CTAB修饰玻璃表面DNA的拉直行为研究

本文利用荧光成像技术研究了DNA在CTAB修饰基底表面的拉直行为,在CTAB修饰基底上,DNA可以被拉直,部分DNA因为两端都固定在基底表面而形成"U"型或因为中间部分固定而形成"V"型.     

Si基底上DNA分子的自组装

利用自组装方法将DNA分子吸附于Si基底表面, 并通过原子力显微镜（AFM）观察不同质量浓度的DNA溶液在Si基底表面进行自组装后的结构： 当DNA溶液的质量浓度较低时, Si基底表面会吸附单个、 拉伸、 环状的分子; 当DNA溶液的质量浓度为60~160 ng/μL时, 在Si基底表面会形成网状结构; 当DNA溶液的质量浓度超过200 ng/μL时, 仅形成DNA薄膜. 实验结果表明, 可以利用该方法制作基于Si材料的DNA分子器件.     

NDA分子双螺旋结构的扫描隧道显微镜（STM）观测

用自制的STM,经高序定向热解石墨（HOPG）对扫描组件进行定标后,采用展开法制样,在常温常压的自然条件下,对猪脾DNA分子进行了观测研究。得到了石墨表面清晰折原子分辩图象以及猪脾DNA分子双螺旋结构的STM形貌图。介绍了生物样品的制备方法,对实验结果进行了分析和讨论。     

基于氮化硅薄膜纳米孔制备及DNA分子检测

通过对影响聚焦离子束溅射氮化硅纳米孔的溅射时间和离子束束流2个主要参数的研究,优化了聚焦离子束溅射纳米孔加工工艺.提出了利用聚焦离子束对氮化硅薄膜进行减薄后再溅射纳米孔的加工工艺.采用该加工工艺不仅可以减小纳米孔的直径和厚度,还可以减小纳米孔的锥度.最后利用氮化硅纳米孔研究了不同孔径的纳米孔对48 kbλ-DNA过孔姿态的影响,结果表明,孔径较大时,DNA分子过孔存在多种过孔姿态,孔径越小,DNA分子越容易被拉直过孔.同时针对DNA过孔时引起的阻塞电流,提出了简易的计算模型.     

原子力显微镜观测DNA分子的表面沉积与扩展

原子力显微镜具有原子级分辨率,能够对生物样品进行观察.用原子力显微镜观察了DNA分子在Si、云母片及修饰过的云母片表面的沉积与扩展,对3种情况作了比较,用超声振荡方法可以有效地切断DNA分子链.     

DNA分子的电性质研究进展

DNA(脱氧核糖核苷酸)分子的电学性质关系到生命信息静态的存储和动态的释放,因此一直备受关注.但仅是随着物理实验手段在生物学研究领域的广泛应用,特别是纳米观测和纳米操纵技术的提高,才使研究单个DNA分子的电学性质成为可能.从20世纪90年代以来开展的大量研究工作表明,探明DNA的电学性质不仅能够帮助理解DNA复制和修复的物理机制,而且指出作为天然的纳米结构材料,DNA分子在分子器件学领域具有巨大的应用潜力.回顾了DNA电学性质的研究成果,并对DNA分子在材料学及分子器件学领域的应用前景作以展望.     

张丰收教授课题组关于DNA构象的转变研究获新进展

北京师范大学低能核物理研究所“京师学者”特聘教授张丰收领导的课题组，利用室温下分子模拟方法研究了DNA在具有不同分子极性的溶剂环境中发生的构象变化规律，研究结果发表于2008年2月29日出版的《物理评论快报》．审稿专家认为该研究从分子层次对DNA构象转变机制进行了阐述，     

应用分子梳技术对DNA单分子的研究

分子梳技术是一种有效的拉伸DNA分子的手段,它利用流体流动过程中施加的力将DNA分子拉伸开并且平铺在固体表面上．在每个玻片上可以同时对很多DNA分子拉伸并且整齐地排列,使之便于统计分析数据．利用分子梳技术可以在单分子水平上研究DNA复制、转录过程以及DNA-蛋白质相互作用．文中主要介绍分子梳技术原理、实现方法及其重要应用．     

血液痕迹中DNA抽提方法的比较与优化

本文总结了6种DNA抽提方法,进行部分优化后对长时间离体血液痕迹中的DNA进行提取对比.结果表明:优化后的CTAB法可以简单、快速、高效地从凝血块儿中获得高纯度的DNA,并可满足后续PCR扩增和分子标记等分子遗传学研究.     

银镜衬底的表面增强拉曼散射机制研究

研究了不同粗糙度的银镜对不同分子的表面拉曼增强效应,实验结果表明：在吸附分子与银镜之间同时存在物理增强和化学增强两种机制,物理增强与银镜衬底的表面粗糙度有关;化学增强则与吸附分子的化学性质有关,总的增强效果因分子而异。     

Direct measurement of compression spring constant of single DNA molecule with AFM

The understanding of mechanical responses of individ-ual macromolecules under a small external load (usually F<0.5 nN) is of profound importance because the induced conformational transition can result in the change of bio-logical functions[1?3]. The advent of new instrumentations, especially the development of Pico-Newton force tech-nology, has made it possible to investigate the dynamic behavior of single biomolecule and manipulate it to make direct measurements of its elastic properties[4?…     

Spermidine-induced two-dimensional DNA condensations on mica surfaces: A different pathway from condensations in solution

With atomic force microscopy （AFM） we systematically studied the DNA condensations on mica surfaces induced by multivalent cation spermidine. The pattern of the DNA condensates is a flat single layer, with a core in the centre and DNA wrapping around it at high density. We assume this to be a two-dimensional condensation of free coiled DNA onto negatively charged mica surfaces by the multivalent cation. The DNA molecules condense on mica surfaces via a pathway different from the formation of toroids, rods or globules in bulk solutions. We give an explanation to why toroid structures are difficult to be observed by AFM, and further discuss the relationship between DNA condensations in solutions and on mica surfaces. The present work will be helpful for understanding the behaviors of DNA on charged surfaces, which might be significantly different from that in solutions.     

原子力显微镜针尖与样品间的材料转移

研究氮化硅针尖在十八烷基三甲氧基硅烷 (OTE) /云母表面的修饰过程。使用原子力 /摩擦力显微镜 ,以云母作为参考样品 ,研究了针尖在样品表面的修饰效应和修饰后针尖的清洁过程 ,并考察了湿度和载荷对针尖修饰效应的影响。修饰过程不是一个渐进的过程 ,在最初几次摩擦扫描中修饰较快 ,然后在 10～ 2 0次扫描后达到平衡态。在 OTE/云母表面修饰后的针尖在云母表面的摩擦力信号比修饰前针尖在云母表面的摩擦力信号小 ,并且大部分吸附在针尖表面的 OTE分子在云母表面的前 10次扫描中就被磨掉。相对湿度对针尖的修饰效应影响不大。在研究不同样品的摩擦性能时 ,尽量使用清洁针尖 ,并使用摩擦性能稳定的参考样品 (如云母 )来检测针尖的表面状态     

Stretching and imaging studies of single DNA molecules

DNA molecules were stretched on silanized mica surface with the molecular combing technique, and detected with fluorescence microscopy and atomic force microscopy. Meantime, DNA molecules were stretched with a modified dynamic molecular combing technique and studied with atomic force microscopy. The results indicate that, compared with the dynamic molecular combing technique, the modified dynamic molecular combing technique has advantages of less-sample demand and less contamination to sample; as compared with the molecular combing technique, it has better aligning effect and reproducibility. Combination of this kind of DNA molecular manipulating technique with the single DNA molecule detecting technique by atomic force microscopy and fluorescence microscopy will play an important role in the basic research of molecular dynamics and the application of gene research.     

胶原蛋白在LB膜上的吸附行为研究

基底的性质和制备方法对吸附胶原层的超分子自组装过程有很大的影响,将一种Gemini表面活性剂C18H37(CH3)2N+-(CH2)12-N+(CH3)2C18H37·2Br-(简写为18-12-18)利用LB技术在零压下转移到云母片上制成基底,浸入到pH值为3.0的胶原溶液中37℃恒温吸附不同的时间,样品用原子力显微镜(AFM)进行表征。结果表明:在恒温过程中,LB膜上的表面活性剂分子会发生移动和翻转,胶原分子优先吸附在LB膜上形成单层网状结构,随吸附时间的延长,胶原分子也会在云母上发生吸附,最后两者会交织成无序的胶原纤维。     

基因转运载体的原子力显微镜研究

通过原子力显微镜观测阳离子脂质体及其与DNA复合物的结构。将一定量的阳离子脂质体以及阳离子脂质体／DAN复合物滴加到新解理的云母片上,干燥后用原子力显微镜观测。结果表明,阳离子脂质体在云母片上形成的颗粒为球形或椭圆形,粒径分布较为均匀;阳离子脂质体／DNA复合物在云母片上的颗粒形状不规则,粒径分布不均且比空白脂质体的粒径大。通过原子力显微镜可以快速有效地观测脂质体以及脂质体／DNA复合物的粒径、表面形态等,为分析脂质体的物理化学性质与基因转运效率的关系提供了一种研究方法。     

HREELS study on coadsorption of oxygen and cyclohexanone on the Pt(111) surface

The coadsorption of cyclohexanone and oxygen on Pt(111) has been investigated by HREE-LS and TDS. At 205 K the presence of oxygen induces an “extra” red-shift of the C = O stretching of coadsorbed cyclohexanone. Heating this coadsorbed surface from 205 to 250 K leads to further dehydrogenation to form intermediate species and to complete disappearance of the C = O stretching band. Above 300 K, the molecule rings of dehydrogenation species cleave to form hydrocarbon fragments and CO molecules which directly desorb into the vacuum or react with preadsorbed oxygen to produrn CO₂ which leave the surface immediately. TDS results provide further evidence that the preadsorbed oxygen promotes the decomposition of cyclohexanone.     

Study on the micro-region structure and properties of two dithienothiophene-dicarboxylic acids

Self-organized dithieno [3,2-b:2',3'-d] thiophene-2,5-dicarboxylic acid (A) and dithieno [2,3-b:3',2'-d] thiophene-2,5-dicarboxylic acid (B) films were prepared through solvent-induced order-disorder transition method.The arrangement of the two molecules on substrates were observed by atomic force microscopy (AFM),which demonstrated that A was arranged orderly in a certain angle on mica,while B was flat-flying on mica.The optical and conductance properties in micro region of these two compound films were ch...     

用STM研究云母表面Au原子团的行为

用扫描隧道显微镜(STM)研究了沉积在白云母(001)表面上的金(Au)薄膜表面的形貌,这个Au膜是在高真空中,蒸发到在大气中解理的白云母(001)表面上,其Au膜厚约为40um。用STM测量样品表面形貌,我们发现在Au膜表面存在原子团,这些原子团作随机运动,其形状和大小随时间变化。     

DNA overwinds when stretched

DNA is often modelled as an isotropic rod, but its chiral structure suggests the possible importance of anisotropic mechanical properties, including coupling between twisting and stretching degrees of freedom. Simple physical intuition predicts that DNA should unwind under tension, as it is pulled towards a denatured structure. We used rotor bead tracking to directly measure twist-stretch coupling in single DNA molecules. Here we show that for small distortions, contrary to intuition, DNA overwinds under tension, reaching a maximum twist at a tension of approximately 30 pN. As tension is increased above this critical value, the DNA begins to unwind. The observed twist-stretch coupling predicts that DNA should also lengthen when overwound under constant tension, an effect that we quantitatively confirm. We present a simple model that explains these unusual mechanical properties, and also suggests a possible origin for the anomalously large torsional rigidity of DNA. Our results have implications for the action of DNA-binding proteins that must stretch and twist DNA to compensate for variability in the lengths of their binding sites. The requisite coupled DNA distortions are favoured by the intrinsic mechanical properties of the double helix reported here.