The category of nanoparticle that can be influenced with magnetic field gradients is termed as Magnetic nanoparticles. These particles generally comprise of magnetic elements such as nickel, iron, cobalt and their chemical compounds. The nanoparticles have diameters less than 1 micrometre, the larger microbeads diameter ranges from 0.5-500 micrometre. Several individual magnetic nanoparticles together form a magnetic nanoparticle cluster that are termed as magnetic nano beads; their diameter ranges from 50- 200 nanometres.
Magnetic nanoparticles have been a very popular topic in the field of research due to its amazing properties. They can be used in catalysis, in biomedicine, magnetic resonance imaging, magnetically tunable colloidal photonic crystals, microfluidics, data storage, environmental remediation, nanofluids, optical filters and defect sensor.
Types Of Magnetic Nanoparticles
Ferrite nanoparticles are the iron oxides in the crystal structure of maghemite or magnetite. They are the most explored magnetic nanoparticles till date. They become supermagnetic when the ferrite particles become lesser than 128 nm which prevent self-agglomeration, because they display their magnetic behaviours only when an external magnetic field is applied.
Ferrites With A Shell
The surface of a magnetite magnetic nanoparticle is inert and usually resists covalent bonds with functionalization molecules. Though, the reactivity can be enhanced by coating a layer of silica on the surface. The silica shell can be easily altered with numerous surface functional groups. Apart from this, some fluorescent dye molecules can also be covalently bonded to the functionalized silica shell.
Some advantage of Ferrite nanoparticle clusters coated with a silica shell over metallic nanoparticles are:
- Advanced chemical stability
- Narrow size distribution
- Developed colloidal constancy
- Magnetic moment are tuned with the nanoparticle cluster size
- Retained superparamagnetic properties
- Silica surface allows direct covalent functionalization
These nanoparticles have multiple uses in technical areas due to their higher magnetic moment Whereas oxides would be beneficial for biomedical applications. There are also certain disadvantages associated with them, they are pyrophoric and reactive to oxidizing agents to various degrees that makes their management tough. It allows unwanted side reactions which decreases their suitability for biomedical applications.
Metallic With A Shell
The metallic core of a magnetic nanoparticle can be passivated by oxidation, surfactants, polymers and precious metals. Nanoparticles with a magnetic core consisting either of elementary iron or cobalt with a nonreactive shell made of graphene have been produced. its advantages compared to ferrite nanoparticles are listed below:
- Developed magnetization
- Greater stability in acidic, basic solution as well as in organic solvents
Properties Of Magnetic Nanoparticles
Magnetic effects are produced by activities of particles that have both mass and electric charges. A rotating, electric-charged particle generates a magnetic dipole termed as magneton. In ferromagnetic materials, magnetons are connected in groups. A magnetic domain refers to a volume of ferromagnetic material in which all magnetons are aligned in the same direction by the exchange forces.
Materials are classified by their reaction to an externally applied magnetic field. Descriptions of orientations of the magnetic moments in a material aid in finding diverse forms of magnetism. The basic types if magnetism can be classified into diamagnetism, paramagnetism, ferromagnetism, antiferromagnetism, and ferrimagnetism. When there is an external applied magnetic field, the atomic current loops formed by the orbital motion of electrons respond to oppose the applied field.
Synthesis Of Magnetic Nanoparticle
Some of the most established methods of synthesis of magnetic nanoparticle are:
- Co-precipitation -
It is a convenient way to synthesize iron oxides from aqueous Fe2+/Fe3+ salt solutions. It is done by adding a base under inert atmosphere at room temperature or at raised temperatures. The size, shape, and composition of the magnetic nanoparticles depends on the type of salts used.
This method is widely used to produce ferrite nanoparticles of controlled sizes and magnetic properties.
- Thermal Decomposition -
The smaller sized magnetic nanocrystals can be synthesized by thermal decomposition of organometallic compounds in high-boiling organic solvents containing stabilizing surfactants.
- Microemulsion -
With this method, platinum alloys, and gold-coated platinum nanoparticles have been manufactured in reverse micelles of cetyltrimethlyammonium bromide.
- Flame spray synthesis -
With the use of flame spray pyrolysis and changing the reaction conditions, oxides, metal or carbon coated nanoparticles are produced at a rate of > 30 g/h.
Applications Of Magnetic Nanoparticles
They have usage in many different fields, few of them are listed below:
Magnetic nanoparticles are used in an experimental cancer treatment called magnetic hyperthermia. Magnetic nanoparticles are used for the detection of cancer. They are conjugated with carbohydrates and used for detection of bacteria.
Treatment Of Wastewater
They have a good potential for treatments of contaminated water. The amazing property of easy separation by applying a magnetic field and the large surface area makes this possible.
They can be used as a catalyst or catalyst supports in chemical reactions. The support may be inert or they may participate in the catalytic reactions.
They can be used for a whole lot of genetics applications. One such application is the isolation of mRNA.
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