Neus G. Bastús

Kinetically Controlled Seeded Growth Synthesis of Citrate-Stabilized Gold Nanoparticles of up to 200 nm: Size Focusing versus Ostwald Ripening

Monodisperse citrate-stabilized gold nanoparticles with a uniform quasi-spherical shape of up to ∼200 nm and a narrow size distribution were synthesized following a kinetically controlled seeded growth strategy via the reduction of HAuCl(4) by sodium citrate. The inhibition of any secondary nucleation during homogeneous growth was controlled by adjusting the reaction conditions: temperature, gold precursor to seed particle concentration, and pH. This method presents improved results regarding the traditional Frens method in several aspects: (i) it produces particles of higher monodispersity; (ii) it allows better control of the gold nanoparticle size and size distribution; and (iii) it leads to higher concentrations. Gold nanoparticles synthesized following this method can be further functionalized with a wide variety of molecules, hence this method appears to be a promising candidate for application in the fields of biomedicine, photonics, and electronics, among others.

Homogeneous Conjugation of Peptides onto Gold Nanoparticles Enhances Macrophage Response

Murine bone marrow macrophages were able to recognize gold nanoparticle peptide conjugates, while peptides or nanoparticles alone were not recognized. Consequently, in the presence of conjugates, macrophage proliferation was stopped and pro-inflammatory cytokines such as TNF-alpha, IL-1beta, and IL-6, as well as nitric oxide synthase (NOS2) were induced. Furthermore, macrophage activation by gold nanoparticles conjugated to different peptides appeared to be rather independent of peptide length and polarity, but dependent on peptide pattern at the nanoparticle surface. Correspondingly, the biochemical type of response also depended on the type of conjugated peptide and could be correlated with the degree of ordering in the peptide coating. These findings help to illustrate the basic requirements involved in medical nanoparticle conjugate design to either activate the immune system or hide from it in order to reach their targets before being removed by phagocytes.

Peptides conjugated to gold nanoparticles induce macrophage activation

Macrophages that react against pathogenic organisms can also be activated with artificial nanometric units consisting of gold nanoparticles (Au NPs) with a peptide coating. Using bone marrow-derived macrophages, here we show that these cells have the capacity to recognize Au NPs once conjugated to two biomedically relevant peptides, the amyloid growth inhibitory peptide (AGIP) and the sweet arrow peptide (SAP), while they do not recognize peptides or NPs alone. The recognition of these conjugates by macrophages is mediated by a pattern recognition receptor, the TLR-4. Consequently, pro-inflammatory cytokines such as TNF-alpha, IL-1 beta and IL-6, as well as nitric oxide synthase were induced and macrophage proliferation was stopped when exposed to the peptide-conjugated Au NPs. Contamination by lipopolysaccharide in our experimental system was excluded. Furthermore, macrophage activation appeared to be independent of peptide length and polarity. As a result of macrophage activation, conjugated Au NPs were internalized and processed. These results open up a new avenue in the world of adjuvants and illustrate the basic requirements for the design of NP conjugates that efficiently reach their target.

Little Adjustments Significantly Improve the Turkevich Synthesis of Gold Nanoparticles

In this report, we show how the classical and widely used Turkevich synthesis can be improved significantly by simple adjustments. The gold nanoparticles (AuNPs) produced with the optimized protocol have a much narrower size distribution (5-8% standard deviation), and their diameters can be reproduced with unrivaled little variation (<3%). Moreover, large volumes of these particles can be produced in one synthesis; we routinely synthesize 1000 mL of ∼3.5 nM AuNPs. The key features of the improved protocol are the control of the pH by using a citrate buffer instead of a citrate solution as the reducing agent or stabilizer and optimized mixing of reagents. Further, the shape uniformity of the particles can be improved by addition of 0.02 mM EDTA. While the proposed protocol is as straightforward as the original Turkevich protocol, it is more tolerant against variations in precursor concentration.

Tunable Plasmon Coupling in Distance-Controlled Gold Nanoparticles

Plasmons are resonant excitations in metallic films and nanoparticles. For small enough static distances of metal nanoparticles, additional plasmon-coupled modes appear as a collective excitation between the nanoparticles. Here we show, by combining poly(N-isopropylacrylamide) micro- and nanospheres and Au nanoparticles, how to design a system that allows controllably and reversibly switching on and off, and tuning the plasmon-coupled mode.

Gold Nanoparticles and Microwave Irradiation Inhibit Beta-Amyloid Amyloidogenesis

Peptide-Gold nanoparticles selectively attached to β-amyloid protein (Aβ) amyloidogenic aggregates were irradiated with microwave. This treatment produces dramatic effects on the Aβ aggregates, inhibiting both the amyloidogenesis and the restoration of the amyloidogenic potential. This novel approach offers a new strategy to inhibit, locally and remotely, the amyloidogenic process, which could have application in Alzheimer’s disease therapy. We have studied the irradiation effect on the amyloidogenic process in the presence of conjugates peptide-nanoparticle by transmission electronic microscopy observations and by Thioflavine T assays to quantify the amount of fibrils in suspension. The amyloidogenic aggregates rather than the amyloid fibrils seem to be better targets for the treatment of the disease. Our results could contribute to the development of a new therapeutic strategy to inhibit the amyloidogenic process in Alzheimer’s disease.

Effect of the Spacer Structure on the Stability of Gold Nanoparticles Functionalized with Monodentate Thiolated Poly(ethylene glycol) Ligands

Poly(ethylene glycol)- (PEG-) based ligands are well-established for the stabilization of nanoparticles in aqueous solution and are especially interesting for applications in medicine and biotechnology because they are known to improve the pharmacokinetic properties of nanomaterials. In this study, we prepared gold nanoparticles (AuNPs) with ligand shells of different monodentate poly(ethylene glycol)-thiol (PEG-SH) ligands. These ligands differed only in the segment connecting the thiol group with the PEG moiety (Mw ≈ 2000 g/mol) through an ester bond, the spacer. All ligands were synthesized by straightforward esterification. Specifically, we used PEG ligands with a long (C10, PEGMUA) or short (C2, PEGMPA) alkylene spacer or a phenylene (PEGMPAA) spacer. The influence of the spacer on the stability of gold nanoparticle-PEG conjugates (AuNP@PEG) was tested by cyanide etching experiments, electrolyte-induced aggregation, and competitive ligand displacement with dithiothreitol (DTT). In the presence of 100 mM cyanide, AuNPs stabilized with PEGMPA or PEGMPAA were completely dissolved by oxidative etching within a few minutes, whereas AuNPs stabilized with PEGMUA needed more than 20 h to be completely etched. By complementary experiments, we deduced a simplified description for the etching process that takes into account the role of excess ligand. In the presence of free ligand, significantly fewer AuNPs are etched, suggesting a competition of etching and ligand binding to AuNPs. We also compared the stabilizing effect of PEGMUA with that of a bidentate PEG-thiol ligand (PEGLIP) and found a reversed stability against cyanide etching and DTT displacement, in agreement with previously reported observations. Our results clearly demonstrate the strong impact of the spacer structure on conjugate stability and provide valuable information for the rational design of more complex AuNP@PEG conjugates, which are of much interest in the context of biotechnology and medical applications.

Shuttling Gold Nanoparticles into Tumoral Cells with an Amphipathic Proline-Rich Peptide

Golden bullets: The amphipathic proline‐rich cell‐penetrating peptide sweet arrow peptide (SAP) is able to transport 12 nm gold nanoparticles efficiently into HeLa cells, as observed by three microscopy techniques: transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM) and transmission X‐ray microscopy (TXM). Multiconjugation to such nanoparticles may provide a convenient method for unifying the key drug properties of high activity, capacity to home onto targets and delivery to therapeutic places of action.

Reactivity of engineered inorganic nanoparticles and carbon nanostructures in biological media

Biocompatibility, biodistribution, biodegradation, inflammation and interference with cell and normal functioning of tissues, among others, will determine the toxicity of engineered inorganic nanoparticles and carbon nanostructures, and therefore the extent of their use. Recent examples in the literature show that engineered inorganic nanoparticles and carbon nanostructures, which may incidentally or intendedly enter into contact with living organisms, normally do not cause acute toxic effects. However, their interaction with living organisms may disrupt normal activity leading to malfunctioning and diseases. Indeed, the observed nanoparticle-biology interactions, which can be used to detect and manipulate biological states and to heal damaged organs, could also lead to environmental and human health hazards. Therefore, there should be proper risk assessments to avoid the consequences of an uncontrolled release of massive amounts of nanoparticles in the environment. This review focuses on the particular physico-chemical properties of inorganic matter at the nanoscale in order to understand and track its evolution within living organisms, and thus monitor their interactions.

Size-Dependent Protein–Nanoparticle Interactions in Citrate-Stabilized Gold Nanoparticles: The Emergence of the Protein Corona

Surface modifications of highly monodisperse citrate-stabilized gold nanoparticles (AuNPs) with sizes ranging from 3.5 to 150 nm after their exposure to cell culture media supplemented with fetal bovine serum were studied and characterized by the combined use of UV-vis spectroscopy, dynamic light scattering, and zeta potential measurements. In all the tested AuNPs, a dynamic process of protein adsorption was observed, evolving toward the formation of an irreversible hard protein coating known as Protein Corona. Interestingly, the thickness and density of this protein coating were strongly dependent on the particle size, making it possible to identify different transition regimes as the size of the particles increased: (i) NP-protein complexes (or incomplete corona), (ii) the formation of a near-single dense protein corona layer, and (iii) the formation of a multilayer corona. In addition, the different temporal patterns in the evolution of the protein coating came about more quickly for small particles than for the larger ones, further revealing the significant role that size plays in the kinetics of this process. Since the biological identity of the NPs is ultimately determined by the protein corona and different NP-biological interactions take place at different time scales, these results are relevant to biological and toxicological studies.