Gold and Silver Nanoparticles Functionalized by the Adsorption of Dialkyl Disulfides

Advances in nanotechnology for the treatment of GBM

Glioblastoma (GBM), a highly malignant glioma of the central nervous system, is the most dread and common brain tumor with a high rate of therapeutic resistance and recurrence. Currently, the clinical treatment methods are surgery, radiotherapy, and chemotherapy. However, owning to the highly invasive nature of GBM, it is difficult to completely resect them due to the unclear boundary between the edges of GBM and normal brain tissue. Traditional radiotherapy and the combination of alkylating agents and radiotherapy have significant side effects, therapeutic drugs are difficult to penetrate the blood brain barrier. Patients receiving treatment have a high postoperative recurrence rate and a median survival of less than 2 years, Less than 5% of patients live longer than 5 years. Therefore, it is urgent to achieve precise treatment through the blood brain barrier and reduce toxic and side effects. Nanotechnology exhibit great potential in this area. This article summarizes the current treatment methods and shortcomings of GBM, and summarizes the research progress in the diagnosis and treatment of GBM using nanotechnology.

Reagents for Mass Cytometry

Mass cytometry (cytometry by time-of-flight detection [CyTOF]) is a bioanalytical technique that enables the identification and quantification of diverse features of cellular systems with single-cell resolution. In suspension mass cytometry, cells are stained with stable heavy-atom isotope-tagged reagents, and then the cells are nebulized into an inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF-MS) instrument. In imaging mass cytometry, a pulsed laser is used to ablate ca. 1 μm² spots of a tissue section. The plume is then transferred to the CyTOF, generating an image of biomarker expression. Similar measurements are possible with multiplexed ion bean imaging (MIBI). The unit mass resolution of the ICP-TOF-MS detector allows for multiparametric analysis of (in principle) up to 130 different parameters. Currently available reagents, however, allow simultaneous measurement of up to 50 biomarkers. As new reagents are developed, the scope of information that can be obtained by mass cytometry continues to increase, particularly due to the development of new small molecule reagents which enable monitoring of active biochemistry at the cellular level. This review summarizes the history and current state of mass cytometry reagent development and elaborates on areas where there is a need for new reagents. Additionally, this review provides guidelines on how new reagents should be tested and how the data should be presented to make them most meaningful to the mass cytometry user community.

Glyco disulfide capped gold nanoparticle synthesis: cytotoxicity studies and effects on lung cancer A549 cells

Background: Glyco disulfide gold nanoparticles (GDAuNPs) were prepared by three methods: direct, photochemical irradiation and ligand substitution. Glyco disulfide acted as reducing and capping agents of gold ions, to produce AuNPs GD1-GD16. Results: Shorter chains of glyco disulfides (n = 1 and 2) offered monodispersed and stable GDAuNPs in physiological pH, while longer chains (n = 3) furnished unstable nanoparticles. ζ-potential study of direct method GDAuNPs revealed surface charge dependency on the alkyl unit length. Transmission electron microscope imaging indicated that sizes/shapes of the ligand exchange AuNPs remained post-exchange step. The mechanism of GDAuNP formation was forecast as the Ostwald ripening effect at low pH of ligand (5.1-8.9) and reinforcement of static stabilization at high pH (12.4-13.0). Conclusion: GDAuNPs recorded moderately anticancer activity against the A549 cancer cell line, with IC₅₀ between 14.95 and 64.95 μg/ml.

Complete ablation of tumors using synchronous chemoradiation with bimetallic theranostic nanoparticles

Synchronous chemotherapy and radiotherapy, termed chemoradiation therapy, is now an important standard regime for synergistic cancer treatment. For such treatment, nanoparticles can serve as improved carriers of chemotherapeutics into tumors and as better radiosensitizers for localized radiotherapy. Herein, we designed a Schottky-type theranostic heterostructure, Bi2S3-Au, with deep level defects (DLDs) in Bi2S3 as a nano-radiosensitizer and CT imaging contrast agent which can generate reactive free radicals to initiate DNA damage within tumor cells under X-ray irradiation. Methotrexate (MTX) was conjugated onto the Bi2S3-Au nanoparticles as a chemotherapeutic agent showing enzymatic stimuli-responsive release behavior. The designed hybrid system also contained curcumin (CUR), which cannot only serve as a nutritional supplement for chemotherapy, but also can play an important role in the radioprotection of normal cells. Impressively, this combined one-dose chemoradiation therapeutic injection of co-drug loaded bimetallic multifunctional theranostic nanoparticles with a one-time clinical X-ray irradiation, completely eradicated tumors in mice after approximately 20 days after irradiation showing extremely effective anticancer efficacy which should be further studied for numerous anti-cancer applications.

Transition metal silicide surface grafting by multiple functional groups and green optimization by mechanochemistry

Chromium disilicide (CrSi2) particles were synthesized by using an arc melting furnace followed by mechanical milling. XRD and DLS analyses show that aggregates of around 3 μm containing about 10 nm sized crystallites were obtained. These aggregates were functionalized in solution by coupling agents with different anchoring groups (silane, phosphonic acid, alkene and thiol) in order to disperse them into an organic polymer. Dodecene was used to modify the CrSi2 surface during mechano-synthesis in a grinding bowl with quite little solvent quantity and the optimization step allowed the aggregate size to be reduced to 500 nm. A thermoelectric composite was then made of alkene CrSi2 grafted samples and poly(p-phénylène-2,6-benzobisoxazole). This study opens the route for new surface grafting of intermetallic silicides for applications linked to electronics and/or energy.

In Situ Growth and Size Regulation of Single Gold Nanoparticles in Composite Microgels

Herein, a novel method for the in situ growth of single gold nanoparticles (AuNPs) in microgel (MG) networks is presented. The key feature in this approach is the localization of β-diketone groups capable of both complexation and reduction of aurate ions in the MGs' core, which allows localization of the nucleation and growth of single AuNPs. The MG synthesis is carried out via precipitation polymerization in water with N-vinylcaprolactam as the main monomer and with the two comonomers acetoacetoxyethyl methacrylate (AAEM) and acrylic acid (AAc), where AAEM is mainly located in the MGs' core and AAc in their shell. For the synthesis of AuNPs, a certain amount of chloroauric acid (HAuCl₄ ) is added to the dispersion, followed by fast reduction with sodium borohydride (NaBH₄ ). In situ synthesized AuNPs in MGs possess a spherical shape, with a diameter of 8.1 ± 0.8 nm, being localized in the center of every MG. In addition, these AuNPs embedded into MG networks can be used as seeds that grow in their size after the addition of HAuCl₄ up to 46.0 ± 9.5 nm under mild reaction conditions (room temperature, aqueous dispersion) and without the use of any additional reducing and stabilizing agents.

Synthesis of unsymmetrical disulfanes bearing 1,2,4-triazine scaffold and their in vitro screening towards anti-breast cancer activity

ABSTRACT

A new series of 1,2,4-triazine unsymmetrical disulfanes were prepared and evaluated as anticancer activity compounds against MCF-7 human breast cancer cells with some of them acting as low micromolar inhibitors. Evaluation of the cytotoxicity using an MTT assay, the inhibition of [3H]-thymidine incorporation into DNA demonstrated that these products exhibit cytotoxic effects on breast cancer cells in vitro. The most effective compounds with 59 and 60 µM compared to chlorambucil with 47 µM were disulfanes bearing methyl and methoxy substituent in an aromatic ring. Furthermore, all new 14 compounds were obtained with 22-74% yield via mild and efficient synthesis of the sulfur-sulfur bond formation from thiols and symmetrical disulfanes using 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ). The molecular structure of the newly obtained compounds was confirmed by X-ray analysis. The conformational preferences of disulfide system were characterized using theoretical calculations at DFT level and statistical distributions of C-S-S-C torsion angle values based on the Cambridge Structural Database (CSD). The DFT calculations and CSD searching show two preferential conformations for C-S-S-C torsion angle close to ± 90° and relatively large freedom of rotation on S-S bond in physiological conditions. The molecular docking studies were performed using the human estrogen receptor alpha (ERα) as molecular target to find possible binding orientation and intermolecular interactions of investigated disulfanes within the active site of ERα. The S…H-S and S…H-C hydrogen bonds between sulfur atoms of bisulfide bridge and S-H and C-H groups of Cys530 and Ala350 as protein residues play crucial role in interaction with estrogen receptor for the most anticancer active disulfane.

GRAPHICAL ABSTRACT

Synthesis of Alkanethiolate-Capped Metal Nanoparticles Using Alkyl Thiosulfate Ligand Precursors: A Method to Generate Promising Reagents for Selective Catalysis

Evaluation of metal nanoparticle catalysts functionalized with well-defined thiolate ligands can be potentially important because such systems can provide a spatial control in the reactivity and selectivity of catalysts. A synthetic method utilizing Bunte salts (sodium S-alkylthiosulfates) allows the formation of metal nanoparticles (Au, Ag, Pd, Pt, and Ir) capped with alkanethiolate ligands. The catalysis studies on Pd nanoparticles show a strong correlation between the surface ligand structure/composition and the catalytic activity and selectivity for the hydrogenation/isomerization of alkenes, dienes, trienes, and allylic alcohols. The high selectivity of Pd nanoparticles is driven by the controlled electronic properties of the Pd surface limiting the formation of Pd⁻alkene adducts (or intermediates) necessary for (additional) hydrogenation. The synthesis of water soluble Pd nanoparticles using ω-carboxylate-S-alkanethiosulfate salts is successfully achieved and these Pd nanoparticles are examined for the hydrogenation of various unsaturated compounds in both homogeneous and heterogeneous environments. Alkanethiolate-capped Pt nanoparticles are also successfully synthesized and further investigated for the hydrogenation of various alkynes to understand their geometric and electronic surface properties. The high catalytic activity of activated terminal alkynes, but the significantly low activity of internal alkynes and unactivated terminal alkynes, are observed for Pt nanoparticles.

Phosphorus-Sulfur Heterocycles Incorporating an O-P(S)-O or O-P(S)-S-S-P(S)-O Scaffold: One-Pot Synthesis and Crystal Structure Study

A new one-pot preparative route was developed to synthesize novel organophosphorus-sulfur heterocycles via the reaction of the four-membered ring thionation reagent [2,4-diferrocenyl-1,3,2,4-diathiadiphosphetane 2,4-disulfide (FcLR, a ferrocene analogue of Lawesson's reagent)] and alkenyl/aryl-diols and I₂ (or SOCl₂) in the presence of triethylamine. Therefore, a series of five- to ten-membered heterocycles bearing an O-P(S)-O or an O-P(S)-S-S-P(S)-O linkage were synthesized. The synthesis features a novel application of the multicomponent reaction, providing an efficient and environmentally benign method for the preparation of the unusual phosphorus-sulfur heterocycles. Seven representative X-ray structures confirm the formation of these heterocycles.

Modified Hyperbranched Polyglycerol as Dispersant for Size Control and Stabilization of Gold Nanoparticles in Hydrocarbons

Hyperbranched polyglycerol (HPG) is modified with dodecanethiol (DS) via the "thiol-ene" click reaction to obtain an amphiphilic product DSHPG. The molecular structures of DSHPG samples are characterized by NMR, FTIR, and GPC, and the thermal behaviors are characterized by DSC and TGA. Gold nanoparticles (Au NPs) are prepared with DSHPG as the stabilizer and surface-modification reagent. The size of Au NPs can be tuned by changing the molecular weight of HPG. It is observed that the HPG molecular weights of 1123, 3826, and 55,075 lead to the NP diameters of 4.1 nm for Au@DSHPG-1, 9.7 nm for Au@DSHPG-2, and 15.1 nm for Au@DSHPG-3, respectively. The morphology and size of Au NPs are characterized by TEM and DLS. Especially, the dispersion abilities of Au NPs in different pure solvents and co-solvent mixtures are investigated. The long alkyl chains on DSHPG give the ability of Au NPs to be well dispersed in nonpolar solvents. Hydrocarbon-based nanofluids can be obtained from the hydrophobic Au NPs dispersed into a series of hydrocarbons. The dispersion stability for Au NPs in hydrocarbons is monitored by UV-Vis spectroscopy, and the relative concentration of Au NPs is observed to still maintain over 80% after 3600 h.

Gold nanoparticles as scaffolds for poor water soluble and difficult to vehiculate antiparkinson codrugs

We report the facile and non-covalent preparation of gold nanoparticles (AuNPs) stabilized by an antiparkinson codrug based on lipoic acid (LA). The obtained AuNPs appear stable in both dimethyl sulfoxide and fetal bovine serum and able to load an amount of codrug double the weight of gold. These NPs were demonstrated to be safe and biocompatible towards primary human blood cells and human neuroblastoma cells, one of the most widely used cellular models to study dopaminergic neural cells, therefore are ideal drug carriers for difficult to solubilize molecules. Very interestingly, the codrug-stabilized AuNPs were shown to reduce the accumulation of reactive oxygen species in SH-SY5Y cells treated with LD and did not change total oxidant status levels in cultured human blood cells, thus confirming the antioxidant role of LA although bound to AuNPs. The characterization of AuNPs in terms of loading and stability paves the way for their use in biomedical and pharmacological applications.

A highly sensitive SERS-based platform for Zn(ii) detection in cellular media

HBA SERS peak frequency shifts in response to coordination are used to analyze the concentration of Zn(ii) with ultra-high sensitivity.

The protonation state of thiols in self-assembled monolayers on roughened Ag/Au surfaces and nanoparticles

The protonation state of thiols in self-assembled monolayers (SAMs) on Ag and Au surfaces and nanoparticles (NPs) has been an issue of contestation. It has been recently demonstrated that deuterating the thiol proton produces ostentatious changes in the Raman spectra of thiols and can be used to detect the presence of the thiol functional group. Surface enhanced Raman spectroscopy (SERS) of H/D substituted aliphatic thiols on Ag surfaces clearly shows the presence of S-H vibration between 2150-2200 cm(-1) which shifts by 400 cm(-1) upon deuteration and a simultaneous >20 cm(-1) shift in the C-S vibration of thiol deuteration. Large shifts (>15 cm(-1)) in the C-S vibration are also observed for alkyl thiol SAMs on Au surfaces. Alternatively, neither the S-H vibration nor the H/D isotope effect on the C-S vibration is observed for alkyl thiol SAMs on Ag/Au NPs. XPS data on Ag/Au surfaces bearing aliphatic thiol SAMs show the presence of both protonated and deprotonated thiols while on Ag/Au NPs only deprotonated thiols are detected. These data suggest that aliphatic thiol SAMs on Au/Ag surfaces are partially protonated whereas they are totally deprotonated on Au/Ag NPs. Aromatic PhSH SAMs on Ag/Au surfaces and Ag/Au NPs do not show these vibrations or H/D shifts as well indicating that the thiols are deprotonated at these interfaces.

Design and Utility of Metal/Metal Oxide Nanoparticles Mediated by Thioether End-Functionalized Polymeric Ligands

The past few decades have witnessed significant advances in the development of functionalized metal/metal oxide nanoparticles including those of inorganic noble metals and magnetic materials stabilized by various polymeric ligands. Recent applications of such functionalized nanoparticles, including those in bio-imaging, sensing, catalysis, drug delivery, and other biomedical applications have triggered the need for their facile and reproducible preparation with a better control over their size, shape, and surface chemistry. In this perspective, the multidentate polymer ligands containing functional groups like thiol, thioether, and ester are important surface ligands for designing and synthesizing stable nanoparticles (NPs) of metals or their oxides with reproducibility and high yield. These ligands have offered an unprecedented control over the particle size of both nanoparticles and nanoclusters with enhanced colloidal stability, having tunable solubility in aqueous and organic media, and tunable optical, magnetic, and fluorescent properties. This review summarizes the synthetic methodologies and stability of nanoparticles and fluorescent nanoclusters of metals (Au, Ag, Cu, Pt, and other transition metal oxides) prepared by using thioether based ligands and highlights their applications in bio-imaging, sensing, drug delivery, magnetic resonance imaging (MRI), and catalysis. The future applications of fluorescent metal NPs like thermal gradient optical imaging, single molecule optoelectronics, sensors, and optical components of the detector are also envisaged.

Magnetic and Electrochemical Properties of a TEMPO-Substituted Disulfide Diradical in Solution, in the Crystal, and on a Surface

A study of the magnetic and electrochemical properties of a TEMPO-substituted disulfide diradical in three different environments was carried out: in solution, in the crystal, and as a self-assembled monolayer (SAM) on an Au(111) substrate, and the relationship between them was explored. In solution, this flexible diradical shows a strong spin-exchange interaction between the two nitroxide functions that depends on the temperature and solvent. Structural, dynamic, and thermodynamic information has been extracted from the EPR spectra of this dinitroxide. The magnetic interactions in the crystal include intra- and intermolecular contributions, which have been studied separately and shown to be antiferromagnetic in both cases. Finally, we demonstrate that both the magnetic and electrochemical properties are preserved upon chemisorption of the diradical on a gold surface. The resulting SAM displayed anisotropic magnetic properties, and angle-resolved EPR spectra of the monocrystal allowed a rough determination of the orientation of the molecules in the SAM.

Redox activity and chemical interactions of metal oxide nano- and micro-particles with dithiothreitol (DTT)

The wide application and production of nanotechnology have increased the interest in studying the toxicity of nano- and micro-sized particles escaping into air from various aspects of the production process. Metal oxides (MOs) are one particular class of particles that exist abundantly in ambient PM. Studies show an emphasis on biological mechanisms by which inhalation exposure to MOs leads to disease. However, different biological assays provide different redox activity rankings making it difficult to assess the contributions of various MOs to measures of aggregate toxicity in multi-pollutant systems such as ambient PM. Therefore, research to evaluate the chemical interaction between these particles and molecules that are relevant to cellular redox activity can help in establishing indicators of reactivity. In particular, this study assesses the redox activity of six MOs mainly emitted from anthropogenic industrial activities using the dithiothreitol (DTT) assay. DTT is commonly used in acellular assays due to its analogous structure to cellular glutathione. The structural and chemical behaviors between active MOs and DTT were elucidated using FTIR, NMR, and BET methods. The results indicate that the health risk (redox activity) associated with MOs is mainly a function of their surface reactivity demonstrated by the ability of the oxidized (S-H) bond in DTT to form a stable bond with the MO surface.

Gold nanoparticles as contrast agents in x-ray imaging and computed tomography

Computed tomography enables 3D anatomic imaging at a high spatial resolution, but requires delivery of an x-ray contrast agent to distinguish tissues with similar or low x-ray attenuation. Gold nanoparticles (AuNPs) have gained recent attention as an x-ray contrast agent due to exhibiting a high x-ray attenuation, nontoxicity and facile synthesis and surface functionalization for colloidal stability and targeted delivery. Potential diagnostic applications include blood pool imaging, passive targeting and active targeting, where actively targeted AuNPs could enable molecular imaging by computed tomography. This article summarizes the current state of knowledge for AuNP x-ray contrast agents within a paradigm of key structure-property-function relationships in order to provide guidance for the design of AuNP contrast agents to meet the necessary functional requirements in a particular application. Functional requirements include delivery to the site of interest (e.g., blood, tumors or microcalcifications), nontoxicity during delivery and clearance, targeting or localization at the site of interest and contrast enhancement for the site of interest compared with surrounding tissues. Design is achieved by strategically controlling structural characteristics (composition, mass concentration, size, shape and surface functionalization) for optimized properties and functional performance. Examples from the literature are used to highlight current design trade-offs that exist between the different functional requirements.

Phase transfer-based synthesis of HgS nanocrystals

Phase transfer techniques possess remarkable advantages for the synthesis of inorganic nanomaterials. In contrast to the abundant reports on the preparation of noble metal nanoparticles using phase transfer, the number of semiconductor nanocrystals syntheses based on phase transfer techniques is still limited. Herein, we report a systematic study of the phase transfer-based synthesis of HgS nanocrystals, including the tuning of their morphology/shape by either solvent choice or temperature. This strategy involves the transfer of Hg(ii) ions from aqueous solution to toluene, oleic acid or oleylamine and subsequent sulfidation at room or elevated temperature. Furthermore, we have extended this phase-transfer based strategy to the fabrication of HgS-Au nanocomposites. The studies in this work might provide a facile route for producing HgS nanocrystals with desirable properties and offer an effective strategy to investigate the influence of the morphology of HgS on the physical/chemical properties of various HgS-based materials.

Nitroxide-coated silver nanoparticles: synthesis, surface physicochemistry and antibacterial activity

We report the synthesis of well-defined silver nanoparticles with high antibacterial activity. Nitroxides on their surface may be oxidized under the influence of ROS to oxoammonium ions which are capable of interacting with bacterial membrane.

DDQ-mediated synthesis of functionalized unsymmetrical disulfanes

We developed a simple and efficient method for the synthesis of functionalized unsymmetrical disulfanes under mild conditions in good yields.

Preparation of PEG-modified PAMAM dendrimers having a gold nanorod core and their application to photothermal therapy

A new type of hybrid dendrimer consisting of a gold nanorod core and polyethylene glycol-modified polyamidoamine dendrons was developed for biomedical applications such as photothermal therapy.

Strong dependence of surface plasmon resonance and surface enhanced Raman scattering on the composition of Au-Fe nanoalloys

Nanoalloys of noble metals with transition metals are crucial components for the integration of plasmonics with magnetic and catalytic properties, as well as for the production of low-cost photonic devices. However, due to synthetic challenges in the realization of nanoscale solid solutions of noble metals and transition metals, very little is known about the composition dependence of plasmonic response in nanoalloys. Here we demonstrate for the first time that the elemental composition of Au-Fe nanoalloys obtained by laser ablation in liquid solution can be tuned by varying the liquid environment. Due to surface passivation and reaction with thiolated ligands, the nanoalloys obtained by our synthetic protocol are structurally and colloidally stable. Hence, we studied the dependence of the surface plasmon resonance (SPR) on the iron fraction and, for the first time, we observed surface enhanced Raman scattering (SERS) in Au-Fe nanoalloys. SPR and SERS performances are strongly affected by the iron content and are investigated using analytical and numerical models. By demonstrating the strong modification of plasmonic properties on the composition, our results provide important insights into the exploitation of Au-Fe nanoalloys in photonics, nanomedicine, magneto-plasmonic and plasmon-enhanced catalysis. Moreover, our findings show that several other plasmonic materials exist beyond gold and silver nanostructures.

Flexible sensors based on nanoparticles

Flexible sensors can be envisioned as promising components for smart sensing applications, including consumer electronics, robotics, prosthetics, health care, safety equipment, environmental monitoring, homeland security and space flight. The current review presents a concise, although admittedly nonexhaustive, didactic review of some of the main concepts and approaches related to the use of nanoparticles (NPs) in flexible sensors. The review attempts to pull together different views and terminologies used in the NP-based sensors, mainly those established via electrical transduction approaches, including, but, not confined to: (i) strain-gauges, (ii) flexible multiparametric sensors, and (iii) sensors that are unaffected by mechanical deformation. For each category, the review presents and discusses the common fabrication approaches and state-of-the-art results. The advantages, weak points, and possible routes for future research, highlighting the challenges for NP-based flexible sensors, are presented and discussed as well.

Robust carboxylic acid-terminated organic thin films and nanoparticle protectants generated from bidentate alkanethiols

A new carboxylic acid-terminated alkanethiol having bidentate character, 16-(3,5-bis(mercaptomethyl)phenoxy)hexadecanoic acid (BMPHA), was designed as an absorbate and protectant to form thermally stable carboxylic acid-terminated organic thin films on flat gold and nanoparticles, respectively. The structural features of the organic thin films derived from BMPHA were characterized by ellipsometry, X-ray photoelectron spectroscopy (XPS), and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and compared to those derived from mercaptohexadecanoic acid (MHA) and 16-(4-(mercaptomethyl)phenoxy)hexadecanoic acid (MMPHA). This study demonstrates that films derived from BMPHA are less densely packed than films derived from MHA and MMPHA. However, the results of solution-phase thermal desorption tests revealed that the carboxylic acid-terminated films generated from BMPHA exhibit an enhanced thermal stability compared to those generated from MHA and MMPHA. Furthermore, as a nanoparticle protectant, BMPHA can be used to stabilize large gold nanoparticles (~45 nm diameter) in solution, and BMPHA-protected gold nanoparticles exhibited a high thermal stability in solution thermolysis studies.

On the mechanism of metal nanoparticle synthesis in the Brust-Schiffrin method

Brust-Schiffrin synthesis (BSS) of metal nanoparticles has emerged as a major breakthrough in the field for its ability to produce highly stable thiol functionalized nanoparticles. In this work, we use a detailed population balance model to conclude that particle formation in BSS is controlled by a new synthesis route: continuous nucleation, growth, and capping of particles throughout the synthesis process. The new mechanism, quite different from the others known in the literature (classical LaMer mechanism, sequential nucleation-growth-capping, and thermodynamic mechanism), successfully explains key features of BSS, including size tuning by varying the amount of capping agent instead of the widely used approach of varying the amount of reducing agent. The new mechanism captures a large body of experimental observations quantitatively, including size tuning and only a marginal effect of the parameters otherwise known to affect particle synthesis sensitively. The new mechanism predicts that, in a constant synthesis environment, continuous nucleation-growth-capping mechanism leads to complete capping of particles (no more growth) at the same size, while the new ones are born continuously, in principle leading to synthesis of more monodisperse particles. This prediction is validated through new experimental measurements.

Molecularly stabilised ultrasmall gold nanoparticles: synthesis, characterization and bioactivity

Gold nanoparticles (AuNPs) are widely used as contrast agents in electron microscopy as well as for diagnostic tests. Due to their unique optical and electrical properties and their small size, there is also a growing field of potential applications in medical fields of imaging and therapy, for example as drug carriers or as active compounds in thermotherapy. Besides their intrinsic optical properties, facile surface decoration with (bio)functional ligands renders AuNPs ideally suited for many industrial and medical applications. However, novel AuNPs may have toxicological profiles differing from bulk and therefore a thorough analysis of the quantitative structure-activity relationship (QSAR) is required. Several mechanisms are proposed that cause adverse effects of nanoparticles in biological systems. Catalytic generation of reactive species due to the large and chemically active surface area of nanomaterials is well established. Because nanoparticles approach the size of biological molecules and subcellular structures, they may overcome natural barriers by active or passive uptake. Ultrasmall AuNPs with sizes of 2 nm or less may even behave as molecular ligands. These types of potential interactions would imply a size and ligand-dependent behaviour of any nanomaterial towards biological systems. Thus, to fully understand their QSAR, AuNPs bioactivity should be analysed in biological systems of increasing complexity ranging from cell culture to whole animal studies.

Gold nanoparticles - the theranostic challenge for PPPM: nanocardiology application

The article overviews the potential biomedical applications of nanoscale gold particles for predictive, preventive and personalised nanomedicine in cardiology. The review demonstrates the wide opportunities for gold nanoparticles due to their unique biological properties. The use of gold nanoparticles in cardiology is promising to develop fundamentally new methods of diagnosis and treatment. The nanotheranostics in cardiovascular diseases allows the non-invasive imaging associated with simultaneous therapeutic intervention and predicting treatment outcomes. Imaging may reflect the effectiveness of treatment and has become a fundamental optimisation setting for therapeutic protocol. Combining the application of biomolecular and cellular therapies with nanotechnologies foresees the development of complex integrated nanodevices. Nanocardiology may challenge existing healthcare system and economic benefits as cardiovascular diseases are the leading cause of morbidity and mortality at present.

Thiolate-protected nanoparticles via organic xanthates: mechanism and implications

The gold nanoparticles (AuNPs) stabilized with amine ligands are converted into robust thiolate-protected AuNPs in the presence of xanthates. This enables decoration of the AuNPs with a diversity of important functional groups, in particular, to introduce the thiol-sensitive unsaturated C-C bonds. The (1)H NMR study on the reaction mechanism provides a new insight into the great mystery of nanoscience-the fate of hydrogen upon the formation of the Au-S bond.

Inorganic nanoparticles based contrast agents for X-ray computed tomography

Nanomaterials have gained considerable attention and interest in the development of new and efficient molecular probes for medical diagnosis and imaging. Heavy metal nanoparticles as such are excellent absorber of X-rays and can offer excellent improvement in medical diagnosis and X-ray imaging. Substantial progress has been made in the synthesis protocol and characterization studies of these materials but a major challenge still lies in the toxicological studies, which are rather incomplete. The worst known cases were those associated with Thorotrast (suspension of ThO(2) nanoparticles) which resulted in many deaths over years. Properly protected nanomaterials conjugated or coated with biocompatible materials can be used for the fabrication of various functional systems with multimodality, targeting properties, reduced toxicity and proper removal from the body. This review aims mainly to provide the advances in the development of inorganic nanoparticle based X-ray contrasting agents with an overview of methods of their preparation, functionalization and applications in medical diagnosis.

Stabilization of nanoparticles under biological assembly conditions using peptoids

Sequence-specific polymers are proving to be a powerful approach to assembly and manipulation of matter on the nanometer scale. This has been most impressive in the case of DNA, and progress has been made toward templating inorganic nanoparticles using DNA nanostructures. One obstacle to this progress is that inorganic nanomaterials are often incompatible with DNA assembly conditions, which involve aqueous solutions high in either or both monovalent and divalent salt. Synthetic oligopeptide ligands have been shown by others to improve nanoparticle stability in high concentrations of monovalent salt. Ligands that are peptoids, or sequence-specific N-functional glycine oligomers, allow precise and flexible control over the arrangement of binding groups, steric spacers, charge, and other functionality. We have synthesized short peptoids that can prevent the aggregation of gold nanoparticles in high-salt environments including divalent salt, and allow coadsorption of a single DNA molecule. This degree of precision and versatility is likely to prove essential in bottom-up assembly of nanostructures and in biomedical applications of nanomaterials.