed. (5) The capacity of the nanopore capture of DNA (capture rate) increased significantly and simultaneously increased the translocation time of DNA in the pore. (6) The TMA-filled nanopore could discriminate between various polynucleotides.

Nanopore single-molecule analysis of DNA-doxorubicin interactions.

Anticancer activity and toxicity of doxorubicin (Dox) are associated with its DNA intercalation. To understand the role in gene regulation and the drug mechanism, it is a challenge to detect the DNA-Dox interaction at the single-molecule level without the use of laborious, time-consuming labeling assays and an error-prone amplification method. Here, we utilized the simplest and cheapest, yet highly sensitive, single-molecule nanopore technology to investigate the DNA-Dox interaction and explore in situ the intercalative reaction kinetics. Distinctive electronic signal patterns between DNA and the DNA-Dox complex allow protein nanopore to readily detect the changes in structure and function of DNA. After Dox insertion, nanopore unzipping time of DNA was elevated 10-fold while the blocking current decreased, demonstrating the higher affinity of the DNA-Dox complex (formation constant K(f) = 3.09 × 10(5) M(-1)). Continuous rapid nanopore detection in real time displayed that Dox intercalation in DNA is a two-state dynamic process: fast binding and slow conformational adaption. The nanopore platform provides a powerful tool for studying small molecule-biomacromolecule interactions and paves the way for novel applications aimed at drug screening and functional analysis.

Chiral superstructure of aragonite similar to Turritella terebra shell induced by CTAB's adsorption chirality.

A twisted dumbbell-like chiral superstructure can be easily assembled in aragonite under the co-action of CTAB and Mg2+, producing a microstructure that is very similar to that of Turritella terebra shell. Asymmetric adsorption of the CTAB head group on aragonite, namely "adsorption chirality", is the reason for the chiral assembly.

Simultaneous determination of dihydroxybenzene positional isomers by capillary electrochromatography using gold nanoparticles as stationary phase.

The paper describes the enhanced separation of o-, m-, p-dihydroxybenzene by capillary electrochromatography (CEC) using gold nanoparticles (AuNPs) as stationary phase. The effect of the AuNPs concentration upon separation was investigated. The experimental parameters, including separation voltage, pH, and concentration of running buffer, were optimized. Under the optimum conditions, a good resolution of three dihydroxybenzene isomers was obtained within 15 min in a 50 cm effective length capillary modified with 0.02 nmol/L AuNPs at a separation voltage of 16 kV in a 50 mmol/L acetate buffer (pH 5.0). The linear ranges were from 10(-6) to 10(-4) mol/L and the detection limits were as low as 10(-7) mol/L. This method was successfully used to analysis two kinds of hair coloring agent sample with recoveries in the range of 90-105% and relative standard deviations (RSD) less than 5.0%.

Studies on the interactions of copper and zinc ions with ß-amyloid peptides by a surface plasmon resonance biosensor.

The aggregation of ß-amyloid peptide (Aß) into fibrils plays an important role in the pathogenesis of Alzheimer's disease (AD). Metal ions including copper and zinc are closely connected to the precipitation and toxicity of Aß. In this study, a surface plasmon resonance (SPR) biosensor was constructed to investigate the interactions between Aß and metal ions. Aß peptide was immobilized on the SPR chip surface through a preformed alkanethiol self-assembled monolayer (SAM). Our observations indicate that the immobilized Aß undergoes a conformational change upon exposure to the metal ions. A difference in metal binding affinity between Aß(1-28) and Aß(1-42) was also detected. The results suggest that SPR is an effective method to characterize the interactions between Aß and metal ions.

Hybridization chain reaction (HCR) for amplifying nanopore signals.

Circulating tumor DNA (ctDNA) in the blood is an important biomarker for noninvasive diagnosis, assessment, prediction and treatment of cancer. However, sensing performance of solid nanopore is limited by the fast kinetics of small DNA targets and unmatched dimensions. Here, we combines hybridization chain reaction (HCR) with nanopore detection to translate the presence of a small DNA target to characteristic nanopore signals of a long nicked DNA polymer. The amplification of nanopore signals obtained by HCR not only overcomes the functional limitation of solid nanopore, but also significantly elevates both selectivity and signal-to-noise ratio, which allows to detect ctDNA at a detection limit of 2.8 fM (S/N = 3) and the single-base resolution. Furthermore, the proposed method can apply in detection of ctDNA of KRAS G12DM in serum sample.

Nanopore biphasic-pulse biosensor.

Nanopores as artificial biomimetic nanodevices are of great importance for their applications in biosensing, nanomedicine and bioelectronics. However, it remains a challenge to detect small biomolecules especially small-sized proteins with high sensitivity and selectivity. In the article, we report a simple and efficient method for small-sized protein detection by constructing biphasic-pulse nanopore biosensor. Unlike the traditional resistive pulse sensing, the biphasic-pulse event can provide unique and abundant fingerprint information. Although the nanopore biphasic-pulse electrical signal is originated from both the molecular exclusion electrical resistance and the surface-charged effect of confined molecule, its frequency and amplitude of the waveform can be adjusted by pH, applied potential and salt concentration. Based on the frequency of the biphasic pulse, nanomolar concentration of proteins could be specifically detected and the limit of detection is 1.2 nM. In addition, the biphasic-pulse nanopore shows well discrimination in similar-sized protein detection and its signal generation is highly reproducible. The nanopore biphasic-pulse biosensor should have broad applications as a new generation of powerful single-molecule device.

Single-molecule porphyrin-metal ion interaction and sensing application.

It remains a significant challenge to study the interactions between metal ions and porphyrin molecules at single ion level. Here, we constructed a nanopore-based sensing for label-free and real-time analysis of the interaction between Cu2+ and 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin (TPPS). The results demonstrate that emerging electronic signatures of the Cu2+-TPPS complex that is completely different form the original free TPPS were observed in the α-hemolysin (α-HL) nanopore. Based on the distinctive electronic signal patterns between TPPS and Cu2+-TPPS complex, the unique nanopore sensor can achieve a highly sensitive detection of Cu2+ in aqueous media. The frequency of signature events showed a linear response toward the concentration of Cu2+ in the range of 0.03 µM - 1.0 µM, with a detection limit of 16 nM (S/N = 3). The sensing system also exhibited high selectivity against other metal ions, and the feasibility of this approach for practical applications was demonstrated with the determination of Cu2+ in running water.

A rapid and sensitive detection of HBV DNA using a nanopore sensor.

Nanopore analysis has emerged as the simplest single-molecule technique. We combined DNA probes with a nanopore electrochemical sensor for the rapid and sensitive detection of pathogenic DNA. The novel nanopore biosensor allows the single-base discrimination and detection of picomolar DNA in serum samples.

Determination of fumaric and maleic acids with stacking analytes by transient moving chemical reaction boundary method in capillary electrophoresis.

The paper presents an on-line transient moving chemical reaction boundary (MCRB) method for simply but efficiently stacking analytes in capillary electrophoresis (CE). The CE technique was developed for a rapid determination of fumaric and maleic acid. Based on the theory of MCRB, Effects of several important factors such as the pH and concentration of running buffer and the conditions of stacking analytes were investigated to acquire the optimum conditions. The optimized separations were carried out in a 20 mmol/L sulphate neutralized with ethylenediamine to pH 6.0 electrolytes using a capillary coated with poly (diallyldimethylammonium chloride) and direct UV detection at 214 nm. The optimized preconcentrations were carried out in 50 mmol/L borax (pH 9.0). The calibration curves were linear in the concentration range of 1.0×10⁻7-1.0×10⁻4 mol/L and 5.0×10⁻7-1.0×10⁻4 mol/L for fumaric and maleic acid with correlation coefficients higher than 0.9991. The detection limits were 5.34×10⁻8 mol/L for fumaric acid and 1.92×10⁻7 mol/L for maleic acid. This method was applied for determination of fumaric acid in apple juice and of fumaric and maleic acid in dl-malic, the recovery tests established for real samples were within the range 95-105%. This work provided a valid and simple approach to detect fumaric and maleic acid.