Quasi 3D imaging of DNA-gold nanoparticle tetrahedral structures

Verification by imaging of the structure of 3D DNA constructs, both bare and conjugated to metal nanoparticles, is challenging. We demonstrate here two transmission electron microscopy (TEM) based methods to distinguish between fully formed tetrahedra, synthesized from DNA conjugated with gold nanoparticles (GNPs) at their vertices, and structures which are only partially formed. When deposited on a surface, fully formed tetrahedra are expected to retain their 3D pyramidal structure, while partially formed structures are expected to form a 2D structure. The first method by which 3D and 2D structures were distinguished was imaging them at different defocusing values. While for 2D structures all the four GNPs acquire Fresnel fringes at the same defocusing value, for 3D structures at least one particle is at a different plane with respect to the others, and so it acquires Fresnel fringes at a different defocusing value. The second method we show is imaging of the structures at different angles. While a single TEM image gives only a 2D projection of the structure, by combining information achieved from imaging at several tilting angles one may verify the structural construct.     

Obtaining DNA aptamers to human interleukin-6 for biomagnetic immunoassay nanosensors

We used aptamers, which are functional equivalents of antibodies, in order to develop a nanosensor immunoassay system based on magnetic nanoparticles and a SQUID magnetometer. Selection was used to obtain DNA aptamers to interleukin-6; their affinity to the target protein was characterized by surface plasmon resonance. It was shown that the biotinylated aptamer binds to magnetic nanoparticles that were functionalized with streptavidin.     

Single-molecule measurements of gold-quenched quantum dots

We report the study of the quenching of quantum dots (CdSe) by gold nanoparticles at the single-molecule level. Double-stranded DNA is used as a rigid spacer to tune the distance between the two nanoparticles. The width of the fluorescent intensity distribution, monitored at different interparticle distances, reflects both the nanoparticle heterogeneity and the fluorescence intermittency of the quantum dot. The fluorescence distribution emitted by single CdSe nanocrystals can easily be distinguished from the fluorescence of partially quenched CdSe. Our results show that the distance-dependence quenching is compatible with a F?rster-type process.     

Stabilization of Pt nanoparticles by single stranded DNA and the binary assembly of Au and Pt nanoparticles without hybridization

The non-specific interaction between single stranded DNA (ssDNA) and 12 nm Pt nanoparticles is investigated in this work. The data show a strong and non-specific interaction between the two which can be exploited for the stabilization of Pt nanoparticles in aqueous solutions. Based on the experimental findings, a non-hybridization based protocol to assemble 17 nm Au and Pt nanoparticles (12 nm cubic and 3.6 nm spherical) by single-stranded DNA was developed. Transmission electron microscopy (TEM) and UV–visible spectroscopy confirmed that Au and Pt nanoparticles could be assembled by the non-specific interaction in an orderly manner. The experimental results also caution against the potential pitfalls in using DNA melting point analysis to infer metal nanoparticle assembly by DNA hybridization.     

DNA银纳米线的制备及其拉曼光谱

根据DNA分子的静电自组装性质,利用加热和紫外照射相结合的方法制备出大小均匀,粒径约为7.8 nm的呈正电性的银纳米颗粒。在预先梳直的小牛胸腺DNA模板上合成了长约2 μm、直径约30 nm、银颗粒较均匀分布的银纳米线。拉曼光谱表明：银颗粒主要结合在DNA主链上,同时脱氧核糖和碱基的振动峰也受到影响。磷酸根骨架的伸缩振动峰782和1 098 cm-1的强度明显减少,且谱线782移动到791 cm-1。脱氧核糖C—O的伸缩特征峰1 011和1 050 cm-1分别移动到1 030和1 064 cm-1。碱基的特征峰1 372,1 334, 1 304和728 cm-1分别移动到1 368,1 320,1 294和731 cm-1。     

Fabrication of silver nanoparticles ring templated by plasmid DNA

Silver nanoparticles ring was successfully fabricated by electrostatic assembling 4-aminothiophenol (4-ATP) capped silver nanoparticles on predefined extended circular plasmid pBR322 DNA. The silver nanoparticles ring which was about 1.5 μm in length, and about 2.2 nm in height can be obtained by adjusting the reaction time. The normal Raman scattering spectra reveal that the 4-ATP has contacted with the silver nanoparticles by forming a strong Ag-S bond. The AFM data show that the assembly of 4-ATP capped silver nanoparticles on DNA is ordered.     

Melting transition of directly linked gold nanoparticle DNA assembly

DNA melting and hybridization is a fundamental biological process as well as a crucial step in many modern biotechnology applications. DNA confined on surfaces exhibits a behavior different from that in free solutions. The system of DNA-capped gold nanoparticles exhibits unique phase transitions and represents a new class of complex fluids. Depending on the sequence of the DNA, particles can be linked to each other through direct complementary DNA sequences or via a ‘linker’ DNA, whose sequence is complementary to the sequence attached to the gold nanoparticles. We observed different melting transitions for these two distinct systems.     

From oleic acid-capped iron oxide nanoparticles to polyethyleneimine-coated single-particle magnetofectins

Various inorganic nanoparticle designs have been developed and used as non-viral gene carriers. Magnetic gene carriers containing polyethyleneimine (PEI), a well-known transfection agent, have been shown to improve DNA transfection speed and efficiency in the presence of applied magnetic field gradients that promote particle–cell interactions. Here we report a method to prepare iron oxide nanoparticles conjugated with PEI that: preserves the narrow size distribution of the nanoparticles, conserves magnetic properties throughout the process, and results in efficient transfection. We demonstrate the ability of the particles to electrostatically bind with DNA and transfect human cervical cancer (HeLa) cells by the use of an oscillating magnet array. Their transfection efficiency is similar to that of Lipofectamine 2000?, a commercial transfection reagent. PEI-coated particles were subjected to acidification, and acidification in the presence of salts, before DNA binding. Results show that although these pre-treatments did not affect the ability of particles to bind DNA they did significantly enhanced transfection efficiency. Finally, we show that these magnetofectins (PEI-MNP/DNA) complexes have no effect on the viability of cells at the concentrations used in the study. The systematic preparation of magnetic vectors with uniform physical and magnetic properties is critical to progressing this non-viral transfection technology.     

Selfassembly of Metallic Nanoparticle Arrays by DNA Scaffolding

We report the self-assembly of metallic nanoparticle arrays using DNA crystals as a programmable molecular scaffolding. Gold nanoparticles, 1.4nm in diameter, are assembled in two-dimensional arrays with interparticle spacings of 4 and 64nm. The nanoparticles form precisely integrated components, which are covalently bonded to the DNA scaffolding. These results show that heterologous chemical systems can be assembled into precise, programmable geometrical arrangements by DNA scaffolding, thereby representing a critical step toward the realization of DNA nanotechnology.     

基于DNA模板与聚二甲基硅氧烷转移制备钯纳米线的新方法

在聚二甲基硅氧烷衬底上梳理得到DNA阵列,并以DNA为模板通过低温乙醇还原得到Pd纳米线,再通过PDMS转移技术将Pd纳米线转移至不同的衬底,这是一种制备高导电性Pd纳米线的新方法.以DNA为模板的选择性生长控制方法可以显著抑制衬底上无规Pd纳米颗粒的出现. SEM观测制备的Pd纳米线的宽度约为80 nm,连续长度可达14 μm. FESEM、XPS和TEM表征揭示出Pd纳米线是由面心立方结构的Pd纳米晶粒组成,电学测量获得的Pd纳米线的电阻率为1.59 μΩm,仅比体电阻率高约一个量级. 研究还发现通过改变反应时间和温度可以有效调控Pd纳米线的生长过程.     

The detection of HBV DNA with gold-coated iron oxide nanoparticle gene probes

Gold-coated iron oxide nanoparticle Hepatitis B virus (HBV) DNA probes were prepared, and their application for HBV DNA measurement was studied. Gold-coated iron oxide nanoparticles were prepared by the citrate reduction of tetra-chloroauric acid in the presence of iron oxide nanoparticles which were added as seeds. With a fluorescence-based method, the maximal surface coverage of hexaethiol 30-mer oligonucleotides and the maximal percentage of hybridization strands on gold-coated iron oxide nanoparticles were (120 ± 8) oligonucleotides per nanoparticle, and (14 ± 2%), respectively, which were comparable with those of (132 ± 10) and (22 ± 3%) in Au nanoparticle groups. Large network aggregates were formed when gold-coated iron oxide nanoparticle HBV DNA gene probe was applied to detect HBV DNA molecules as evidenced by transmission electron microscopy and the high specificity was verified by blot hybridization. Our results further suggested that detecting DNA with iron oxide nanoparticles and magnetic separator was feasible and might be an alternative effective method.     

Hydrophobically modified chitosan/gold nanoparticles for DNA delivery

Present study dealt an application of modified chitosan gold nanoparticles (Nac-6-Au) for the immobilization of necked plasmid DNA. Gold nanoparticles stabilized with N-acylated chitosan were prepared by graft-onto approach. The stabilized gold nanoparticles were characterized by different physico-chemical techniques such as UV-vis, TEM, ELS and DLS. MTT assay was used for in vitro cytotoxicity of the nanoparticles into three different cell lines (NIH 3T3, CT-26 and MCF-7). The formulation of plasmid DNA with the nanoparticles corresponds to the complex forming capacity and in-vitro/in-vivo transfection efficiency was studied via gel electrophoresis and transfection methods, respectively. Results showed the modified chitosan gold nanoparticles were well-dispersed and spherical in shape with average size around 10～12 nm in triple distilled water at pH 7.4, and showed relatively no cytotoxicity at low concentration. Addition of plasmid DNA on the aqueous solution of the nanoparticles markedly reduced surface potential (50.0～66.6%) as well as resulted in a 13.33% increase in hydrodynamic diameters of the formulated nanoparticles. Transfection efficiency of Nac-6-Au/DNA was dependent on cell type, and higher β-galactosidase activity was observed on MCF-7 breast cancer cell. Typically, this activity was 5 times higher in 4.5 mg/ml nanoparticles concentration than that achieved by the nanoparticles of other concentrations (and/or control). However, this activity was lower in in-vitro and dramatically higher in in-vivo than that of commercially available transfection kit (Lipofectin®) and DNA. From these results, it can be expected to develop alternative new vectors for gene delivery.     

In situ size measurement of Si nanoparticles and formation dynamics after laser ablation

We have developed a technique to detect Si nanoparticles selectively and to measure size in situ. Applying the technique, we have investigated formation process of Si nanoparticles after pulsed laser ablation of Si targets in Ar gas. Time-resolved photoluminescence (PL) spectroscopy revealed that PL only from Si nanoparticles is observed below 2.4 eV while PL from Si nanoparticles as well as defects in SiO₂ is observed above 2.4 eV. Therefore, Si nanoparticles can be detected selectively by excitation light with a photon energy below 2.4 eV. It is found that the onset of the PL from Si nanoparticles is delayed by approximately 0.3 ms from that of the defects and smaller Si nanoparticles. A size can be estimated by a band gap, which is roughly equal to the lowest photon energy at which Si nanoparticles can be excited. Thus, we estimated the sizes of growing Si nanoparticles. PACS 61.46.+w; 78.66.w; 07.60.Yi     

Quasi-nanowires from fluorescent semiconductor nanocrystals on the surface of oriented DNA molecules

Ordered structures in the form of quasi-nanowires were obtained from CdSe/ZnS fluorescent semiconductor nanoparticles of spherical (quantum dots) or rodlike (quantum rods) form by their electrostatic deposition on DNA molecules with subsequent stretching of the molecules on a solid substrate. Positively charged nanoparticles were fixed along the negatively charged backbones of DNA molecules by electrostatic interactions in an aqueous solution of a mixture of DNA with quantum particles at different stoichiometric ratios. Strands of single DNA molecules with quantum particles fixed along them were immobilized and stretched on hydrophobic surfaces using the molecular combing technique. It is shown that, by varying the nanoparticle charge and the stoichiometry of complexes of DNA with particles, it is possible to create fluorescent structures with predetermined morphology and properties.     

DNA模板自组装正电荷纳米金基底的增强SERS效应

本文将合成的直径为10 nm的正电荷金纳米颗粒通过静电作用高密度自组装到带负电荷的长链λ-DNA分子上, 形成了高密度的具有纳米间隙的金纳米颗粒网络结构。研究了孤立的金纳米颗粒和所自组装的金纳米颗粒-DNA复合材料作为表面增强拉曼散射(SERS)基底的活性。原本对SERS信号响应较弱的10 nm直径的金纳米颗粒, 在自组装到DNA上形成具有纳米间隙的金纳米颗粒网络后, 产生了均匀、一致、强烈的SERS增强响应。我们利用用该基底对罗丹明G(R6G)、吡啶(Py)和对巯基苯胺(4-ATP)等不同类型的小分子化合物进行SERS检测的结果表明, 此方法制备SERS基底产率高、均一, 具有较好的SERS增强效果好, SERS信号稳定性和重复性相对常规孤立的金纳米颗粒SERS基底有很大提高。     

Colorimetric Biosensors Based on DNAzyme-Assembled Gold Nanoparticles

Taking advantage of recent developments in the field of metallic nanoparticle-based colorimetric DNA detection and in the field of in vitro selection of functional DNA/RNA that can recognize a wide range of analytes, we have designed highly sensitive and selective colorimetric biosensors for many analytes of choice. As an example of the sensor design strategy, a highly sensitive and selective colorimetric lead biosensor based on DNAzyme-directed assembly of gold nanoparticles is reviewed. The DNAzyme consists of an enzyme and a substrate strand, which can be used to assemble DNA-functionalized gold nanoparticles. The aggregation brings gold nanoparticles together, resulting in a blue-colored nanoparticle assembly. In the presence of lead, the DNAzyme catalyzes specific hydrolytic cleavage of the substrate strand, which disrupts the formation of the nanoparticle assembly, resulting in red-colored individual nanoparticles. The application of the sensor in lead detection in leaded paint is also demonstrated. In perspective, the use of allosteric DNA/RNAzymes to expand the range of the nanoparticle-based sensor design method is described.     

Molecular Self‐Assembly of Multifunctional Nanoparticle Composites with Arbitrary Shapes and Functions: Challenges and Strategies

The assembly of nanoparticles into complicated, anisotropic shapes has much promise for advanced materials and devices. Developing effective and efficient anisotropic mono‐functionalization strategies is an imperative step in realizing this potential. By functionalizing DNA one at a time to the nanoparticle, a DNA‐nanoparticle building block could have distinct DNA sequences at different locations on the surface of the particle. Since this technology could incorporate nanoparticles of different composition, generating toolboxes of various nanoparticle building blocks (“nano‐toolboxes”) with DNA at defined locations and in defined 3D orientations on a nanoparticle, it promises not only complicated shapes, but also the ability to tune the function of the assembly. The challenges of programmable and scalable multifunctional nanostructure self‐assembly with DNA conjugated to nanoparticles are reviewed. The first difficulty is to control the assembly process so that designed products are formed, and unwanted products are minimized. The design problem for nanostructure construction is both physically and computationally complex. Thus, the other major challenge is to devise design methodologies that move nanostructure construction from trial and error to principled approaches. Strategies to overcome these challenges are also presented by realizing greater control over the final shapes and functions of the self‐assembled nanostructures. Finally, the future perspectives of nano‐toolboxes and their promise in applications such as multifunctional, multicolor, and multimodal contrast nanoagents for medical therapy and diagnostics (theranostics) are described.     

DNA and PNA as templates for building nanoassemblies via electrostatic complexation with gold nanoparticles

Organisation of nanoparticles on structurally well-defined templates is a first step towards creating nanomachines. In this respect, nucleic acids are ideal structural templates and a variety of secondary structures realizable from DNA/RNA––e.g., duplexes, hairpins, triplexes, cruciforms, tetraplexes can be exploited to engineer nanoparticle organization at will. We have used oligonucleotides and their analogues such as phosphorothioates and peptide nucleic acids to electrostatically encapsulate cationic-capped gold nanoparticles. This article describes synthesis and characterization of DNA/PNA-gold nanoparticle composites using TEM and UV-T_m techniques. These types of assemblies may have potential for creating nanowires and lithographic circuits.     

Formation process of Si nanoparticles in rare gas observed by a decomposition method

We have investigated the formation process of silicon nanoparticles after laser ablation of silicon targets in argon gas. The nanoparticles exhibit bright photoluminescence in the visible wavelength range and can be applied to opto-electronic devices. In order to observe silicon nanoparticles, we have developed a decomposition method. The nanoparticles were probed by detecting light emission resulting from decomposition using a second laser. This method enables us to observe nanoparticles that cannot be observed directly by the methods applied so far. We have observed that the nanoparticles grow in time periods of 1.0-1.8 ms following ablation in Ar gas at 5 Torr when Si targets are ablated at 5 J/cm² with a pulse width of 7 ns. The nanoparticles begin to grow above ablation spots slightly apart from the targets just after thermalization of the plume. We also found that the growth is delayed at higher fluxes of ablation laser light.     

Synthesis of ZnS nanoparticles on a solid surface: Atomic force microscopy study

In this work, zinc sulfide (ZnS) nanoparticles had been synthesized on DNA network/mica and mica surface, respectively. The synthesis was carried out by first dropping a mixture of zinc acetate and DNA on a mica surface for the formation of the DNA networks or zinc acetate solution on a mica surface, and subsequently transferring the sample into a heated thiourea solution. The Zn²⁺ adsorbed on DNA network/mica or mica surface would react with S²⁻ produced from thiourea and form ZnS nanoparticles on these surfaces. X-ray diffraction and atomic force microscopy (AFM) were used to characterize the ZnS nanoparticles in detail. AFM results showed that ZnS nanoparticles distributed uniformly on the mica surface and deposited preferentially on DNA networks. It was also found that the size and density of ZnS nanoparticles could be effectively controlled by adjusting reaction temperature and the concentration of Zn²⁺ or DNA. The possible growth mechanisms have been discussed in detail.