Functionalized Fe₃O₄@Au superparamagnetic nanoparticles: in vitro bioactivity

Gold Nanoparticles (AuNPs)-Toxicity, Safety and Green Synthesis: A Critical Review

In recent years, the extensive exploration of Gold Nanoparticles (AuNPs) has captivated the scientific community due to their versatile applications across various industries. With sizes typically ranging from 1 to 100 nm, AuNPs have emerged as promising entities for innovative technologies. This article comprehensively reviews recent advancements in AuNPs research, encompassing synthesis methodologies, diverse applications, and crucial insights into their toxicological profiles. Synthesis techniques for AuNPs span physical, chemical, and biological routes, focusing on eco-friendly "green synthesis" approaches. A critical examination of physical and chemical methods reveals their limitations, including high costs and the potential toxicity associated with using chemicals. Moreover, this article investigates the biosafety implications of AuNPs, shedding light on their potential toxic effects on cellular, tissue, and organ levels. By synthesizing key findings, this review underscores the pressing need for a thorough understanding of AuNPs toxicities, providing essential insights for safety assessment and advancing green toxicology principles.

Novel Organoid Culture System for Improved Safety Assessment of Nanomaterials

Over the past few decades, the increased application of nanomaterials has raised questions regarding their safety and possible toxic effects. Organoids have been suggested as promising tools, offering efficient assays for nanomaterial-induced toxicity evaluation. However, organoid systems have some limitations, such as size heterogeneity and poor penetration of nanoparticles because of the extracellular matrix, which is necessary for organoid culture. Here, we developed a novel system for the improved safety assessment of nanomaterials by establishing a 3D floating organoid paradigm. In addition to overcoming the limitations of two-dimensional systems including the lack of in vitro-in vivo cross-talk, our method provides multiple benefits as compared with conventional organoid systems that rely on an extracellular matrix for culture. Organoids cultured using our method exhibited relatively uniform sizing and structural integrity and were more conducive to the internalization of nanoparticles. Our floating culture system will accelerate the research and development of safe nanomaterials.

Oleic acid/oleylamine ligand pair: a versatile combination in the synthesis of colloidal nanoparticles

A variety of colloidal chemical approaches has been developed in the last few decades for the controlled synthesis of nanostructured materials in either water or organic solvents. Besides the precursors, the solvents, reducing agents, and the choice of surfactants are crucial for tuning the composition, morphology and other properties of the resulting nanoparticles. The ligands employed include thiols, amines, carboxylic acids, phosphines and phosphine oxides. Generally, adding a single ligand to the reaction mixture is not always adequate to yield the desired features. In this review, we discuss in detail the role of the oleic acid/oleylamine ligand pair in the chemical synthesis of nanoparticles. The combined use of these ligands belonging to two different categories of molecules aims to control the size and shape of nanoparticles and prevent their aggregation, not only during their synthesis but also after their dispersion in a carrier solvent. We show how the different binding strengths of these two molecules and their distinct binding modes on specific facets affect the reaction kinetics toward the production of nanostructures with tailored characteristics. Additional functions, such as the reducing function, are also noted, especially for oleylamine. Sometimes, the carboxylic acid will react with the alkylamine to form an acid-base complex, which may serve as a binary capping agent and reductant; however, its reducing capacity may range from lower to much lower than that of oleylamine. The types of nanoparticles synthesized in the simultaneous presence of oleic acid and oleylamine and discussed herein include metal oxides, metal chalcogenides, metals, bimetallic structures, perovskites, upconversion particles and rare earth-based materials. Diverse morphologies, ranging from spherical nanoparticles to anisotropic, core-shell and hetero-structured configurations are presented. Finally, the relation between tuning the resulting surface and volume nanoparticle properties and the relevant applications is highlighted.

A brief insight to the role of glyconanotechnology in modern day diagnostics and therapeutics

Carbohydrate-protein and carbohydrate-carbohydrate interactions are very important for various biological processes. Although the magnitude of these interactions is low compared to that of protein-protein interaction, the magnitude can be boosted by multivalent approach known as glycocluster effect. Nanoparticle platform is one of the best ways to present diverse glycoforms in multivalent manner and thus, the field of glyconanotechnology has emerged as an important field of research considering their potential applications in diagnostics and therapeutics. Considerable advances in the field have been achieved through development of novel techniques, use of diverse metallic and non-metallic cores for better efficacy and application of ever-increasing number of carbohydrate ligands for site-specific interaction. The present review encompasses the recent developments in the area of glyconanotechnology and their future promise as diagnostic and therapeutic tools.

Toxicity of gold nanoparticles (AuNPs): A review

Gold nanoparticles are a kind of nanomaterials that have received great interest in field of biomedicine due to their electrical, mechanical, thermal, chemical and optical properties. With these great potentials came the consequence of their interaction with biological tissues and molecules which presents the possibility of toxicity. This paper aims to consolidate and bring forward the studies performed that evaluate the toxicological aspect of AuNPs which were categorized into in vivo and in vitro studies. Both indicate to some extent oxidative damage to tissues and cell lines used in vivo and in vitro respectively with the liver, spleen and kidney most affected. The outcome of these review showed small controversy but however, the primary toxicity and its extent is collectively determined by the characteristics, preparations and physicochemical properties of the NPs. Some studies have shown that AuNPs are not toxic, though many other studies contradict this statement. In order to have a holistic inference, more studies are required that will focus on characterization of NPs and changes of physical properties before and after treatment with biological media. So also, they should incorporate controlled experiment which includes supernatant control Since most studies dwell on citrate or CTAB-capped AuNPs, there is the need to evaluate the toxicity and pharmacokinetics of functionalized AuNPs with their surface composition which in turn affects their toxicity. Functionalizing the NPs surface with more peculiar ligands would however help regulate and detoxify the uptake of these NPs.

Magnetic Nanodiscs-A New Promising Tool for Microsurgery of Malignant Neoplasms

Magnetomechanical therapy is one of the most perspective directions in tumor microsurgery. According to the analysis of recent publications, it can be concluded that a nanoscalpel could become an instrument sufficient for cancer microsurgery. It should possess the following properties: (1) nano- or microsized; (2) affinity and specificity to the targets on tumor cells; (3) remote control. This nano- or microscalpel should include at least two components: (1) a physical nanostructure (particle, disc, plates) with the ability to transform the magnetic moment to mechanical torque; (2) a ligand-a molecule (antibody, aptamer, etc.) allowing the scalpel precisely target tumor cells. Literature analysis revealed that the most suitable nanoscalpel structures are anisotropic, magnetic micro- or nanodiscs with high-saturation magnetization and the absence of remanence, facilitating scalpel remote control via the magnetic field. Additionally, anisotropy enhances the transmigration of the discs to the tumor. To date, four types of magnetic microdiscs have been used for tumor destruction: synthetic antiferromagnetic P-SAF (perpendicular) and SAF (in-plane), vortex Py, and three-layer non-magnetic-ferromagnet-non-magnetic systems with flat quasi-dipole magnetic structures. In the current review, we discuss the biological effects of magnetic discs, the mechanisms of action, and the toxicity in alternating or rotating magnetic fields in vitro and in vivo. Based on the experimental data presented in the literature, we conclude that the targeted and remotely controlled magnetic field nanoscalpel is an effective and safe instrument for cancer therapy or theranostics.

Magnetic Iron Nanocubes Effectively Capture Epithelial and Mesenchymal Cancer Cells

Current methods for capturing circulating tumor cells (CTCs) are based on the overexpression of cytokeratin (CK) or epithelial cell-adhesion molecule (EpCAM) on cancer cells. However, during the process of metastasis, tumor cells undergo epithelial-to-mesenchymal transition (EMT) that can lead to the loss of CK/EpCAM expression. Therefore, it is vital to develop a capturing technique independent of CK/EpCAM expression on the cancer cell. To develop this technique, it is important to identify common secondary oncogenic markers overexpressed on tumor cells before and after EMT. We analyzed the biomarker expression levels in tumor cells, before and after EMT, and found two common proteins-human epidermal growth factor receptor 2 (Her2) and epidermal growth factor receptor (EGFR) whose levels remained unaffected. So, we synthesized immunomagnetic iron nanocubes covalently conjugated with antibodies of Her2 or EGFR to capture cancer cells irrespective of the EMT status. The nanocubes showed high specificity (6-9-fold) in isolating the cancer cells of interest from a mixture of cells spiked in serum. We characterized the captured cells for identifying their EMT status. Thus, we believe the results presented here would help in the development of novel strategies for capturing both primary and metastatic cancer cells from patients' blood to develop an effective treatment plan.

Highly efficient and recyclable catalyst: porous Fe3O4-Au magnetic nanocomposites with tailored synthesis

In this work, we reported the tailored design of highly efficient Fe₃O₄-Au magnetic nanocomposite (MNP) catalysts. Fe₃O₄ nanocrystals with three different morphologies have been developed with engineered amounts of urea, and the plausible mechanism has been proposed. Then by controlling the amount of Au seeds, Fe₃O₄-Au MNPs with different morphologies and tunable Au deposition have been realized. Characterizations including x-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectra, and elemental mapping are implemented to unveil the structural and physical characteristics of the successfully developed Fe₃O₄-Au MNPs with different morphologies. The catalytic ability of Fe₃O₄-Au MNPs with different morphologies have been compared by applying them to degrading RhB and 4-NP, meanwhile the correlation between the amount of Au seeds and the turnover frequency as well as the catalytic ability of Fe₃O₄-Au MNPs is investigated systematically. We found that the flower-like Fe₃O₄-Au MNPs with 20 ml Au seeds added achieved the best degradation efficiency of 96.7%, and their catalytic ability were almost unchanged after recycling. Out study sheds the light into the tailored design of highly efficient and recyclable catalysts for RhB and 4-NP.

Simultaneous detection of TNOS and P35S in transgenic soybean based on magnetic bicolor fluorescent probes

A magnetic-separation-dual-targets fluorescent biosensor was fabricated to detect terminator nopaline synthase (TNOS) and promoter of cauliflower mosaic virus 35s (P35S) in transgenic soybean based on incorporation of bicolor CdTe quantum dots carried by silica nanospheres. In this protocol, the fixed probes for TNOS or P35S were magnetized firstly with Fe3O4@Au magnetic nanosphere by Au-S covalent bonding to achieve magnetized probes. Meanwhile, the capture probes for TNOS or P35S were functionalized with green or red fluorescent microspheres respectively to obtain fluorescently-labeled probes, which could emit relative strong green or red fluorescent signal. Two terminals of TNOS or P35S were recognized by magnetized probes and fluorescently-labeled probes respectively to form the sandwiched structures in the process of biosensor development subsequently, and it was separated by a magnet instantly. The fluorescence intensities of remnant supernatant were measured and analyzed accordingly to achieve simultaneous detection of TNOS and P35S. This biosensor exhibited a good dynamic range, low limit of detection and excellent selectivity in detecting transgenic soybean.

Multifunctional Magnetic Gold Nanomaterials for Cancer

The integration of multiple imaging and therapeutic agents into a customizable nanoplatform for accurate identification and rapid prevention of cancer is attracting great attention. Among the available theranostic nanosystems, magnetic gold nanoparticles are particularly promising as they exhibit unique physicochemical properties that can support multiple functions, including cancer diagnosis by magnetic resonance imaging, X-ray computed tomography, Raman and photoacoustic imaging, drug delivery, and plasmonic photothermal and photodynamic therapies. This review gives an overview of recent advances in the fabrication of multifunctional gold nanohybrids with magnetic and optical properties and their successful demonstration in multimodal imaging and therapy of cancer. Concerns around toxicity of these nanomaterials are also discussed in view of an imminent transition to clinical practice.

Mn-Doping level dependence on the magnetic response of MnxFe3−xO4 ferrite nanoparticles

Manganese/iron ferrite nanoparticles with different Mn^2+/3+ doping grades have been prepared by a thermal decomposition optimized approach so as to ascertain the doping effect on the magnetic hyperthermia response.

Polyaspartamide-based graft copolymers encapsulating iron oxide nanoparticles for imaging and fluorescence labelling of immune cells

Iron oxide nanoparticles (NPs) were encapsulated with polyaspartamide-based graft copolymers to bind and track the immune cells as imaging probes. Mono-disperse iron oxide NPs with a mean diameter of 10.7 nm were synthesized by the thermal decomposition method, and their shape and distribution were measured by electrophoretic light scattering and transmission electron microscopy. To enhance their biocompatibility, interfacial and hydrodynamic stability, and fluorescence detection, biodegradable polysuccinimide (PSI) grafted with several functional groups of octadecylamine (C18), ethanolamine (EA), ethylenediamine (EDA), 4-(N-maleimidomethyl) cyclohexane carboxylic acid N-hydroxysuccinimide ester (SMCC), and fluorescein isothiocyanate (FITC) was coated on the iron oxide NPs. The structure of the C18/EA/SMCC/FITC-g-PSI copolymer was confirmed using ¹H-NMR and FTIR spectroscopy, and its cell binding ability was investigated by flow cytometry and confocal laser scanning microscopy. The synthesized C18/EA/SMCC/FITC-g-PSI copolymer showed an excellent binding affinity to CD4+ T cells, and was highly biocompatible as the cell viability at the highest polymer concentration of 0.4 mg mL^-1 was greater than 85 and 75% after 24 and 48 h, respectively, from MTT assay.

Molecular Tools for Facilitative Carbohydrate Transporters (Gluts)

Facilitative carbohydrate transporters-Gluts-have received wide attention over decades due to their essential role in nutrient uptake and links with various metabolic disorders, including diabetes, obesity, and cancer. Endeavors directed towards understanding the mechanisms of Glut-mediated nutrient uptake have resulted in a multidisciplinary research field spanning protein chemistry, chemical biology, organic synthesis, crystallography, and biomolecular modeling. Gluts became attractive targets for cancer research and medicinal chemistry, leading to the development of new approaches to cancer diagnostics and providing avenues for cancer-targeting therapeutics. In this review, the current state of knowledge of the molecular interactions behind Glut-mediated sugar uptake, Glut-targeting probes, therapeutics, and inhibitors are discussed.

Block copolymer conjugated Au-coated Fe3O4 nanoparticles as vectors for enhancing colloidal stability and cellular uptake

BACKGROUND

Polymer surface-modified inorganic nanoparticles (NPs) provide a multifunctional platform for assisting gene delivery. Rational structure design for enhancing colloidal stability and cellular uptake is an important strategy in the development of safe and highly efficient gene vectors.

RESULTS

Heterogeneous Au-coated Fe3O4 (Fe3O4@Au) NPs capped by polyethylene glycol-b-poly1-(3-aminopropyl)-3-(2-methacryloyloxy propylimidazolium bromine) (PEG-b-PAMPImB-Fe3O4@Au) were prepared for DNA loading and magnetofection assays. The Au outer shell of the NPs is an effective platform for maintaining the superparamagnetism of Fe3O4 and for PEG-b-PAMPImB binding via Au-S covalent bonds. By forming an electrostatic complex with DNA at the inner PAMPImB shell, the magnetic nanoplexes offer steric protection from the outer corona PEG, thereby promoting high colloidal stability. Transfection efficiency assays in human esophageal cancer cells (EC109) show that the nanoplexes have high transfection efficiency at a short incubation time in the presence of an external magnetic field, due to increased cellular internalization via magnetic acceleration. Finally, after transfection with the magnetic nanoplexes EC109 cells acquire magnetic properties, thus allowing for selective separation of transfected cells.

CONCLUSION

Precisely engineered architectures based on neutral-cationic block copolymer-conjugated heterogeneous NPs provide a valuable strategy for improving the applicability and efficacy of synthesized vectors.

Development of magneto-plasmonic nanoparticles for multimodal image-guided therapy to the brain

Magneto-plasmonic nanoparticles are one of the emerging multi-functional materials in the field of nanomedicine. Their potential for targeting and multi-modal imaging is highly attractive. In this study, magnetic core/gold shell (MNP@Au) magneto-plasmonic nanoparticles were synthesized by citrate reduction of Au ions on magnetic nanoparticle seeds. Hydrodynamic size and optical properties of magneto-plasmonic nanoparticles synthesized with the variation of Au ions and reducing agent concentrations were evaluated. The synthesized magneto-plasmonic nanoparticles exhibited superparamagnetic properties, and their magnetic properties contributed to the concentration-dependent contrast in magnetic resonance imaging (MRI). The imaging contrast from the gold shell part of the magneto-plasmonic nanoparticles was also confirmed by X-ray computed tomography (CT). The transmigration study of the magneto-plasmonic nanoparticles using an in vitro blood-brain barrier (BBB) model proved enhanced transmigration efficiency without disrupting the integrity of the BBB, and showed potential to be used for brain diseases and neurological disorders.

Gold-nanoparticles coated with the antimicrobial peptide esculentin-1a(1-21)NH2 as a reliable strategy for antipseudomonal drugs

Naturally occurring antimicrobial peptides (AMPs) hold promise as future therapeutics against multidrug resistant microorganisms. Recently, we have discovered that a derivative of the frog skin AMP esculentin-1a, Esc(1-21), is highly potent against both free living and biofilm forms of the bacterial pathogen Pseudomonas aeruginosa. However, bringing AMPs into clinics requires to overcome their low stability, high toxicity and inefficient delivery to the target site at high concentrations. Importantly, peptide conjugation to gold nanoparticles (AuNPs), which are among the most applied inorganic nanocarriers in biomedical sciences, represents a valuable strategy to solve these problems. Here we report that covalent conjugation of Esc(1-21) to soluble AuNPs [AuNPs@Esc(1-21)] via a poly(ethylene glycol) linker increased by ∼15-fold the activity of the free peptide against the motile and sessile forms of P. aeruginosa without being toxic to human keratinocytes. Furthermore, AuNPs@Esc(1-21) resulted to be significantly more resistant to proteolytic digestion and to disintegrate the bacterial membrane at very low concentration (5nM). Finally, we demonstrated for the first time the capability of peptide-coated AuNPs to display a wound healing activity on a keratinocytes monolayer. Overall, these findings suggest that our engineered AuNPs can serve as attractive novel biological-derived material for topical treatment of epithelial infections and healing of the injured tissue.

STATEMENT OF SIGNIFICANCE

Despite conjugation of AMPs to AuNPs represents a worthwhile solution to face some limitations for their development as new therapeutics, only a very limited number of studies is available on peptide-coated AuNPs. Importantly, this is the first report showing that a covalent binding of a linear AMP via a poly(ethylene glycol) linker to AuNPs highly enhances antipseudomonal activity, preserving the same mode of action of the free peptide, without being harmful. Furthermore, AuNPs@Esc(1-21) are expected to accelerate recovery of an injured skin layer. All together, these findings suggest our peptide-coated AuNPs as attractive novel nanoscale formulation to treat bacterial infections and to heal the injured tissue.

Use of aerosol route to fabricate positively charged Au/Fe3O4 Janus nanoparticles as multifunctional nanoplatforms

Gold (Au)-decorated iron oxide (Fe₃O₄), Au/Fe₃O₄, Janus nanoparticles were fabricated via the continuous route for aerosol Au incorporation with Fe₃O₄ domains synthesized in an aqueous medium as multifunctional nanoplatforms. The fabricated nanoparticles were subsequently exposed to 185-nm UV light to generate positive charges on Au surfaces, and their activities were tested in computed tomography (CT) and magnetic resonance (MR) imaging, gene-delivery and photothermal therapy. No additional polymeric coatings of the Janus particles also had a unique ability to suppress inflammatory responses in macrophages challenged with lipopolysaccharide, which may be due to the absence of amine groups.

Recent advances in biosensing using magnetic glyconanoparticles

In this critical review we discuss the most recent advances in the field of biosensing applications of magnetic glyconanoparticles. We first give an overview of the main synthetic routes to obtain magnetic-nanoparticle-carbohydrate conjugates and then we highlight their most promising applications for magnetic relaxation switching sensing, cell and pathogen detection, cell targeting and magnetic resonance imaging. We end with a critical perspective of the field, identifying the main challenges to be overcome, but also the areas where the most promising developments are likely to happen in the coming decades.

Efficient synthesis of a maghemite/gold hybrid nanoparticle system as a magnetic carrier for the transport of platinum-based metallotherapeutics

The preparation and thorough characterization of a hybrid magnetic carrier system for the possible transport of activated platinum-based anticancer drugs, as demonstrated for cisplatin (cis-[Pt(NH₃)₂Cl₂], CDDP), are described. The final functionalized mag/Au–LA–CDDP* system consists of maghemite/gold nanoparticles (mag/Au) coated by lipoic acid (HLA; LA stands for deprotonated form of lipoic acid) and functionalized by activated cisplatin in the form of cis-[Pt(NH₃)₂(H₂O)₂]²⁺ (CDDP*). The relevant techniques (XPS, EDS, ICP-MS) proved the incorporation of the platinum-containing species on the surface of the studied hybrid system. HRTEM, TEM and SEM images showed the nanoparticles as spherical with an average size of 12 nm, while their superparamagnetic feature was proven by ⁵⁷Fe Mössbauer spectroscopy. In the case of mag/Au, mag/Au–HLA and mag/Au–LA–CDDP*, weaker magnetic interactions among the Fe³⁺ centers of maghemite, as compared to maghemite nanoparticles (mag), were detected, which can be associated with the non-covalent coating of the maghemite surface by gold. The pH and time-dependent stability of the mag/Au–LA–CDDP* system in different media, represented by acetate (pH 5.0), phosphate (pH 7.0) and carbonate (pH 9.0) buffers and connected with the release of the platinum-containing species, showed the ability of CDDP* to be released from the functionalized nanosystem.

Chelate-free metal ion binding and heat-induced radiolabeling of iron oxide nanoparticles

A novel reaction for chelate-free, heat-induced metal ion binding and radiolabeling of ultra-small paramagnetic iron oxide nanoparticles (USPIOs) has been established. Radiochemical and non-radioactive labeling studies demonstrated that the reaction has a wide chemical scope and is applicable to p-, d- and f-block metal ions with varying ionic sizes and formal oxidation states from 2+ to 4+. Radiolabeling studies found that 89Zr-Feraheme (89Zr-FH or 89Zr-ferumoxytol) can be isolated in 93 ± 3% radiochemical yield (RCY) and >98% radiochemical purity using size-exclusion chromatography. 89Zr-FH was found to be thermodynamically and kinetically stable in vitro using a series of ligand challenge and plasma stability tests, and in vivo using PET/CT imaging and biodistribution studies in mice. Remarkably, ICP-MS and radiochemistry experiments showed that the same reaction conditions used to produce 89Zr-FH can be employed with different radionuclides to yield 64Cu-FH (66 ± 6% RCY) and 111In-FH (91 ± 2% RCY). Electron magnetic resonance studies support a mechanism of binding involving metal ion association with the surface of the magnetite crystal core. Collectively, these data suggest that chelate-free labeling methods can be employed to facilitate clinical translation of a new class of multimodality PET/MRI radiotracers derived from metal-based nanoparticles. Further, this discovery is likely to have broader implications in drug delivery, metal separation science, ecotoxicology of nanoparticles and beyond.

Inorganic Janus particles for biomedical applications

Based on recent developments regarding the synthesis and design of Janus nanoparticles, they have attracted increased scientific interest due to their outstanding properties. There are several combinations of multicomponent hetero-nanostructures including either purely organic or inorganic, as well as composite organic-inorganic compounds. Janus particles are interconnected by solid state interfaces and, therefore, are distinguished by two physically or chemically distinct surfaces. They may be, for instance, hydrophilic on one side and hydrophobic on the other, thus, creating giant amphiphiles revealing the endeavor of self-assembly. Novel optical, electronic, magnetic, and superficial properties emerge in inorganic Janus particles from their dimensions and unique morphology at the nanoscale. As a result, inorganic Janus nanoparticles are highly versatile nanomaterials with great potential in different scientific and technological fields. In this paper, we highlight some advances in the synthesis of inorganic Janus nanoparticles, focusing on the heterogeneous nucleation technique and characteristics of the resulting high quality nanoparticles. The properties emphasized in this review range from the monodispersity and size-tunability and, therefore, precise control over size-dependent features, to the biomedical application as theranostic agents. Hence, we show their optical properties based on plasmonic resonance, the two-photon activity, the magnetic properties, as well as their biocompatibility and interaction with human blood serum.

Engineered magnetic nanoparticles for biomedical applications

In the past decades, magnetic nanoparticles (MNPs) have been used in wide range of diverse applications, ranging from separation to sensing. Here, synthesis and applications of functionalized MNPs in the biomedical field are discussed, in particular in drug delivery, imaging, and cancer therapy, highlighting also recent progresses in the development of multifunctional and stimuli-responsive MNPs. The role of their size, composition, and surface functionalization is analyzed, together with their biocompatibility issues.

Magnetism in nanoparticles: tuning properties with coatings

This paper reviews the effect of organic and inorganic coatings on magnetic nanoparticles. The ferromagnetic-like behaviour observed in nanoparticles constituted by materials which are non-magnetic in bulk is analysed for two cases: (a) Pd and Pt nanoparticles, formed by substances close to the onset of ferromagnetism, and (b) Au and ZnO nanoparticles, which were found to be surprisingly magnetic at the nanoscale when coated by organic surfactants. An overview of theories accounting for this unexpected magnetism, induced by the nanosize influence, is presented. In addition, the effect of coating magnetic nanoparticles with biocompatible metals, oxides or organic molecules is also reviewed, focusing on their applications.

Cu impedance-based detection of superparamagnetic nanoparticles

A novel method for superparamagnetic nanoparticle detection using copper impedance as the sensing property is presented. The increase of impedance produced by the proximity of the nanoparticles in the copper is comparable to that of classical magnetoimpeditive materials. A physical interpretation of the detection in terms of the induction of eddy currents in the copper element by the oscillating magnetic moments of the particles is proposed. Experimental research has been done to support this hypothesis, namely, analyses of the influence of the driving current frequency and amplitude, and of the geometry and size of the sensing conductor. The ability of copper to quantify the number of nanoparticles was successfully verified, evidencing the great potential of this new method.

Lysine-based surfactants in nanovesicle formulations: the role of cationic charge position and hydrophobicity in in vitro cytotoxicity and intracellular delivery

Understanding nanomaterial interactions within cells is of increasing importance for assessing their toxicity and cellular transport. Here, the authors developed nanovesicles containing bioactive cationic lysine-based amphiphiles and assessed whether these cationic compounds increase the likelihood of intracellular delivery and modulate toxicity. Different cytotoxic responses were found among the formulations, depending on surfactant, cell line and endpoint assayed. The induction of mitochondrial dysfunction, oxidative stress and apoptosis were the general mechanisms underlying cytotoxicity. Fluorescence microscopy analysis demonstrated that nanovesicles were internalised by HeLa cells and evidenced that their ability to release endocytosed materials into cell cytoplasm depends on the structural parameters of amphiphiles. The cationic charge position and hydrophobicity of surfactants determine the nanovesicle interactions within the cell and, thus, the resulting toxicity and intracellular behaviour after cell uptake of the nanomaterial. The insights into some toxicity mechanisms of these new nanomaterials contribute in reducing the uncertainty surrounding their potential health hazards.