Jose Garcia-Torres

Measurement of the giant magnetoresistance effect in cobalt-silver magnetic nanostructures: nanoparticles.

Cobalt-silver (Co-Ag) core-shell nanoparticles with different silver thicknesses were prepared by the microemulsion method in a two-step reduction process. Transmission electron microscopy (TEM) characterization revealed the almost monodispersity and nanometric size (in the range 3-5 nm depending on the shell thickness) of the synthesized nanoparticles. However, it was the use of high-resolution TEM that revealed the correct core-shell formation of the nanometric material. The selected area electron diffraction pattern indicated the fcc (face-centered cubic) and hcp (hexagonal close packed) nature for silver and cobalt, respectively. Cyclic voltammetry also allowed the correct core-shell formation to be assured. The magnetic properties revealed the presence of both superparamagnetic and ferromagnetic contributions. Because of the lack of methodology, it was necessary to develop a method to measure the magnetotransport properties of the prepared nanoparticles. The strategy which followed was successful as it was possible to measure these properties: giant magnetoresistance values of 0.1% at room temperature were obtained. The numerical analysis of magnetic and magnetoresistance data indicated the presence of superparamagnetic particles showing interaction among the magnetic moments.

Magnetic Propulsion of Recyclable Catalytic Nanocleaners for Pollutant Degradation

Electrochemically fabricated magnetic mesoporous CoNi@Pt nanorods are excellent nanomotors with controlled magnetic propulsion and excellent catalytic properties. The core-shell structure allows a double functionality: (i) controlled motion of the nanorods by applying rotating magnetic fields at different frequencies and field strengths and (ii) effective catalytic activity of the platinum shell for reactions involving sodium borohydride. The structure and magnetic properties of the CoNi core are not modified by the presence of the Pt shell. Nanorods were propelled via a tumbling-like dynamic by a rotating magnetic field. While in absence of NaBH4, nanorods move at constant speed showing a linear path; in the presence of NaBH4, they showed an intermittent trajectory. These catalytic nanorods can be used as nanocleaners with controlled directionality for pollutants degradation in the presence of borohydride. Their magnetic character allows control of the velocity and the direction throughout the contaminated solution by degrading the different pollutants in their path. The magnetic character of nanorods also allows their easy recycling.

Magnetically tunable bidirectional locomotion of a self-assembled nanorod-sphere propeller

Field-driven direct assembly of nanoscale matter has impact in disparate fields of science. In microscale systems, such concept has been recently exploited to optimize propulsion in viscous fluids. Despite the great potential offered by miniaturization, using self-assembly to achieve transport at the nanoscale remains an elusive task. Here we show that a hybrid propeller, composed by a ferromagnetic nanorod and a paramagnetic microsphere, can be steered in a fluid in a variety of modes, from pusher to puller, when the pair is dynamically actuated by a simple oscillating magnetic field. We exploit this unique design to build more complex structures capable of carrying several colloidal cargos as microscopic trains that quickly disassemble at will under magnetic command. In addition, our prototype can be extended to smaller nanorods below the diffraction limit, but still dynamically reconfigurable by the applied magnetic field.Controlled transport at the micro and nanoscale is a challenge and strategies are needed for applications such as targeted drug delivery and soft microrobotics. Here the authors propose a hybrid nanorod and microsphere propeller which can be actuated and reconfigured by an oscillating magnetic field.

Magnetic Actuation of Multifunctional Nanorobotic Platforms to Induce Cancer Cell Death

Single‐bath potentiostatic‐pulsed electrodeposition enables the synthesis of bicomponent (i.e., gold and nickel–nickel oxide) multi‐segmented magnetic nanowires that, with extraordinarily low cytotoxicity, are ideal three‐functional medical nanoplatforms because they can transport two types of functional molecules and be magnetically actuated for both controlled targeting and inducing cancer cell death. Alternated segments of Au and Ni–Ni oxide are selected to confer a magnetic character to the nanowires, prevent their dissolution in the cellular medium, and permit selective bio‐functionalization with thiol and porphyrin test molecules. The bi‐functionalized nanowires internalized in HeLa cancer cells, similar to other organelles, move inside the living cells. Applying the rotating magnetic fields cause them vibrate and increase their motion, although high viscosity and the presence of the cytoskeleton and other protein matrices preclude their rotation inside cells. Since no magneto‐mechanical destruction of the HeLa cells occurs on their membranes, organelles, or cytoskeletons programmed cancer cell death is likely induced by the vibration and translation of the nanowires, not by mechanical destruction.