Isaac Ojea-Jiménez

Synthesis of Platinum Cubes, Polypods, Cuboctahedrons, and Raspberries Assisted by Cobalt Nanocrystals

The introduction of metallic traces into the synthesis of platinum nanocrystals (Pt NCs) has been investigated as a surfactant-independent means of controlling shape. Various nanocrystal morphologies have been produced without modification of the reaction conditions, composition, and concentration other than the presence of cobalt traces (<5%). In the presence of metallic cobalt (a strong reducer for Pt cations) cubic Pt NCs are obtained, while cobalt ions or gold NCs have no effect on the synthesis, and as a result, polypods are obtained. Intermediate shapes such as cemented cubes or cuboctahedron NCs are also obtained under similar conditions. Thus, various NC shapes can be obtained with subtle changes, which illustrates the high susceptibility and mutability of the NC shape to modification of the reaction kinetics during the early reduction process. Our studies help progress toward a general mechanism for nanocrystal shape control.

Citrate-coated gold nanoparticles as smart scavengers for mercury(II) removal from polluted waters.

Colloidal gold nanoparticles (Au NPs) have been employed as single entities for rapid scanning and sequestration of Hg(II) from multicomponent aqueous solutions containing low pollutant concentrations. Under the studied conditions, sodium citrate has been identified as the reducing agent and Au NPs as the catalyst in the reduction of Hg(II), which is efficiently trapped in the presence of other cations such as Cu(II) and Fe(III). The effect of Hg(II) uptake implies amalgam formation, which leads to remarkable morphological transformations. The hydrophobicity of the resulting amalgam and consequent expulsion from water eases its recovery. The interaction between Au and Hg has been studied using UV-vis, ICP-MS, (S)TEM, SEM, EDX, and XRD.

Engineered Inorganic Nanoparticles for Drug Delivery Applications

Inorganic nanoparticles (NPs) currently have immense potential as drug delivery vectors due to their unique physicochemical properties such as high surface area per unit volume, their optical and magnetic uniqueness and the ability to be functionalized with a large number of ligands to enhance their affinity towards target molecules. These features, together with the therapeutic activity of some drugs, render the combination of these two entities (NP-drug) as an attractive alternative in the area of drug delivery. One of the major advantages of these conjugates is the possibility to have a local delivery of the drug, thus reducing systemic side effects and enabling a higher efficiency of the therapeutic molecule. This review highlights the direct implications of nanoscale particles in the development of drug delivery systems. In more detail, it is also remarked the extensive use of inorganic NPs for targeted cancer therapies. As the range of nanoparticles and their applications continues to increase, human safety concerns are gaining importance, which makes it necessary to better understand the potential toxicity hazards of these materials.

Detection, quantification and derivation of number size distribution of silver nanoparticles in antimicrobial consumer products

In 2011 the European Commission published its recommendation for a definition for the term nanomaterial which requires the materials to be characterized in terms of the number size distribution of their constituent particles. More recently, the definition has begun to be applied to the labelling of food and cosmetic products where any components present in the form of engineered nanomaterials must now be clearly indicated in the list of ingredients. The implementation of this definition requires that methods be developed and validated to accurately size particles with at least one external dimension in the range of 1–100 nm, and to quantify them on a ‘number-based’ particle size distribution. An in-house developed method based on Asymmetric Flow Field Flow Fractionation-Inductively Coupled Plasma Mass Spectrometry (AF4-ICP-MS) for the simultaneous detection and quantification of citrate-stabilised silver nanoparticles (AgNPs) in water, has been applied to real-world liquid antimicrobial consumer products based on colloidal silver. This transfer of the method from ideal model systems to real products was assessed in light of other techniques including Centrifugal Liquid Sedimentation (CLS), Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM). Five out of six analysed products were found to contain AgNPs in the nano-range by means of a number of techniques including AF4-ICP-MS. Comparative analysis shows that CLS has sufficient size resolution to size AgNPs in the consumer products while DLS was unsuccessful probably due to sample polydispersivity. Despite the silver nanoparticles having unknown surface properties and stabilisation agents which could have influenced the sizing with AF4, a relatively good agreement between TEM and AF4-ICP-MS was observed. The AF4-ICP-MS data could be converted from mass-based to number-based distributions; this transformation, despite the possibility of experimental artefacts being mathematically amplified, has shown promising results.

Simultaneous Determination of Size and Quantification of Silica Nanoparticles by Asymmetric Flow Field-Flow Fractionation Coupled to ICPMS Using Silica Nanoparticles Standards

This work proposes the use of multimodal mixtures of monodispersed silica nanoparticles (SiO2-NPs) standards for the simultaneous determination of size and concentration of SiO2-NPs in aqueous suspensions by asymmetric flow field-flow fractionation (AF4) coupled to inductively coupled plasma mass spectrometry (ICPMS). For such a purpose, suspensions of SiO2-NPs standards of 20, 40, 60, 80, 100, and 150 nm were characterized by transmission electronic microscopy (TEM), centrifugal liquid sedimentation (CLS), dynamic light scattering (DLS) and by measuring the Z-potential of the particles as well as the exact concentration of NPs by offline ICPMS. An online AF4-ICPMS method which allowed the separation of all the different sized SiO2-NPs contained in the mixture of standards was developed and the analytical figures of merit were systematically evaluated. The method showed excellent linearity in the studied concentration range (0.1-25 mg L(-1)), limits of detection between 0.16 and 0.3 mg L(-1) for smaller and greater particles, respectively, besides a satisfactory accuracy. AF4 calibration with particles with identical nature to those to be analyzed, also permitted accurate size determination in a pragmatic way. Similarly, by using prechannel calibration with NPs for mass determination it was possible to overcome common quantification problems associated with losses of material during the separation and size-dependent effects. The proposed methodology was successfully applied to the characterization in terms of size and concentration of aqueous test samples containing SiO2-NPs with monomodal size distributions.

Engineered nonviral nanocarriers for intracellular gene delivery applications

The efficient delivery of nucleic acids into mammalian cells is a central aspect of cell biology and of medical applications, including cancer therapy and tissue engineering. Non-viral chemical methods have been received with great interest for transfecting cells. However, further development of nanocarriers that are biocompatible, efficient and suitable for clinical applications is still required. In this paper, the different material platforms for gene delivery are comparatively addressed, and the mechanisms of interaction with biological systems are discussed carefully.

Structuration and integration of magnetic nanoparticles on surfaces and devices

Different experimental approaches used for structuration of magnetic nanoparticles on surfaces are reviewed. Nanoparticles tend to organize on surfaces through self-assembly mechanisms controlled by non-covalent interactions which are modulated by their shape, size and morphology as well as by other external parameters such as the nature of the solvent or the capping layer. Further control on the structuration can be achieved by the use of external magnetic fields or other structuring techniques, mainly lithographic or atomic force microscopy (AFM)-based techniques. Moreover, results can be improved by chemical functionalization or the use of biological templates. Chemical functionalization of the nanoparticles and/or the surface ensures a proper stability as well as control of the formation of a (sub)monolayer. On the other hand, the use of biological templates facilitates the structuration of several families of nanoparticles, which otherwise may be difficult to form, simply by establishing the experimental conditions required for the structuration of the organic capsule. All these experimental efforts are directed ultimately to the integration of magnetic nanoparticles in sensors which constitute the future generation of hybrid magnetic devices.

Pt nanocrystal evolution in the presence of Au(III)-salts at room temperature: spontaneous formation of AuPt heterodimers

Room temperature synthesis of AuPt heterodimers is reported using a simple protocol. The role of oleylamine and Pt NCs in the reduction and nucleation of Au has been investigated. There are two unique aspects in this synthesis. Firstly, the synthesis was conducted at room temperature, which enabled the heterodimer growth to progress at a slower rate and thus allowed monitoring of the Au nucleation process. Secondly, these conditions allowed epitaxial growth with no crystal modification at the Au–Pt interphase. The presence of Pt NC seeds markedly accelerated the reaction, serving both as nucleation platforms and as an initial catalytic reducer of the Au ions in solution. The growth of Au on Pt NCs was monitored at different times by UV-vis, HRTEM and XRD.

Changes in Caco-2 cells transcriptome profiles upon exposure to gold nanoparticles

Higher efficacy and safety of nano gold therapeutics require examination of cellular responses to gold nanoparticles (AuNPs). In this work we compared cellular uptake, cytotoxicity and RNA expression patterns induced in Caco-2 cells exposed to AuNP (5 and 30nm). Cellular internalization was dose and time-dependent for both AuNPs. The toxicity was observed by colony forming efficiency (CFE) and not by Trypan blue assay, and exclusively for 5nm AuNPs, starting at the concentration of 200μM (24 and 72h of exposure). The most pronounced changes in gene expression (Agilent microarrays) were detected at 72h (300μM) of exposure to AuNPs (5nm). The biological processes affected by smaller AuNPs were: RNA/zinc ion/transition metal ion binding (decreased), cadmium/copper ion binding and glutathione metabolism (increased). Some Nrf2 responsive genes (several metallothioneins, HMOX, G6PD, OSGIN1 and GPX2) were highly up regulated. Members of the selenoproteins were also differentially expressed. Our findings indicate that exposure to high concentration of AuNPs (5nm) induces metal exposure, oxidative stress signaling pathways, and might influence selenium homeostasis. Some of detected cellular responses might be explored as potential enhancers of anti-cancer properties of AuNPs based nanomedicines.

Biocompatible polydopamine-like particles for the removal of heavy metals at extremely low concentrations

A family of catechol-based submicron particles, with sizes between 200 and 300 nm, was tested for the removal of Cd(II), Pb(II) and Cr(VI) in water. The highest adsorption capacity was obtained with catecholbased particles in the case of Pb(II), followed by Cd(II). However, the catechol particles failed to adsorb Cr(VI). Our results indicate an up to four-fold increase of the adsorption capacity of these particles compared to that of activated carbon under the same experimental conditions. To check the biocompatible character of the submicron particles, their stability was evaluated in a phosphate buffer solution (PBS) and in a cell culture medium. The results confirmed that the presence of proteins in the medium favors their stability. A bioluminescent Vibrio fischeri test and a cytotoxicity assay on the HepG2 cell line were used to determine that the catechol particles did not exhibit any substantial toxicity. The results show that these catechol-based particles can be used as an efficient biocompatible adsorbent to remove heavy metals at extremely low concentrations.