Direct Synthesis of Gold Nanoparticle‐Over‐Nanosheet for Sensitive SERS Detection

A simple ethanol sol‐based method for the synthesis of gold nanosheets (AuNSs) and gold nanoparticle‐over‐nanosheet (AuNP/NS) is developed. Gold nanoparticles (AuNPs) with average sizes of ≈8 nm are grown in situ on the surface of the AuNS, which forms a NP/NS structure that obtains strong, significantly improved, surface‐enhanced Raman spectroscopy activity with the magnitude ≈2 and ≈6 orders higher than the simplex AuNP and AuNS, respectively. This performance is mainly attributed to uniform AuNPs that are closely packed over AuNS and coupled with NP–NS and NP–NP interactions. The NP–NS–GP (the gap between NP–NS) is narrower than NP–NP–GP in which much stronger and steadier plasmon resonance is obtained that can significantly enhance the Raman signal. The results show that single‐crystalline AuNS is an ideal substrate, which can be further coated with other metallic NPs to form a new flexible, high‐activity and AuNS‐based nanocomposite for a wide variety of applications.     

Flow Synthesis of Plasmonic Gold Nanoshells via a Microreactor

Gold nanoshells with tunable surface plasmon resonances are a promising material for optical and biomedical applications. They are produced through seed‐mediated growth, in which gold nanoparticles (AuNPs) are seeded on the core particle surface followed by growth of the gold seeds into a shell. However, synthetic gold nanoshell production is typically a multistep, time‐consuming batch‐type process, and a simple and scalable process remains a challenge. In the present study, a continuous flow process for the seed‐mediated growth of silica–gold nanoshells is established by exploiting the excellent mixing performance of a microreactor. In the AuNP‐seeding step, the reduction of gold ions in the presence of core particles in the microreactor enables the one‐step flow synthesis of gold‐decorated silica particles through heterogeneous nucleation. Flow shell growth is also realized using the microreactor by selecting an appropriate reducing agent. Because self‐nucleation in the bulk solution phase is suppressed in the microreactor system, no washing is needed after each step, thus enabling the connection of the microreactors for the seeding and shell growth steps into a sequential flow process to synthesize gold nanoshells. The established system is simple and robust, thus making it a promising technology for producing gold nanoshells in an industrial setting.     

Negative‐Imaging of Citrate Layers on Gold Nanoparticles by Ligand‐Templated Metal Deposition: Revealing Surface Heterogeneity

Surface heterogeneity of a metal nanoparticle is typically regarded as boundary defects and various crystalline facets. While organic capping ligands of a single type are assumed to be homogeneously distributed on the nanoparticle surface, heterogeneous surface coverage of citrate molecules on individual facets of gold nanoparticles (AuNPs) is revealed. Pt metallic clusters with 2 nm in diameter, epitaxially grown on the surface of AuNPs by chemical reaction and imaged by high‐resolution transmission electron microscopy, are utilized as negative‐imaging probes for densely packed adlayers where the underneath gold surface may not be accessible for Pt deposition. At pH > 5.0, citrate anions form only a loosely packed layer. At pH 4.5, citrates and citric acids form both loosely packed and densely packed layers that appear phase separated, and the densely packed domain as small as 5 nm × 5 nm is likely composed of fully protonated citric acids. IR spectra indicate that citric acid binds to a surface Au adatom through the oxygen atom of the central hydroxyl group, and similarly, citrate anions bind to Au adatoms through the carboxylate oxygen atom. This study also reveals the role of Au adatom in the adsorption of citrate species on the metallic surface of AuNPs.     

Efficient and Rapid Synthesis of Radioactive Gold Nanoparticles by Dielectric Barrier Discharge

A compact bench‐top system based on a dielectric barrier plasma discharge (DBD), enables the rapid, automatable, and continuous‐flow synthesis of gold nanoparticles (AuNPs) and radioactive gold nanoparticles (¹⁹⁸AuNPs). AuNPs are used as radiosensitizers in oncology, and ¹⁹⁸AuNPs (half‐life: 2.7 d) have been suggested as potential cancer brachytherapy sources. Plasma applied at the surface of a liquid containing gold ions (AuCl₄^?) and dextran induces the production of AuNPs directly in water. This synthesis is monitored in real time by UV–visible spectrometry: the change of absorbance of the solution provides new insights on the growth dynamics of AuNPs by plasma synthesis. By balancing gold ions and surfactant molecules, particles with a diameter lying in the optimal range for radiosensitizing applications (28 ± 9 nm) are produced. The method yields a reduction of more than 99% of the gold ions within only 30 min of plasma treatment. A postsynthesis ripening of the AuNPs is revealed, monitored by UV–visible spectrometry, and quantified within the first few hours following plasma treatment. Radioactive ¹⁹⁸AuNPs are also produced by DBD synthesis and characterized by electron microscopy and single‐photon emission computed tomography imaging. The results confirm the efficiency of DBD reactors for AuNPs synthesis in oncology applications.     

Assembly of Gold Nanoparticles on Gold Nanorods Using Functionalized Poly(N‐isopropylacrylamide) as Polymeric “Glue”

A telechelic thermoresponsive polymer, α‐amino‐ω‐thiol‐poly(N‐isopropylacrylamide) (H₂N‐PNiPAM‐SH), is used as the polymeric glue to assemble gold nanoparticles (AuNPs) around gold nanorods (AuNRs) into a satellite structure. Prepared by reversible addition‐fragmentation chain transfer polymerization followed by hydrazinolysis, H₂N‐PNiPAM‐SH is able to interlink the two types of the gold building blocks with the thiol‐end grafting on AuNRs and the amine‐end coordinating on the AuNP surface. The density of the grafted AuNPs on AuNRs can be tuned by adjusting the molar ratio between AuNPs and AuNRs in the feed. The resulted satellite‐like assembly exhibits unique optical property that was responsive to temperature change.     

Nuclear Uptake of Gold Nanoparticles Deduced Using Dual‐Angle X‐Ray Fluorescence Mapping

Studies into the cell nucleus' incorporation of gold nanoparticles (AuNPs) are often limited by ambiguities arising from conventional imaging techniques. Indeed, it is suggested that to date there is no unambiguous imaging evidence for such uptake in whole cells, particularly at the single nanoparticle level. This shortcoming in understanding exists despite the nucleus being the most important subcellular compartment in eukaryotes and gold being the most commonly used metal nanoparticle in medical applications. Here, dual‐angle X‐ray flouresence is used to show individually resolved nanoparticles within the cell nucleus, finding them to be well separated and 79% of the intranuclear population to be monodispersed. These findings have important implications for nanomedicine, illustrated here through a specific exemplar of the predicted enhancement of radiation effects arising from the observed AuNPs, finding intranuclear dose enhancements spanning nearly five orders of magnitude.     

A Paper‐Based Platform for Long‐Term Deposition of Nanoparticles with Exceptional Redispersibility,Stability, and Functionality

Although nanoparticles (NPs) can be carefully engineered to have maximal stability and functionality desirable for use in diverse applications, they are generally not suitable for long‐term storage in solution. It is also difficult to store NPs in a dry state because dried NPs generally become aggregated and cannot easily be redispersed. Thus, a new strategy allowing long‐term storage of NPs with high stability, redispersibility, and functionality is highly demanded. By passivating the 13 nm gold nanoparticle (AuNP) surface with stabilizing agents and treating a paper substrate with both bovine serum albumin and sucrose after coating with a hydrophobic polyvinyl butyral layer, it is possible to fully redisperse (≈100%) dried AuNPs with colloidal stability comparable to that of as‐prepared AuNPs. Furthermore, AuNPs physically stabilized with polyvinylpyrrolidone can react with thiol‐containing compounds, such as 1,4‐dithiothreitol (DTT). Taking advantage of the oxidation reaction of hypochlorous acid with DTT, it is possible to demonstrate a paper‐based colorimetric sensor for detection of residual chlorine in water. Since this strategy is applicable to large‐sized AuNPs (30–90 nm), silver NPs, oleic acid‐capped magnetic NPs, and cetrimonium bromide‐passivated gold nanorods, it can be used for diverse NPs requiring long‐term storage for many applications.     

Tunable Aminooxy‐Functionalized Monolayer‐Protected Gold Clusters for Nonpolar and Aqueous Oximation Reactions

Aminooxy (–ONH₂) groups are well known for their chemoselective reactions with carbonyl compounds, specifically aldehydes and ketones. The versatility of aminooxy chemistry has proven to be an attractive feature that continues to stimulate new applications. This work describes application of aminooxy click chemistry on the surface of gold nanoparticles. A trifunctional amine‐containing aminooxy alkane thiol ligand for use in the functionalization of gold monolayer‐protected clusters (Au MPCs) is presented. Diethanolamine is readily transformed into an organic‐soluble aminooxy thiol ( AOT ) ligand using a short synthetic path. The synthesized AOT ligand is coated on ≤2‐nm‐diameter hexanethiolate‐(C₆S)‐capped Au MPCs using a ligand‐exchange protocol to afford organic‐soluble AOT /C₆S (1:1 ratio) Au mixed monolayer‐protected clusters (MMPCs). The synthesis of these Au(C₆S)( AOT ) MMPCs and representative oximation reactions with various types of aldehyde‐containing molecules is described, highlighting the ease and versatility of the chemistry and how amine protonation can be used to switch solubility characteristics.     

Gold Nanoparticles‐Based DNA Logic Gate for miRNA Inputs Analysis Coupling Strand Displacement Reaction and Hybridization Chain Reaction

The molecular level DNA logic gates assisted by nanomaterials hold great promise for disease diagnosis applications. However, designing convenient and sensitive logic gates for molecular diagnostics still remains challenging. In this work, a DNA logic gate platform for miRNA inputs analysis based on the observation of localized surface plasmon resonance variation of gold nanoparticles (AuNPs) is fabricated. As a demonstration, two biomarkers to differentiate indolent and aggressive forms of prostate cancer, miR‐200c and miR‐605, are selected as examples of logical inputs. In addition, five DNA probes are designed according to strand displacement reaction and hybridization chain reaction which are required for DNA logical operation. Since target miRNA inputs are able to trigger DNA structural transformations, which are further used to precisely regulate salt‐induced AuNPs aggregation, miRNA inputs information can be converted to the information of AuNPs states as outputs. This developed system performs amplified detection of low‐abundant target miRNAs without the requirement of any enzymes. In addition, single base‐pair mismatched miRNAs can be effectively differentiated. High‐order logic gates can also be developed with further modifications. Therefore, the DNA AND logic gate is successfully constructed with flexible operations, which has potential in biochemical study and disease diagnosis.     

Seedless synthesis of gold nanorods by using hydrogen peroxide as a weak reducing agent

Abstract

A new seedless wet chemistry synthesis of gold nanorods by using hydrogen peroxide as the weak reducing agent is reported. A reduced concentration of hexadecyltrimethylammonium bromide is used in our experiment, and the synthesized gold nanorods exhibit tunable longitudinal surface plasmon resonance peaks ranging from 725 to 945?nm. The influence on gold nanorods growth by adjusting the amounts of sodium hydroxide, silver nitrate, sodium borohydride, and hexadecyltrimethylammonium bromide were investigated by the visible-near infrared spectroscopy. Under the proper experimental parameters, the longitudinal surface plasmon resonance peaks can be tuned by varying the hydrogen peroxide amounts. Furthermore, it can be seen that the redshift of the longitudinal absorption peak of the prepared gold nanorods with increasing hydrogen peroxide amount is consistent with the increase tendency of the length-to-width aspect ratio obtained from the transmission electron microscopy images. The method provides a facile pathway to prepare gold nanorods with tunable longitudinal surface plasmon resonance peaks, which have potential applications in biomedicine and nanophotonics.     

Visible‐Light‐Induced Directed Gold Microwires by Self‐Organization of Nanoparticles on Aspergillus Niger

A directional point‐to‐point growth of microwires of gold nanoparticles (AuNPs) self‐organized on Aspergillus niger (A. niger) templates by utilizing positive phototropic fungal response to different spectral ranges of visible light is reported. A. niger serves as a living template for the self‐organization of monosodium glutamate (MSG) capped gold colloids under controlled nutrient trigger and appropriate light, temperature, and humidity conditions. The experimental results show that control of these parameters eliminates the need for any microchannels for the directional growth of microwires. The growth rate of fungal hyphae increases exponentially under light illumination compared to its growth in the dark under similar conditions. White light is found to be most suitable to trigger the directional growth. Gold microwires of about 1 to 2 μm diameter and length exceeding 1 mm are grown within a week with a maximum divergence of 40–50° from the light path regardless of the wavelength of the light irradiation. Phototropic response of fungi has been investigated intensively over the last three decades, but this is the first report on the collective use of microbial tropism and directed biomimetic self‐organization of metallic nanoparticles on living organisms.     

The Competitive Dynamic Binding of Some Blood Proteins Adsorbed on Gold Nanoparticles

Nanoparticle (NP) surfaces are modified immediately by the adsorption of proteins when injected into human blood, leading to the formation of a protein corona. The protein‐coated NPs may be recognized by living cells. Furthermore, the adsorption of serum proteins is a continuous competitive dynamic process that is the key to exploring the bioapplication and biosafety of NPs. In this study, the competitive dynamic adsorption of some serum proteins on gold nanoparticles (AuNPs) is investigated by fluorescence emission, dynamic light scattering, and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. Serum proteins with different AuNPs binding affinities are used to address the competitive dynamic process of protein‐AuNP interactions in vitro. The results show that more abundant serum proteins, such as human serum albumin, adsorb on AuNPs first, and then the higher binding affinity and lower concentration serum proteins, such as fibrinogen (FIB), replace the abundant and lower binding affinity serum proteins. However, the lower binding affinity serum proteins, such as hemoglobin, do not replace the higher binding affinity proteins from the protein‐AuNP conjugates. During the dynamic exchange process, the larger the binding affinities difference between two proteins, the faster the exchange rate. This dynamic exchange process usually takes longer in inner protein‐AuNP conjugates (hard corona) than the external surface of protein‐AuNP conjugates (soft corona).     

Unravelling Malaria Antigen Binding to Antibody‐Gold Nanoparticle Conjugates

Conjugates formed by antibody adsorption to gold nanoparticles (AuNP) have found extensive utilization in immunoassays due to the high surface area and interesting optical and electronic properties of the nanomaterials. Nevertheless, the mechanism of formation of antibody‐AuNP conjugates and their antigen binding characteristics have not been sufficiently explored in terms of specificity and consequent clinical applicability. Dynamic light scattering and related techniques have been successfully employed to detect antigen binding to antibody‐AuNP complexes. Here, a range of different techniques from the bionanotechnology realm have been applied to obtain a detailed picture of a competitive immunoassay for malaria antigen detection, based on fluorescence‐quenching by AuNPs. Both agarose gel electrophoresis and differential centrifugal sedimentation (DCS) analyses provide binding constants in the same order of magnitude, for antibody binding to AuNP and for antigen binding to antibody‐AuNP conjugates. Both techniques are also able to reveal inhibition of antigen binding in the presence of a major blood plasma protein, transferrin (via competitive binding). DCS is further used to show inhibition of the binding of the antigen in the presence of human plasma, a realistic testing condition, of high relevance to the implementation of immunoassays at the clinical level.     

Gold Nanoparticles Stabilized by Single Tripodal Ligands

In order to coat the entire surface of gold nanoparticles (AuNPs) by a single ligand, tripodal macromolecules comprising benzylic thioethers coordinating to the AuNP surface are synthesized and their abilities to stabilize AuNPs are investigated. Out of the five studied ligands 1 – 5 , the tetraphenylmethane‐based oligomers 4 and 5 display excellent AuNP coating features. Both ligand structures are able to control the dimensions of the AuNPs by stabilizing particles of narrow size distributions during their syntheses (1.05 ± 0.28 nm for Au‐4 , and 1.15 ± 0.34 nm for Au‐5 ). Closer inspection of these AuNPs by transmission electron microscopy and thermogravimetric analyses suggests that single ligands 4 and 5 are able to stabilize entire AuNPs. These particles Au‐4 and Au‐5 are obtained in good yields and display promising thermal stabilities (110 °C for Au‐4 , and 95 °C for Au‐5 ), making them interesting nanoscale inorganic–organic building blocks for further functionalization/processing by wet chemistry.     

Detection of the potential tumor marker of AFP using surface‐enhanced Raman scattering‐based immunoassay

The development of rapid, highly sensitive detection methods for α‐fetoprotein (AFP) is very important. As hepatocellular carcinoma is closely related to the level of AFP in the blood, it is necessary to maintain an AFP concentration below the safety limit. In this paper, we propose a universal, rapid, sensitive, and highly specific immunoassay system utilizing gold nanoparticles (AuNPs) and surface‐enhanced Raman scattering (SERS). This new system features a sandwich structure combining mercaptobenzoic acid‐labeled immunogold nanoparticles with the antigen and the antibody atop a pre‐designed substrate made of a glass slide modified with AuNPs. This SERS‐based immunoassay can detect AFP concentrations as low as 100 pg/ml, which is a significant improvement on the capabilities of the enzyme‐linked immunosorbent assay method. A good linear relationship between the SERS peak intensity and the logarithm of antigen concentrations (from 1 ng/ml to 100 ng/ml) was observed. This technique provides an effective model for the detection of biomarkers in medical diagnostics, criminal investigation, and other fields. Copyright © 2013 John Wiley & Sons, Ltd.     

金纳米粒子的电化学合成及光谱表征

采用电化学方法合成各种形状的金纳米粒子,生成的金纳米粒子形貌与施加电流有关,通过匀速递增电流电解的方法,可制备得到哑铃形,球形以及棒状金纳米粒子,采用恒电流电解方法主要获得球形及哑铃形纳米粒子。利用透射电镜、紫外-可见光谱及拉曼光谱对金纳米粒子进行相关表征。紫外-可见光谱研究发现金纳米棒出现位于近红外区间的吸收峰(985 nm),由此推测棒的长径比约为6。以结晶紫为探针分子,研究了金纳米粒子的表面增强拉曼光谱(SERS)效应,并分析得出其平躺的吸附模式。根据形貌表征的结果推断了纳米粒子的生长机理。     

Ordered Networks of Gold Nanoparticles Crosslinked by Dithiol‐Oligomers

Controlled aggregation of nanoparticles into superlattices is a grand challenge in material science, where ligand based self‐assembly is the dominant route. Here, the self‐assembly of gold nanoparticles (AuNPs) that are crosslinked by water soluble oligo‐(ethylene glycol)‐dithiol (oEG‐dithiol) is reported and their 3D structure by small angle X‐ray scattering is determined. Surprisingly, a narrow region is found in the parameter space of dithiol linker‐length and nanoparticle size for which the crosslinked networks form short‐ranged FCC crystals. Using geometrical considerations and numerical simulations, the stability of the formed lattices is evaluated as a function of dithiol length and the number of connected nearest‐neighbors, and a phase diagram of superlattice formation is provided. Identifying the narrow parameter space that allows crystallization facilitates focused exploration of linker chemical composition and medium conditions such as thermal annealing, pH, and added solutes that may lead to superior and more robust crystals.     

Novel Synthesis and Characterization of Doxycycline‐Loaded Gold Nanoparticles: The Golden Doxycycline for Antibacterial Applications

Doxycycline (DOXY) is a tetracycline antibiotic with a potent antibacterial activity against a wide variety of bacteria. One potential strategy to enhance the penetration and the antibacterial activity of antibiotics is the use of nanotechnology. In this work, an innovative synthesis of stable PEGylated‐gold nanoparticles (PEG‐AuNPs) loaded with DOXY is reported. As far as it is known, this is the first report on the combination of DOXY with AuNPs as polymeric complex. The obtained nanoparticles are fully characterized by transmission electron microscopy, dynamic light scattering, zeta‐potential, and UV–vis and Raman spectroscopy. The stability and sustained activity of the drug in nanoparticles is determined on a panel of Gram‐positive and Gram‐negative bacteria in comparison with the native form of the drug. This combined therapeutic agent restores the susceptibility of DOXY and shows an antibacterial activity against major human pathogens.     

High–Yield Production of Uniform Gold Nanoparticles with Sizes from 31 to 577 nm via One‐Pot Seeded Growth and Size‐Dependent SERS Property

In this work, uniform, quasi‐spherical gold nanoparticles (Au NPs) with sizes of 31–577 nm are prepared via one‐pot seeded growth with the aid of tris‐base (TB). Distinct from the seeded growth methods available in literature, the present method can be simply implemented by subsequently adding the aqueous dispersion of the 17 nm Au‐NP seeds and the aqueous solution of HAuCl₄ into the boiling aqueous TB solution. It is found that at the optimal pH range, the sizes of the final Au NPs and their concentrations are simply controlled by either the particle number of the Au seed dispersion or the concentration of the HAuCl₄ solution, while the latter enables us to produce large Au NPs at very high concentration. Moreover, as‐prepared Au NPs of various sizes are coated on glass substrates to test their surface‐enhanced Raman scattering (SERS) activities by using 4‐aminothiophenol (4‐ATP) molecules as probes, which exhibit “volcano type” dependence on the Au NP sizes at fixed excitation wavelength. Furthermore, the Au NPs with sizes of ≈97 and 408 nm exhibit the largest SERS enhancement at the excitation wavelength of 633 and 785 nm, respectively.