扫描探针显微镜系统的各种组合方式

综述了扫描探针显微镜(SPM)系统中显微镜主体部分的各种结构方式，分析其优缺点，对新型SPM的设计提供了参考。

4H-SiC基底Al_2O_3/SiO_2双层减反射膜的设计和制备

在4H-SiC基底上设计并制备了Al2O3/SiO2紫外双层减反射膜,通过扫描电镜(SEM)和实测反射率谱来验证理论设计的正确性。利用编程计算得到Al2O3和SiO2的最优物理膜厚分别为42.0nm和96.1nm以及参考波长λ=280nm处最小反射率为0.09%。由误差分析可知,实际镀膜时保持双层膜厚度之和与理论值一致有利于降低膜系反射率。实验中应当准确控制SiO2折射率并使Al2O3折射率接近1.715。用电子束蒸发法在4H-SiC基底上淀积Al2O3/SiO2双层膜,厚度分别为42nm和96nm。SEM截面图表明淀积的薄膜和基底间具有较强的附着力。实测反射率极小值为0.33%,对应λ=276nm,与理论结果吻合较好。与传统SiO2单层膜相比,Al2O3/SiO2双层膜具有反射率小,波长选择性好等优点,从而论证了其在4H-SiC基紫外光电器件减反射膜上具有较好的应用前景。

Distribution of rDNA in the nucleus of Giardia lamblia - Detection by Ag-I silver stain

OBJECTIVE: To determine whether rDNA of Giardia lamblia forms a nucleolus organizer region (NOR)-like structure and is in a very primitive state. STUDY DESIGN: G lamblia was used as the experimental animal, with Euglena gracilis as the control. The distribution was demonstrated indirectly by the modified Ag-I silver technique, which can specifically indicate the NOR under both light and electron microscopes. RESULTS: In the ultrathin sections of silver-stained Euglena cells, all the silver grains were concentrated in the fibrosa of the nucleolus, while no grains found in the cytoplasm, nucleoplasm, condensed chromosomes or pars granulosa of the nucleus. In the silver-stained Giardia cells, no nucleolus was found; a few silver grains were scattered in the nucleus but were not concentrated in any specific region. CONCLUSION: The distribution of silver grains in G lamblia showed that the transcription of rDNA occurs inside the nucleus, though no nucleolus is present. It is possible that chromosomes are in a very primitive state in diplomonad cells; as each chromosome has few prRNA genes, the transcription is independent of a nucleolus. These results imply that the rDNA of Giardia does not form a NOR-like structure and seems to represent a very primitive state in the evolution of the nucleolus.

Sediment sources and the flood record from Wanghu lake, in the middle reaches of the Yangtze River

A sediment core was collected from the centre of Wanghu Lake, in the Middle Reaches of the Yangtze River. The recent part of the core was dated using a combination of Pb-210 and spheroidal carbonaceous particle (SCP) techniques. Extrapolating this chronology dated the laminated section of the core, between 723 and 881 mm, to the first half of the 18th century and this section was selected for detailed study. The thicknesses of the laminae were measured using reflecting and polarizing microscopes whilst geochemistry was determined by an electron probe. The thickness of the dark layers was found to be positively correlated with titanium concentrations, and negatively correlated with aluminium and potassium concentrations. The thickness of the light layers was found to be negatively correlated with the concentrations of titanium. It is concluded that the dark layers were deposited from the Fushui River, a tributary of the Yangtze River, under periods of normal flow whilst the light Layers were mainly deposited from the Yangtze River itself during flood periods. Documentary evidence for floods occurring in the take catchment corresponded with thick laminations of high titanium concentration. Further, two of the three thickest, light laminations with low titanium concentrations were found to be synchronous with recorded flood dates of the main Yangtze River in its Middle Reaches, but one was synchronous with a local drought. These data suggest that the Lake sediment provides an archive of the relative water levels of the Yangtze and Wanghu including floods of both the main Yangtze River and the local hydrological regime. (c) 2006 Elsevier B.V. All rights reserved.

运用含有偶氮苯的自组装单层膜在光化学条件下可逆地控制细胞黏附

细胞生物学研究的一个重要方向是动态地控制细胞在基底上的黏附。最近，随着表面化学的研究深入，尤其是对烷基硫醇在金基底上形成自组装单层膜（self-assembled monolayers, SAMs）这一体系的研究，使得人们能在分子水平的表面上控制细胞黏附。精氨酸-甘氨酸-天冬氨酸（arginine-glycine-aspartate, RGD）序列首先是从细胞外基质蛋白中分离出来的，能够识别并非共价结合细胞膜表面的整合素受体，从而促进细胞黏附。以前的一些工作已经证实，将含有RGD的肽链连接到SAMs表面之后，能够生物特异性地黏附动物细胞。已有的手段比如光照、电压、加热、微电极、微流控以及表面纳米形貌的梯度变化，都不能真正实现可逆地控制细胞黏附，原因是这些方法所用的化学有限；这些方法也不能得到完全抗拒细胞黏附的表面，原因是这些方法产生的表面缺陷等不完整。用两种不同波长的光（紫外光和可见光）照射偶氮苯，偶氮苯会发生可逆的光致异构变化，因此，偶氮苯的光致异构性质可以用来可逆地控制细胞在表面黏附。运用含有偶氮苯的混合SAMs，偶氮苯的末端连接GRGDS肽，混合SAMs中是以末端为六聚乙二醇的硫醇为背景，该SAMs修饰而成的表面能够黏附或者抗拒细胞黏附，其表面黏附性质取决于SAMs中偶氮苯的构象。该方法提供了一种在分子水平的表面上我们所了解到的唯一能可逆控制细胞黏附的方法，该方法需要用到的光源来自于标准荧光显微镜所配置的汞灯。 为了实现在金基底表面可逆的控制细胞黏附，我们合成了如下三个化合物： 由于化合物1的溶解性很差，几乎在所有溶剂里都不溶，所以不能直接用化合物1制备SAMs；化合物2能高效地抗拒细胞的黏附；化合物3的偶氮苯末端是活化酯，能够连接GRGDS肽，从而控制细胞黏附。 将化合物2和化合物3以一定的比例均匀混合在金基底表面形成SAMs，然后将GRGDS肽连接到偶氮苯(反式)的末端（通过GRGDS肽的甘氨酸上的伯胺基与偶氮苯末端的活化酯反应），从而得到细胞黏附的表面。用紫外光照射该细胞黏附表面5-10小时，随着偶氮苯的构象由反式变为顺式，偶氮苯末端的GRGDS肽淹没在化合物2的六聚乙二醇中，得到抗拒细胞黏附的惰性表面。再用可见光照射该惰性表面1个小时，随着偶氮苯的构象由顺式变为反式，原先埋没在六聚乙二醇中的GRGDS肽伸展至单层膜的末端，又得到了细胞黏附的表面。因此，该表面能完全可逆地控制细胞在金表面黏附。 An important area in cell biology is the dynamic control of cell adhesion on substrates. Recent advancements in surface chemistry, in particular, self-assembled monolayers (SAMs) of alkanethiols on gold substrates, have permitted unprecedented control of cell adhesion via molecularly defined surfaces. The tri-peptide sequence arginine-glycine-aspartate (RGD), initially isolated from the extracellular matrix (ECM) proteins, can recognize and non-covalently bind with integrin receptors on cell membranes to promote cell adhesion. Some previous work has demonstrated that RGD peptide grafted on SAMs can allow bio-specific adhesion of mammalian cells that mimic natural adhesion. Existing technologies such as light, voltage, heat, microelectrodes, microfluidic systems and surface gradient of nanotopography, either cannot realize fully reversible control of cell adhesion, due to the limitation in the chemistry used, or cannot yield a surface completely resistant against cell adhesion, due to the imperfection of surfaces. Azobenzenes undergo reversible photo-induced isomerization rapidly at two different wavelengths of light (UV and visible light), it therefore potentially allows the reversible control of cell adhesion on a surface. By using a mixed SAMs presenting azobenzene groups terminated in GRGDS peptides in a background of hexa(ethylene glycol) groups, the surface can either accommodate or resist cell adhesion depending on the conformation of the azobenzene embedded in SAMs. This method provides the only means we know to control cell adhesion reversibly on a molecularly well-defined surface by using light generated by a mercury lamp equipped on standard fluorescence microscopes. To realize the reversible control of cell adhesion on gold surface, we synthesized three kinds of compounds as following, We found that it was difficult to obtain SAMs directly from compound 1 because of its poor solubility in almost all kinds of solvents; compound 2 can resist cell adhesion efficiently; compound 3 presents an azobenzene terminated with NHS-activated ester, which can couple with a GRGDS peptide to control cell adhesion. After coating a gold surface with compound 2 and 3 in appropriate ratios to form a SAM followed by coupling the GRGDS peptides with NHS-activated esters at the end of azobenzene (E configuration) resulted in a cell-adhesive SAM. Irradiating this cell-adhesive SAM with UV light for 5-10 h converted the E configuration of azobenzene into the Z form, the GRGDS peptides becoming masked in the PEG, resulting in a cell-resistant surface. These SAM could again support cell adhesion as a result of the conformational switch of azobenzene from Z to E with the irradiation of visible light for 1 h. This surface, therefore, allows completely reversible control of cell adhesion on a gold surface.