A Novel Electrochemical DNA Biosensor Fabricated with Layer‐by‐Layer Covalent Attachment of Multiwalled Carbon Nanotubes and Gold Nanoparticles

A novel DNA biosensor has been fabricated for the detection of DNA hybridization based on layer‐by‐layer (LBL) covalent assembly of gold nanoparticles (GNPs) and multiwalled carbon nanotubes (MWCNTs). The stepwise LBL assembly process was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The hybridization events were monitored by differential pulse voltammetry (DPV) measurement of the intercalated doxorubicin, and the factors influencing the performance of the DNA hybridization was investigated in detail. The signal was linearly changed with target DNA concentration increased from 0.5 to 0.01 nM, and had a detection limit of 7.5 pM (signal/noise ratio of 3). In addition, the DNA biosensor showed an excellent reproducibility and stability under the DNA‐hybridization conditions.     

Using the Aggregation of Latex Polymers in the Fabrication of Reproducible Enzyme Electrodes

An enzyme electrode for glucose is described as a model system to demonstrate a fabrication method using latex aggregation and entrapment of enzyme. Electrosterically‐stabilized latex particles synthesized by emulsion polymerization in batch from acrylic acid, methyl methacrylate and butyl acrylate, and glucose oxidase were coagulated together at pH 5.5 with ethanol. A platinum disk electrode dipped in the solution becomes coated with latex/enzyme. The relative thickness of the film and relative amount of enzyme may be controlled by the time the electrode is in contact with the solution. The enzyme was then immobilized by covalent attachment of amine groups to carboxylic moieties in the polymer using 1‐ethyl‐3(3‐dimethylaminopropyl)‐carbodiimide hydrochloride and N‐hydroxysuccinimide. Five minutes contact with the latex/enzyme solution and subsequent amide coupling, gave electrodes with a reproducibility of 5.7% RSD, a wide dynamic range (0–100 mM) and good storage properties.     

Single-Atom Catalysts on Covalent Triazine Frameworks: at the Crossroad between Homogeneous and Heterogeneous Catalysis

Heterogeneous single-site and single-atom catalysts potentially enable combining the high catalytic activity and selectivity of molecular catalysts with the easy continuous operation and recycling of solid catalysts. In recent years, covalent triazine frameworks (CTFs) found increasing attention as support materials for particulate and isolated metal species. Bearing a high fraction of nitrogen sites, they allow coordinating molecular metal species and stabilizing particulate metal species, respectively. Dependent on synthesis method and pretreatment of CTFs, materials resembling well-defined highly crosslinked polymers or materials comparable to structurally ill-defined nitrogen-containing carbons result. Accordingly, CTFs serve as model systems elucidating the interaction of single-site, single-atom and particulate metal species with such supports. Factors influencing the transition between molecular and particulate systems are discussed to allow deriving tailored catalyst systems.     

共价固定亲和素的磁性纳米粒子用于快速测定蛋白A含量

采用溶剂热法制备了Fe₃O₄磁性纳米粒子(MNPs), 以戊二醛为交联剂, 将亲和素共价固定于MNPs表面. 用透射电子显微镜(TEM)、 X射线衍射(XRD)、 紫外-可见吸收光谱(UV-Vis)、 傅里叶变换红外光谱(FTIR)和荧光光谱等手段对蛋白固定过程进行了监控和表征. 采用荧光光谱法评价了固定亲和素的磁性纳米粒子(Avi-MNPs)的活性, 并将Avi-MNPs应用于分光光度法测定蛋白A的含量. TEM结果表明, 功能化前后MNPs的粒度分布均匀, 粒径大小分别约为30和50 nm. XRD分析结果表明, MNPs与Fe₃O₄的特征衍射峰完全一致, 晶体纯度良好. UV-Vis, FTIR和荧光光谱结果表明, 亲和素已固定在MNPs表面. Avi-MNPs活性评价结果表明, 其结合生物素的活力为4.706 U/mg Avi-MNPs, 低于游离的亲和素活力(14.1 U/mg D-biotin). 该方法用于检测蛋白A含量比传统酶联免疫法省时、 省力, 且对检测仪器要求低.     

Synthesis and Hybridization Properties of Oligodeoxynucleotides with Long‐Chain Linkers

New oligonucleotides with a long‐chain linker (6,9‐dioxa‐3,12‐diazatetradecane‐1,14‐diyl) in their backbone were synthesized, and their hybridization properties were studied by measurement of their T_m curves and fluorescence spectra. The T_m analyses revealed that these oligonucleotides could bind to their complementary strands despite the presence of the long‐chain linker. We also demonstrated interesting fluorescence properties of oligodeoxynucleotides with an anthracen‐9‐ylmethyl group on one of the two N‐atoms in the long‐chain linker. The fluorescence intensity of these oligonucleotides increased upon their hybridization to the complementary strands and was sensitive to the presence of the mismatch base pairs at a specific position.     

金纳米粒子通过形成Au-S键的组装

利用湿化学法以纳米粒子为基本单元构筑各种纳米复合结构,具有灵活简便、通用性强等特点,近年来受到了广泛的重视．Ｎａｔａｎ［１-４］等最先开展了在固体表面上制备金纳米粒子单层膜的研究,他们借助双官能团硅烷化试剂对硅氧化物基底（如玻璃、石英等）进行表面修饰?..     

长链DNA在金基底上的固定化和电化学标记

本文提出在金基底上用阳离子聚电解质———聚二烯丙基二甲基胺氯化物 (poly(dial lyldimethylammoniumchloride) ,PDDA)自组装膜固定长链DNA的方法 ,用DiffuseReflectanceIn frared ,XPS和STM技术进行表征 ,并对DNA杂交进行电化学标记     

Preparation and Properties of Urease Immobilized onto Glutaraldehyde Cross-linked Chitosan Beads

Urease was immobilized onto the glutaraldehyde cross-linked chitosan beads that were prepared under microwave irradiation. The activity and the yield of activity of immobilized urease was 10.83 U/g B and 47.7%, respectively. The conditions of urease immobilization were optimized. The properties of the immobilized urease were investigated and compared with that of the free enzyme.     

Substituent Effects on the Photocatalytic Properties of a Symmetric Covalent Organic Framework

Symmetric covalent organic framework (COF) photocatalysts generally suffer from inefficient charge separation and short-lived photoexcited states. By performing density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations, we find that partial substitution with one or two substituents (N or NH\begin{document}$_2$\end{document}) in the linkage of the representative symmetric COF (N\begin{document}$_0$\end{document}-COF) gives rise to the separation of charge carriers in the resulting COFs (\emph{i.e}., N\begin{document}$_1$\end{document}-COF, N\begin{document}$_2$\end{document}-COF, (NH\begin{document}$_2$\end{document})\begin{document}$_1$\end{document}-N\begin{document}$_0$\end{document}-COF, and (NH\begin{document}$_2$\end{document})\begin{document}$_2$\end{document}-N\begin{document}$_0$\end{document}-COF). Moreover, we also find that the energy levels of the highest occupied crystal orbital (HOCO) and the lowest unoccupied crystal orbital (LUCO) of the N\begin{document}$_0$\end{document}-COF can shift away from or toward the vacuum level, depending on the electron-withdrawing or electron-donating characters of the substituent. Therefore, we propose that partial substitution with carefully chosen electron-withdrawing or electron-donating substituents in the linkages of symmetric COFs can lead to efficient charge separation as well as appropriate HOCO and LUCO positions of the generated COFs for specific photocatalytic reactions. The proposed rule can be utilized to further boost the photocatalytic performance of many symmetric COFs.     

四取代羧基酞菁锌与白蛋白共价结合物的制备与光谱性质

通过成酰胺键的方式制备了一系列含羧基酞菁和白蛋白(牛血清白蛋白(BSA),人血清白蛋白(HSA))之间的共价结合物,所涉及到的酞菁分别是α-四(4-羧基苯氧基)酞菁锌(1)和α-四[4-(2-羧基乙基)苯氧基]酞菁锌(3),以及它们相应的β位四取代酞菁锌(化合物2和4).比较了游离酞菁以及它们的白蛋白结合物在磷酸盐缓冲溶液(PBS)中的光谱性质.结果表明,当酞菁被共价固定于白蛋白大分子上之后,展现出比游离酞菁更明显的单体特征吸收,而且结合物中的酞菁光谱特征不受体系pH值变化的影响.羧基在酞菁环上的取代位置,对酞菁与白蛋白结合前后的光谱转变幅度有影响,α位取代比β位取代更有利于光谱的变化.化合物1和3的白蛋白共价结合物在PBS溶液中甚至呈现出单体形式为主的光谱特征,Q带最大吸收波长分别位于697和706nm附近.     

单壁碳纳米管对C-C键水解酶BphD的固定化性能

采用修饰与未修饰单壁碳纳米管固定C-C键水解酶BphD,并对固定化酶的相对活性、稳定性、重复使用性进行了考察.结果表明,未修饰单壁碳纳米管固定的BphD相对活性为游离态的52.5%,其热稳定性和在变性剂中的稳定性均有所提高,且重复使用10次仍可保持初始活力的90%.修饰单壁碳纳米管固定的BphD相对活性可达99.7%,但其稳定性没有明显提高.同源模建及分子对接分析结果显示,未修饰的单壁碳纳米管对BphD亚基之间的联系可能存在干扰作用,从而对其活性产生影响.     

Gradually Tuning the Flexibility of Two-Dimensional Covalent Organic Frameworks via Stepwise Structural Transformation and Their Flexibility-Dependent Properties

Flexible covalent organic frameworks (COFs) are intriguing for their dynamic properties distinctive from rigid counterparts but still suffer from limited accessibility. Especially, controlling flexibility of COFs is challenging and the impact of different flexibility on properties of COFs has rarely been unveiled. This article reports stepwise adjustment on flexibility of two-dimensional COFs, which is realized by the designed synthesis of rigid COF (R-COF), semi-flexible COF (SF-COF), and flexible COF (F-COF) through polymerization, linker exchange, and linkage conversion with a newly developed method for reduction of hydrazone, respectively. Significant difference in breathing behavior and self-adaptive capability of the three COFs are uncovered through vapor response and iodine capture experiments. Gas sorption experiments indicate that the porosity of F-COF could switch from “close” state in nitrogen to “open” state in carbon dioxide, which are not observed for R-COF and SF-COF. This study not only develops a strategy to adjust the flexibility of COFs by tuning their linkers and linkages, but also provides a deep insight into the impact of different flexibility on properties of COFs, which lays a foundation for the development of this new class of dynamic porous materials.     

Strategies for Improving the Catalytic Performance of 2D Covalent Organic Frameworks for Hydrogen Evolution and Oxygen Evolution Reactions

Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been deemed as clean and sustainable strategies to solve the energy crisis and environmental problems. Various catalysts have been developed to promote the process of HER and OER. Among them, two-dimensional covalent organic frameworks (2D COFs) have received great attention due to their diverse and designable structure. In this minireview, we mainly summarize the diverse linkages of 2D COFs and strategies for enhancing the catalytic performance of 2D COFs for HER and OER, such as introducing active building blocks, metal ions and tailored linkages. Furthermore, a brief outlook for the development directions of COFs in the field of HER and OER is provided, expecting to stimulate new opportunities in future research.     

Scanning Electrochemical Microscopy (SECM) Based Detection of Oligonucleotide Hybridization and Simultaneous Determination of the Surface Concentration of Immobilized Oligonucleotides on Gold

The direct mode of scanning electrochemical microscopy (SECM) was used for the local deposition of oligonucleotide (ODN) patterns on thin gold films and the generation‐collection (GC) mode was applied for the determining the amount of surface‐accessible oligonucleotides. The local deposition was achieved through the micrometer‐sized formation of a conducting polymer bearing 15^mer single‐stranded oligonucleotide strands. After the interaction of the oligonucleotide with its biotin‐labeled complimentary strand, streptavidin was bound. The molecular assembly was completed by linking biotin‐labeled β‐galactosidase from Escherichia coli to the streptavidin. The activity of the linked β‐galactosidase was mapped with SECM in the GC mode by monitoring the oxidation of p‐aminophenol (PAP) formed in the enzyme‐catalyzed hydrolysis of p‐aminophenyl‐β‐D ‐galactopyranoside. The feedback effect due to recycling of the reaction product at the gold surface was analyzed. It was shown experimentally that this effect becomes insignificant at ultramicroelectrode (UME)‐substrate distances larger than 3 UME radii. The flux of formed PAP allowed the determination the surface density of accessible oligonucleotide strands in the functionalized polymer. It was shown that that thicker pyrrole/ODN–Pyrrole polymer films do not lead to a significantly increased accessible ODN surface concentration.     

Adjustable Plane Curvature of Covalent Organic Framework Enabling Outstanding Dielectric,Electret, and High-Temperature Processing Properties

With the rapid development of integrated circuits towards miniaturization and complexity, there is an urgent need for materials with low dielectric constant/loss and high processing temperatures to effectively prevent signal delay and crosstalk. With high porosity, thermal stability, and easy structural modulation, covalent organic frameworks have great potential in the field of low dielectric materials. However, the optimization of dielectric properties by modulating the conjugated/plane curvature structure of covalent organic frameworks (COFs) has rarely been reported. Accordingly, we herein innovatively prepare COF films with adjustable planar curvature, hence possessing ultralow dielectric constant (1.9 at 1 kHz), ultralow dielectric loss at 1 kHz (0.0029 at room temperature, 0.0052 at 200 °C), high thermal decomposition temperature (5 % weight loss temperature, 473 °C) and good hydrophobicity (water contact angle, 105.3°). Also, to the best of our knowledge, we are the first to report that the resulting COF film enables high surface potential (≈320 V) for one week, attributing to its intrinsic high porosity, thus presenting great potential in electret applications. Accordingly, this innovative work provides a readily available and scalable idea to prepare materials with comprehensively excellent dielectric and electret properties as well as high processing temperatures simultaneously for advanced electronic device applications.     

通过硅烷偶联剂在硅和铟锡氧化物(ITO)表面嫁接寡聚芴分子

通过硅烷偶联剂γ-氨丙基三乙氧基硅烷(3-aminopropyl-triethoxysilane,APTES)的“分子桥梁”作用,采用两种不同的方法,把修饰后的寡聚芴分子键联到硅表面和铟锡氧化物(ITO)表面上。X射线光电子能谱(XPS)、原子力显微镜(AFM)和循环伏安(CV)方法等的表征证实了通过硅烷偶联剂在硅表面和ITO表面嫁接寡聚芴分子可行性。     

Isomeric Oligo(Phenylenevinylene)-Based Covalent Organic Frameworks with Different Orientation of Imine Bonds and Distinct Photocatalytic Activities

Imine-linked covalent organic frameworks (COFs) have been extensively studied in photocatalysis because of their easy synthesis and excellent crystallinity. The effect of imine-bond orientation on the photocatalytic properties of COFs, however, is still rarely studied. Herein, we report two novel COFs with different orientations of imine bonds using oligo(phenylenevinylene) moieties. The COFs showed similar structures but great differences in their photoelectric properties. COF-932 demonstrated a superior hydrogen evolution performance compared to COF-923 when triethanolamine was used as the sacrificial agent. Interestingly, the use of ascorbic acid led to the protonation of the COFs, further altering the direction of electron transfer. The photocatalytic performances were increased to 23.4 and 0.73 mmol g⁻¹ h⁻¹ for protonated COF-923 and COF-932, respectively. This study provides a clear strategy for the design of imine-linked COF-based photocatalysts and advances the development of COFs.     

Covalent organic frameworks functionalized carbon fiber paper for the capture and detection of hydroxyl radical in the atmosphere

Developing a fast, sensitive and convenient method for the detection of hydroxyl radicals (OH) in the atmosphere could help us know the precursor levels of atmospheric species and control air pollution. In this work, the carbon fiber paper (CFP) functionalizing with a kind of covalent organic frameworks (COFs), formed from 1,3,5-triformylphloroglucinol (Tp) and benzidine (BD) (COF(TpBD)), was firstly used a new platform for OH trapping and detection. The COF(TpBD) modified CFP was acted as a filter to impregnate salicylic acid (SA) and a detector to detect 2,5-dihydroxybenzoic acid (2,5-DHBA) which was produced from the reaction between the impregnated SA and OH in the atmosphere. This method provided a linearity for 2,5-DHBA from 5.0 × 10⁻¹⁴ mol/L 1.0 × 10⁻⁹ mol/L with a detection limit of 6.9 × 10⁻¹⁵ mol/L, which is corresponding to the amount of OH from 3.0 × 10⁷ to 6.0 × 10¹¹ molecules/cm³ with the detection limit of 4.1 × 10⁶ molecules/cm³. This COF(TpBD)-CFP platform has been successfully applied for the detection of OH concentration under different conditions of Yangzhou when the sampling time was shortened to 30 min. This work has provided a new method for atmospheric OH detection with excellent sensitivity, simplicity, and high speed.     

Porous Covalent Organic Framework Based Hydrogen-Bond Nanotrap for the Precise Recognition and Separation of Gold

Utilizing weak interactions to effectively recover and separate precious metals in solution is of great importance but the practice remains a challenge. Herein, we report a novel strategy to achieve precise recognition and separation of gold by regulating the hydrogen-bond (H-bond) nanotrap within the pore of covalent organic frameworks (COFs). It is found that both COF-HNU25 and COF-HNU26 can efficiently capture Au^III with fast kinetics, high selectivity, and uptake capacity. In particular, the COF-HNU25 with the high density of H-bond nanotraps exhibits an excellent gold uptake capacity of 1725 mg g⁻¹, which is significantly higher than that (219 mg g⁻¹) of its isostructural COF (COF-42) without H-bond nanostrap in the pores. Importantly, the uptake capacity is strongly correlated to the number of H-bonds between phenolic OH in the COF and [AuCl₄]⁻ in water, and multiple H-bond interactions are the key driving force for the excellent gold recovery and reusability of the adsorbent.     

Covalent functionalization of single-walled carbon nanotubes with polytyrosine: Characterization and analytical applications for the sensitive quantification of polyphenols

This work reports the synthesis and characterization of single-walled carbon nanotubes (SWCNT) covalently functionalized with polytyrosine (Polytyr); the critical analysis of the experimental conditions to obtain the efficient dispersion of the modified carbon nanotubes; and the analytical performance of glassy carbon electrodes (GCE) modified with the dispersion (GCE/SWCNT-Polytyr) for the highly sensitive quantification of polyphenols. Under the optimal conditions, the calibration plot for the amperometric response of gallic acid (GA) shows a linear range between 5.0 × 10⁻⁷ and 1.7 × 10⁻⁴ M, with a sensitivity of (518 ± 5) m AM⁻¹ cm⁻², and a detection limit of 8.8 nM. The proposed sensor was successfully used for the determination of total polyphenolic content in tea extracts.