Search

Gold nanostars (AuNSs) have achieved special relevance for potential biomedical applications, e.g., in theranostics. In relation to this, some authors have explored controlling the conditions that trigger structural and morphological changes in these structures. In this work, we studied conditions that can trigger morphological changes of AuNSs or maintain their stability, such as ligand exchange to nonthiolated and thiolated species. First, the synthesis stabilizing ligand of AuNS, 4-(2-hydroxyethyl)-1-piperazinapropanesulfonic acid (EPPS), was exchanged for nonthiolated species to trigger or prevent morphological changes. One of these species, triphenylphosphine-monosulfonate (TPPMS), generated a stable and unexplored nanostructure even at acidic pH, with interaction mediated mainly by aromatic groups and the phosphine moiety, in comparison to hexadecyltrimethylammonium bromide (CTAB) and citrate, which are ligands that trigger morphological changes of AuNS. Moreover, TPPMS-coated AuNSs can be exchanged by thiolated species, such as carboxylated poly-(ethylene glycol) (HS-PEG-COOH), offering more versatility through covalent strategies. In addition, properties related to the application of these stabilized AuNSs were explored, such as photothermia and biocompatibility. The photothermal transduction efficiency and cell viability of AuNSs coated with EPPS, TPPMS, and PEG-COOH were evaluated, showing a temperature increment of the colloidal solutions and optimal mitochondrial activity. We believe that this work contributes to understanding the phenomena and conditions that trigger changes in the morphology or stability of AuNSs and that AuNSs coated with TPPMS and PEG-COOH possess optimal properties for potential biomedical applications. [ABSTRACT FROM AUTHOR]

Dacarbazine (DB) is an antineoplastic drug extensively used in cancer therapy. However, present limitations on its performance are related to its low solubility, instability, and non-specificity. To overcome these drawbacks, DB was included in β-cyclodextrin (βCD), which increased its aqueous solubility and stability. This new βCD@DB complex has been associated with plasmonic gold nanoparticles (AuNPs), and polyethylene glycol (PEG) has been added in the process to increase the colloidal stability and biocompatibility. Different techniques revealed that DB allows for a dynamic inclusion into βCD, with an association constant of 80 M−1 and a degree of solubilization of 0.023, where βCD showed a loading capacity of 16%. The partial exposure of the NH2 group in the included DB allows its interaction with AuNPs, with a loading efficiency of 99%. The PEG-AuNPs-βCD@DB nanosystem exhibits an optical plasmonic absorption at 525 nm, a surface charge of −29 mV, and an average size of 12 nm. Finally, laser irradiation assays showed that DB can be released from this platform in a controlled manner over time, reaching a concentration of 56 μg/mL (43% of the initially loaded amount), which, added to the previous data, validates its potential for drug delivery applications. Therefore, the novel nanosystem based on βCD, AuNPs, and PEG is a promising candidate as a new nanocarrier for DB. [ABSTRACT FROM AUTHOR]

Chemically synthesized gold nanoparticles (AuNPs) have attracted much interest for application in various technologically relevant fields including nanoelectronics. In this particular research area, the most promising approach to take full advantage of the tunability in size, shape, and ligand composition of nanoparticles is the integration of a well‐defined number of AuNPs into a nanoscale device. This short review highlights recent progress in the introduction of AuNP into nanoelectronic circuitry by means of selected examples, that demonstrate a "proof‐of‐concept". Synthetic concepts to obtain isotropic and Janus‐like particles as well as lithographic techniques that allow for the fabrication of nanoelectrode structures, which enable the electrical addressing of individual nanoparticles, are presented. A particular focus of this work is the question of how distinct molecular properties can be addressed in a technologically applicable device geometry by controlling the molecular functionalities in the proximity of semiconductor technology. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) devices are well known for mass-sensitive sensor applications. In biosensing applications, chemical and biochemically evoked binding processes on surfaces are detected in liquid environments using delay line or resonator sensor configurations, preferably in combination with the appropriate microfluidic devices. All configurations share the common feature of analyzing the transmission characteristic of the propagating SAW. In this paper, a novel SAW-based impedance sensor type is introduced which uses only one interdigital transducer (IDT), simultaneously as the SAW generator and the sensor element. Here, the input port reflection coefficient S11 is measured at the IDT instead of the commonly used S21 transmission forward gain parameter. Thus, a sharp and distinct peak of the S11 spectrum is obtained, enabling a comfortable direct readout of the sensor signal. Proof of the concept was gained by analyzing the specific binding of the 4-mercaptophenylacetic acid gold nanoparticles (MPA-AuNP) directly to the IDT surface. The corresponding binding kinetic of the MPA-AuNP on the functionalized gold surface has been analyzed and a sensitivity of 7.4 mW nM-1 has been determined. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) have been extensively explored in biomedical applications, for example as drug carriers, contrast agents, or therapeutics. However, AuNP can exhibit cytotoxic profile, when the size is below 2 nm (ultrasmall AuNP; usAuNP) and when the stabilizing ligands allow for access to the gold surface either for the direct interaction with biomolecules or for catalytic activity of the unshielded gold surface. Furthermore, usAuNP exhibits significantly different biodistribution and enhanced circulation times compared to larger AuNP. This review gives an overview about the synthesis and the physico-chemical properties of usAuNP and, thereby, focusses on 1.4 nm sized AuNP, which are derived from the compound Au(PPh)Cl and which are the most intensively studied usAuNP in the field. This part is followed by a summary of the toxic properties of usAuNP, which include in vitro cytotoxicity tests on different cell lines, electrophysiological tests following FDA guidelines as well as studies on antibacterial effects. Finally, the biodistribution and pharmacokinetics of ultrasmall AuNP are discussed and compared to the properties of more biocompatible, larger AuNP. [ABSTRACT FROM AUTHOR]

We studied the effect of gold nanoparticle (AuNP) size, surface charge, concentration and morphology on the integrity of the blood–brain barrier (BBB) in a well-established in vitro model set-up. We focused on the effect of peptide functionalized hollow gold nanospheres and gold nanorods, which selectively bind to amyloidogenic β -amyloid structures. These AuNP conjugates have already been successfully tested as photothermal absorbers for potential application in Alzheimer's disease (AD) therapy in an in vitro set-up, but may exhibit a low passage through the BBB due to their overall negative charge. Our results show that: (i) small (1.4 nm) AuNPs strongly affects the BBB integrity, (ii) negative surface charge impedes BBB passage, and (iii) this charge effect caused by the peptide is compensated by covalent coupling to a polyethylene glycol ligand stabilizing the particles in diluted manner. [ABSTRACT FROM AUTHOR]

Interactions between nanoparticles (NPs) and biomembranes depend on the physicochemical properties of the NPs, such as size and surface charge. Here we report on the size-dependent interaction of gold nanoparticles (AuNPs), stabilized with ligands differing in charge, i.e. sodium 3-(diphenylphosphino)benzene sulfonate (TPPMS) and sodium 3,3′,3″-triphenylphosphine sulfonate (TPPTS), respectively, with artificial membranes (black lipid membranes; BLMs) and HeLa cells. The TPPTS-stabilized AuNPs affect BLMs at lower size than TPPMS-stabilized ones. On HeLa cells we found decreasing cytotoxicity with increasing particle size, however, with an overall lower cytotoxicity for TPPTS-stabilized AuNPs. We attribute size-dependent BLM properties as well as reduced cytotoxicity of TPPTS-stabilized AuNPs to weaker shielding of the AuNP core when stabilized with TPPTS. We hypothesize that the partially unshielded hydrophobic gold core can embed into the hydrophobic membrane interior. Thereby we demonstrate that ligand-dependent cytotoxicity of NP can occur even when the NPs are not translocated through the membrane. From the Clinical Editor The use of nanoparticles (NPs) in the clinical setting means that there will be interactions between NPs and cell membranes. The authors investigated the underlying processes concerning cellular uptake and potential toxicity of gold nanoparticles (AuNPs) using particles with ligands different sizes and charges. The findings should further enhance existing knowledge on future design of safer NPs in the clinic. [ABSTRACT FROM AUTHOR]

Understanding the mechanism of toxicity of nanomaterials remains a challenge with respect to both mechanisms involved and product regulation. Here we show toxicity of ultrasmall gold nanoparticles (AuNPs). Depending on the ligand chemistry, 1.4-nm-diameter AuNPs failed electrophysiology-based safety testing using human embryonic kidney cell line 293 cells expressing human ether-á-go-go-Related gene (hERG), a Food and Drug Administration-established drug safety test. In patch-clamp experiments, phosphine-stabilized AuNPs irreversibly blocked hERG channels, whereas thiol-stabilized AuNPs of similar size had no effect in vitro, and neither particle blocked the channel in vivo. We conclude that safety regulations may need to be reevaluated and adapted to reflect the fact that the binding modality of surface functional groups becomes a relevant parameter for the design of nanoscale bioactive compounds. [ABSTRACT FROM AUTHOR]

We investigated the possibility of tuning the local switching properties of memristive crystalline SrTiO 3 thin films by inserting nanoscale defect nucleation centers. For that purpose, we employed chemically-synthesized Au nanoparticles deposited on 0.5 wt%-Nb-doped SrTiO 3 single crystal substrates as a defect formation template for the subsequent growth of SrTiO 3 . We studied in detail the resulting microstructure and the local conducting and switching properties of the SrTiO 3 thin films. We revealed that the Au nanoparticles floated to the SrTiO 3 surface during growth, leaving behind a distorted thin film region in their vicinity. By employing conductive-tip atomic force microscopy, these distorted SrTiO 3 regions are identified as sites of preferential resistive switching. These findings can be attributed to the enhanced oxygen exchange reaction at the surface in these defective regions. [ABSTRACT FROM AUTHOR]

As a novel strategy to overcome some of the therapeutic disadvantages of 6-thioguanine (TG) and 6-mercaptopurine (MP), we propose the inclusion of these drugs in βcyclodextrin (βCD) to form the complexes βCD-TG and βCD-MP, followed by subsequent interaction with gold nanoparticles (AuNPs), generating the ternary systems: βCD-TG-AuNPs and βCD-MP-AuNPs. This modification increased their solubility and improved their stability, betting by a site-specific transport due to their nanometric dimensions, among other advantages. The formation of the complexes was confirmed using powder X-ray diffraction, thermogravimetric analysis and one and two-dimensional NMR. A theoretical study using DFT and molecular modelling was conducted to obtain the more stable tautomeric species of TG and MP in solution and confirm the proposed inclusion geometries. The deposition of AuNPs onto βCD-TG and βCD-MP via sputtering was confirmed by UV–vis spectroscopy. Subsequently, the ternary systems were characterized by TEM, FE-SEM and EDX to directly observe the deposited AuNPs and evaluate their sizes, size dispersion, and composition. Finally, the in vitro permeability of the ternary systems was studied using parallel artificial membrane permeability assay (PAMPA). [ABSTRACT FROM AUTHOR]

Photoacoustic (PA) imaging attracts a great deal of attention as an innovative modality for longitudinal, non-invasive, functional and molecular imaging in oncology. Gold nanoparticles (AuNPs) are identified as superior, NIR-absorbing PA contrast agents for biomedical applications. Until now, no systematic comparison of the optical extinction and PA efficiency of water-soluble AuNPs of various geometries and small sizes has been performed.Here spherical AuNPs with core diameters of 1.0, 1.4 and 11.2 nm, nanorods with longitudinal/transversal elongation of 38/9 and 44/12 nm and hollow nanospheres with outer/inner diameters of 33/19, 57/30, 68/45 and 85/56 nm were synthesized. The diode laser set-up with excitations at 650, 808, 850 and 905 nm allowed us to correlate the molar PA signal intensity with the molar extinction of the respective AuNPs. Deviations were explained by differences in heat transfer from the particle to the medium and, for larger particles, by the scattering of light. The molar PA intensity of 1.0 nm AuNPs was comparable to the commonly used organic dye methylene blue, and rapidly increased with the lateral size of AuNPs. [ABSTRACT FROM AUTHOR]

Here, we report an approach to use infrared reflection absorption spectroscopy (IRRAS) for the unambiguous proof of the presence as well as the spatial distribution of organic ligands on the Janus gold nanoparticle (AuNP) surface. For this purpose we synthesized amphiphilic and zwitterionic Janus AuNPs and immobilized these on pretreated gold surfaces by directed self-assembly, exploiting hydrophilic/hydrophobic or electrostatic interactions, respectively. Thus, we obtained macroscopic two-dimensional arrays of Janus AuNPs exhibiting a specific orientation. These arrays were investigated by IRRAS, and the obtained spectra revealed only peaks of the ligands facing the IR beam, while the ligands facing the gold substrate were not detected due to reflection of the IR beam on the AuNP cores. Thus, we describe a straightforward spectroscopic procedure to prove the Janus character of zwitterionic and amphiphilic AuNPs in the size range of 10-15 nm. [ABSTRACT FROM AUTHOR]

A cysteine-substituted mutant ofthe ring-shaped protein TRAP (trp-RNA binding attenuationprotein) can be induced to self-assembleinto large, monodisperse hollow spherical cages in the presence of1.4 nm diameter gold nanoparticles. In this study we use high-speedatomic force microscopy (HS-AFM) to probe the dynamics of the structuralchanges related to TRAP interactions with the gold nanoparticle aswell as the disassembly of the cage structure. The dynamic aggregationof TRAP protein in the presence of gold nanoparticles was observed,including oligomeric rearrangements, consistent with a role for goldin mediating intermolecular disulfide bond formation. We were alsoable to observe that the TRAP-cage is composed of multiple, closelypacked TRAP rings in an apparently regular arrangement. A potentialrole for inter-ring disulfide bonds in forming the TRAP-cage was shownby the fact that ring–ring interactions were reversed uponthe addition of reducing agent dithiothreitol. A dramatic disassemblyof TRAP-cages was observed using HS-AFM after the addition of dithiothreitol.To the best of our knowledge, this is the first report to show directhigh-resolution imaging of the disassembly process of a large proteincomplex in real time. [ABSTRACT FROM AUTHOR]

Integration of molecule-capped goldnanoparticles (AuNP) into nanoelectronicdevices requires detailed knowledge about the AuNP–electrodeinterface. Here, we report the pH-dependent adsorption of amine orcarboxylic acid-terminated gold nanoparticles on platinum or gold/palladium(30% Pd) alloy, respectively. We synthesized amine-terminated AuNP,applying a new solid phase supported approach, as well as AuNP exhibitingcarboxylic acid as terminal groups. The pH-induced agglomeration ofthe synthesized AuNP was investigated by UV–vis, DLS, and ζ-potentialmeasurements. Depending on the pH and the ionic strength of the AuNPsolution a preferential adsorption on the different metals occurred.Thereby, we demonstrate that by choosing the appropriate functionalgroup and adjusting the pH as well as the ionic strength a directedbinding can be achieved, which is an essential prerequisite for applicationsof these particles in nanoelectronics. These findings will pave theway for a controlled designing of the interface between molecule-cappedAuNP and metallic electrodes for applications in nanoelectronics. [ABSTRACT FROM AUTHOR]

We report the formation of thiol nanopatterns on SAMcovered siliconwafers by converting sulfonic acid head groups via e-beam lithography.These thiol groups act as binding sites for gold nanoparticles, whichcan be enhanced to form electrically conducting nanostructures. Thisapproach serves as a proof-of-concept for the combination of top-downand bottom-up processes for the generation of electrical devices onsilicon. [ABSTRACT FROM AUTHOR]

Abstract: Gold nanoparticles (GNP) provide many opportunities in imaging, diagnostics, and therapies of nanomedicine. Hence, their biokinetics in the body are prerequisites for specific tailoring of nanomedicinal applications and for a comprehensive risk assessment. We administered 198Au-radio-labelled monodisperse, negatively chargedGNP of five different sizes (1.4, 5, 18, 80, and 200nm) and 2.8nm GNP with opposite surface charges by intravenous injection into rats. After 24h, the biodistribution of the GNP was quantitatively measuredby gamma-spectrometry. The size and surface charge of GNP strongly determine the biodistribution. Most GNP accumulated in the liver increased from 50% of 1.4nm GNP to >99% of 200nm GNP. In contrast, there was little size-dependent accumulation of 18–200nm GNP in most other organs. However, for GNP between 1.4nm and 5nm, the accumulation increased sharply with decreasing size; i.e. a linear increase with the volumetric specific surface area. The differently charged 2.8nm GNP led to significantly different accumulations in several organs. We conclude that the alterations of accumulation in the various organs and tissues, depending on GNP size and surface charge, are mediated by dynamic protein binding and exchange. A better understanding of these mechanisms will improve drug delivery and dose estimates used in risk assessment. [Copyright &y& Elsevier]