Self-assembled monolayer growth of phospholipids on hydrophobic surface toward mimetic biomembranes: Scanning probe microscopy study

Atomic force microscopy (AFM) and lateral force microscopy (LFM) were used simultaneously to analyze a model membrane bilayer structure consisting of a phospholipid outer monolayer deposited onto organosilane-derivatized mica surfaces, which were constructed by using painting and self-assembly methods. The phospholipid used as outer monolayer was dimyristoylphosphatidylcholine (DMPC). The hydrocarbon-covered substrate that formed the inner half bilayer was composed of a self-assembly monolayer (SAM) of octadecyltrichloroorganosilane (OTS) on mica. SAMs of DMPC were formed by exposing hydrophobic mica to a solution of DMPC in decane/isobutanol and subsequently immersing into pure water. AFM images of samples immersed in solution for varying exposure times showed that before forming a complete monolayer the molecules aggregated into dense islands (2.2-2.6 nm high) on the surface. The islands had a compact and rounded morphology. LFM, coupled with topographic data obtained with the atomic force mode, had made possible the distinction between DMPC and OTS. The rate constant of DMPC growth was calculated. This is the first systematic study of the SAM formation of DMPC by AFM and LFM imaging. It reveals more direct information about the film morphology than previous studies with conventional surface analytical techniques such as infrared spectroscopy, X-ray, or fluorescence microscopy.

Ultrathin multilayer films incorporating Keggin-type heteropolyanion clusters

Two new ultrathin multiplayer films have been successfully prepared fi-om Keggin-type heteropoly acids H-4[SiW12O40] and H-3[PMo12O40] with polyelectrolytes PEI, PSS, and PAH, using the electrostatic layer-by-layer self-assembly, technique. The XR results reveal their film thickness at nanoscale (similar to 20 nm). According to the AFM images, it is believed that the surface roughness (rough degree of film surface) of the polyelectrolyte-polyoxometalate film greatly depends on the kind of polyoxometalates.

Molecular component structures mediated formation of self-assemblies

Molecular recognition directed self-assemblies from complementary molecular components, melamine and barbituric acid derivatives were studied by means of NMR, fluorescence, and TEM. It was found that both the process of the self-assembly and the morphologies of the resulted self-assemblies could be mediated by modifying the structures of the molecular components used. The effect of the structures of the molecular components on the formation of the self-assemblies was discussed in terms of intermolecular interactions.

Rapid electron propagation through molecular wire monolayers sandwiched between two gold electrodes

Conjugated bisthioester 1 was synthesized applying Sonogashira coupling reactions. Using self-assembly in combination with nanoparticles deposition techniques, we developed a novel method to fabricate a "gold electrode-molecular wire monolayers-gold nanoparticles" sandwich-like structure. Rapid electron propagation through this sandwich-like structure was observed by cyclic voltammetry and ac impedance measurements.

Preparation and characterization of self-assembled monolayers of trichlorogermanyl propanoic acid and its derivatives

Self-assembled monolayers(SAMs) of trichlorogermanyl propanoic acid derivatives on hydroxylated silicon substrates are prepared for the first time. Contact angle measurement, ellipsometry and X-ray photoelectron spectrometry(XPS) are used to characterize these SAMs, It is demonstrated that a quasi-2D network is formed on the surface of the substrate after molecules adsorbed on it. The molecular chains have certain tilt angles to the substrate surface, The wettabilities of the SAMs are various,because the molecules adsorbed and liquids used in the experiments are different. It can be concluded that trichlorogermanes have similar self-assembly behavior as trichlorosilanes, Four SAMs are studied together: they are acid, ethyl, butyl and hexyl surfaces whose results are of good consistency.

Self-assembled monolayers of thiols on gold electrodes for bioelectrochemistry and biosensors

Monolayers of biological compounds including redox proteins and enzymes, and phospholipids have been immobilized on a gold electrode surface through self-assembling. These proteins and enzymes, such as cytochrome c, cytochrome c oxidase and horseradish peroxidase (HRP), immobilized covalently to the self-assembled monolayers (SAMs) of 3-mercaptopropionic acid on a gold electrode, communicate directly electrons with the electrode surface without mediators and keep their physiological activities. The electron transfer of HRP with the gold electrode can also be mediated by the alkanethiol SAMs with electroactive group viologens on the gold electrode surface. All these direct electrochemistries of proteins and enzymes might offer an opportunity to build a third generation of biosensors without mediators for analytes, such as H2O2, glucose and cholesterol. Monensin and valinomycin have been incorporated into the bilayers on the gold electrode consisting of the SAMs of alkanethiol and a lipid monolayer, which have high selectivity for monovalent ions, and the resulting Na+ or K+ sensor has a wide linear range and high stability. These self-assembly systems provide a good mimetic model for studying the physiological function of a membrane and its associated enzyme. (C) 1997 Elsevier Science S.A.

Role Of Convection Flow On The Pattern Formation In The Drying Process Of Colloidal Suspension

We study the macroscopic drying patterns of aqueous suspensions of colloidal silica spheres. It was found that convection strength can influence pattern formation. Uniformed films are obtained at weaker convection strength. In addition, we make clear that it is not reasonable to discuss individually the effect of temperature and humidity on the colloid self-assembly. The physical mechanism is that these factors have relationship with the evaporation rate, which can affect the convection strength.

带电胶体粒子结晶过程的实验研究

利用带电单分散聚苯乙烯胶体粒子,通过自组装机理,制备了体积百分比为4·8%的具有多晶结构的胶体晶体,并用Kossel衍射技术和紫外可见分光光度计分别对晶体的生长过程进行了监测.通过对Kossel的图像分析检测不同阶段相应的晶格结构,发现胶体结晶过程晶体结构演变顺序为由液态—随机层结构—堆无序结构—面心立方孪晶结构到面心立方结构.定量地确定了结晶过程中晶体不同晶面的晶面间距和晶体的晶格常数,通过紫外可见分光光度计测量的晶体透射谱图,计算得到111晶面的晶面间距和晶体的晶格常数,与用Kossel衍射技术得到的结果相一致,还发现随样品放置时间的延长,衰减峰变窄和加深,并向短波方向移动,对应着晶体的晶格常数减小的现象.

Influence Of Gravity On Structure Of Colloidal Crystal Using Simulated Microgravity

Liquid mixtures of water and deuterium oxide as the liquid phase, were used to match the density of charged colloidal particles. Kossel diffraction method was used to detect the crystal structures. The experiments under the density-matched (g=0) and unmatched (g=1) conditions are compared to examine the influence of gravity on the crystal structures formed by self-assembly of 110 nm (in diameter) polystyrene microspheres. The result shows that die gravity tends to make the lattice constants of colloidal crystals smaller at lower positions, which indicates that the effect of gravity should be taken into account in the study of the colloidal crystals.

1.55-mu m resonant cavity enhanced photodiode based on MBE grown Ge quantum dots

Self-assembly Ge quantum dots (QD) on Si and Si/Ge mutli-quantum-wells (MQW) are grown by MBE. The island size and island density was investigated by atomics force microscopy. Ten-layer and twenty-layer MQW were selected for photodiode device fabrication. In photoluminescence (PL), a broad peak around 1.55-mu m wavelength was observed with higher peak intensity for the 10-layer MQW which had less defects than the 20-layer sample. Resonant cavity enhanced (RCE) photodiodes were fabricated by bonding on a SOI wafer. Selected responsivity at 1.55 mu m was successfully demonstrated. (c) 2005 Elsevier B.V. All rights reserved.

In composition dependence of lateral ordering in InGaAs quantum dots grown on (311)B GaAs substrates

Self-assembled InxGa1-xAs quantum dots (QDs) on (311)A/B GaAs surfaces have been grown by molecular beam epitaxy (MBE). Spontaneously ordering alignment of InxGa1-xAs with lower In content around 0.3 have been observed. The direction of alignment orientation of the QDs formation differs from the direction of misorientation of the (311)B surface, and is strongly dependent upon the In content x. The ordering alignment become significantly deteriorated as the In content is increased to above 0.5 or as the QDs are formed on (100) or (311)A substrates. (C) 1999 Elsevier Science B.V. All rights reserved.

Molecular-beam epitaxial growth of position controlled InAs islands on cleaved edge of InGaAs/GaAs superlattice

A promising approach for positioning of InAs islands on (110)GaAs is demonstrated. By combining self-assembly of quantum dots with solid source molecular beam epitaxy (MBE) on cleaved edge of InGaAs/GaAs superlattice (SL), linear alignment of InAs islands on the InGaAs strain layers have been fabricated The cleaved edge of InGaAs/GaAs SL acts as strain nanopattern for InAs selective growth. Indium atoms incident on the surface will preferentially migrate to InGaAs regions where favorable bonding sites are available. The strain nanopattern's effect is studied by the different indium fraction and thickness of InxGa1-xAs/GaAs SL. The ordering of the InAs islands is found to depend on the properties of the underlying InGaAs strain layers.

1.55-mu m resonant cavity enhanced photodiode based on MBE grown Ge quantum dots

Self-assembly Ge quantum dots (QD) on Si and Si/Ge mutli-quantum-wells (MQW) are grown by MBE. The island size and island density was investigated by atomics force microscopy. Ten-layer and twenty-layer MQW were selected for photodiode device fabrication. In photoluminescence (PL), a broad peak around 1.55-mu m wavelength was observed with higher peak intensity for the 10-layer MQW which had less defects than the 20-layer sample. Resonant cavity enhanced (RCE) photodiodes were fabricated by bonding on a SOI wafer. Selected responsivity at 1.55 mu m was successfully demonstrated. (c) 2005 Elsevier B.V. All rights reserved.

层层组装制备低介电常数超薄膜

低介电常数材料可作为微电子器件的层间或是导线间的绝缘材料，以提高微电子芯片的信号传输速率。在聚合物材料中引入氟元素或引入空洞可以有效降低聚合物材料介电常数。本文利用层层组装的方法在聚合物中引入空洞以降低聚合物材料的介电常数。这样，不仅能够获得低介电常数材料，而且可以得到超薄膜，对于降低电子元件的尺寸、提高芯片的信号传输速率具有实际的应用价值。 对具有笼状结构的八苯代聚倍半硅氧烷（OPS）采取先用发烟硝酸硝化为带有硝基的产物ONPS，然后再以水合肼作为还原剂将硝基还原为胺基的两步反应方法，制得了带有胺基的聚倍半硅氧烷（OAPS）。用NMR、FTIR方法对合成过程从原料、中间产物、及目标产物进行跟踪分析证明反应结束后，OAPS仍然具有完整的笼状结构，并且胺基化很完全。另外，利用发烟硫酸作为磺化试剂，采用一步合成的方法制得了磺化OPS（SOPS）。经NMR、FTIR表征，确认了SOPS的结构，磺酸基是在苯环上Si的间位发生了取代。经XPS分析得知，OPS上约有91％的苯环参与了磺化反应。在合适的条件下SOPS与OAPS都可以溶于水，分别带有负电荷与正电荷。 然后，利用合成的SOPS与聚丙烯胺(PAH)进行组装。当PAH溶液的pH值小于7.5时，SOPS在PAH溶液中产生脱落现象。通过调节PAH溶液的pH值，可以控制SOPS在PAH溶液中的脱落现象。当PAH溶液的pH值为9.0时，SOPS在PAH溶液中不再脱落。紫外数据表明，尽管组装过程中SOPS在PAH溶液中会有部分脱落，但这并不影响SOPS/PAH复合多层膜的组装。当溶液的pH为3.0时，OAPS溶于水中并带有正电荷。带有负电荷的聚对苯乙烯磺酸钠（PSS）、聚丙烯酸（PAcA）分别与带有正电荷的OAPS实现层层组装。经过QCM、Contact Angle、XPS、UV等方法表征，证明OAPS/PSS与OAPS/PAcA复合多层膜组装过程中生长均匀，并且多层膜厚度可控。用椭圆偏振的方法测得OAPS/PAcA多层膜的折光指数，运用Maxwell方程将其转化为介电常数为2.01，较纯聚丙烯酸的介电常数（2.56）有明显的降低。加热处理OAPS/PAcA多层膜，红外（FTIR）光谱数据显示OAPS与PAcA间发生了交联反应，形成新的酰胺键。紫外可见（UV-Vis）光谱数据也表明，加热后的OAPS/PAcA多层膜在强酸性溶液中的稳定性较加热前的样品有极大的提高。 合成了聚酰胺酸，并将其制成可溶于水的聚酰胺酸三乙胺盐（PAAs）。调节PAAs溶液的pH值为7.5，使之带有负电荷，可以与带有正电荷的OctaAmmonium（OA-POSS）纳米粒子进行组装。QCM数据显示，当OA-POSS的pH为4.5时，PAAs与OA-POSS的组装量相当，组装量比较大。UV-Vis、XPS数据表明，OA-POSS与PAAs可以实现层层组装，并且组装均匀，可控。加热交联后，PAAs能够很容易地转化为聚酰亚胺（PI）。 调节溶液的pH值，使豇豆花叶病毒（CPMV）表面带有负电。以聚阳离子的聚二烯丙基二甲基胺盐酸盐（PDDA）和聚丙烯胺（PAH）作为插层材料可以实现PAAs与CPMV的层层组装，制得复合多层膜[PDDA/CPMV+(PDDA/PAAs)m]n和[PAH/CPMV+(PAH/PAAs)m]n。QCM、UV-Vis数据表明，多层组装膜的厚度可以通过改变[PAH/CPMV+(PAH/PAAs)m]或[PDDA/CPMV+(PDDA/PAAs)m]的组装循环层数进行调节。而且，薄膜中CPMV与PAAs的比例也可以通过改变（PAH/PAAs）或（PDDA/PAAs）的循环个数进行调节。得到组装多层膜后，将其进行加热处理。FTIR数据显示，以PAH、PDDA作为插层所制备得到的CPMV/PAAs复合多层膜经过加热处理后，PAAs向PI的转化非常完全。用椭圆偏振的方法测试加热交联前后的多层膜样品[PAH/CPMV+(PAH/PAAs)m]n的厚度及折光指数，可以得知，加热处理后，薄膜的厚度稍有降低。将折光指数用Maxwell方程转化为介电常数为2.32，这一数值比纯聚酰亚胺的介电常数值（3.40）降低很多，归因于聚酰亚胺中引入带有空洞结构的CPMV，使聚酰亚胺的密度降低，从而降低材料的介电常数。

可生物降解的两亲性嵌段共聚物的自聚集行为研究

可生物降解的两亲性嵌段共聚物PLA-PEG飞所制备的胶束或纳术粒子，作为潜在的药物控制释放体系弓！起人们广泛的兴趣。，方们授有寿比山于PEG链的空间位阴．效应可以避免单核噬菌体的吞噬，、并且可以通过控制可降解部分的降解行为实现药物的持续释放，使在微载体内所包载的药物分子持续释放出来。尽管高聚物的胶束和纳米粒子作为药物的胶体载体已作厂泛研究，但是对其本身物理化学性质与应用之间的联系研究甚少。因此本文对一系列PLLA和PEG两嵌段和三嵌段共聚物的自聚集行为进行了细致研究，得到了以卜结论：1．以花为"模型药物"，通过荧光探针技术对一系列两亲性共聚物在水呀招夜和NaCI溶液种的胶束化行为进行了研究。这些共聚物是由一种新型氨钙催化利，以人分J，的聚乙二醇（PEG）为引发剂，引发丙交酷开环聚合得到，，其中囚定长度阴 PEG段分剐为44，104和113环氧乙烷早兀，PLLA的长没在15-280乳酸中元之间。由于氨钙准活性的特点，这些共聚物的分散度较低，均在1.1-1.3之间。其临界胶束浓度cmc发现随PLLA的含量增加I荆氏。具有同一PEG长度的两嵌段和三嵌段共聚物cmc值的截然差别为它们胶束的构型不同提供了证据。同时也发现了NaCI的加入对丫EG段和争LLA段较短洪聚物的cmc的降低有明掀笋作用，而对具有较长PEG段或较长PLLA段的共聚物的cmc基本上没有什么影响。2．通过荧光探余十技术测定花在这一系列共聚物胶束溶液锄勺配分系数在0.2*10~5至1.9*10~5之间，对于同-PEG段的共聚物，花在其胶柬相中的配分系数随PLLA的含量的增加而增加。另外发现NaCl的加入能够促进花在胶束相中的配分。3．通过透射电子显微镜研究了两嵌段共聚物水溶液胶束的形貌，发现胶束的粒径和分散度均随PLLA段的增加而增加：通过原子力显微镜研究"这些纳米粒子退火前后的形貌变化，发现退火后纳米粒子重新自聚集为类似于神经网络红脚乏的"纳米条带"结构，其中心为类似"神经元"的团簇结构，而周困为支化的车由突"分支结构，这与文献上提到的只有三嵌段共聚物能够形成支化的"纳米条带"结构截然不同，其自聚集机理在进，步研究之中。4．以亲水性的荧光素为荧光探针研究了两嵌段共聚物在甲苯中的胶束化行为，发现其clnc值随PLLA段的含量增加而降低，相对于PEG段，PLLA段在其胶宋化过程中起主要作用。通过1HNMR证明两嵌段共聚物在甲苯中的胶束具伯以PLLA段为"核"、PEG段为"壳"的"核-壳"结构，这种胶柬化行为通过溶解度参数的差异进行了解释。5.通过原子力显微镜发现，当这些胶束滴加在云母表面上经过热处理后，这些胶束重新自聚集成为规则的具有平缓隆起的纳米结构，这与由水中得到的胶柬热处理后的形貌截然不同，并对此进行了进一步解释。由XPS分析认为主要是PEG段覆盖在PLLA段表面。