Peptides on GaAs surfaces: comparison between features generated by microcontact printing and dip-pen nanolithography

Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) were employed to understand the size, composition, and conformation of lithographic patterns composed of peptide molecules. GaAs surfaces were patterned by microcontact printing (microCP) and dip-pen nanolithography (DPN) using a peptide sequence composed of 15 amino acids. The detailed surface evaluation showed that the patterns have similar chemical compositions but differ in the bonding among the molecules anchored on the GaAs substrate. Both types of patterns were crystalline-like in nature. The features created by DPN exhibited interchain hydrogen bonding, while the ones generated by microCP displayed non-hydrogen bonding. The differences in the lithographic structures can be utilized in future biorecognition experiments that take advantage of the electronic properties of the GaAs substrate and the tunable behavior of the covalently anchored biomolecules on the surface.     

Microscopic study of ultra-thin gold layers on polyethyleneterephthalate

Continuous and discontinuous gold layers sputtered on polyethyleneterephthalate (PET) were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM) and by reflection of microwave radiation. The changes in the surface morphology of the continuous and discontinuous gold layers as a function of the sputtering time were clearly observed by AFM technique. SEM imaging of very thin gold layers was adversely affected by specimen charging. For medium sputtering times, when a continuous gold coverage is already formed, the SEM technique still show the presence of regions with very thin gold coverage which gradually disappear at longer sputtering times. Both, the AFM and SEM techniques confirmed that in the course of the gold deposition the initially small gold clusters grow and finally associate in a continuous layer. It was shown that the sub-microne metallic structures could be modeled by artificial, significantly larger structures prepared on PET by lithographic etching.     

利用AFM和SNOM对淋巴细胞膜表面超微结构及其光学性质的初步研究

利用原子力显微镜(Atomic Force Microscopy，AFM)对淋巴细胞表面形貌进行了形态学的初步研究，观察到了其膜表面其他显微技术所不能发现的超微结构．同时也运用扫描近场光学显微镜(Scanning Near field Optical Microscopy，SNOM)对淋巴细胞进行成像，观察了其对光的透射、吸收等光学性质，并对两种成像方法进行了比较．研究发现：淋巴细胞膜表面凹凸不平，分布着大量直径几十到几百纳米不等的小颗粒；淋巴细胞中央部位有自发荧光现象．结果表明，AFM和SNOM可作为进一步探讨淋巴细胞的结构与功能关系的有力工具．     

Vapor phase polymerization of EDOT from submicrometer scale oxidant patterned by dip-pen nanolithography

Some of the most exciting recent advances in conducting polymer synthesis have centered around the method of vapor phase polymerization (VPP) of thin films. However, it is not known whether the VPP process can proceed using significantly reduced volumes of oxidant and therefore be implemented as part of nanolithography approach. Here, we present a strategy for submicrometer scale patterning of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) via in situ VPP. Attolitre (10(-18) L) volumes of oxidant "ink" are controllably deposited using dip-pen nanolithography (DPN). DPN patterning of the oxidant ink is facilitated by the incorporation of an amphiphilic block copolymer thickener, an additive that also assists with stabilization of the oxidant. When exposed to EDOT monomer in a VPP chamber, each deposited feature localizes the synthesis of conducting PEDOT structures of several micrometers down to 250 nm in width. PEDOT patterns are characterized by atomic force microscopy (AFM), conductive AFM, two probe electrical measurement, and micro-Raman spectroscopy, evidencing in situ vapor phase synthesis of conducting polymer at a scale (picogram) which is much smaller than that previously reported. Although the process of VPP on this scale was achieved, we highlight some of the challenges that need to be overcome to make this approach feasible in an applied setting.     

Horseradish Peroxidase Catalyzed Polymerization of Tyrosine Derivatives for Nanoscale Surface Patterning

Abstract

Tyrosine and its derivatives can be polymerized by enzymatic catalysis with horseradish peroxidase (HRP). In the present study, tyrosine ethyl ester hydrochloride was nanopatterned on mercaptohexadecanoic acid (MHA) modified gold surfaces using dip‐pen nanolithography (DPN). Enzymatic polymerization was carried out on the well‐organized nanofeatures and confirmed by atomic force microscopy (AFM) phase images and electrostatic force microscopy (EFM) phase‐lag images. The results extend DPN to amino acid derivatives as biocompatible conducting circuitry with nanoscale features.     

Fabricating protein immunoassay arrays on nitrocellulose using dip-pen lithography techniques

Advancements in lithography methods for printing biomolecules on surfaces are proving to be potentially beneficial for disease screening and biological research. Dip-pen nanolithography (DPN) is a versatile micro and nanofabrication technique that has the ability to produce functional biomolecule arrays. The greatest advantage, with respect to the printing mechanism, is that DPN adheres to the sensitive mild conditions required for biomolecules such as proteins. We have developed an optimised, high-throughput printing technique for fabricating protein arrays using DPN. This study highlights the fabrication of a prostate specific antigen (PSA) immunoassay detectable by fluorescence. Spot sizes are typically no larger than 8 μm in diameter and limits of detection for PSA are comparable with a commercially available ELISA kit. Furthermore, atomic force microscopy (AFM) analysis of the array surface gives great insight into how the nitrocellulose substrate functions to retain protein integrity. This is the first report of protein arrays being printed on nitrocellulose using the DPN technique and the smallest feature size yet to be achieved on this type of surface. This method offers a significant advance in the ability to produce dense protein arrays on nitrocellulose which are suitable for disease screening using standard fluorescence detection.     

钙钛矿型复合稀土铁氧化物电子结构的第一性原理研究

采用基于赝势平面波基组的第一性原理方法对一系列具有钙钛矿结构的复合稀土铁氧化物RFeO₃ (R＝镧系稀土元素)的构型和电子结构进行了系统研究. 考察了铁磁(FM)和反铁磁(AFM)两种磁结构, 其中AFM型在常温下更为稳定, 且其构型优化结果更接近于实验测量值. 不论是FM还是AFM构型, R原子的磁距均与自由R^3＋离子相同; 对于Fe原子, 在FM结构中的磁距较AFM类型来得小; 随着R原子序数的增加, 两种磁结构中Fe原子的磁距均呈减小趋势; 对于相同类型的RFeO₃化合物, 具有非常类似的能带结构, 其中AFM构型在费米能级处存在明显的带隙, 而FM型化合物则具有金属特性.     

Structural characterization of artificial self-assembling porphyrins that mimic the natural chlorosomal bacteriochlorophylls c, d, and e

We report two crystal structures of a synthetic porphyrin molecule which was programmed for self-assembly. The same groups which ensure that bacteriochlorophylls c, d, and e can self-assemble into the chlorosomal nanorods, the photosynthetic antenna system of some green bacteria, have been engineered into desired positions of the tetrapyrrolic macrocycle. In the case of the 5,15-meso-substituted anchoring groups, depending upon the concentration, by using the same crystallization solvents, either a tetragonal or a layered structure of porphyrin stacks were encountered. Surprisingly, pi-pi interactions combined with extensive dispersive interactions, which also encompass cyclohexane, one of the crystallization solvents, win over putative hydrogen bonding. We are aware that our compounds differ considerably from the natural bacteriochlorophylls, but based upon our findings, we now question the hydrogen-bonding network, previously proposed to organize stacks of bacteriochlorophylls. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS) on various isomeric compounds support our challenge of current models for the chlorosomal antenna as these show structures, astonishingly similar to those of chlorosomes.     

Moving beyond molecules: patterning solid-state features via dip-pen nanolithography with sol-based inks

Herein, we described a new dip-pen nanolithography (DPN)-based method for the direct patterning of organic/inorganic composite nanostructures on silicon and oxidized silicon substrates. The approach works by the hydrolysis of metal precursors in the meniscus between an AFM tip and a surface according to the reaction 2MCln + nH2O --> M2On + 2nHCl; M = Al, Si, and Sn. The inks are hybrid composites of inorganic salts with amphiphilic block copolymer surfactants. Three proof-of-concept systems involving Al2O3, SiO2, and SnO2 nanostructures on silicon and silicon oxide surfaces have been studied. Arrays of dots and lines can be written easily with control over feature size and shape on the sub-200 nm level. The structures have been characterized by atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray analysis. This work is important because it opens up the opportunity for using DPN to deposit solid-state materials rather than simple organic molecules onto surfaces with the resolution of an AFM without the need for a driving force other than chemisorption (e.g., applied fields).     

Stabilization of phospholipid multilayers at the air-water interface by compression beyond the collapse: a BAM, PM-IRRAS, and molecular dynamics study

Compression beyond the collapse of phospholipid monolayers on a modified Langmuir trough has revealed the formation of stable multilayers at the air-water interface. Those systems are relevant new models for studying the properties of biological membranes and for understanding the nature of interactions between membranes and peptides or proteins. The collapse of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-di[cis-9-octadecenoyl]-sn-glycero-3-[phospho-l-serine] (DOPS), 1,2-di[cis-9-octadecenoyl]-sn-glycero-3-phosphocholine (DOPC), and 1,2-di[cis-9-octadecenoyl]-sn-glycero-3-[phospho-1-rac-glycerol] (DOPG) monolayers has been investigated by isotherm measurements, Brewster angle microscopy (BAM), and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). In the cases of DMPC and DOPS, the collapse of the monolayers revealed the formation of bilayer and trilayer structures, respectively. The DMPC bilayer stability has been analyzed also by a molecular dynamics study. The collapse of the DOPC and DOPG systems shows a different behavior, and the Brewster angle microscopy reveals the formation of luminous bundles, which can be interpreted as diving multilayers in the subphase.     

一维[Pd(mnt)2]-自旋体系磁交换作用的密度泛函理论(DFT)分析

4个一维磁链化合物[R-BzPy][Pd(mnt)2](R-BzPy+=对位取代苄基吡啶阳离子;R=Cl(化合物1),Br(化合物2),I(化合物3)和NO2(化合物4))具有相似的晶体堆积结构,即,[Pd(mnt)2]-和R-BzPy+分别形成完全分列的柱状堆积。这一结构特征与其类似化合物[R-BzPy][Ni(mnt)2]相似。但是,[Pd(mnt)2]-和[Ni(mnt)2]-2个系列化合物结构之间存在明显差异:(1)室温下,[R-BzPy][Ni(mnt)2]晶体中[Ni(mnt)2]-和R-BzPy+堆积柱是均匀的;而[R-BzPy][Pd(mnt)2]晶体中[Pd(mnt)2]-和R-BzPy+堆积柱是不均匀的。(2)在两个系列化合物阴离子堆积柱内,相邻[Pd(mnt)2]-分子平面之间距离比相邻[Ni(mnt)2]-分子平面之间距离短。在[Pd(mnt)2]-堆积柱内,[Pd(mnt)2]-离子之间反铁磁交换作用非常强,导致了化合物几乎呈抗磁性。在密度泛函理论框架下,利用对称性破损方法,我们计算了[Pd(mnt)2]-离子之间磁交换常数。在svwn/lanl2dz和bpw91/lanl2dz水平上的计算结果与磁化率拟合结果一致。理论分析揭示,在[Pd(mnt)2]-堆积柱内,[Pd(mnt)2]-离子之间强反铁磁交换与其π-型前线轨道有效重叠密切相关。     

Formation of hybrid 2D polymer-metal microobjects

This paper describes a fabrication strategy based on polymer brushes (20-150 nm thick) and soft lithographic techniques, for creating hydrophobic, cross-linked, laterally patterned polymer films. The hydrophobicity of the resulting micrometer-scale "quasi-2D" objects is shown to allow the polymer to act as an etch resist. By adjusting the etching time, we demonstrate that underetching of the gold from underneath the edges of the laterally patterned films can be used to create free-standing polymer-gold hybrid structures. These structures retain their structural integrity when lifted wholly or partially from the substrate and can hence be imaged in suspension. Characterization of the quasi-2D objects was carried out using atomic force microscopy (AFM), ellipsometry, optical microscopy, and Fourier transform infrared spectroscopy (FTIR). A continuous film, containing embedded polymer-gold objects, can be lifted, folded, and re-deposited onto a substrate without damaging the conductivity of the embedded metallic objects.     

"Dip-Pen" nanolithography on semiconductor surfaces

Dip-Pen Nanolithography (DPN) uses an AFM tip to deposit organic molecules through a meniscus onto an underlying substrate under ambient conditions. Thus far, the methodology has been developed exclusively for gold using alkyl or aryl thiols as inks. This study describes the first application of DPN to write organic patterns with sub-100 nm dimensions directly onto two different semiconductor surfaces: silicon and gallium arsenide. Using hexamethyldisilazane (HMDS) as the ink in the DPN procedure, we were able to utilize lateral force microscopy (LFM) images to differentiate between oxidized semiconductor surfaces and patterned areas with deposited monolayers of HMDS. The choice of the silazane ink is a critical component of the process since adsorbates such as trichlorosilanes are incompatible with the water meniscus and polymerize during ink deposition. This work provides insight into additional factors, such as temperature and adsorbate reactivity, that control the rate of the DPN process and paves the way for researchers to interface organic and biological structures generated via DPN with electronically important semiconductor substrates.     

Surface thermodynamic properties of monolayers versus reconstitution of a membrane protein in solid-supported bilayers

Atomic force microscopy (AFM) was used to study the influence of a membrane protein, lactose permease of Escherichia coli (LacY), on the surface spreading behavior and the features of self-assembled phospholipids bilayers on mica. The miscibility of phospholipids used, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), was investigated by surface pressure area isotherm measurements at the air-water interface. A composition with an equimolar proportion of POPC and DMPC was used to form the liposomes. Surface layers formed with DMPC:POPC (0.5:0.5, mol/mol) or LacY reconstituted in proteoliposomes with the same phospholipid composition were imaged by using AFM. When lactose permease was reconstituted in DMPC:POPC (0.5:0.5, mol/mol), self-assembled structures that remained firmly adsorbed onto the mica surface were observed. These sheets had an irregular shape and their upper layer was more corrugated than that obtained for the phospholipid matrix.     

Patterning functional materials using channel diffused plasma-etched self-assembled monolayer templates

A simple and cost-effective methodology for large-area micrometer-scale patterning of a wide range of metallic and oxidic functional materials is presented. Self-assembled monolayers (SAM) of alkyl thiols on Au were micropatterned by channel-diffused oxygen plasma etching, a method in which selected areas of SAM were protected from plasma oxidation via a soft lithographic stamp. The patterned SAMs were used as templates for site-selective electrodeposition, electroless deposition and solution-phase deposition of functional materials such as ZnO, Ni, Ag thin films, and ZnO nanowires. The patterned SAMs and functional materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and tunneling AFM (TUNA).     

Au-Ag template stripped pattern for scanning probe investigations of DNA arrays produced by dip pen nanolithography

We report on DNA arrays produced by dip pen nanolithography (DPN) on a novel Au-Ag micropatterned template stripped surface. DNA arrays have been investigated by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) showing that the patterned template stripped substrate enables easy retrieval of the DPN-functionalized zone with a standard optical microscope permitting multi-instrument and multitechnique local detection and analysis. Moreover the smooth surface of the Au squares ( approximately 5-10 A roughness) allows AFM/STM to be sensitive to the hybridization of the oligonucleotide array with label-free target DNA. Our Au-Ag substrates, combining the retrieving capabilities of the patterned surface with the smoothness of the template stripped technique, are candidates for the investigation of DPN nanostructures and for the development of label-free detection methods for DNA nanoarrays based on the use of scanning probes.     

Molecular-level helical stack of a nucleotide-appended oligo(p-phenylenevinylene) directed by supramolecular self-assembly with a complementary oligonucleotide as a template

The nucleotide-appended oligo(p-phenylenevinylene), {bis[2,5-bis(2-methoxyethoxy)-1,4-phenylene]bis(2,1-ethenediyl-1,4-phenylenemethylene)}bis(2'-deoxy-3'-thymidylic acid) (8), has been synthesized, and self-assembly of the single-component 8 and binary self-assembly of 8 with a complementary single-stranded 20-meric oligodeoxyadenylic acid (9) have been examined in aqueous solutions. Atomic force microscopy (AFM), UV-visible (UV-vis), and circular dichroism (CD) measurements revealed that right-handed helical stacks with 6.4- and 5.1-nm diameters self-assemble from the binary components of 8 and 9 as a template depending on the residual stoichiometry of the two components (thymine (T):adenine (A) = 1:1 and T:A = 2:1, respectively). The concentration of 9 was found to strongly influence the CD spectra of 8 in aqueous solutions. Consequently, we concluded that the one side of the thymine moieties in the stacked assemblies of 8 complexes with a single chain of 9. Complementary T-A base pairs thus formed and induced helical stack of the oligo(p-phenylenevinylene)s in the binary self-assembly. In contrast, self-assembly of the single-component 8 and binary self-assembly of 8 with the noncomplementary 20-meric oligothymidylic acid (10) produced no remarkable formation of fibrous structures like helical stacks.     

脂双层膜表面结构与稳定性的原子力显微镜研究

用原子力显微镜研究了1,2－二油酸甘油－3－磷酸－1甘油（DOPG）脂双层膜 的表面结构与稳定性。实验结果表明,原子力显微镜的探针与脂双层膜的相互作用 导致脂双层膜表面产生一个永久的损伤。静电相互作用对脂双层膜结构和稳定性的 影响表明,在NaCl溶液中制成的脂质体,随着NaCl浓度的增加,它们的双层膜更稳 定。在低的NaCl浓度则经常被损伤,在1 mol/L NaCl溶液中制备的指双层变得更稳 定。在KCl溶液中结果恰好相反。在高的KCl浓度中经常被损伤,随着KCl浓度的降 低,它们的双层膜更稳定。葡萄糖和蔗糖对脂双层膜结构有稳定作用。     

Immobilization of histidine-tagged proteins on nickel by electrochemical dip pen nanolithography

Dip-pen nanolithography (DPN) is becoming a popular technique to "write" molecules on a surface by using the tip of an atomic force microscope (AFM) coated with the desired molecular "ink". In this work, we demonstrate that poly-histidine-tagged peptides and proteins, and free-base porphyrins coated on AFM probes, can be chelated to ionized regions on a metallic nickel surface by applying an electric potential to the AFM tip in the DPN process. DPN has been accomplished in the Tapping Mode of AFM, which creates many possible applications of positioning and subsequently imaging biomolecules, especially on soft surfaces.     

Imaging of reconstituted purple membranes by atomic force microscopy

The organization of bacteriorhodopsin (bR) within reconstituted purple membranes (RPM) was examined using atomic force microscopy (AFM). Five reconstituted species were examined: RPM 3 (bR/native polar lipids/dimyristoylphosphatidylcholine (DMPC) in a 1:9:14 molar ratio), RPM 4 (bR/native polar lipids in a 1:7 molar ratio), RPM 5 (bR/native polar lipids/1,2-di-O-phytanyl-sn-glycerol in a 1:3.5:6.1 molar ratio), RPM 6 (bR/native polar lipids/1,2-di-O-phytanyl-sn-glycero-3-phosphocholine in a 1:3.5:4.9 molar ratio), and RPM 7 (bR/native polar lipids/1,2-diphytanoyl-sn-glycero-3-[phospho-l-serine] in a 1:3.5:4.6 molar ratio). RPM 3 patches adsorbed onto mica exhibit domains of crystallized bR trimers arranged in a hexagonal packing structure, similar to those found in native purple membrane (NPM). These domains are enclosed by DMPC-rich regions. RPM 4 patches were observed to have larger domains of crystallized bR, with trimer orientation 30° different from that found in NPM. The bR-rich domains are enclosed by a large, protein-free, lipid-rich region. The topography of RPM 5 was difficult to resolve as the surface had no discernable patterns or structure. The topographies of RPM 6 and 7 were similar to that found in RPM 3 in that higher domains were formed within the patch adsorbed onto mica. They may contain protein-rich regions, but clear images of protein arrangement could not be obtained using AFM. This may be a result of imaging limitations or of the lack of organization of bR within these domains.