Synthesis of core-shell structured PS/Fe3O4 microbeads and their magnetorheology

Most magnetic materials possess serious sedimentation problem due to their large density when they are adopted as magnetorheological (MR) materials. In this communication, we fabricated novel core-shell structured polystyrene(PS)/Fe₃O₄ microbeads via a facile method. Porous morphology of the PS obtained by etching silica particles and the loaded Fe₃O₄ was observed via both SEM and TEM images. XRD pattern confirms crystalline structure of the synthesized iron species. VSM data indicate the change in saturation magnetization before and after introducing organic PS core. Finally, MR performances of the PS/Fe₃O₄ based MR fluid were investigated via a rotational rheometer and sedimentation stability was found to be improved with a decreased density of the synthesized microbeads.     

微珠对隧道工程混凝土性能的影响及机理研究

针对广州新白云国际机场隧道工程建设中大体积混凝土的温度裂缝问题,通过复掺微珠和粉煤灰,研究了微珠掺量对混凝土的力学性能、干燥收缩、水化热以及早期抗裂性能的影响,并采用SEM分析了微珠对水泥水化反应的作用机理。结果表明:当矿物掺合料总量一定时,随着微珠掺量的增加,混凝土的力学性能早期变化较小,后期呈现出先增加后下降的趋势,且微珠掺量为10%时,混凝土养护60 d的抗压强度、劈裂抗拉强度以及弹性模量最高;混凝土干缩率随着微珠掺量的增加而减小,且这种趋势随龄期的增加而增大,当微珠掺量15%时,60 d混凝土的干缩率最小;当微珠掺量为10%时,混凝土早期抗裂性能最佳,平板试件表面24 h内无裂缝;微珠掺量对胶凝材料水化热总量影响较小,但对水化放热峰值及峰值产生时间影响较大;微珠可以加速浆体早期的水化进程,减少硬化浆体的孔隙,使其结构更密实。     

Quantitative analysis of the number of antigens immobilized on a glass surface by AFM

To develop force measurements using an atomic force microscope (AFM) in a quantitative manner, it is necessary to estimate the number density of target molecules on a sample surface, and for this, the sensitivity of detection should be known. In this study, the AFM was used as a mechanical detector and an antigen and its antibody were used as a model to evaluate the sensitivity of detection. Antigens were immobilized on a glass surface and number density was estimated by monitoring optical absorbance due to product formation by the reaction of crosslinkers. The concentration of antigen was controlled by mixing control peptides. A microbead was used as a probe and antibodies were immobilized on the bead. AFM force measurements were then made for a range of number densities in the order of 10–10⁶ antigen molecules per square micrometer of surface and were compared to evaluate the sensitivity of detection. Our result establishes the reliability of estimating a number of molecules like receptors on the cell surface, and indicates that the AFM is useful as a mechanical detector with high sensitivity.     

Effect of the Anodic Diffusion Layer on the Performance of Liquid Fuel Cells

Novel diffusion layers for liquid direct methanol fuel cells (DMFCs) are designed and fabricated. The factors affecting the performance of DMFCs are determined. The results demonstrate that the diffusion layers made by micrometer scale particles and a hydrophilic binder can reduce the liquid sealing effect and increase the mass transfer property. The performance of DMFCs made using novel diffusion layers is greatly improved. The porous structure of such diffusion layers may improve the channels therein, which allows liquid methanol to diffuse in and gaseous CO₂ to diffuse out easily. Higher methanol concentrations can be used due to the formation of a larger three‐phase interfacial area.     

初始结构对中间相碳微球摩擦性能的影响

在不同温度下对中间相碳微球(MCMB)进行热处理，将处理过的：MCMB作为添加剂分散到季戊四醇酯中，利用0ptimal SRV高温摩擦磨损试验机在300℃下考察了它们的摩擦性能。原始MCMB粉末的透射电镜分析和激光喇曼分析表明：热处理强度对MCMB的结构有不同程度的影响，可以改变：MCMB的层状构造。定义的摩擦处理强度(W)可以用来比较MCMB在摩擦过程中结构转变的难易，形计算值小的MCMB容易发生结构转化。磨损表面的喇曼光谱分析结果表明：原始层状结构好、形计算值小的MCMB容易在摩擦过程中向更为有序的结构转化，得到最大尺寸的微晶石墨。     

Directed evolution of angiotensin II-inhibiting peptides using a microbead display

Angiotensin II (ang II), an octapeptide (DRVYVHPF), can regulate blood pressure by binding specifically to its receptor, AT1. A peptide (VVIVIY) in the first transmembrane of AT1 has been found, via peptide array technology, to have an affinity for ang II. In this study, the peptide P2, which contained the VVIVIY sequence, was mutated and screened using microbead display technology that utilized emulsion PCR and cell-free protein synthesis. After one round of screening, the binding activities of collected mutants were estimated using flow cytometry and a peptide array. Two of these exhibited improved association rate constants to ang II, compared to the P2 peptide.     

微珠芯片免疫法对肉制品中莱克多巴胺残留的检测

构建了一个基于功能化微珠表面竞争性免疫反应的流控芯片体系,在环氧化微珠表面固定小分子莱克多巴胺的蛋白全抗原,然后依次与一抗和携带荧光的二抗反应,最后输出荧光信号。在检测中,采用内标-标准曲线法,先利用标准品制作竞争性免疫反应的标准曲线,然后进行实际样本检测。该系统检测的莱克多巴胺的最低检测限达到0.03μg/L,检测时间不超过45 min。     

Preparation of D-phenylalanine imprinted microbeads by the modified suspension polymerization using a magnetic impeller

Molecularly imprinted polymeric microbeads (MIPMs) were prepared by using a magnetic impeller by the modified suspension polymerization method with D-phenylalanine (Phe) as the water-soluble template without derivatization, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, toluene as the porogen, polyvinyl alcohol as the stabilizer, and sodium dodecyl sulfate as the surfactant. The mean diameter of MIPMs decreased from 12.45 μm to 8.86 μm by using a simple magnetic impeller instead of a conventional simple straight-blade turbine impeller during suspension polymerization. The adsorption selectivity of MIPMs prepared with a magnetic impeller was much improved as compared to the adsorption selectivity of MIPMs prepared with a conventional simple straight-blade turbine impeller. The adsorption selectivity of MIPMs changed from reversed adsorption (less than 1) to positive (higher than 1) as the washing time increased after suspension polymerization.