2) Nanoparticles and Magnetic Nanostructures

Figure. Dependence of the fraction of surface atoms (called also dispersion, F) increases steeply for very small particles, and, the properties of the surface atoms have a large contribution to the whole particle properties. (Yolanda Piñeiro Redondo, M. Arturo López-Quintela, and José Rivas Chapter 4. The emergence of quantum confinement in atomic quantum clusters In, Colloidal Foundations of Nanoscience, Edited by D. Berti and G. Palazzo , Elsevier, 2014.)

Nanoparticles with a sizes below to 100 nm, have a large ratio of surface-to-volume atoms with different electronic profiles depending on their coordination to the core structure , that dominate the response of the system. Nanoscale is therefore characterized by deviation of properties from the macroscopic behaviour (melting point, optical transition properties, ionisation potentials, hardness, catalytic activity, etc) and emergence of newly ones as surface plasmon band resonance, superparamagnetism or magnetization tunnelling, etc. Therefore size and morphology are fundamental design parameters in the development of NPs with tailored properties.

In this research area, our group is mainly focused on the synthesis, physicochemical study, development and design of nanoparticles and hybrid nanostructures based on different types of materials. The versatility of the nanomaterials, which are the building blocks of much more complex nanostructures with tailored multimodal performance, opens the door to the design of different biomedical and environmental applications. Our studies involve the following research lines:

1) Magnetic nanomaterials (iron/transition metal oxides) with controlled size, morphology , composition and magnetic properties:

Figure. Hollow Fe3O4 spheres

Figure. Fe@Fe3O4 spheres

Figure. Fe3O4 nanocubes

Figure. Fe3O4@SiO2 NPs

2) Optically responsive nanoparticles based on metal ( Au, Ag, Cu ) or inorganic (Carbon-dots) substances with tailored sizes and properties:

Figure. Ag-NPsresponse under vis light, and UV-vis spectra

Figure. Au-NPs response under vis light, and UV-vis spectra

Figure. C-Dots and optical response under vis light, and UV-vis spectra

3) Hybrid multimodal nano/micro/structures composed with a mixture of magnetic or metallic NPs embedded in matrices containing organic ( biopolymers, sythetic polymers, short organic molecules ) and/or inorganic materials (mesoporous materials, graphene or graphene oxide GO films ) , with tailored size and properties:

Figure: Fe3O4@Al(OH)3 nanostructures for MRI/PET; b) mesoporous silica shells for drug delivery, multicore magnetite NPs embedded in a graphene oxide film and d) sericin microflowers for heavy metals capture.

4) Biomedical applications.

We synthesize magnetic nanostructures with tailored texture, morphology and properties for different biomedical applications: tissue engineering, cell tracking and molecular imaging nanoprobes, contrast agents for MRI/PET, theragnostic agents ( drug delivery& imaging), nanoprobes for early detection of biomarkers in highly sensitive and specific kits.

Agar phantom of different NPs concentrations. (A) Scheme of the phantom NPs concentration distribution: A=0.25mg/mL; B=0.1mg/mL; C=0.05mg/mL; D=0.025mg/mL; E=0.005mg/mL; F=0.0025mg/mL and G=0mg/mL. (B) MR T2-weighted image of the agar phantom. (C) MR T2*-weighted image of the agar phantom.

a) TEM images of the core/shell structure of magnetite/carbon, and b) magnetization curves of multi-Fe3O4@C MBs up to 25 kOe performed at different temperatures (T={250,275,300,320} K). No coercive forces or remanence can be appreciated, showing SPM behavior.

Phase-contrast and bright-field optical microscopy of MSCs incubated with 200 µg/mL of Fe3O4@C ferrofluid and 1.5 µg/mL of (PLL), respectively. Scale bar 100µm.

Spherical core@shell (multi-Fe3O4@C) magnetic beads (MBs) (DMB~100 nm) composed of several single cores of magnetite nanoparticles (Dsingle-core~15 nm) surrounded by a wide carbon shell (δ~20 nm), have been used as cell labelling nanoprobes and efficient MRI contrast agents.

In vitro testing with rat mesenchymal cells show high stability and high labeling capacities combined with Poly-L-Lysine for further cell tracking applications. The so-obtained multi-core MNPs, present: superparamagnetic (SPM) behavior with a saturation magnetization around 70 emu/g Fe3O4 at 25 kOe and room temperature; negligible heating by magnetic hyperthermia (MH) procedure and an enhanced Magnetic Resonance Imaging (MRI) response.

The simultaneous fulfillment of all the above listed properties makes these multi- Fe3O4@C NPs ideal candidates for MRI brain multifunctional applications, where deleterious heating of tissues is a major restriction that ends up in the rejection of, otherwise, magnetically and chemically well-engineered NPs.

Z. Vargas-Osorio, B. Argibay, Y. Piñeiro, C. Vázquez-Vázquez, A. López-Quintela, T. Sobrino, F. Campos, J. Castillo and J. Rivas. Multicore magnetic Fe3O4@C beads with enhanced magnetic response for MRI in brain biomedical applications
IEEE Transactions on Magnetics ,V 52, Issue 7 Date: July 2016,2300604

SEM and TEM micrographs of MANC nanocomposite.

Heating curves of LMNC, HMNC, MANC and CSNC nanocomposites by magnetic induction

SBA-15 mesoporous silica matrices with ordered pore structure, large surface area and high pore volume, were the key to obtain different types of nanocomposites with a variety of properties. The physicochemical and structural characterization showed that the magnetic NCs primarily maintain the morphology of SBA-15 ceramics with ordered hexagonal distribution and high surface area, but larger pore diameters are mainly obtained. The nanocomposites presented superparamagnetic (SPM) response. The best SPM response was presented by HMNC nanocomposites due to magnetite disposition onto the outer surface of SBA-15 materials. In general, all the materials presented interesting magnetic behavior, showing even higher magnetic response than similar nanocomposites reported in the literature. Variable responses were obtained by magnetic hyperthermia that makes them suitable for different targets; in particular, LMNC and HMNC samples show no temperature increase. Their thermal activities are restricted by the very low thermal conductivity of the silica present in both the mesoporous matrix and the SiO2 coating. Therefore, these magnetic NCs are unique candidates for brain applications, allowing controlled drug delivery from the inside matrix without provoking an external deleterious thermal activity, since the appearance of hyperthermia are related with neurological and cognitive consequences.

Novel synthetic routes of large-pore magnetic mesoporous nanocomposites (SBA-15/Fe3O4) as potential multifunctional theranostic nanodevicesJ. Z. Vargas-Osorio1,*, M.A. González-Gómez1, Y. Piñeiro1, C. Vázquez-Vázquez2, C. Rodríguez-Abreu3, M.A. López-Quintela2 and J. Rivas1. Mater. Chem. B, 2017, 5, 9395–9404 )

Line 2.2. Environmental applications.

Cleaning and magnetic removal of organic and inorganic pollutants in waste water or water for human or animal consumption; food matrices and beverages and polluted air, is nowadays a very demanding area for a sustainable and circle economy. In addition magnetic separation of cleaning agents from the polluted matrices is a green technology, highly seeked. Based on the composition of superparamagnetic NPs embedded in ionroganic and/or organic matrices, complex hybrid materials are under development for different depuration applications in water and food/beverages matrices.

Magnetic nanoparticles as agents to reduce cyanotoxins content in freshwater. Jesús M González, Amparo Alfonso, MJ Sainz, M. R. Vieytes, Y. Piñeiro-Redondo,J. Rivas, Luis M Botana. V CIC Iberoameriacano Symposium of Cianotoxins.Lugo – España 2017, 17-19 Julio
Cyanotoxins produced by excessive growth of cyanobacteria in aquatic ecosystems is of special environmental relevance since these compounds have been associated with animal and human poisonings after water ingestion. Conventional drinking water treatment procedures like flocculation-filtration processes are not effective for removing these toxins. Therefore, new cleanup techniques to reduce or eliminate cyanotoxins from freshwater resources are needed to ensure health protection. The potential of magnetic nanoparticles as agents to reduce the cyanotoxins content in water has been assessed through the study with analytical standards of artificially contaminated water by cyanotoxins. Effectiveness of inorganic functionalized magnetic nanoparticles as toxin adsorbents attains above 50% of toxins removal.
Microcystins Nodularins Cylindrospermopsins Adsorption of cyanotoxins by magnetic nanoparticles as a function of time (0, 0.5, 1.5, 3 hours)
	Silica-coated magnetic nanoparticles (Fe3O4@SiO2) for covalent immobilization of laccase from Trametes versicolor : Application of SPM nanostructures as nanobiocatalyst Different concentrations of the functionalization agent (3-aminopropyltriethoxysilane), cross-linker (glutaraldehyde), and laccase allows maximum enzyme loading. Several factors, including pH, T, presence of inactivating compounds, enzyme stability, and reusability of the support, were evaluated. The oxidative action of the enzyme toward xenobiotics was proven in the formation of the chromogenic radical of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and the biotransformation of the endocrine-disrupting compound Bisphenol A (BPA). The enhancement of catalytic activity and stability of the nanobiocatalyst was evidenced by the increase of ABTS oxidation. Moreover, the superparamagnetic characteristic of the support allowed simple and fast recovery of the nanobiocatalyst.

Development of a Superparamagnetic Laccase Nanobiocatalyst for the Enzymatic Biotransformation of Xenobiotics. Y. Moldes-Diz; M. Gamallo; G. Eibes; Z. Vargas-Osorio; C. Vazquez-Vazquez;G. Feijoo; J. M. Lema; and M. T. Moreira. J. Environ. Eng., 2018, 144(3): 04018007