Advances in surface design and biomedical applications of magnetic nanoparticles.

Despite significant efforts by scientists in the development of advanced nanotechnology materials for smart diagnosis devices and drug delivery systems, the success of clinical trials remains largely elusive. In order to address this biomedical challenge, magnetic nanoparticles (MNPs) have gained attention as a promising candidate due to their theranostic properties, which allow the simultaneous treatment and diagnosis of a disease. Moreover, MNPs have advantageous characteristics such as a larger surface area, high surface-to-volume ratio, enhanced mobility, mass transference and, more notably, easy manipulation under external magnetic fields. Besides, certain magnetic particle types based on the magnetite (Fe3O4) phase have already been FDA-approved, demonstrating biocompatible and low toxicity. Typically, surface modification and/or functional group conjugation are required to prevent oxidation and particle aggregation. A wide range of inorganic and organic molecules have been utilized to coat the surface of MNPs, including surfactants, antibodies, synthetic and natural polymers, silica, metals, and various other substances. Furthermore, various strategies have been developed for the synthesis and surface functionalization of MNPs to enhance their colloidal stability, biocompatibility, good response to an external magnetic field, etc. Both uncoated MNPs and those coated with inorganic and organic compounds exhibit versatility, making them suitable for a range of applications such as drug delivery systems (DDS), magnetic hyperthermia, fluorescent biological labels, biodetection and magnetic resonance imaging (MRI). Thus, this review provides an update of recently published MNPs works, providing a current discussion regarding their strategies of synthesis and surface modifications, biomedical applications, and perspectives.

Observation of magnetic skyrmions in unpatterned symmetric multilayers at room temperature and zero magnetic field.

Magnetic skyrmions are promising candidates for the next generation of spintronic devices due to their small size and topologically protected structure. One challenge for using these magnetic states in applications lies on controlling the nucleation process and stabilization that usually requires an external force. Here, we report on the evidence of skyrmions in unpatterned symmetric Pd/Co/Pd multilayers at room temperature without prior application of neither electric current nor magnetic field. Decreasing the ferromagnetic interlayer thickness, the tuning of the physical properties across the ferromagnetic/non-magnetic interface gives rise to a transition from worm like domains patterns to isolated skyrmions as demonstrated by magnetic force microscopy. On the direct comparison of the measured and simulated skyrmions size, the interfacial Dzyaloshinskii-Moriya interaction (iDMI) was estimated, reveling that isolated skyrmions are just stabilized at zero magnetic field taking into account non-null values of iDMI. Our findings provide new insights towards the use of stabilized skyrmions for room temperature devices in nominally symmetric multilayers.

Ultrafast sonochemistry-based approach to coat TiO2 commercial particles for sunscreen formulation.

TiO2 is a common inorganic filter used in sunscreens due to its photoprotective effect on the skin against UV radiation. However, the use of this kind of material in cosmetics is limited by its inherent photocatalytic activity. It is known that coating on TiO2 surface can improve some features. Although, many of the methodologies used for this purpose are still laborious and time-consuming. Thus, this work reports a novel, easy, cheap and fast strategy to coat TiO2 particles by using a sonochemistry approach, aiming to decrease photocatalytic activity and to enhance colloidal stability. For this proposal, SiO2, Al2O3, ZrO2 and sodium polyacrylate (PAANa) were used to tune the surface of commercial TiO2 particles and they were applied in a sunscreen formulation. The samples were characterized by XRPD, FT-IR, DLS, EDS, SEM and TEM. The photocatalytic activity and UV-shielding ability were also evaluated. The sunscreen formulations were prepared and characterized by zeta potential, DLS, and Sun Protection Factor (SPF). FT-IR, EDS, and charge surface of the particles confirmed the success of the sonochemistry coating. Additionally, TiO2@Al2O3, TiO2@SiO2 and TiO2@PAANa show a lower photocatalytic activity than original TiO2 with similar UV-shielding ability. The sunscreens produced with the coated TiO2 have similar SPF to the one with commercial TiO2. Specifically, the sunscreen with TiO2@PAANa shows an increase in colloidal stability. Herein, the incorporation of the sonochemical-coated TiO2 particles in sunscreen formulations may produce sunscreens with better aesthetic appearance and a greater health security due to its lower free radicals production.

Fast ultrasound assisted synthesis of chitosan-based magnetite nanocomposites as a modified electrode sensor.

Chitosan-based magnetite nanocomposites were synthesized using a versatile ultrasound assisted in situ method involving one quick step. This synthetic route approach results in the formation of spheroidal nanoparticles (Fe3O4) with average diameter between 10 and 24nm, which were found to be superparamagnetic with saturation magnetization (Ms) ranges from 32-57emug(-1), depending on the concentration. The incorporation of Fe3O4 into chitosan matrix was also confirmed by FTIR and TG techniques. This hybrid nanocomposite has the potential application as electrochemical sensors, since the electrochemical signal was excepitionally stable. In addition, the in situ strategy proposed in this work allowed us to synthesize the nanocomposite system in a short time, around 2min of time-consuming, showing great potential to replace convencional methods. Herein, the procedure will permit a further diversity of applications into nanocomposite materials engineering.

A soft/hard magnetic nanostructure based on multisegmented CoNi nanowires.

In this paper we have introduced a new soft/hard nanostructure based on multisegmented CoNi nanowire arrays having diameters of around 110 nm and made of five segments with nominal compositions of Co, Co66Ni33, Co50Ni50, Co33Ni66 and Ni, each of which has a length of 800 nm, so that the total length of the multisegmented nanowire is 4 µm. These arrays have been synthesized by means of potentiostatic electrodeposition into the pores of hard-anodic alumina templates. The morphology, chemical composition and microstructure of the multisegmented CoNi nanowires were determined by high-resolution scanning electron microscopy, energy dispersive X-ray microanalysis, and powder X-ray diffraction method, respectively. The room temperature magnetic behavior of the multisegmented nanowire arrays is also studied and compared with CoNi nanowire arrays with homogeneous composition (non-segmented nanowires), synthesized in the same templates and having the same dimensions as the segmented ones. These nanostructures could be used to control the movement of magnetic domain walls. In this way, these nanostructures can be an alternative to store information or even perform logic functions.

Superparamagnetism and other magnetic features in granular materials: a review on ideal and real systems.

An overview on magnetic of nanostructured magnetic materials is presented, with particular emphasis on the basic features displayed by granular nanomagnetic solids. Besides a review of the basic concepts and experimental techniques, the role of structural disorder (mainly the distribution of grain sizes), interparticle magnetic interactions and surface effects are also discussed with some detail. Recent results, models and trends on the area are also discussed.

Geometry dependence of coercivity in Ni nanowire arrays.

Magnetic properties of arrays of nanowires produced inside the pores of anodic alumina membranes have been studied by means of vibrating sample magnetometer techniques. In these systems the length of the wires strongly influences the coercivity of the array. A simple model for the coercivity as a function of the geometry is presented which exhibits good agreement with experimental results. Magnetostatic interactions between the wires are responsible for a decrease of the coercive field.