University of Louisiana at Lafayette (Lafayette, LA) Professor of Metallurgy Dr. Devesh K. Misra discloses how to make dendritic magnetic nanostructures for use in medical, sensor, drug delivery and magnetic recording applications in U.S. Patent 7,635,518. Dendrites are typically the tree-like structures, examples of which include crystals that grow as molten metal freezes; the tree-like structures that form during the freezing of many nonmetallic substances such as ice; and the like. Dendrites are sometimes referred to as having a "spiky" morphology.
Each nanorod of the dendritic magnetic nanostructure is comprised of a chain of nanoparticles that are held together by dipole interaction during their formation by precipitation within the aqueous core of a reverse micelle when an effective magnetic field is applied. Each nanoparticle is comprised of at least two elements, one of which is a magnetic metal.
Each nanorod of the dendritic magnetic nanostructure is comprised of a chain of nanoparticles that are held together by dipole interaction during their formation by precipitation within the aqueous core of a reverse micelle when an effective magnetic field is applied. Each nanoparticle is comprised of at least two elements, one of which is a magnetic metal.
Misra prepares dendritic magnetic nanostructures at room temperature by applying a magnetic field to a reverse micelle system wherein at least one salt of a magnetic metal is being precipitated within the core of the reverse micelle.
Quasi one-dimensional magnetic nanostructures, such as nanorods, nanowires, and nanotubes have attracted significant scientific and technological interest because they exhibit unique magnetic properties not displayed by their bulk or nanoparticle counterparts. Crystalline magnetic nanorods belong to this class of magnetic materials known for their spontaneous magnetization. There are multiple potential uses for such nanostructures, such as: their use for high density magnetic recording media; their use in sensors; their use in spintronic devices, and their use in drug delivery applications.
Misra also created titania coated magnetic nanostructures that are suitable for use in biomedical applications because the photocatalytic properties of the titania can be exploited for antimicrobial, or germicidal, activity. The magnetic properties of the nanorods are used to remove the titania coated nanostructures, when applied to the human body, such as when applied to a wound.
A variety of methods have been proposed for synthesizing various types of nanorods. These synthetic methods are typically anisotropic growth with the intrinsic anisotropic crystal structure in a solid material, anisotropic growth using tubular templates, and anisotropic growth kinetically controlled by super-saturation or by using an appropriate capping surfactant. Other approaches to fabricate one-dimensional nanostructures include thermal evaporation and template assisted growth, vapor phase transport process with the assistance of metal catalysts, hydrothermal methods, and electrospinning.
A variety of methods have been proposed for synthesizing various types of nanorods. These synthetic methods are typically anisotropic growth with the intrinsic anisotropic crystal structure in a solid material, anisotropic growth using tubular templates, and anisotropic growth kinetically controlled by super-saturation or by using an appropriate capping surfactant. Other approaches to fabricate one-dimensional nanostructures include thermal evaporation and template assisted growth, vapor phase transport process with the assistance of metal catalysts, hydrothermal methods, and electrospinning.
Misra’s method for producing magnetic nanostructures is comprised of an assembly of magnetic nanorods held together by dipole interaction in a dendritic pattern, includes the following steps:
a) dissolving an effective amount of a surfactant into a non-polar organic solvent with sufficient mixing to cause the formation of a reverse micelle microemulsion;
b) dividing said reverse micelle microemulsion into a first fraction and a second fraction;
c) blending into said first fraction an aqueous solution having dissolved therein one or more metal salts wherein at least one of the metals has magnetic properties, thereby forming a metal salt microemulsion comprised of reverse micelles in a continuous non-polar organic phase, which reverse micelles are comprised of an aqueous core of metal salt solution encased in a surfactant shell;
d) blending into said second fraction an effective amount of an aqueous precipitating agent solution, thereby resulting in the formation of a precipitating agent microemulsion comprised of reverse micelles in a continuous non-polar organic phase, which reverse micelles are comprised of an aqueous core of precipitating agent solution encased in a surfactant shell;
e) simultaneously: (i) applying a magnetic field of effective strength; and (ii) blending at least a portion of the metal salt microemulsion with at least a portion of the precipitating agent microemulsion, thereby resulting in the simultaneous precipitation and formation of magnetic nanostructures comprised of an assembly of magnetic nanorods held together by dipole interaction in a dendritic pattern, which nanorods are comprised of a series of magnetic nanoparticles held together by dipole magnetic forces, in the aqueous core of said reverse micelles;
f) extracting at least a portion of the magnetic nanostructures with an effective amount of a C2 to about a C6 alcohol wherein the magnetic nanostructures migrate to the alcohol phase in the form of a colloidal dispersion alcohol phase;
g) separating the colloidal dispersion alcohol phase from the non-polar organic phase; and h) heating said colloidal dispersion alcohol phase of step g) above at an effective temperature for an effective amount of time to drive off at least a portion of any remaining water and surfactant, thereby resulting in substantially dried magnetic nanostructures comprised of assemblies of magnetic nanorods held together in a dendritic pattern by dipole interaction.
Nanoparticles that can comprise the nanorods include M-Au, M-Ag, M-Pt, M-Pd, M-Au--Pt, M-Sm, and Nd-M-B wherein M is a magnetic metal selected from iron, nickel and cobalt.
