Anisotrope Gold-Nanopartikel: Synthese, Eigenschaften, Anwendungen und Toxizität

Tunable Aminooxy-Functionalized Monolayer-Protected Gold Clusters for Non-Polar or 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. We present here a trifunctional amine-containing aminooxy alkane thiol ligand for use in the functionalization of gold monolayer protected clusters (Au MPCs). Diethanolamine is readily transformed into an organic-soluble aminooxy thiol (AOT) ligand using a short synthetic path. The synthesized AOT ligand was 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). This work describes the synthesis of Au(C6S)(AOT) MMPCs and representative oximation reactions with various types of aldehyde-containing molecules, highlighting the ease and versatility of the chemistry and how amine protonation can be used to switch solubility characteristics.

Robust Synthesis of Gold Nanotriangles and their Self-Assembly into Vertical Arrays

We report an efficient, seed-mediated method for the synthesis of gold nanotriangles (NTs) which can be used for controlled self-assembly. The main advantage of the proposed synthetic protocol is that it relies on using stable (over the course of several days) intermediate seeds. This stability translates into increasing time efficiency of the synthesis and makes the protocol experimentally less demanding ('fast addition' not required, tap water can be used in the final steps) as compared to previously reported procedures, without compromising the size and shape monodispersity of the product. We demonstrate high reproducibility of the protocol in the hands of different researchers and in different laboratories. Additionally, this modified seed-mediated method can be used to produce NTs with edge lengths between ca. 45 and 150 nm. Finally, the high 'quality' of NTs allows the preparation of long-range ordered assemblies with vertically oriented building blocks, which makes them promising candidates for future optoelectronic technologies.

Role of Stabilizing Surfactants on Capacitance, Charge, and Ion Transport in Organic Nanoparticle-Based Electronic Devices

Deposition of functionalized nanoparticles onto solid surfaces has created a new revolution in electronic devices. Surface adsorbates such as ionic surfactants or additives are often used to stabilize such nanoparticle suspensions; however, little is presently known about the influence of such surfactants and additives on specific electronic and chemical functionality of nanoparticulate electronic devices. This work combines experimental measurements and theoretical models to probe the role of an ionic surfactant in the fundamental physical chemistry and electronic charge carrier behavior of photodiode devices prepared using multicomponent organic electronic nanoparticles. A large capacitance was detected, which could be subsequently manipulated using the external stimuli of light, temperature, and electric fields. It was demonstrated that analyzing this capacitance through the framework of classical semiconductor analysis produced substantially misleading information on the electronic trap density of the nanoparticles. Electrochemical impedance measurements demonstrated that it is actually the stabilizing surfactant that creates capacitance through two distinct mechanisms, each of which influenced charge carrier behavior differently. The first mechanism involved a dipole layer created at the contact interfaces by mobile ions, a mechanism that could be replicated by addition of ions to solution-cast devices and was shown to be the major origin of restricted electronic performance. The second mechanism consisted of immobile ionic shells around individual nanoparticles and was shown to have a minor impact on device performance as it could be removed upon addition of electronic charge in the photodiodes through either illumination or external bias. The results confirmed that the surfactant ions do not create a significantly increased level of charge carrier traps as has been previously suspected, but rather, preventing the diffusion of mobile ions through the nanoparticulate film and their accumulation at contacts is critical to optimize the performance.

Synthesis and Application of Dendritic Fibrous Nanosilica/Gold Hybrid Nanomaterials

Morphologically unique silica nanoparticles can be used as effective templates to prepare silica-metal hybrid nanomaterials, which are highly applicable in a variety of areas. Mesoporous silica nanoparticles, which have high surface areas and an abundance of pores, can be used to synthesize mesoporous silica core-metal shell nanostructures with catalytically active sites. In this work, dendritic fibrous nanosilica (DFNS) with a high surface area is successfully employed as a template to synthesize DFNS/Au hybrid nanomaterials. Au nanodots are initially synthesized through the selective reduction of Au ions on the surface of the DFNS after surface modification to form DFNS/Au dots. A seed-mediated growth method is used to controllably grow Au nanoparticles on the DFNS/Au dots to generate DFNS core-Au nanoparticles shell nanohybrids (DFNS/Au NPs) and DFNS core-Au layer shell nanohybrids (DFNS/Au layers). The catalytic activities of DFNS/Au NPs and DFNS/Au layers in the 4-nitrophenol reduction reaction are compared.

Directed Assembly of Gold Nanorods by Terminal-Base Pairing of Surface-Grafted DNA

Directed assemblies of anisotropic metal nanoparticles exhibit attractive physical and chemical properties. However, an effective methodology to prepare differently directed assemblies from the same anisotropic nanoparticles is not yet available. Gold nanorods (AuNRs) region-selectively modified with different DNA strands can form side-by-side (SBS) and end-to-end (ETE) assemblies in a non-crosslinking manner. When the complementary DNA is hybridized to the surface-bound DNA, stacking interaction between the blunt ends takes place in the designated regions. Such AuNRs assemble into highly ordered structures, assisted by capillary forces emerging on the substrate surface. Moreover, insertion of a mercury(II)-mediated thymine-thymine base pair into the periphery of the DNA layer allows selective formation of the SBS or ETE assemblies from the strictly identical AuNRs with or without mercury(II).

Gold-Triggered Uncaging Chemistry in Living Systems

Recent advances in bioorthogonal catalysis are increasing the capacity of researchers to manipulate the fate of molecules in complex biological systems. A bioorthogonal uncaging strategy is presented, which is triggered by heterogeneous gold catalysis and facilitates the activation of a structurally diverse range of therapeutics in cancer cell culture. Furthermore, this solid-supported catalytic system enabled locally controlled release of a fluorescent dye into the brain of a zebrafish for the first time, offering a novel way to modulate the activity of bioorthogonal reagents in the most fragile and complex organs.

Sterical ligand stabilization of nanocrystals versus electrostatic shielding by ionic compounds: a principle model study with TEM and XPS

Electrostaticversussterical ligand stabilization: competitive stabilization mechanism play a key role in the control of nanomaterial properties.

Assessing the Role of Capping Molecules in Controlling Aggregative Growth of Gold Nanoparticles in Heated Solution

This report describes findings of an investigation of the role of capping molecules in the size growth in the aggregative growth of pre-formed small-sized gold nanoparticles capped with alkanethiolate monolayers toward monodispersed larger sizes. The size controllability depends on the thiolate chain length and concentration in the thermal solution. The size evolution in solution at different concentrations of alkanethiols is analyzed in relation to adsorption isotherms and cohesive energy. The size dependence on thiolate chain length is also analyzed by considering the cohesive energy of the capping molecules, revealing the importance of cohesive energy in the capping structure. Theoretical and experimental comparisons of the surface plasmonic resonance optical properties have also provided new insights into the mechanism, thus enabling the exploitation of size-dependent nanoscale properties.

One-step synthesis of collagen hybrid gold nanoparticles and formation on Egyptian-like gold-plated archaeological ivory

A one-step method is reported to synthesize hybrid gold nanoparticles (AuNPs) by reduction of HAuCl4 in acetic solution in the presence of collagen (Col), dicarboxylic acid-terminated polyethylene glycol (PEG), and cetyltetrammonium bromide (CTAB) mixed with hydoxyapatite (HAP) as surfactants. Such formation process of AuNPs was shown to be responsible for purple stains naturally formed on Egyptianizing archaeological gilded ivories from 8th BC Syria. The understanding of this formation mechanism, which most likely involves a step with hybrid AuNPs, allows the establishing of an authenticity marker of ancient gold-plated ivories.