Assembly Of AuNPs Research Articles

Linear self-assembly formation between gold nanoparticles and aminoglycoside antibiotics.

Ribostamycin is a broad-spectrum aminoglycoside antibiotic with a molecular weight of 454.5 g/mol. Under neutral pH conditions, ribostamycin is highly positive charged because it carries multiple amino groups in its structure. Negatively charged citrate ligand capped-gold nanoparticles (AuNPs) have been studied extensively for their interactions with a wide range of biomolecules including proteins, carbohydrates, and small drug compounds. These studies are aimed at developing new therapeutics and diagnostics by exploiting the unique properties of gold nanoparticles. Under this general aim, we studied the interaction between ribostamycin and AuNPs. Using a suite of analytical techniques including dynamic light scattering (DLS), UV-vis absorption spectroscopy, and dark field optical microscope imaging (DFM), we analyzed the mixture products of AuNPs with various sizes and ribostamycin under different concentrations. Our study revealed for the first time that ribostamycin has a tendency to self-assemble into linear oligomers at increased concentrations (above 250-500 μM). Such self-assembled oligomers then interact with negatively charged AuNPs to produce rod-like AuNP assemblies. Similar findings were observed from another structurally related aminoglycoside antibiotic, amikacin. It is technically challenging to detect and characterize oligomer formation of small molecules. It is especially challenging when the interactions that are holding the oligomers are not very strong. Through their interaction with gold nanoparticles that have exceptionally strong light scattering properties, we were able to observe the self-assembling of ribostamycin and amikacin in solution using various spectroscopic and microscopic techniques. This concentration-dependent self-assembling behavior of ribostamycin and amikacin may have direct relevance to the antibiotic effect of ribostamycin, amikacin and other structurally similar antibiotics.

DNA origami-templated assembly of plasmonic nanostructures with enhanced Raman scattering

DNA origami have been established as versatile templates to fabricate plasmonic nanostructures in predefined shapes and multiple dimensions. Limited to the size of DNA origami, which are approximate to 100 nm, it is hard to assemble more intricate plasmonic nanostructures in large scale. Herein, we used rectangular DNA origami as the template to anchor two 30-nm gold nanoparticles (AuNPs) which induced dimers nanostructures. Transmission electron microscopy (TEM) images showed the assembly of AuNPs with high yields. Using the linkers to organize the DNA origami templates into nanoribbons, chains of AuNPs were obtained, which was validated by the TEM images. Furthermore, we observed a significant Raman signal enhancement from molecules covalently attached to the AuNP-dimers and AuNP-chains. Our method opens up the prospects of high-ordered plasmonic nanostructures with tailored optical properties.

Molecular Patterning and Directed Self-Assembly of Gold Nanoparticles on GaAs.

The ability to create micro-/nanopatterns of organic self-assembled monolayers (SAMs) on semiconductor surfaces is crucial for fundamental studies and applications in a number of emerging fields in nanoscience. Here, we demonstrate the direct patterning of thiolate SAMs on oxide-free GaAs surface by dip-pen nanolithography (DPN) and microcontact printing (μCP), facilitated by a process of surface etching and passivation of the GaAs. A quantitative analysis on the molecular diffusion on GaAs was conducted by examining the writing of nanoscale dot and line patterns by DPN, which agrees well with surface diffusion models. The functionality of the patterned thiol molecules was demonstrated by directed self-assembly of gold nanoparticles (Au NPs) onto a template of 4-aminothiophenol (ATP) SAM on GaAs. The highly selective assembly of the Au NPs was made evident with atomic force microscopy (AFM) and scanning electron microscopy (SEM). The ability to precisely control the assembly of Au NPs on oxide-free semiconductor surfaces using molecular templates may lead to an efficient bottom-up method for the fabrication of nanoplasmonic structures.

Formation of Uniform and High-Coverage Monolayer Colloidal Films of Midnanometer-Sized Gold Particles over the Entire Surfaces of 1.5-in. Substrates.

We report a simple and facile method for fabricating monolayer colloidal films of alkanethiol-capped gold nanoparticles (AuNPs) on glass substrates. The new method consists of two sequential sonication processes. The first sonication is performed to obtain a well-dispersed state of alkanethiol-capped AuNPs in hexane/acetone in the presence of a substrate. After additional static immersion in the colloidal solution for 5 min, the substrate is subjected to sonication in hexane. By using this method, we succeeded in forming uniform and stable assemblies of midnanometer-sized AuNPs (14, 34, and 67 nm in diameter) over the entire surface of 10-mm square glass substrates in a short processing time of less than 10 min. It was also demonstrated that this method can be applied to a 1.5-in. octagonal glass substrate. The mechanism of monolayer colloidal film formation was discussed based on scanning electron microscopy observations at each preparation step. We found that the second sonication was the key process for uniform and high-surface-coverage colloidal film formation of midnanometer-sized AuNPs. The second sonication promotes the migration of AuNPs on top of the monolayer in contact with the substrate surface, decreasing both the multilayer region and the bare surface area. Eventually, a nearly perfect monolayer colloidal film is formed.

DNA‐Mediated Assembly of Gold Nanoparticles and Applications in Bioanalysis

AbstractDNA‐mediated gold nanoparticles (AuNPs) assembly has drawn great attention due to the controllable parameters and properties. In general, DNA sequences working as linkers or templates precisely control the assembly of AuNPs through the Watson–Crick base pairing. Diverse assembly structures show great potential in bioanalysis due to the unique optical characteristics, which can be tuned by the shape, size, composition, particles interactive status and the dielectric constant of the surrounding medium of AuNPs. They exhibit excellent performances for the detection of nucleic acids, proteins, small molecules and other biomarkers. In this review, we present a general overview of the construction of DNA‐mediated AuNP assemblies and the recent advances of these assemblies as high‐performance biosensors. Future directions and major challenges in bioanalysis are also discussed.

Sensitive detection of microRNAs based on the conversion of colorimetric assay into electrochemical analysis with duplex-specific nuclease-assisted signal amplification.

miRNAs have emerged as new biomarkers for the detection of a wide variety of cancers. By employing duplex-specific nuclease for signal amplification and gold nanoparticles (AuNPs) as the carriers of detection probes, a novel electrochemical assay of miRNAs was performed. The method is based on conversion of the well-known colorimetric assay into electrochemical analysis with enhanced sensitivity. DNA capture probes immobilized on the electrode surface and ferrocene (Fc)-labeled DNA detection probes (denoted “Fc-DNA-Fc”) presented in the solution induced the assembly of positively charged AuNPs on the electrode surface through the electrostatic interaction. As a result, a large number of Fc-DNA-Fc molecules were attached on the electrode surface, thus amplifying the electrochemical signal. When duplex-specific nuclease was added to recycle the process of miRNA-initiated digestion of the immobilized DNA probes, Fc-DNA-Fc-induced assembly of AuNPs on the electrode surface could not occur. This resulted in a significant fall in the oxidation current of Fc. The current was found to be inversely proportional to the concentration of miRNAs in the range of 0–25 fM, and a detection limit of 0.1 fM was achieved. Moreover, this work presents a new method for converting colorimetric assays into sensitive electrochemical analyses, and thus would be valuable for design of novel chemical/biosensors.

Label-free electrochemiluminescence assay for aqueous Hg2+ through oligonucleotide mediated assembly of gold nanoparticles

Development of ultrasensitive method for Hg2+ analysis is important for human health protection and environment monitoring. In this work, we present a highly sensitive and selective electrochemiluminescence (ECL) assay in a “turn-on” mode for the detection of Hg2+ through selective assembly of gold nanoparticles (AuNPs) on the surface of indium tin oxide (ITO) electrode. In the absence of Hg2+, the nonthiolated ssDNA could protected AuNPs against its assembly on ITO surface, producing rather low ECL emission for Ru(bpy)32+/TPA system. Conversely, binding of Hg2+ with the Hg2+-specific oligonucleotide through thymine-Hg2+-thymine coordination formed the double-stranded structure, which could not effectively adsorb to AuNPs in solution. The assembly of free-state AuNPs is achieved, which well preserves electronical conductivity. The presence of AuNPs can catalyze the electro-oxidation of TPA, producing significantly enhanced ECL signal. Through detecting the ECL signal mediated by assembly of AuNPs, the proposed method was able to ensure substantial signal amplification and a low background. It was demonstrated that the ECL intensity was correlated with the ssDNA-based recognition reaction, enabling quantitative analysis of Hg2+ over the range of 8pM to 2nM, with a detection limit of 2pM. ECL intensity of the system were extremely specific for Hg2+ even in the presence of 1000-fold higher concentrations of other metal ions. Analytical results of Hg2+ spiked into water samples by the proposed ECL method were in good agreement with that obtained by atomic fluorescent spectrometry or mass spectrometry data.

Ferroelectric-assisted gold nanoparticles array for centimeter-scale highly reproducible SERS substrates

Assemble metal nanoparticles into various ordered structures with scale up to centimeter area is required to meet diverse needs of lab-on-a-chips and analytic components. Here, we present the uniform and high-yield fabrication of centimeter-scale gold nanoparticles (AuNPs) array for SERS substrates. Ferroelectric-assisted assembly of AuNPs line array is successfully fabricated by using a periodically poled LiNbO3 (PPLN) single crystal as a template. SNOM-Raman shows that the uniform assembly of AuNPs exhibits a high density of “hot spots” arising from strong electromagnetic (EM) field coupling induced by adjacent AuNPs. Quantitative analysis based on SERS detection describes an excellent reproducibility with an intensity variation less than 7% at 1649 cm−1 of Rhodamine 6G. SERS spectra combined with 3D-FDTD modelling indicate that the EM enhancement occurs at all three excitation wavelength of 515, 561 and 633 nm and the 561-nm-laser displays the strongest Raman enhancement with an enhancement factor in an order of 109. The corresponding experimental and theoretical results present a new strategy to fabricate large-area, highly reproducible and sensitive SERS substrates for practical applications.

Thermally Triggered in Situ Assembly of Gold Nanoparticles for Cancer Multimodal Imaging and Photothermal Therapy.

The assembly of gold nanoparticles (AuNPs) to AuNP assemblies is of interest for cancer therapy and imaging. Herein we introduce a new and general paradigm, thermally triggered AuNP assembly, for the development of novel intelligent platforms for cancer photothermal therapy (PTT) and multimodal imaging. Site-specific conjugation of a thermally sensitive elastin-like polypeptide (ELP) to AuNPs yields thermally sensitive ELP-AuNPs. Interestingly, ELP-AuNPs can in situ form AuNP assemblies composed of short necklace-like gold nanostructures at elevated temperatures and thus show strong near-infrared light absorption and high photothermal effect. These thermally responsive properties of ELP-AuNPs enable simultaneous photothermal/photoacoustic/X-ray computed tomographic imaging and PTT of melanoma after single intratumoral injection of ELP-AuNPs. The thermally triggered assembly of a variety of nanoparticles with optical, electronic, and magnetic properties into nanoparticle assemblies may open new ways for the establishment of intelligent platforms for various applications in biomedicine.

Recent advances in molecular machines based on toehold‐mediated strand displacement reaction

BackgroundThe DNA strand displacement reaction, which uses flexible and programmable DNA molecules as reaction components, is the basis of dynamic DNA nanotechnology, and has been widely used in the design of complex autonomous behaviors.ResultsIn this review, we first briefly introduce the concept of toehold‐mediated strand displacement reaction and its kinetics regulation in pure solution. Thereafter, we review the recent progresses in DNA complex circuit, the assembly of AuNPs driven by DNA molecular machines, and the detection of single nucleotide polymorphism (SNP) using DNA toehold exchange probes in pure solution and in interface state. Lastly, the applications of toehold‐mediated strand displacement in the genetic regulation and silencing through combining gene circuit with RNA interference systems are reviewed.ConclusionsThe toehold‐mediated strand displacement reaction makes DNA an excellent material for the fabrication of molecular machines and complex circuit, and may potentially be used in the disease diagnosis and the regulation of gene silencing in the near future.

Gold nanoparticles-based electrochemical method for the detection of protein kinase with a peptide-like inhibitor as the bioreceptor.

This article presents a general method for the detection of protein kinase with a peptide-like kinase inhibitor as the bioreceptor, and it was done by converting gold nanoparticles (AuNPs)-based colorimetric assay into sensitive electrochemical analysis. In the colorimetric assay, the kinase-specific aptameric peptide triggered the aggregation of AuNPs in solution. However, the specific binding of peptide to the target protein (kinase) inhibited its ability to trigger the assembly of AuNPs. In the electrochemical analysis, peptides immobilized on a gold electrode and presented as solution triggered together the in situ formation of AuNPs-based network architecture on the electrode surface. Nevertheless, the formation of peptide–kinase complex on the electrode surface made the peptide-triggered AuNPs assembly difficult. Electrochemical impedance spectroscopy was used to measure the change in surface property in the binding events. When a ferrocene-labeled peptide (Fc-peptide) was used in this design, the network of AuNPs/Fc-peptide produced a good voltammetric signal. The competitive assay allowed for the detection of protein kinase A with a detection limit of 20 mU/mL. This work should be valuable for designing novel optical or electronic biosensors and likely lead to many detection applications.

Selective colorimetric analysis of spermine based on the cross-linking aggregation of gold nanoparticles chain assembly

A selective colorimetric assay for spermine was proposed in this work. In a weak alkaline medium, the conformational structure of double-stranded calf thymus DNA (ctDNA) was loosened to install gold nanoparticles (AuNPs) into chains. While, the chain assembly of AuNPs could form cross-linking aggregates when spermine was present, which was attributed to the electrostatic interaction between the positive change of spermine and negative change both of AuNPs and ctDNA, as well as the groove binding between ctDNA and spermine. Under the optimum conditions, the aggregation degree of AuNPs was proportional to the concentration of spermine in the range of 0.1–2.0μM with a limit of detection of 11.6nM. More interestingly, AuNPs changed from red to purple and even to blue depending on the concentration of spermine, which could be developed as the colorimetric analysis of spermine. ctDNA-AuNPs assembly was demonstrated as a novel visual probe for the specific sensing of spermine with high specificity and sensitivity.

Robust Gold Nanoparticle Sheets by Ligand Cross-Linking at the Air-Water Interface.

We report the results of cross-linking of two-dimensional gold nanoparticle (Au-NP) assemblies at the air-water interface in situ. We introduce an aqueous soluble ruthenium benzylidene catalyst into the water subphase to generate a robust, elastic two-dimensional network of nanoparticles containing cyclic olefins in their ligand framework. The most striking feature of the cross-linked Au-NP assemblies is that the extended connectivity of the nanoparticles enables the film to preserve much of its integrity under compression and expansion, features that are absent in its non-cross-linked counterparts. The cross-linking process appears to "stitch" the nanoparticle crystalline domains together, allowing the cross-linked monolayers to behave like a piece of fabric under lateral compression.

Enzyme mediated assembly of gold nanoparticles for ultrasensitive colorimetric detection of hepatitis C virus antibody

A novel enzyme mediated AuNP assembly based colorimetric method for ultrasensitive detection of hepatitis C virus antibody.

Gold Nanoparticles Assembly on Silicon and Gold Surfaces: Mechanism, Stability, and Efficiency in Diclofenac Biosensing

We investigated the assembly of gold nanoparticles (AuNPs) on gold and silicon sensors with two final objectives: (i) understanding the factors governing the interaction and (ii) building up a nanostructured piezoelectric immunosensor for diclofenac, a small-sized pharmaceutical pollutant. Different surface chemistries were devised to achieve AuNPs assembly on planar substrates. These surface chemistries included amines to immobilize AuNPs via electrostatic interaction or a mixture of amines and thiols to covalently attach the AuNPs. We also generated PEG-amine-terminated surfaces to benefit from the well-known non-biofouling properties of PEG-coated surfaces. The functional substrates and the resulting gold nanoparticle layers were characterized in detail by surface IR, contact angle measurements, and scanning electron microscopy (SEM). The mechanism of adsorption is discussed herein considering the nature of the terminal groups and their charge at the pH of AuNPs adsorption. The coverage and the dispersion of AuNPs were strongly dependent on the anchoring points on the surfaces; the optimal were reached when the attachment layer offered multiple interaction points, in particular, for NH2/SH- and PEG/NH2-terminated surfaces, where the percentage of isolated particles was up to 78%. In addition, PEG-coated surfaces led to a stable AuNPs layer resistant to ultrasounds and to further functionalization of the immobilized nanoparticles. These surfaces were used to engineer quartz crystal microbalance (QCM) biosensors for diclofenac detection. The AuNPs nanostructured substrates significantly enhanced the biosensor sensitivity as compared to planar substrates (up to 6 times higher). This enhancement presages a higher sensitivity in the competitive detection of diclofenac on these systems. More importantly, despite the biorecognition and the drastic regeneration conditions, SEM images show that gold nanoparticles layers are stable and reliable, which paves the way for their use as nanostructured platforms for multiple applications.

In Situ Observation of Enhanced Photoinduced Charge Separation in a Gold Nanoparticle Assembly Immobilized on TiO2

AbstractPhotoinduced charge separation on a hybrid titanium dioxide (TiO2) surface with a gold nanoparticle (AuNP) assembly immobilized via a biotin‐streptavidin interaction was visualized by Kelvin force microscopy (KFM). Biotinylated AuNP (Biot‐AuNP) with a diameter of ca. 15 nm was assembled using streptavidin (STV) and the AuNP assembly was immobilized on a TiO2 surface modified with 1‐(3‐aminopropyl)silatrane. KFM reveals that the local contact potential difference (CPD) of dispersed AuNP, which is −17 ± 4.2 mV in the dark, undergoes a negative shift of −46 ± 3.0 mV upon UV‐irradiation (λ=240‐300 nm). In contrast, the AuNP assembly on the TiO2 surface exhibits a greater negative shift of −58 ± 6.0 mV of the CPD, although the CPD value of −16 ± 5.8 mV in the dark is similar to that of the dispersed AuNP. KFM visualization demonstrates that assembly of the AuNP on the TiO2 surface contributes to efficient storage of the negative charge generated by excited electrons in TiO2 during photoinduced charge separation.

Gold Nanoparticle-Based Colorimetric and Electrochemical Methods for Dipeptidyl Peptidase-IV Activity Assay and Inhibitor Screening

We presented the colorimetric and electrochemical methods for determination of the dipeptidyl peptidase-IV (DPP-IV) activity and screening of its inhibitor using gold nanoparticle (AuNP) as the probe. In the colorimetric assay, the substrate peptide with a sequence of Arg-Pro-Arg induced the aggregation and color change of AuNPs, whereas cleavage of the peptide by DPP-IV prevented the aggregation of AuNPs. Furthermore, the aggregation of AuNPs in the solution was easily initiated on a solid/liquid (electrode/electrolyte) surface, which induced a decrease in the electron-transfer resistance. However, once the peptide was clipped by DPP-IV, the assembly of AuNPs on electrode surface was prevented. Consequently, a higher electron-transfer resistance was observed. The colorimetric and electrochemical assays allowed for the determination of DPP-IV with the detection limits of 70 μU/mL and 0.55 μU/mL, respectively. Meanwhile, the proposed methods were used to determine DPP-IV inhibitor with satisfactory results. Both the colorimetric and electrochemical methods are simple, rapid and sufficiently sensitive for DPP-IV activity assay and inhibitor screening. The results also demonstrated that the AuNP-based colorimetric assay could be converted into an enhanced surface tethered electrochemical assay with improving sensitivity. The simple detection principle may be extended to the design of other peptidases biosensors with easy manipulation procedures.

The Study of Self-Assembled Au Nanoparticles As an Efficient SERS Substrate for Environmental Sensing Applications

The formation of self-assembled monolayers (SAM) of noble metals for optical sensing applications faces serious challenges when trying to achieve simplicity, cost efficacy, specificity, and versatility. Utilizing stable, SAM-forming alkanethiols, such as glutathione (GSH), enable for simple assembly and specific detection of proteins, trace metals, oxidants, etc., thus providing a sensing platform that not only can detect low levels of reactive oxygen species (ROS) for early determination of neurodegenerative diseases, but can also assess trace metals in freshwaters and marine waters, for example. Providing a universal device for detecting varieties of target materials would adapt, simplify, and reduce costs that come from current detection methods. Our research on improving these detection methods is demonstrated using the frequency-controlled self-assembly of a GSH-functionalized gold nanoparticle (Au NP) film as a platform for highly specific and sensitive sensing. We have previously demonstrated the use of an eco-friendly and highly sensitive surface enhanced Raman spectroscopy (SERS) substrate for biomedical diagnostic applications using an ultraviolet photochemical reaction of gold (III) chloride trihydrate (HAuCl4) to create a densely packed Au NP film that exhibits localized surface plasmon resonances [1]. By the firm anchoring of a thiol group to the Au NP surface, GSH assembles the Au NPs for SERS into a densely packed, dendritic structure. At a pH of ~1 in solution, GSH forms a y-shape [2], allowing its carboxyl and amino groups to create a hydrophilic interface and, therefore, be fully available for bonding to various functional molecules. Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and ultraviolet-visible spectroscopy (UV-vis) were used to confirm the presence of GSH and enhancement capabilities of the SERS substrate. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirmed the Au NP film to be 90nm thick, with an average Au NP size of 125nm in diameter [1], and visually confirmed the dendritic assembly of the GSH-functionalized Au NPs. For application purposes, this study will evaluate the trace metal Pb2+ in water. The contamination of lead, and heavy metals in general, have a damaging impact on the health of both humans and our planet. The chelation of the GSH ligands with Pb2+ enables highly specific detection of Pb2+ in water. This method provides a simple, versatile SERS substrate with a dendritic assembly that creates intriguing optical properties and broadens the capability for potential applications. [1] G. Rutherford et al., ECS J. Solid State Sci. Tech. 4, S3071 (2015). [2] M. Bieri and T. Burgi, Langmuir 2005, 21, 1354-1362. Figure 1

Green Synthesis of High-Purity Mesoporous Gold Sponges Using Self-Assembly of Gold Nanoparticles Induced by Thiolated Poly(ethylene glycol).

A facile and green synthesis method for mesoporous gold sponges has been developed, which involves a simple mixing of a very small amount of thiolated-poly(ethylene glycol) (SH-PEG) and citrate-covered gold nanoparticles (Au NPs) in aqueous solution at room temperature. While SH-PEG molecules have been widely used as biocompatible hydrophilic capping agents for Au NPs for stable dispersion in aqueous solution, here they are used as destabilizing agents. When SH-PEG molecules are mixed with citrate-covered Au NPs at the molar ratio ranging from 3 to 20 (SH-PEG/Au NP), mesoporous gold sponges with randomly interconnected 3D network structures are formed within 2 to 3 h. This is driven by the destabilization of negatively charged citrate molecules on Au NPs by a small number of SH-PEG molecules bonded on the particle surface, which results in the decrease in zeta potential and thus the assembly of Au NPs into porous sponges. The use of very low concentration of SH-PEG (ca. 20-200 nM) in aqueous solution at room temperature makes the method highly eco-friendly as well as results in high-purity as-synthesized gold sponges (98.7 wt %). The mesoporous gold sponges fabricated with the present method exhibit a high SERS activity, making them highly applicable for sensitive SERS detection of molecules.

Controlled assembly of gold nanoparticles decorated with bis-imidazolium moieties and application for ATP sensing

Abstract Gold nanoparticles (AuNPs) have attracted intensive interests due to their promising applications in sensing, catalysis, optical and electric fields. Herein, we present a novel colorimetric adenosine-5′-triphosphate (ATP) sensor based on AuNPs modified with bis-imidazolium moieties. The positive charges with high density on bis-imidazolium groups show a strong affinity towards the triphosphate part of ATP, leading to subsequent aggregation of neighboring nanoparticles. By changing the ATP concentration, the aggregation extent of AuNPs can be easily controlled. At the same time, a readily detectable colorimetric shift from red to blue is also displayed, which is favorable for ATP sensing. It is found that triphosphate are more effective than di- or mono-phosphate groups in the aggregation formation process, which can easily distinguish ATP from ADP and AMP. Moreover, this ATP detection by Au@BIMEG is less interfered by other representative anions and cations. We provide a facile, efficient and cost-effective strategy to colorimetric ATP sensing via controllable assembly of AuNPs.