Towards Maintenance‐Free Biosensors for Hundreds of Bind/Release Cycles

A single aptamer bioreceptor layer was formed using a common streptavidin–biotin immobilization strategy and employed for 100–365 bind/release cycles. Chemically induced aptamer unfolding and release of its bound target was accomplished using alkaline solutions with high salt concentrations or deionized (DI) water. The use of DI water scavenged from the ambient atmosphere represents a first step towards maintenance‐free biosensors that do not require the storage of liquid reagents. The aptamer binding affinity was determined by surface plasmon resonance and found to be almost constant over 100–365 bind/release cycles with a variation of less than 5 % relative standard deviation. This reversible operation of biosensors based on immobilized aptamers without storage of liquid reagents introduces a conceptually new perspective in biosensing. Such new biosensing capability will be important for distributed sensor networks, sensors in resource‐limited settings, and wearable sensor applications.     

一步电沉积纳米铜/石墨烯/壳聚糖复合膜修饰玻碳电极测定邻苯二酚

用一步电沉积法制备了纳米铜/石墨烯/壳聚糖复合膜修饰玻碳电极。用循环伏安法(CV)和差分脉冲伏安法(DPV)对邻苯二酚在该修饰电极的电化学行为进行了研究。实验结果表明,在pH值为7.0的磷酸盐缓冲液(PBS)中,该修饰电极对邻苯二酚具有良好的电催化作用,其电化学信号与邻苯二酚的浓度在1.0×10-6～2.0×10-4mol/L范围内呈良好的线性关系,线性相关系数为0.991。检出限为1×10-7mol/L。结果表明,纳米铜/石墨烯/壳聚糖复合膜修饰电极显著提高了邻苯二酚的电化学响应信号,并表现出良好的选择性和重现性。该方法成功用于水样中邻苯二酚含量的测定。     

Paclitaxel-Loaded Magnetic Nanoparticles Based on Biotinylated N-Palmitoyl Chitosan: Synthesis,Characterization and Preliminary In Vitro Studies

A considerable interest in cancer research is represented by the development of magnetic nanoparticles based on biofunctionalized polymers for controlled-release systems of hydrophobic chemotherapeutic drugs targeted only to the tumor sites, without affecting normal cells. The objective of the paper is to present the synthesis and in vitro evaluation of the nanocomposites that include a magnetic core able to direct the systems to the target, a polymeric surface shell that provides stabilization and multi-functionality, a chemotherapeutic agent, Paclitaxel (PTX), and a biotin tumor recognition layer. To our best knowledge, there are no studies concerning development of magnetic nanoparticles obtained by partial oxidation, based on biotinylated N-palmitoyl chitosan loaded with PTX. The structure, external morphology, size distribution, colloidal and magnetic properties analyses confirmed the formation of well-defined crystalline magnetite conjugates, with broad distribution, relatively high saturation magnetization and irregular shape. Even if the ability of the nanoparticles to release the drug in 72 h was demonstrated, further complex in vitro and in vivo studies will be performed in order to validate the magnetic nanoparticles as PTX delivery system.     

Chemically programmed supramolecular assembly of hemoprotein and streptavidin with alternating alignment

Alternating: a cofactor dyad consisting of a heme group (red in picture) and a bis(biotin) unit (blue) was synthesized and shown to specifically bind to both apomyoglobin and streptavidin. In the presence of the dyad, the 1:1 association of a disulfide-bridged myoglobin dimer (green) with streptavidin (gray) afforded a submicrometer-sized fibrous alternating copolymer.     

Strategies for the Biofunctionalization of Straining Flow Spinning Regenerated Bombyx mori Fibers

High-performance regenerated silkworm (Bombyx mori) silk fibers can be produced efficiently through the straining flow spinning (SFS) technique. In addition to an enhanced biocompatibility that results from the removal of contaminants during the processing of the material, regenerated silk fibers may be functionalized conveniently by using a range of different strategies. In this work, the possibility of implementing various functionalization techniques is explored, including the production of fluorescent fibers that may be tracked when implanted, the combination of the fibers with enzymes to yield fibers with catalytic properties, and the functionalization of the fibers with cell-adhesion motifs to modulate the adherence of different cell lineages to the material. When considered globally, all these techniques are a strong indication not only of the high versatility offered by the functionalization of regenerated fibers in terms of the different chemistries that can be employed, but also on the wide range of applications that can be covered with these functionalized fibers.     

Comparative studies on zirconia and graphene composites obtained by one-step and stepwise electrodeposition for deoxyribonucleic acid sensing

In this paper, the comparison of two kinds of electrochemically reduced graphene oxide (ERGNO) and zirconia composites, obtained by one-step (ZrO₂–ERGNO) and stepwise (ZrO₂/ERGNO) electrodeposition for DNA sensing, is systematically studied. The resulting composites were characterized by scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry. The results indicated that the ZrO₂–ERGNO presented fine globular nanostructure. However, ZrO₂/ERGNO presented agglomerate massive microstructure due to the absence of the oxygen-containing groups of graphene oxide, confirming the oxygen-containing groups provided a better affinity for the deposition of ZrO₂. Due to the strong binding of the phosphate groups of DNA with the zirconia film, DNA probes were attached on the ZrO₂-based composites. ZrO₂–ERGNO/Au owning fine nanostructure presented larger surface area than microstructured ZrO₂/ERGNO/Au. Moreover, compared with microstructured ZrO₂/ERGNO, the nanostructured ZrO₂–ERGNO provided more accessible space for immobilized DNA probe hybridization with target sequence, which consequently resulted in higher hybridization efficiency. Therefore, the ZrO₂–ERGNO was chosen for fabricating DNA sensor with a limit of detection 1.21 × 10⁻¹⁴ mol L⁻¹.     

Chitosan Membranes Filled with Cyclosporine A as Possible Devices for Local Administration of Drugs in the Treatment of Breast Cancer

The aim of this work is the design, preparation and characterization of membranes based on cyclosporine A (CsA) and chitosan carboxylate (CC) to be used as an implantable subcutaneous medical device for a prolonged therapeutic effect in the treatment of breast cancer. The choice to use CsA is due to literature data that have demonstrated its possible antitumor activity on different types of neoplastic cells. To this end, CsA was bound to CC through an amidation reaction to obtain a prodrug to be dispersed in a chitosan-based polymeric membrane. The reaction intermediates and the final product were characterized by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (¹H-NMR). Membranes were analyzed by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The data obtained showed the effective formation of the amide bond between CsA and CC and the complete dispersion of CsA inside the polymeric membrane. Furthermore, preliminary tests, conducted on MDA-MB-231, a type of breast cancer cell line, have shown a high reduction in the proliferation of cancer cells. These results indicate the possibility of using the obtained membranes as an interesting strategy for the release of cyclosporin-A in breast cancer patients.     

电沉积普鲁士蓝/壳聚糖修饰金电极的电化学研究

应用控制电位电解法在金电极上进行了普鲁士蓝(PB)/壳聚糖(CS)修饰膜的电沉积。在pH2、溶液组成为2.5 mmol/L FeCl3 2.5 mmol/L K3[Fe(CN)6] 0.01%CS 0.01 mol/L HCl和0.1 mol/L KCl的溶液中,于0.4 V(vs.SCE)电沉积300 s,获得性能理想的沉积膜。对修饰膜进行了红外和显微表征,结果表明,PB和CS同时沉积在电极上,且膜结构较纯PB沉积膜粗糙,修饰量大,具有更强的空间结构性。研究了PB/CS/金修饰电极(PB/CS/Au/CME)的电化学行为,该电极在中性(pH7.0~8.0)条件下性能比纯PB修饰膜更稳定,具有良好的电化学活性和对H2O2的电催化性能。氧化峰电流与H2O2浓度在1×10-6~5×10-3mol/L范围内呈良好线性关系,为研制基于酶催化反应的电化学生物传感器奠定了良好基础。     

壳聚糖硫酸酯的合成及其抑菌作用

以壳聚糖为原料,研究了合成壳聚糖硫酸酯的条件及其分子量对抑菌效果的影响。结果表明:改变反应温度可制备不同分子量的壳聚糖硫酸酯,并且其对金黄葡萄球菌、大肠杆菌有不同的抑菌效果。     

Chemically Modified Chitosan Beads as Molecularly Imprinted Polymer Matrix for Adsorptive Separation of Proteins

In a phosphate buffer, a hemoglobin (Hb)-imprinted polymer complex was preparedusing maleic anhydride (MAH) modified chitosan beads as matrix, acrylamide (AM) as functionalmonomer, N,N-methylenebisacrylamide (MBA) as cross-linker and potassiumpersulfate (KPS) /sodium hydrogen sulfite (NaHSO3) as initiators. Langmuir analysis showed that an equal class ofadsorption was formed in the molecular imprinting polymer (MIP), and the MIP has highadsorption capacity and selectivity for the imprinted molecule. The MIP can be reused and therecovery was approximately 100% at low concentration.     

Fabrication and Characterization of the Egg-White Protein Chitosan Double-Layer Emulsion

Egg-white protein has an abundance of hydrophobic amino acids and could be a potential emulsifier after modification. Here, egg-white protein was modified via ultrasonic and transglutaminase treatments to destroy the globular structure. The egg-white protein gel particles (EWP-GPs) were prepared and then a novel highly stable EWP-chitosan double-layer emulsion was constructed. When ultrasonic treatment was applied at 240 W and TGase (20 U/g EWP) treatment, the EWP-GPs had a low particle size and good emulsification performance. The particle size of EWP-GPs was a minimum of 287 nm, and the polymer dispersity index (PDI) was 0.41. The three-phase contact angle (θ_o/w) of EWP-GPs was 79.6° (lower than 90°), performing with good wettability. Based on these results, the EWP-chitosan double-layer emulsion was prepared through the EWP-GPs being treated with 240 W ultrasound, TGase, and chitosan in this study. When the double-layer emulsion had 0.6% (v/v) chitosan, the zeta potential of the double-layer emulsion was −1.1 mV and the double-layer emulsion had a small particle size (56.87 µm). The creaming index of double-layer emulsion at 0.6% (v/v) chitosan was 16.3% and the droplets were dispersed uniformly. According to the rheological results, the storage modulus (G′) was larger than the loss modulus (G″) in the whole frequency, indicating the formation of an elastic gel network structure in the emulsion. It is hoped to develop a novel food-grade stabilizer and a stable double-layer emulsion, providing new environment-friendly processing in hen egg products and delivery systems.     

Novel Enzyme-Linked Aptamer Assay for the Determination of Aflatoxin B1 in Peanuts

Abstract

A novel enzyme-linked aptamer assay is reported for the determination of aflatoxin B₁ (AFB₁). AFB₁ can competitively bind with the immobilized biotin-aptamer and release biotin complementary DNA, leading to the gradual fading of the detection system color with increasing of AFB₁ concentration. In the absence of AFB₁, the biotinylated complementary DNA is not be released from the fixed aptamer. Therefore, the enzyme reaction occurs in the detection system. Under the optimized experimental conditions, the proposed method possessed a wide linear range for AFB₁ from 1 to 80?ng/mL (R² of 0.990) with a low detection limit of 0.36?ng/mL. The method was then applied to detect uncontaminated peanuts fortified with different concentrations of AFB₁. The recovery values were from 82.60% to 94.43%, which indicated the proposed method may be used to detect AFB₁ in food and has potential for the development of test kits.     

壳聚糖/羧甲基壳聚糖金属配合物对氧自由基的清除作用研究

以NADH-PMS-NBT体系产生超氧阴离子自由基(o2-·)和EDTANa2·Fe(Ⅱ)-H2O2体系产生 羟自由基(·OH)来研究壳聚糖Cu(Ⅱ)、Zn(Ⅱ)配合物、羧甲基壳聚糖Cu(Ⅱ)、Zn(Ⅱ)配合物时氧自由基的 清除作用。结果显示配合物对O2-·和·OH均具有明显的清除作用,其中铜(Ⅱ)配合物对O2-·的清除活 性最高,而锌(Ⅱ)配合物比铜(Ⅱ)配合物具有更强的清除·OH的能力,羧甲基壳聚糖Cu(Ⅱ)、Zn(Ⅱ)配合 物与含有相同金属离子的壳聚糖配合物相比对O2-·和·OH具有更高的抑制活性。     

Monte Carlo Simulation of the Assembly of bis‐Biotinylated DNA and Streptavidin

We present Monte Carlo simulations of the self‐assembly of bivalent bis‐biotinylated DNA molecules with the tetravalent biotin‐binding protein streptavidin (STV). By fitting the STV binding probabilities for the four possible valencies, the modelling correctly reproduces the dependencies of various network parameters experimentally observed in an earlier study. The combined results from the experimental and theoretical studies suggest that the binding probability for divalent STV formation is about 50 times larger than for the formation of trivalent and about 200 times larger than for tetravalent STV. In accordance with the experimental results, the modelling also indicates that the mixture of an equimolar ratio of DNA and STV leads to a maximum in size of the oligomeric DNA–STV clusters formed. Furthermore, we found a percolation transition in which the DNA cluster size increases rapidly with increasing DNA concentration resulting in the formation of a single supercluster at elevated concentrations. This behaviour coincides with the occurrence of an immobile band previously observed in electrophoretic experiments, indicating the formation of extremely large DNA–STV aggregate networks.     

大豆分离蛋白与壳聚糖复合材料的制备

蛋白质与多糖的静电作用是生物体内一个基本医学-化学现象,是实现自组装的主要驱动力,可利用这种非共价作用设计和构筑理想的微结构。 以大豆分离蛋白(Soybean Protein Isolates,SPI)和壳聚糖(Chitosan,CS)为原料,采用浊度法考察了配比、溶液pH值、离子强度和温度对SPI与CS在溶液中相互作用的影响。 结果显示,由于pH值影响静电作用强度,从而成为影响SPI与CS相互作用的主要因素,其中,当pH值为5.5~6.6时,SPI与CS可以实现有效结合。在较低的离子强度下,有利于形成具有紧凑结构的CS/SPI聚集体,较高离子强度下聚集体发生解离。 蛋白质受热发生变性,多肽链上的疏水氨基酸残基暴露在溶液中,导致与壳聚糖链的疏水作用增强。 DLS结果显示,CS与SPI自组装形成了分布均一的纳米粒子,变性后的SPI与CS形成的纳米粒子粒径有所增大,分布均一;经戊二醛交联,粒径有所减小。 SEM显示,壳聚糖单层膜表面存在龟裂现象,与SPI形成双层膜后龟裂消失;同时,单层膜厚度约为300 nm,双层膜厚度约为500 nm。     

High Substitution Synthesis of Carboxymethyl Chitosan for Properties Improvement of Carboxymethyl Chitosan Films Depending on Particle Sizes

This study investigated the effect of chitosan particle sizes on the properties of carboxymethyl chitosan (CMCh) powders and films. Chitosan powders with different particle sizes (75, 125, 250, 450 and 850 µm) were used to synthesize the CMCh powders. The yield, degree of substitution (DS), and water solubility of the CMCh powders were then determined. The CMCh films prepared with CMCh based on chitosan with different particle sizes were fabricated by a solution casting technique. The water solubility, mechanical properties, and water vapor transmission rate (WVTR) of the CMCh films were measured. As the chitosan particle size decreased, the yield, DS, and water solubility of the synthesized CMCh powders increased. The increase in water solubility was due to an increase in the polarity of the CMCh powder, from a higher conversion of chitosan into CMCh. In addition, the higher conversion of chitosan was also related to a higher surface area in the substitution reaction provided by chitosan powder with a smaller particle size. As the particle size of chitosan decreased, the tensile strength, elongation at break, and WVTR of the CMCh films increased. This study demonstrated that a greater improvement in water solubility of the CMCh powders and films can be achieved by using chitosan powder with a smaller size.     

呋喃甲酰壳聚糖的制备、表征及其抗氧化活性

以壳聚糖与呋喃甲酰氯反应得到呋喃甲酰壳聚糖。通过FT-IR、1 H-NMR、X射线衍射、热重分析、溶解度实验、元素分析、抗氧化活性测试等手段对产物进行了结构和性能表征。结果表明：产物为目标产物且热稳定性好于壳聚糖;在水中的溶解性能良好,溶解度为0.04g/mL;取代度为0.69;当对羟基自由基的清除率达到50%时,呋喃甲酰壳聚糖的质量浓度为1.1mg/mL,其还原能力随质量浓度增加而增强,抗氧化活性优于壳聚糖。     

甲壳素、壳聚糖的改性

综述了壳聚糖的化学改性和物理改性。通过对壳聚糖的改性,一方面可增进其在有机溶剂中溶解行为,为进一步应用提供反应前体;另一方面增强机械或生化性质,扩展其应用范围。     

Polypyrrole electrodeposition on inorganic semiconductors CuInSe2 and CuInS2 for photovoltaic applications

Thin polypyrrole (PPy) layers with an average thickness of about 0.5 μm were deposited, using potentiostatic and galvanostatic techniques, on CuInSe₂ (CISe) structures prepared electrochemically on glass/ITO substrates and on CuInS₂ (CIS) structures fabricated on Cu tape substrates. The polymer layer of p-type is considered as an alternative to the traditional buffer layer and window layer in the conventional cell structure. The deposition proceeded from an aqueous solution containing sodium naphthalene-2-sulfonate as a dopant. In order to prepare stable PPy films of high quality with a good adherence to the surface of inorganic semiconductors CIS and CISe, the optimal concentrations of reagents, current densities and electrodepositing potentials were selected experimentally. Electrochemical polymerization of pyrrole to PPy on CIS surfaces is faster under white light irradiation and the polymerisation starts at lower potential than in the dark. Significant photovoltage and photocurrent of the fabricated CISe/PPy and CIS/PPy structures have been observed under standard white light illumination.