Elena Bellido

Understanding the Colloidal Stability of the Mesoporous MIL-100(Fe) Nanoparticles in Physiological Media

The colloidal and chemical stability of nanoparticles of the nontoxic and biodegradable iron(III) trimesate MIL-100(Fe) nanocarrier have been evaluated in the presence of a series of simulated physiological fluids for intravenous and oral administration. MIL-100(Fe) nanoparticles exhibit an appropriate colloidal stability and biodegradability, mainly dependent on both the nature of their physicochemical surface and the media composition, being a priori compatible with their biomedical use.

Controlling the Number of Proteins with Dip‐Pen Nanolithography

This work was supported by projects MAT2009-13977-C03, Nanomateria-DGA, and PI091/08. D.M. thanks the Ministerio de Ciencia y Tecnologia for a RyC contract. A. L. thanks ARAID for financial support. R. de M. is indebted to MICINN for receiving a predoctoral FPU fellowship. Funding from the European Network of Excellence MAGMANet is also acknowledged.

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.

Nanoscale Positioning of Inorganic Nanoparticles using Biological Ferritin Arrays Fabricated by Dip-Pen Nanolithography

In this manuscript we demonstrate the spatially controlled immobilization of ferritin proteins by directly writing them on a wide range of substrates of technological interest. Optical and fluorescence microscopy, AFM and TOF-SIMS studies confirm the successful deposition of the protein on those surfaces. Control on nanostructure shape and size, by miniaturizing the dot-like features down to a 100 nm, demonstrates the particular capabilities of the DPN approach. Ultimately, this study gives the opportunity to design nanoparticle-based arrays regarding the growing interest in the use of nanoparticles as structural and functional elements for fabricating nanodevices. Herein, we demonstrate how the protein shell of ferritins can be removed by a simple heat-treatment process while maintaining the encapsulated inorganic nanoparticle intact on the same location of the nanoarray. As a result, this study establishes how direct-write DPN approach could give the opportunity to design not only protein-based nanoarrays but also nanoparticle-based nanoarrays with high-resolution and control.

Alternating current magnetic susceptibility of a molecular magnet submonolayer directly patterned onto a micro superconducting quantum interference device

We report the controlled integration, via Dip Pen Nanolithography, of monolayer dots of ferritin-based CoO nanoparticles (12 Bohr magnetons) into the most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling between these nanomagnets and the microSQUID improves the achievable sensitivity by a factor 100, enabling us to measure the linear susceptibility of the molecular array down to very low temperatures (13 mK). This method opens the possibility of applying ac susceptibility experiments to characterize two-dimensional arrays of single molecule magnets within a wide range of temperatures and frequencies.We report the controlled integration, via dip pen nanolithography, of monolayer dots of ferritin-based CoO nanoparticles (12 μB) into the most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling between these nanomagnets and the microSQUID improves the achievable sensitivity by a factor 102, enabling us to measure the linear susceptibility of the molecular array down to very low temperatures (13 mK). This method opens the possibility of applying ac susceptibility experiments to characterize two-dimensional arrays of single molecule magnets within a wide range of temperatures and frequencies.

Synthesis of Nanoscale Coordination Polymers in Femtoliter Reactors on Surfaces

In the present work, AFM-assisted lithography was used to perform the synthesis of a coordination polymer inside femtoliter droplets deposited on surfaces. For this, solutions of the metal salt and the organic ligand were independently transferred to adjacent tips of the same AFM probe array and were sequentially delivered on the same position of the surface, creating femtoliter-sized reaction vessels where the coordination reaction and particle growth occurred. Alternatively, the two reagents were mixed in the cantilever array by loading an excess of the inks, and transferred to the surface immediately after, before the precipitation of the coordination polymer took place. The in situ synthesis allowed the reproducible obtaining of round-shaped coordination polymer nanostructures with control over their XY positioning on the surface, as characterized by microscopy and spectroscopy techniques.

Robust spin crossover platforms with synchronized spin switch and polymer phase transition

The idea of developing magnetic molecular materials into real functional electronic devices with low-cost and scalable techniques appeared with the emergence of the field several years ago. Today, even though great advances have been done with this aim, the promise of a functional device working at the micro-/nanoscale and at room temperature has unfortunately not completely materialized yet, as their use still strongly depends on the fabrication methodology of a robust device that can be handled and integrated without compromising their functionality. Here we propose the use of polymeric matrices as a platform for the development of such robust switchable structures exhibiting reproducible results independently of the dimension -from macro to micro-/nanoscale- and morphology -from thin-films to nanoparticles and nanoimprinted motives- while allowing to induce an irreversible hysteresis, reminiscent of a non-volatile memory, by synchronization with the polymer phase transition.

Controlled Positioning of Nanoparticles on Graphene by Noninvasive AFM Lithography

Atomic force microscopy is shown to be an excellent lithographic technique to directly deposit nanoparticles on graphene by capillary transport without any previous functionalization of neither the nanoparticles nor the graphene surface while preserving its integrity and conductivity properties. Moreover this technique allows for (sub)micrometric control on the positioning thanks to a new three-step protocol that has been designed with this aim. With this methodology the exact target coordinates are registered by scanning the tip over the predetermined area previous to its coating with the ink and deposition. As a proof-of-concept, this strategy has successfully allowed the controlled deposition of few nanoparticles on 1 μm(2) preselected sites of a graphene surface with high accuracy.

Ultrasensitive Broad Band SQUID Microsusceptometer for Magnetic Measurements at Very Low Temperatures

In this work we report the development and calibration of an ultrasensitive SQUID susceptometer capable of operating over an extremely wide frequency range (0.001 Hz-1 MHz) at extremely low temperatures (13 mK). Starting with 2-stage SQUID sensors fabricated at PTB-Berlin, an integrated susceptometer with experimental spin sensitivity of 104 Bohr magneton/Hz1/2 is obtained by rerouting some SQUID input circuit connections. Modification of the chips is carried out using Focused Ion Beam Induced Deposition (FIBID) of amorphous W, using W(CO)6 as precursor gas. We have demonstrated that superconducting connections between W FIBID lines and Nb films can be fabricated and that they operate at 4.2 K, providing a powerful technique for fixing errors in device designs, repairing damaged circuits, or modifying existing ones. The microsusceptometer offers new possibilities in the study of thin films or even monolayers of nanosized magnets, and has potential applications in diverse fields such as quantum computing, high-density information storage or on-chip magnetic refrigeration.

Quantification of the cellular dose and characterization of nanoparticle transport during in vitro testing

The constant increase of the use of nanomaterials in consumer products is making increasingly urgent that standardized and reliable in vitro test methods for toxicity screening be made available to the scientific community. For this purpose, the determination of the cellular dose, i.e. the amount of nanomaterials effectively in contact with the cells is fundamental for a trustworthy determination of nanomaterial dose responses. This has often been overlooked in the literature making it difficult to undertake a comparison of datasets from different studies. Characterization of the mechanisms involved in nanomaterial transport and the determination of the cellular dose is essential for the development of predictive numerical models and reliable in vitro screening methods. This work aims to relate key physico-chemical properties of gold nanoparticles (NPs) to the kinetics of their deposition on the cellular monolayer. Firstly, an extensive characterization of NPs in complete culture cell medium was performed to determine the diameter and the apparent mass density of the formed NP-serum protein complexes. Subsequently, the kinetics of deposition were studied by UV-vis absorbance measurements in the presence or absence of cells. The fraction of NPs deposited on the cellular layer was found to be highly dependent on NP size and apparent density because these two parameters influence the NP transport. The NP deposition occurred in two phases: phase 1, which consists of cellular uptake driven by the NP-cell affinity, and phase 2 consisting mainly of NP deposition onto the cellular membrane. The fraction of deposited NPs is very different from the initial concentration applied in the in vitro assay, and is highly dependent of the size and density of the NPs, on the associated transport rate and on the exposure duration. This study shows that an accurate characterization is needed and suitable experimental conditions such as initial concentration of NPs and liquid height in the wells has to be considered since they strongly influence the cellular dose and the nature of interactions of NPs with the cells.BackgroundThe constant increase of the use of nanomaterials in consumer products is making increasingly urgent that standardized and reliable in vitro test methods for toxicity screening be made available to the scientific community. For this purpose, the determination of the cellular dose, i.e. the amount of nanomaterials effectively in contact with the cells is fundamental for a trustworthy determination of nanomaterial dose responses. This has often been overlooked in the literature making it difficult to undertake a comparison of datasets from different studies. Characterization of the mechanisms involved in nanomaterial transport and the determination of the cellular dose is essential for the development of predictive numerical models and reliable in vitro screening methods.ResultsThis work aims to relate key physico-chemical properties of gold nanoparticles (NPs) to the kinetics of their deposition on the cellular monolayer. Firstly, an extensive characterization of NPs in complete culture cell medium was performed to determine the diameter and the apparent mass density of the formed NP-serum protein complexes. Subsequently, the kinetics of deposition were studied by UV-vis absorbance measurements in the presence or absence of cells. The fraction of NPs deposited on the cellular layer was found to be highly dependent on NP size and apparent density because these two parameters influence the NP transport. The NP deposition occurred in two phases: phase 1, which consists of cellular uptake driven by the NP-cell affinity, and phase 2 consisting mainly of NP deposition onto the cellular membrane.ConclusionThe fraction of deposited NPs is very different from the initial concentration applied in the in vitro assay, and is highly dependent of the size and density of the NPs, on the associated transport rate and on the exposure duration. This study shows that an accurate characterization is needed and suitable experimental conditions such as initial concentration of NPs and liquid height in the wells has to be considered since they strongly influence the cellular dose and the nature of interactions of NPs with the cells.