Visual Detection of Adenosine Triphosphate by Taylor Rising: A Simple Point-of-Care Testing Method Based on Rolling Circle Amplification

Rapid and sensitive point-of-care testing (POCT) is an extremely critical mission in practical applications, especially for rigorous military medicine, home health care, and in the third world. Here, we report a visual POCT method for adenosine triphosphate (ATP) detection based on Taylor rising in the corner of quadratic geometries between two rod surfaces. We discuss the principle of Taylor rising, demonstrating that it is significantly influenced by contact angle, surface tension, and density of the sample, which are controlled by ATP-dependent rolling circle amplification (RCA). In the presence of ATP, RCA reaction effectively suppresses Taylor-rising behavior, due to the increased contact angle, density, and decreased surface tension. Without addition of ATP, untriggered RCA reaction is favorable for Taylor rising, resulting in a significant height. With this proposed method, visual sensitive detection of ATP without the aid of other instruments is realized with only a 5 μL droplet, which has good selectivity and a low detection limit (17 nM). Importantly, this visual method provides a promising POCT tool for user-friendly molecular diagnostics.     

Logarithmic decrease of adhesion force with lateral dynamic revealed by an AFM cantilever at different humidities

Adhesion forces between a tipless cantilever and an Au film were determined to investigate the influence of lateral velocity by recording force curves with an atomic force microscope at 20%–90% relative humidities. The sample was moved laterally, forth and back, with a frequency of 0.001–100 Hz and scan distances of 0.8, 8, and 80 μm to achieve a velocity ranging over 7 orders of magnitude. Experimental results show that at low lateral velocities (between 1.6 nm/s and 1–10 μm/s), the adhesion force either increases or decreases or remains stable with the lateral velocity without a certain characteristic trend. However, after a critical velocity, the adhesion force decreases logarithmically with the lateral velocity (between 1–10 and 16,000 μm/s). The decreasing magnitude can be as large as 97.3% of the maximum adhesion force. This decrease is well-explained by the contact time dependence of water bridges formed by capillary condensation.     

加压毛细管电色谱测定甘蔗中三种多酚类化合物

为建立加压毛细管电色谱(pCEC)分离检测甘蔗中多酚类化合物绿原酸、阿魏酸、表儿茶素的方法,采用C₁₈毛细管色谱柱,以NaH₂PO₄和甲醇为流动相,优化了流动相比例、缓冲盐pH、缓冲盐浓度、分离电压、流速等色谱条件。结果表明,在流动相为15.0 mmol/L NaH₂PO₄+12.5 mmol/L庚烷磺酸钠(pH5.0)/甲醇(50:50,V/V)、分离电压为1 kV、流动相总流速为0.06 mL/min、检测波长为220 nm的色谱条件下,绿原酸、阿魏酸、表儿茶素分离较好,在20~320 μg/mL线性关系良好,相关系数分别为0.9978、0.9922、0.9971,检出限分别为0.14、0.75、1.65 μg/mL,相对标准偏差分别为2.82%、2.69%、1.18%,平均回收率分别为96.79%、100.71%、99.01%。该方法快速、准确、重复性好,适用于甘蔗中多酚类化合物的分离检测。     

基于荧光显微镜的毛细管电泳系统的构建

毛细管电泳仪具有灵敏度高、分析速度快等优势,为降低其生产成本,基于电泳原理,以荧光显微镜为基础,设计了一套毛细管电泳系统。以20 bp(base pairs,碱基对)DNA ladder和100 bp DNA ladder为样本,全面分析了系统的稳定性、灵敏度和分离效果。结果表明:该系统在9 min内可以实现1500 bp以内DNA片段的高效分离,系统检测极限为0.1 ng/μL;在优化的电泳条件下,对限制性内切酶φX174-HincⅡ作用过的λ-DNA片段5 min内实现了291 bp与297 bp DNA片段的区分。     

毛细管电泳在食品安全检测中的应用进展

“民以食为天，食以安为先。”作为一个全球性问题，食品安全不仅影响每个人的健康水平与生活质量，更关乎整个国家的经济与发展。近年来，“毒奶粉”、“地沟油”、“染色馒头”、“毒豆芽”等频繁发作的食品安全恶性事件引起了社会的极大关注，也使人们对食品安全检测的需求进一步提高。而食物种类多样、成分复杂、及加工工艺繁琐等特点也为食品安全检测技术和方法带来了更大的难度和挑战。众多检测方式中，毛细管电泳（CE）以分析成本低、样品用量少、分离模式灵活多样、对环境污染小等优势被广泛应用。本文综述了2015年以来CE在食品安全检测中农药残留、兽药残留、多种食品添加剂、食品包装材料中双酚A和塑化剂等多个方面的分析应用，并对其未来的发展方向作了简要的展望。     

UHMWPE/HDPE/纳米SiO2共混体系的毛细管挤出流变行为

采用毛细管流变仪,研究了超高分子量聚乙烯(UHMWPE)/高密度聚乙烯(HDPE)/纳米二氧化硅(SiO2)共混体系,及其对照组的流变行为和挤出过程中的不稳定流动现象,分析了共混物发生鲨鱼皮畸变和整体破裂的临界剪切应力和临界剪切速率的变化情况。结果表明,经过偶联剂改性的纳米SiO2粒子,在PE基质的共混体系中存在一定的界面黏附作用,降低了纳米共混体系的挤出胀大比,弹性特征减轻。这种界面相互作用限制了纳米共混材料在口模区域的黏性流动以及分子链离开口模后的构象恢复,降低了发生流动不稳定现象的临界剪切速率,发生鲨鱼皮畸变的临界剪切应力增大,整体破裂后,形成交替出现"鲨鱼皮-破裂"的振荡性变化外观。     

A comparison of different geometrical elements to model fluid wicking in paper-based microfluidic devices

Recently, microfluidic paper-based analytical devices (μPADs) have outstripped polymeric microfluidic devices in the ease of fabrication and simplicity. Surface tension-based fluid motion in the paper's porous structure has made the paper a suitable substrate for multiple biological assays by directing fluid into multiple assay zones. The widespread assumption in most works for modeling wicking in a paper is that the paper is a combination of capillaries with the same diameter equal to the effective pore diameter. Although assuming paper as a bundle of capillaries gives a good insight into pressure force that drives the fluid inside the paper, there are some difficulties using the effective pore radius. The effective pore radius is totally different from the average geometrical pore radius which makes it impossible to predict wicking in μPADs based on geometrical parameters. In this article, we introduce different analytical and numerical models to investigate the possibility of determining the permeability of the paper, based on geometrical parameters rather than effective parameters. The lattice Boltzmann method is used for numerical simulations. The permeability of each of the proposed models was compared with the experimental permeability. Results indicated that assuming paper as a combination of capillaries and annuluses leads to accurate results that totally depend on average geometrical values rather than effective values. This paves the way for prediction of the fluid wicking only by considering average geometrical pore and fiber diameters.