Covalent deposition of ferritin nanoparticles onto gold surfaces

Ferritin nanoparticles have been deposited immobilized onto a properly modified gold surface by specific covalent bonding through lysine rests at the ferritin external surface. Atomic force microscopy (AFM) images confirmed the existence of a single ferritin monolayer. This is an easy and flexible route to form stable ferritin networks, which are covalently fixed to a gold substrate.     

Covalent assembly of gold nanoparticles for nonvolatile memory applications

This work reports a versatile approach for enhancing the stability of nonvolatile memory devices through covalent assembly of functionalized gold nanoparticles. 11-mercapto-1-undecanol functionalized gold nanoparticles (AuNPs) with a narrow size distribution and particle size of about 5 nm were synthesized. Then, the AuNPs were immobilized on a SiO(2) substrate using a functionalized polymer as a surface modifier. Microscopic and spectroscopic techniques were used to characterize the AuNPs and their morphology before and after immobilization. Finally, a metal-insulator-semiconductor (MIS) type memory device with such covalently anchored AuNPs as a charge trapping layer was fabricated. The MIS structure showed well-defined counterclockwise C-V hysteresis curves indicating a good memory effect. The flat band voltage shift was 1.64 V at a swapping voltage between ±7 V. Furthermore, the MIS structure showed a good retention characteristic up to 20,000 s. The present synthetic route to covalently immobilize gold nanoparticles system will be a step towards realization for the nanoparticle-based electronic devices and related applications.     

Synthesis of CdS nanoparticles based on DNA network templates

CdS nanoparticles have been successfully synthesized by using DNA networks as templates. The synthesis was carried out by first dropping a mixture of cadmium acetate and DNA on a mica surface for the formation of the DNA network template and then transferring the sample into a heated thiourea solution. The Cd(2+) reacted with thiourea at high temperature and formed CdS nanoparticles on the DNA network template. UV-vis spectroscopy, photoluminescence, x-ray diffraction and atomic force microscopy (AFM) were used to characterize the CdS nanoparticles in detail. AFM results showed that the resulted CdS nanoparticles were directly aligned on the DNA network templates and that the synthesis and assembly of CdS nanoparticles was realized in one step. CdS nanoparticles fabricated with this method were smaller than those directly synthesized in a thiourea solution and were uniformly aligned on the DNA networks. By adjusting the density of the DNA networks and the concentration of Cd(2+), the size and density of the CdS nanoparticles could be effectively controlled and CdS nanoparticles could grow along the DNA chains into nanowires. The possible growth mechanism has also been discussed in detail.     

Covalent binding of streptavidin on gold magnetic nanoparticles for bead array fabrication

In this study, we report the chemical synthesis and functionalization of streptavidin coated gold magnetic nanoparticles (GMNPs) and the immobilization of single-stranded biotinylated oligonucleotides onto these particles. By using covalent interaction or physical adsorption, two kinds of streptavidin coated GMNPs (SA-GMNPs) were prepared. The quantity and stability of streptavidin bound to the GMNPs using different methods were determined by UV-Vis spectrometer. The results indicated that by physical absorption the GMNPs can capture more streptavidin, the SA-GMNPs with either physical adsorption or covalent reaction were both stable in PBS buffer. In contrast, SA-GMNPs with covalent reaction was stable in SDS buffer, while most of the SA-GMNPs by physical adsorption would be eluted from the particles in SDS buffer. Therefore, the SA-GMNPs by covalent immobilization were more suitable for fabrication of bead array. To evaluate the binding efficiency and capacity of DNA on SA-GMNPs, the capture of biotinylated oligonucleotide or PCR products on SA-GMNPs at different concentrations were examined. A magnetic beads array was fabricated by immobilizing DNA-MNPs complexes onto a glass slide using a magnetic field. The synthesized DNA targets with different concentrations were detected with a detection limit of approximately 0.05 nM, indicating the potential application of this MNPs array to high-throughput DNA detection.     

Fluorescence near gold nanoparticles for DNA sensing

We investigated fluorescence quenching and enhancement near gold nanoparticles (GNP) of various sizes using fluorescently labeled hairpin DNA probes of different lengths. A closed hairpin caused intimate contact between the fluorophore and the gold, resulting in an efficient energy transfer (quenching). Upon hybridization with complementary DNA, the DNA probes were stretched yielding a strong increase in fluorescence signal. By carefully quantifying the amount of bound fluorescent probes and the GNP concentrations, we were able to determine the quenching and enhancement efficiencies. We also studied the size and distance dependence theoretically, using both FDTD simulations and the Gersten-Nitzan model and obtained a good agreement between experiments and theory. On the basis of experimental and theoretical studies, we report over 96.8% quenching efficiency for all particle sizes tested and a maximal signal increase of 1.23 after DNA hybridization. The described results also demonstrate the potential of gold nanoparticles for label free DNA sensing.     

Patterned self-assembly of gold nanoparticles on chemical templates fabricated by soft UV nanoimprint lithography

Chemical templates for the patterned immobilization of gold nanoparticles were fabricated by soft UV nanoimprint lithography. The template structures were fabricated by means of the consecutively performed process steps of nanoimprint lithography, reactive ion etching, chemical functionalization with amino groups, and lift-off of imprint resist. These chemical templates were used for the defined assembly of 20 nm diameter citrate stabilized gold nanoparticles from aqueous solution. By reducing the ionic strength of the solution, one- and zero-dimensional particle assemblies were generated on sub-100-nm template structures. By this means, the pattern resolution predefined by the lithography process could be easily enhanced by dilution of the nanoparticle solution.     

Fabrication and characterization of Ag nanoparticles based on plasmid DNA as templates

Ag nanoparticles have been synthesized successfully by using plasmid DNA as templates based on photoinduced method at room temperature. The plasmid DNA with an average size of 3980 base pairs was separated from Bacillus by using molecular biology methods. The morphology and composition of the samples were characterized by Transmission electron microscopy (TEM) and Energy dispersive spectroscopy (EDS). The UV-vis spectrum was applied to study the different stages of the synthesis processes. The results showed that the Ag was successfully deposited on the surface of plasmid DNA and formed the Ag nanoparticles with average sizes of ~ 30 nm. It was suggested that this high efficiency approach has promising application for the synthesis of other metal or alloy nanoparticles.     

Enhancement of radiation cytotoxicity in breast-cancer cells by localized attachment of gold nanoparticles

Gold nanoparticles (GNPs) and modified GNPs having two kinds of functional molecules, cysteamine (AET) and thioglucose (Glu), are synthesized. Cell uptake and radiation cytotoxicity enhancement in a breast-cancer cell line (MCF-7) versus a nonmalignant breast-cell line (MCF-10A) are studied. Transmission electron microscopy (TEM) results show that cancer cells take up functional Glu-GNPs significantly more than naked GNPs. The TEM results also indicate that AET-capped GNPs are mostly bound to the MCF-7 cell membrane, while Glu-GNPs enter the cells and are distributed in the cytoplasm. After MCF-7 cell uptake of Glu-GNPs, or binding of AET-GNPs, the in vitro cytotoxicity effects are observed at 24, 48, and 72 hours. The results show that these functional GNPs have little or no toxicity to these cells. To validate the enhanced killing effect on cancer cells, various forms of radiation are applied such as 200 kVp X-rays and gamma-rays, to the cells, both with and without functional GNPs. By comparison with irradiation alone, the results show that GNPs significantly enhance cancer killing.     

Impedance sensing of DNA binding drugs using gold substrates modified with gold nanoparticles

Interfacial interactions between immobilized DNA probes and DNA-specific sequence binding drugs were investigated using impedance spectroscopy toward the development of a novel biosensing scheme. The impedance measurements are based on the charge-transfer kinetics of the [Fe(CN)6]3-/4- redox couple. Compared to bare gold surfaces, the immobilization of DNA and then the DNA-drug interaction on electrode surfaces altered the capacitance and the interfacial electron resistance and thus diminished the charge-transfer kinetics by reducing the active area of the electrode or by preventing the redox species from approaching the electrode. Electrochemical deposition of gold nanoparticles on a gold electrode surface showed significant improvement in sensitivity. DNA-capped gold nanoparticles on electrodes act as selective sensing interfaces with tunable sensitivity due to higher amounts of DNA probes and the concentric orientation of the DNA self-assembled monolayer. The specificity of the interactions of two classical minor groove binders, mythramycin, a G-C specific-DNA binding anticancer drug, netropsin, an A-T specific-DNA binding drug and an intercalator, nogalamycin on AT-rich DNA-modified substrate and GC-rich DNA-modified substrate are compared. Using gold nanoparticle-deposited substrates, impedance spectroscopy resulted in a 20-40-fold increase in the detection limit. Arrays of deposited gold nanoparticles on gold electrodes offered a convenient tool to subtly control probe immobilization to ensure suitably adsorbed DNA orientation and accessibility of other binding molecules.     

Uniformly gold nanoparticles derived from P2VP-b-PCHMA block copolymer templates with different reduction methods

The micellization of poly(2-vinylpyridine)-block-poly(cyclohexyl methacrylate) (P2VP-b-PCHMA) in THF can be induced by the complexation between the P2VP blocks and HAuCl4, forming composite polymeric micelles with PCHMA being the shell and P2VP/HAuCl4 complex being the core. In order to obtain regular arrays of gold nanoparticles (Au NPs), monolayer of HAuCl4-loaded surface micelles have been produced by spin-coating the micellar solution, and Au NPs in different size have been obtained by oxygen plasma with different reduction processes. In addition, pyrole (PY) has been used as an efficient reducing agent to fabricate dispersed Au NPs within micellar structure in a short reducing time, resulting in a raspberry-like morphology of the Au-polymer composites. With the addition of annealing processes or longer reducing time (one month), different shapes of Au NPs have been observed in the cast films. Furthermore, core-shell nanostructures of gold-polypyrole (Au-PPY) have also been observed by employing vapor phase polymerization of PY onto HAuCl4-loaded polymeric solution-cast films.     

Specific binding of dacarbazine to DNA bases and oligonucleotides based on gold nanoparticles

We studied the specific binding of an anticancer drug, dacarbazine (DTIC), to DNA bases and oligonucleotides attached to gold nanoparticles by using electrochemical methods, and the results indicate that the presence of gold nanoparticles could facilitate the binding of dacarbazine to specific DNA bases and remarkably enhance the relative detection sensitivity. The results of the study on interaction of dacarbazine with oligonucleotides also illustrate that dacarbazine could recognize some specific sequence in DNA chain and sensitively detect single-base mismatch in DNA helix.     

Immobilization of gold nanoparticles on solid supports utilizing DNA hybridization

Self-organization of colloidal metal nanoparticles into micro- and nanostructured assemblies is currently of tremendous interest promising to find new size- and structure-dependent physical properties. Owing to its unique recognition capabilities and physicochemical stability, DNA can be used as a molecular linker for gold nanoparticles and is a promising construction material for their precise spatial positioning. Due to the enormous specificity of nucleic acid hybridization, the site-specific immobilization of DNA-functionalized gold colloids (1–40 nm) to solid supports, previously functionalized with a complementary DNA array, allows the fabrication of novel nanostructured surface architectures. Scanning force microscopy (SFM), used to characterize the intermediate steps of the DNA-directed immobilization (DDI) on a gold substrate, provides initial insight into the specificity and efficiency of this technique.     

Gadolinium-loaded nanoparticles engineered from microemulsion templates

Microemulsions (oil-in-water) have been used as templates to engineer stable emulsifying wax and Brij 72 (polyoxyl 2 stearyl ether) nanoparticles. The technique is simple, reproducible, and amenable to large-scale production of stable nanoparticles having diameters below 100 nm. Investigation of the process variables showed that the amount of surfactant used in the preparation of microemulsion templates had the greatest influence on the microemulsion window, as well as the properties and stability of the cured nanoparticles. Emulsifying wax and Brij 72 nanoparticles (2 mg/mL) made with 3 mM polyoxyl 20 stearyl ether and 2.3 mM polysorbate 80, respectively, were the most stable based on retention of nanoparticle size over time. Gadolinium acetylacetonate (GdAcAc), a potential anticancer agent for neutron capture therapy (NCT), was entrapped in stable nanoparticles. The apparent water solubility of GdAcAc was increased more than 2000-fold by entrapment into nanoparticles. The entrapment efficiency of GdAcAc was about 100% for emulsifying wax nanoparticles and 86% for Brij 72 nanoparticles, as determined by gel permeation chromatography (GPC). Elution profiles were obtained with light scattering (counts per second) to detect nanoparticles and ultraviolet (UV) absorption of GdAcAc at 288 nm. Challenges of these cured nanoparticles in biologically relevant media such as 10% fetal bovine serum, 10 mM phosphate-buffered saline, 150 mM NaCl, and 10% lactose at 37°C for 60 min demonstrated that these nanoparticles are stable. The ease of preparation of these very small and stable nanoparticles, and the ability to entrap lipophilic drugs such as GdAcAc with high efficiency, suggested that these systems may have potential in cell targeting, especially for specific delivery to tumor cells for NCT.     

Imaging gold nanoparticles for DNA sequence recognition in biomedical applications

The hybridization of single-stranded oligonucleotide-derivatized gold nanoparticles (Au nanoprobes) with double stranded complementary DNA was directly observed by atomic force microscopy (AFM). This specific interaction is the basis for an Au nanoprobe-based homogeneous assay for specific DNA sequence detection, based on salt-induced particle aggregation that is prevented when a complementary target is present. For long DNA targets (linearized plasmid DNA) complicated hybridized target DNA-Au-nanoprobes structures were formed, that were interpreted as the basis for stability of the Au nanoprobes against salt-induced aggregation. For shorter DNA targets (PCR amplified fragments) hybridization with the Au nanoprobes occurred, in the majority of cases, in the expected location of the DNA target fragment containing the specific sequence. The formation of the observed DNA hybridized structures provides evidence at the molecular level for specific hybridization to the target sequence as the method of binding of the Au nanoprobes.     

DNA-functionalized monolithic hydrogels and gold nanoparticles for colorimetric DNA detection

Highly sensitive and selective DNA detection plays a central role in many fields of research, and various assay platforms have been developed. Compared to homogeneous DNA detection, surface-immobilized probes allow washing steps and signal amplification to give higher sensitivity. Previously research was focused on developing glass or gold-based surfaces for DNA immobilization; we herein report hydrogel-immobilized DNA. Specifically, acrydite-modified DNA was covalently functionalized to the polyacrylamide hydrogel during gel formation. There are several advantages of these DNA-functionalized monolithic hydrogels. First, they can be easily handled in a way similar to that in homogeneous assays. Second, they have a low optical background where, in combination with DNA-functionalized gold nanoparticles, even ～0.1 nM target DNA can be visually detected. By using the attached gold nanoparticles to catalyze the reduction of Ag+, as low as 1 pM target DNA can be detected. The gels can be regenerated by a simple thermal treatment, and the regenerated gels perform similarly to freshly prepared ones. The amount of gold nanoparticles adsorbed through DNA hybridization decreases with increasing gel percentage. Other parameters including the DNA concentration, DNA sequence, ionic strength of the solution, and temperature have also been systematically characterized in this study.     

Chemical alignment of DNA origami to block copolymer patterned arrays of 5 nm gold nanoparticles

We have used block copolymer patterned arrays of 5 nm gold nanoparticles (AuNPs) for chemically aligned surface attachment of DNA origami. Addition of single-stranded DNA-thiol to AuNPs allowed a base paired attachment of sticky end modified DNA origami. Results indicate a stable, selective attachment between the DNA origami and ssDNA modified AuNPs. Yield data showed 74% of AuNP binding sites forming an attachment with a DNA origami rectangle, and control surfaces showed less than 0.5% nonspecific adsorption.     

Gold and silica-coated gold nanoparticles as thermographic labels for DNA detection

The infrared emissivity of Au and silica-coated Au nanoparticles (Au NPs) deposited on indium tin oxide substrates was investigated. NPs were irradiated with laser light at a frequency close to the Au plasmon resonance band, and the blackbody radiation emitted as a result was monitored with an IR camera equipped with an InAs array detector. The differences in temperature before and after laser irradiation were recorded (T-jumps) and were found to be directly proportional to the number of particles present on the slide and to the laser power used in the experiment. Coating Au NPs with silica increased the measured T-jumps 2-5 times, depending on the thickness of the silica shell. This was in agreement with the observation that silica has a much higher IR emissivity than Au. Both Au and silica-coated Au NPs were then tested as labels for thermographic DNA detection. Target DNA concentrations as low as 100 pM were recorded when Au NPs were used as labels and as low as 10 pM when silica-coated Au NPs were used.