新型的DNA金属化制作工艺

生物与微细加工技术的结合日益成为一种新趋势,DNA分子具有热力学上的稳定性、线性的分子结构及机械刚性等优点,可以作为制备纳米线的理想模板。通过DNA为模板的金属化,形成导电性好的金属纳米线和金属团簇的纳米结构,使得DNA分子作为纳米导线构筑纳米器件成为可能。在本文中,我们对几种具有代表性的DNA金属化工艺的原理进行了讨论,研究了其新型的制作工艺,通过进一步的自组装和自识别技术,金属化过的DNA就可以被用来构建电路,并作为后续的金属沉积模板,在构筑生物纳米器件的领域将有广阔的应用前景。     

类过氧化物DNA酶在生物传感器领域的研究进展

随着对DNA酶研究的进展,DNA酶的很多优点已经超越了传统的蛋白质酶,具有过氧化物酶催化活性的DNA酶在电化学生物检测上拥有很大的潜力。我们简要阐述了DNA酶的特性和应用,描述了其基本性质,对DNA酶在生物分析领域的应用进行了展望。     

DNA多面体数学模型的研究进展

近年来,越来越多的DNA多面体在实验室中被合成出来,深入理解这些新颖的多面体结构和性质成了新的挑战,迫切需要综合运用数学、生物、化学等理论和手段进行研究。现在综述文献的基础上,以两种十四面体为例,系统介绍通过DNA多面体的新欧拉公式和两种示性数来刻画DNA多面体的拓扑结构,探索DNA多面体的组装规律和性质。     

三种提取乳酸菌中内源性质粒DNA方法的比较

采用3种不同抽提质粒DNA的方法普查了6株不同乳酸菌的内源性质粒DNA,并对3种不同方法进行比较。在相同条件下,琼脂糖凝胶电泳检测的结果显示:效果最佳者为改进的Anderson-Mckay方法,其次为液氮反复冻融方法,最差者为改进的碱裂解方法。为抽提革兰阳性细菌乳酸菌类的内源性质粒DNA提供了行之有效的方法。     

哺乳动物DNA聚合酶及其功能研究的进展

本文介绍了哺乳动物的三个主要的DNA聚合酶及其生物功能的研究进展,特别是1975年以后的研究进展。简要地比较了DNA聚合酶α、β、γ的物理化学性质和生物化学性质,并选择有说服力的材料阐明了DNA聚合酶α是负责DNA复制的主要聚合酶;DNA聚合酶β在DNA修复中发挥作用;而DNA聚合酶γ通过单链置换合成(single strand displacment synthesis)在线粒体中起复制作用,在细胞核中则可能起基因放大等作用。     

DNA损伤检测技术

检测DNA损伤的方法有很多,根据其原理大致可以分为3类：基于损伤DNA理化性质的改变检测DNA损伤、基于分子杂交检测DNA损伤以及基于DNA损伤后形成的产物检测DNA损伤。检测DNA损伤的方法目前还在不断快速发展、完善中。本文就DNA损伤的检测方法及其发展做一综述。     

原子力显微镜拉伸吸附在金膜表面的短单链DNA分子

对单根DNA分子的操纵和拉伸可以直接研究DNA的弹性等力学性质. 首先通过将金沉积到云母表面制备了表面粗糙度小于0.3 nm的金膜,然后一段硫代的单链DNA (100 bases) 吸附到金膜表面. 利用原子力显微镜观察不同浓度的DNA吸附在金膜上的表面形貌. 进一步用原子力显微镜的力曲线模式拉伸DNA分子,在50％的情况下DNA可以被针尖拉伸,观察到了由于针尖和DNA分子间作用力的不同导致的多种不同力曲线.     

DNA分子量标准制备技术：方法与进展

DNA分子量标准是一组分子量大小已知的DNA片段混合物,用于指示核酸电泳中未知样品的分子量大小,从而帮助实验人员判断DNA样品的性质。因而DNA分子量标准成为目前分子生物学和基因工程领域不可或缺的一种电泳耗材。综述了目前各种DNA分子量标准产品的制备方法和技术原理及近年来该领域的一些技术进展情况。     

几种耐热DNA聚合酶的比较

耐热DNA聚合酶广泛应用在PCR技术。本文将常用的几种耐热DNA聚合酶分为三大类,对它们的性质、差异、用途做一个简单的介绍。     

降解性质粒DNA的裂解气液色谱分析

用GC-9A气相色谱仪和PYR-2A管式炉裂解器,对四种降解性质粒DNA进行了裂解气液色谱鉴别,通过对指纹图的分析,较好地区分了不同降解性质粒DNA问的差异。证明了裂解气液色谱法分析质粒的可行性。另外,对分析质粒IDNA的邑谱柱、进样量．裂解温度和时间等色谱条件也进行了试验。     

Characterization of DNA degradation using direct current conductivity and dynamic dielectric relaxation techniques

The purpose of this study was to evaluate DNA degradation upon thermal heating using dielectric relaxation and direct current (DC) conductivity methods. Herring sperm DNA, human growth hormone (HgH) plasmid DNA, and secreted alkaline phosphatase (SEAP) plasmid DNA were used as the examples. DNA was heated at 80°C for 1 hour. The dielectric relaxation spectra as a function of the applied field frequency were measured for HgH DNA at 0.5 hours and at 1 hour. The frequency range covered was from 10 kHz to 100 kHz. The DC conductivity measurements were made for all 3 kinds of DNA at 4 time points: 0 hours, 0.5 hours, 0.75 hours, and 1 hour. At each time point the DC conductivity was measured for each sample as a function of concentration via water dilution. The results show that the dielectric relaxation method is less sensitive in characterizing heat-driven DNA degradation. Conversely, DC conductivity is very sensitive. The semiquantitative dependence of the conductivity upon heating suggests that DNA degradation involves more than plasmid DNA nicking. Double strand and single strand breaks may also occur. In addition, herring sperm DNA, HgH DNA, and SEAP DNA, though similar in their DC conductivity functional forms upon dilution, exhibit significant differences in their responses to sustained heating.     

Ni2+-enhanced charge transport via π-π stacking corridor in metallic DNA

The mechanism underlying DNA charge transport is intriguing. However, poor conductivity of DNA makes it difficult to detect DNA charge transport. Metallic DNA (M-DNA) has better conducting properties than native DNA. Ni(2+) may chelate in DNA and thus enhance DNA conductivity. On the basis of this finding, it is possible to reveal the mechanisms underlying DNA charge transport. The conductivity of various Ni-DNA species such as single-stranded, full complement, or mismatched sequence molecules was systematically tested with ultraviolet absorption and electrical or chemical methods. The results showed that the conductivity of single-stranded Ni-DNA (Ni-ssDNA) was similar to that of a native DNA duplex. Moreover, the resistance of Ni-DNA with a single basepair mismatch was significantly higher than that of fully complementary Ni-DNA duplexes. The resistance also increased exponentially as the number of mismatched basepairs increased linearly after the tunneling current behavior predicted by the Simmons model. In conclusion, the charges in Ni(2+)-doped DNA are transported through the Ni(2+)-mediated π-π stacking corridor. Furthermore, Ni-DNA acts as a conducting wire and exhibits a tunneling barrier when basepair mismatches occur. This property may be useful in detecting single basepair mismatches.     

Ni-Enhanced Charge Transport via π-π Stacking Corridor in Metallic DNA

The mechanism underlying DNA charge transport is intriguing. However, poor conductivity of DNA makes it difficult to detect DNA charge transport. Metallic DNA (M-DNA) has better conducting properties than native DNA. Ni²⁺ may chelate in DNA and thus enhance DNA conductivity. On the basis of this finding, it is possible to reveal the mechanisms underlying DNA charge transport. The conductivity of various Ni-DNA species such as single-stranded, full complement, or mismatched sequence molecules was systematically tested with ultraviolet absorption and electrical or chemical methods. The results showed that the conductivity of single-stranded Ni-DNA (Ni-ssDNA) was similar to that of a native DNA duplex. Moreover, the resistance of Ni-DNA with a single basepair mismatch was significantly higher than that of fully complementary Ni-DNA duplexes. The resistance also increased exponentially as the number of mismatched basepairs increased linearly after the tunneling current behavior predicted by the Simmons model. In conclusion, the charges in Ni²⁺-doped DNA are transported through the Ni²⁺-mediated π−π stacking corridor. Furthermore, Ni-DNA acts as a conducting wire and exhibits a tunneling barrier when basepair mismatches occur. This property may be useful in detecting single basepair mismatches.     

Premelting effects in DNA under saltfree conditions

We have studied the electrical conductivity of NaDNA solutions under “saltfree” conditions at temperatures well below the melting point of DNA, using radio-frequency dielectric and noise measurements. A conductivity discontinuity is observed at a temperature well below that at which the usual denaturation processes and trans conformation may commence. The radio-frequency permittivity also exhibits a discontinuity at the same temperature. For the premelting phase, the conductivity versus temperature curves consist of two linear regions with a change in slope occurring at 23°C. This effect is related to the behavior of the ionic sheath covering the DNA macromolecule. The activation energy of the alternative current conductivity as well as that the equivalent noise conductivity results as 3.11 kcal/mole below and 4.08 kcal/mole.     

Monitoring the progression of loop-mediated isothermal amplification using conductivity

Loop-mediated isothermal amplification (LAMP) yields a large amount of DNA, as well as magnesium pyrophosphate precipitate, causing a decrease in ionic strength that can be measured with a conductivity meter. There is a clear relationship between the conductivity of the LAMP mixture solution and the duration of biochemical reaction. Moreover, there is also a clear relationship between the change in conductivity and the amount of initial template DNA over the range of 0.08 to 3.2 ng. These results demonstrate the feasibility not only for detecting the LAMP product qualitatively but also for real-time monitoring the biochemical reaction progression quantitatively using conductivity measurements.     

基于DNA分子导线的纳米生物传感器

DNA分子导线具有独特的导电性能和塞贝克(Seebeck)效应,它是构筑电化学纳米生物传感器和热电偶生物传感器的理想材料。文章简要介绍了DNA分子导线的制备方法及导电机理,以及基于DNA分子导线的纳米生物传感器的分子识别机制,着重分析了基于DNA分子导线的纳米生物传感器的传感原理。文章还介绍了基于DNA分子导线的纳米生物传感器在基因分析、单碱基突变检测等方面的应用。     

DNA溶液的导电行为

将链长不同的两种DNA溶解在超纯水中,分别测定它们在不同浓度不同温度下的电导行为。试验证明,同种DNA的电导率随着溶液中DNA的浓度增大而显著增大。而对于两种不同的DNA,短链DNA(<50bp)的电导能力较长链DNA(>1000bp)好。在本文测试的浓度范围内,短链DNA水溶液常温下电导率达到0.99×10-4S/cm。而且,电导率随DNA浓度的变化规律与指数方程(δ/δ0=aCm)符合得很好。当温度升高时长链和短链DNA溶液的电导率都有明显增大,并且随温度的变化趋势基本一致。     

On the mechanism of dielectric relaxation in aqueous DNA solutions.

The complex dielectric response of calf thymus DNA in aqueous saline solutions has been measured from 1 MHz to 1 GHz. The results are presented in terms of the relaxation of the incremental contributions to the permittivity and conductivity from the condensed counterions surrounding the DNA molecules. Measurements of the low-frequency conductivity of the samples also lends support to the condensed counterion interpretation.     

Conductivity of natural and modified DNA measured by scanning tunneling microscopy. The effect of sequence, charge and stacking

The conductivity of DNA covalently bonded to a gold surface was studied by means of the STM technique. Various single- and double-stranded 32-nucleotide-long DNA sequences were measured under ambient conditions so as to provide a better understanding of the complex process of charge-carrier transport in natural as well as chemically modified DNA molecules. The investigations focused on the role of several features of DNA structure, namely the role of the negative charge at the backbone phosphate group and the related complex effects of counterions, and of the stacking interactions between the bases in Watson-Crick and other types of base pairs. The measurements have indicated that the best conductor is DNA in its biologically most relevant double-stranded form with Watson-Crick base pairs and charged phosphates equilibrated with counterions and water. All the studied modifications, including DNA with non-Watson-Crick base pairs, the abasic form, and especially the form with phosphate charges eliminated by chemical modifications, lower the conductivity of natural DNA.     

Measurement of the electrode dispersion in very low frequency DNA solutions

Based on the four electrodes technique, an apparatus is described which measures the Very Low Frequency (VLF) conductivity of ionic solutions, all electrode effects being completely eliminated. It is thus possible to measure the conductivity frequency dependence between 0.8 and 500 cps, with a relative error of 10^?4. Applying this method to DNA solutions, one always finds a conductivity dispersion in the VLF range, which disappears when the biopolymer is heat-denatured. The relaxation time is different from one solution to another, but is always greater than 10 msee. approximately, sometimes even greater than 0.1 sec., the upper limit which one can estimate with our apparatus. The different, explanations of the DNA very low frequency polarization, assuming that its relaxation is connected with the rotational diffusion of the biopolymer long axis, is discussed.