Iole Venditti

How toxic are gold nanoparticles? The state-of-the-art

With the growing interest in the applications of gold nanoparticles in biotechnology and their physiological effects, possible toxicity of gold nanoparticles is becoming an increasingly important issue. A large number of studies carried out over the past few years under a variety of experimental conditions and following different protocols have produced conflicting results, leading to divergent views about the actual safety of gold nanoparticles in human applications.This work is intended to provide an overview of the most recent experimental results and thereby summarize current state-of-the-art. Rather than presenting a comprehensive review of the available literature in this field, which would be impractically broad, we have selected representative examples of both in vivo and in vitro studies, which clearly demonstrate the need for urgent and rigorous standardization of experimental protocols. Despite their significant potential, the safety of gold nanoparticles is highly controversial at this time, and important concerns have been raised that need to be properly addressed. Factors such as shape, size, surface charge, coating, and surface functionalization are expected to influence the interactions of particles with biological systems to a different extent, resulting in different outcomes and influencing the potential of gold nanoparticles for biomedical applications.Moreover, despite continuous attempts to establish a correlation between structure of the particles and their interactions with biological systems, we are still far from elucidating the toxicological profile of gold nanoparticles in an indisputable manner. This review is intended to contribute towards this goal, offering a number of suggestions on how to achieve the systematization of data on the most relevant physico-chemical parameters, which govern and control the toxicity of gold nanoparticles at cellular and whole-organism levels.

Osmosis based method drives the self-assembly of polymeric chains into micro-and nanostructures

Polymers derived from monomers with a variety of functionalities provide materials with a vast range of properties and applications. Worldwide research has recently developed a wide number of methods suitable for the preparation of polymeric materials of nanometric dimensions, in view of the fact that, at the nanoscale level, new and unexpected properties emerge and lead to innovative applications. In this framework, we have exploited an easy method for the generation of nanostructures, regardless of the chemical structure of the pristine amorphous polymers, that is, biopolymers (e.g., polysaccharides) and synthetic, functional, and structural polymers (i.e, polystyrene, polymethylmethacrylates, polyacetylenes, and polymetallaynes). The nanostructure of these macromolecules, considered as the prototypes of various classes of polymeric materials, was achieved by using a simple and versatile procedure based on an osmotic method (OBM). Depending on the choice of solvent/nonsolvent pairs, the dialysis membrane molecular weight cutoff (MWCO), temperature, and polymer concentration, different morphologies can be obtained (e.g., spheres, sponges, disks, and fibers); also, a tuning of the nanoparticle dimensions ranging from the micro- to nanoscale has been obtained.

Gold nanoparticles and gold nanoparticle-conjugates for delivery of therapeutic molecules. Progress and challenges

This article reviews the most recent literature data on the applications of gold nanoparticles and their various conjugates which make them suitable structures towards biomedical and clinical purposes, with an emphasis on their use as drug delivery vehicles for selective targeting of cancer cells. With the rapid surge in the development of nanomaterials, new methodologies and treatment strategies have been explored and these topics should be taken into consideration when a current scenario is required in the design of new experimental approaches or in a comprehensive data interpretation. We present here a summary of the main properties of gold nanoparticles and their conjugates and the state-of-the-art of non-conventional treatment in targeted drug delivery based on gold nanoparticles as carriers, with the aim to give the reader an overview of the most significant advances in this field.

Functionalized gold nanoparticles for topical delivery of methotrexate for the possible treatment of psoriasis.

Gold nanoparticles (AuNPs) represent an effective choice for topical drug delivery systems thanks to their small size, general non-toxicity, ease of functionalization and high surface to volume ratio. Even if systemic, methotrexate still plays an important role in psoriasis treatment: its topical use shows insufficient percutaneus penetration owing to limited passive diffusion, high molecular weight and dissociation at physiological pH. The aim of our study was to design a new drug delivery nanocarrier for Methotrexate and to improve its solubility, stability and biodistribution. AuNPs were on purpose prepared with a hydrophilic stabilizing layer, in order to improve the colloidal stability in water. Water-soluble gold nanoparticles functionalized by sodium 3-mercapto-1-propansulfonate (Au-3MPS) were prepared and loaded with methotrexate (MTX). The loading efficiency of MTX on Au-3MPS was assessed in the range 70-80%, with a fast release (80% in one hour). The release was studied up to 24h reaching the value of 95%. The Au-3MPS@MTX conjugate was fully characterized by spectroscopic techniques (UV-vis, FTIR) and DLS. Preliminary toxicity tests in the presence of keratinocytes monolayers allowed to assess that the used Au-3MPS are not toxic. The conjugate was then topically used on C57BL/6 mouse normal skin in order to trace the absorption behavior. STEM images clearly revealed the distribution of gold nanoparticles inside the cells. In vitro studies showed that Methotrexate conjugated with Au-3MPS is much more efficient than Methotrexate alone. Moreover, DL50, based on MTT analysis, is 20 folds reduced at 48 h, by the presence of nanoparticles conjugation. UV-vis spectra for in vivo tracing of the conjugate on bare mouse skin after 24h of application, show increased delivery of Methotrexate in the epidermis and dermis using Au-3MPS@MTX conjugate, compared to MTX alone. Moreover we observed absence of the Au-3MPS in the dermis and in the epidermis, suggesting that these layers of the skin do not retain the nanoparticles. Based on our data, we found that the novel Au-3MPS@MTX conjugate is an effective non-toxic carrier for the satisfactory percutaneous absorption of Methotrexate and could help in possible topical treatment of psoriasis.

Direct interaction of hydrophilic gold nanoparticles with dexamethasone drug: Loading and release study

Water-soluble gold nanoparticles functionalized by sodium 3-mercapto-1-propansulfonate (Au-3MPS) were synthesized with different Au/thiol molar ratios for their ability to interact with biomolecules. In particular, a synthetic glucocorticoid steroid, i.e. dexamethasone (DXM) was selected. Herein, the formation of the Au-3MPS/DXM bioconjugate is reported. Au-3MPS nanoparticles show a plasmon resonance at 520 nm, have a spherical morphology and average size of 7-10 nm. The total number of gold atoms was estimated to be about 10600, with a surface component of 8800 atoms and a number of thiol ligands of about 720, roughly one anchored thiol every 10 surface gold atoms. The drug-nanoparticle interaction occurs through the fluorine atom of DXM and Au(I) atoms on the gold nanoparticle surface. The 3MPS ligands closely pack apart each other to leave room for the DXM, that lies at the gold surface in an unusual, almost parallel feature. The loading efficiency of DXM on Au-3MPS was assessed in the range 70-80%, depending on the thiol content. Moreover, our studies confirmed the drug release of about 70% in 5 days. Thanks to their unique properties, i.e. high water solubility, small size and almost monodispersity, Au-3MPS display high potential in biotechnological and biomedical applications, mainly for the loading and release of water insoluble drugs.

Core shell hybrids based on noble metal nanoparticles and conjugated polymers: synthesis and characterization.

Noble metal nanoparticles of different sizes and shapes combined with conjugated functional polymers give rise to advanced core shell hybrids with interesting physical characteristics and potential applications in sensors or cancer therapy. In this paper, a versatile and facile synthesis of core shell systems based on noble metal nanoparticles (AuNPs, AgNPs, PtNPs), coated by copolymers belonging to the class of substituted polyacetylenes has been developed. The polymeric shells containing functionalities such as phenyl, ammonium, or thiol pending groups have been chosen in order to tune hydrophilic and hydrophobic properties and solubility of the target core shell hybrids. The Au, Ag, or Pt nanoparticles coated by poly(dimethylpropargylamonium chloride), or poly(phenylacetylene-co-allylmercaptan). The chemical structure of polymeric shell, size and size distribution and optical properties of hybrids have been assessed. The mean diameter of the metal core has been measured (about 10-30 nm) with polymeric shell of about 2 nm.

Candida rugosa lipase immobilization on hydrophilic charged gold nanoparticles as promising biocatalysts: Activity and stability investigations.

In this work, a simple and versatile methodology to obtain two different bioconjugated systems has been developed by the immobilization of Candida rugosa lipase (CRL) on hydrophilic gold nanoparticles functionalized with 2-diethylaminoethanethiol hydrochloride (DEA) or with sodium 3-mercapto-1-propanesulfonate (3MPS), namely Au-DEA@CRL and Au-3MPS@CRL. Both spectroscopic and morphological properties of metal nanoparticles have been deeply investigated. The enzyme loading and lipolytic activity of AuNPs@CRL bioconjugates have been studied with respect to different surface functionalization and compared with the free enzyme. Some physical and chemical parameters had a strong effect on enzyme activity and stability, that were improved in the case of the Au-DEA@CRL bioconjugate, which showed a remarkable biocatalytic performance (95% of residual lipolytic activity compared with free CRL) and stability in experimental conditions concerning pH (range 5-8) and temperature (range 20-60°C), as often required for the industrial scale up of catalytic systems.

Dielectric relaxations of ionic thiol-coated noble metal nanoparticles in aqueous solutions: Electrical characterization of the interface

The radiowave dielectric properties of organothiol monolayer-protected Au and Ag metallic nanoparticles have been investigated in the frequency range of 10 kHz to 2 GHz, where a dielectric relaxation, due to the polarization of the ionic atmosphere at the aqueous interface, occurs. The simultaneous measurement of the particle size, by means of dynamic light scattering technique, and of the particle electrical charge, by means of laser microelectrophoresis technique, allow us to describe the whole dielectric behavior at the light of the standard electrokinetic model for charged colloidal particles. Au and Ag metallic nanoparticles experience a large charge renormalization, in agreement with the counterion condensation effect for charged spherical colloidal particles. The value of the effective valence Z(eff) of each nanoparticle investigated has been evaluated thanks to the dielectric parameters of the observed relaxation process and further confirmed by direct current electrical conductivity measurements. All in all, these results provide support for the characterization of the electrical interfacial properties of metallic nanoparticles by means of dielectric relaxation measurements.

Self-assembled nanoparticles of functional copolymers for photonic applications

A modified emulsion copolymerization of phenylacetylene (PA) with hydrophilic monomers having different functions, i.e., acrylic acid (AA) and N,N-dimethylpropargylamine (DMPA) respectively, yields functionalized polymeric P(PA-co-AA) and P(PA-co-DMPA) nanoparticles. The systematic investigation on the experimental parameters affecting size, surface charge and polydispersity of the copolymers (initiator concentration, reaction time, cosolvent and PA/comonomer ratios) allows to modulate the nanoparticle physico-chemical properties. Spherical shaped particles with diameters in the range 80-500 nm, low polydispersity (PI values in the range 1.11-1.30) and different surface charge densities, between 0.44 and 2.87 microC/cm(2), have been consistently obtained and characterized by means of Dynamic Light Scattering (DLS), laser Doppler electrophoretic and Scanning Electron Microscopy (SEM) studies. XPS measurements have provided information on the nanoparticles chemical surface structure and suggest that AA and DMPA units are preferentially distributed on the surface of the spheres. The nanospheres self-assemble giving large domains (9.5 x 14.5 microm). Photonic analysis of the self-assembled copolymeric nanoparticles has been performed by means of Spectroscopic Ellipsometry (SE) and Bragg reflection spectroscopy, both of them demonstrating a three-dimensional photonic crystal property of these systems.

Functional polymeric nanoparticles for dexamethasone loading and release.

Poly(phenylacetylene) (PPA) and poly(phenylacetylene-co-acrylic acid) (P(PA-co-AA)), nanoparticles bioconjugated with dexamethasone (DXM) during the synthesis, named PPA@DXM and P(PA-co-AA)@DXM, were prepared by a modified surfactant free emulsion method. The loading was studied as a function of different functionality grades of the copolymer and different amounts of drug, obtaining up to 90% of drug loading for P(PA-co-AA)@DXM with 8/1 PA/AA monomer ratio. The SEM images and DLS measurements showed spheres with average diameters in the range 190-500 nm, depending on the content of acrylic acid monomer units in the copolymer and of DXM loading. ζ-potential and surface charge density of DXM loaded nanoparticles were also investigated and confirm the charge density modulation in the range 0.62-2.68σ (μC/m(2)). The results highlight the enhanced capability of our copolymer of hosting DXM, with the advantage of a control of size, surface functionality, charge and release. Moreover we demonstrate for the first time the ability of P(PA-co-AA) DXM loaded nanoparticles to be used in the apoptosis inhibition of human tumor cells (HeLa). On the basis of the results obtained by comparing the effects elicited in HeLa cells by free DXM versus DXM loaded nanoparticles we confirmed the biological efficacy of our preparation.