Magnetic nanoparticles

Magnetic nanoparticles

Magnetic nanoparticles are a class of nanoparticle which can be manipulated using magnetic field. Such particles commonly consist of magnetic elements such as iron, nickel and cobalt and their chemical compounds. While nanoparticles are smaller than 1 micrometer in diameter (typically 5–500 nanometers), the larger microbeads are 0.5–500 micrometer in diameter. The magnetic nanoparticles have been the focus of much research recently because they possess attractive properties which could see potential use in catalysis,[1] biomedicine,[2] magnetic resonance imaging,[3] magnetic particle imaging,[4] data storage[5], environmental remediation,[6], nanofluids,[7] and optical filters.[8]



The physical and chemical properties of magnetic nanoparticles largely depend on the synthesis method and chemical structure. In most cases, the particles range from 1 to 100 nm in size and may display superparamagnetism.[9]

Types of magnetic nanoparticles

Cobalt nanoparticle with graphene shell.
Cobalt nanoparticle with graphene shell (note: The individual graphene layers are visible)

Currently, three different kinds of magnetic nanoparticles are being produced and used.

Oxides: ferrite

Ferrite nanoparticles are the most explored magnetic nanoparticles up to date. Once the ferrite nanoparticles become smaller than 128 nm[10] they become superparamagnetic which prevents self agglomeration since they exhibit their magnetic behavior only when an external magnetic field is applied. With the external magnetic field switched off, the remanence falls back to zero. Just like non-magnetic oxide nanoparticles, the surface of ferrite nanoparticles is often modified by surfactants, silicones or phosphoric acid derivatives to increase their stability in solution.[11]


Metallic nanoparticles have the great disadvantage of being pyrophoric and reactive to oxidizing agents to various degrees. Making their handling difficult and enabling unwanted sidereactions.

Metallic with a shell

The metallic core of magnetic nanoparticles may be passivated by gentle oxidation, surfactants, polymers and precious metals.[9] In an oxygen environment, Co nanoparticles form an anti-ferromagnetic CoO layer on the surface of the Co nanoparticle. Recently, work has explored the synthesis and exchange bias effect in these Co core CoO shell nanoparticles with a gold outer shell.[12] Nanoparticles with a magnetic core consisting either of elementary Iron or Cobalt with a nonreactive shell made of graphene have been synthesized recently.[13] The advantages compared to ferrite or elemental nanoparticles are:

  • Higher magnetization
  • Higher stability in acidic and basic solution as well as organic solvents
  • Chemistry[14] on the graphene surface via methods already known for carbon nanotubes


The established methods of magnetic nanoparticle synthesis include:


Co-precipitation is a facile and convenient way to synthesize iron oxides (either Fe3O4 or γ-Fe2O3) from aqueous Fe2+/Fe3+ salt solutions by the addition of a base under inert atmosphere at room temperature or at elevated temperature. The size, shape, and composition of the magnetic nanoparticles very much depends on the type of salts used (e.g.chlorides, sulfates, nitrates), the Fe2+/Fe3+ ratio, the reaction temperature, the pH value and ionic strength of the media.[9],In recent years, co-precipitation approach has been used extensively to produce ferritenanoparticles of controlled sizes and magnetic properties.[15],[16],[17],[18]

Thermal decomposition

Monodisperse magnetic nanocrystals with smaller size can essentially be synthesized through the thermal decomposition of organometallic compounds in high-boiling organic solvents containing stabilizing surfactants.[9]


Using the microemulsion technique, metallic cobalt, cobalt/platinum alloys, and gold-coated cobalt/platinum nanoparticles have been synthesized in reverse micelles of cetyltrimethlyammonium bromide, using 1-butanol as the cosurfactant and octane as the oil phase.[9],[19]

Flame spray synthesis

Using flame spray pyrolysis [13][20] and varying the reaction conditions, oxides, metal or carbon coated nanoparticles are produced at a rate of > 30 g/h .

Various flame spray conditions and their impact on the resulting nanoparticles
Various flame spray conditions and their impact on the resulting nanoparticles
Operational layout differences between conventional and reducing flame spray synthesis
Operational layout differences between conventional and reducing flame spray synthesis


A wide variety of applications have been envisaged for this class of particles these include:

Medical diagnostics and treatments

Magnetic nanoparticles are used in an experimental cancer treatment called magnetic hyperthermia in which the fact that nanoparticles heat when they are placed in an alternative magnetic field is used.

Another potential treatment of cancer includes attaching magnetic nanoparticles to free-floating cancer cells, allowing them to be captured and carried out of the body. The treatment has been tested in the laboratory on mice and will be looked at in survival studies.[21][22]

Magnetic nanoparticles can be used for the detection of cancer. Blood can be inserted onto a microfluidic chip with magnetic nanoparticles in it. These magnetic nanoparticles are trapped inside due to an externally applied magnetic field as the blood is free to flow through. The magnetic nanoparticles are coated with antibodies targeting cancer cells or proteins. The magnetic nanoparticles can be recovered and the attached cancer-associated molecules can be assayed to test for their existence.

Magnetic nanoparticles can be conjugated with carbohydrates and used for detection of bacteria. Iron oxide particles have been used for the detection of Gram negative bacteria like Escherichia coli and for detection of Gram positive bacteria like Streptococcus suis[23][24]

Magnetic immunoassay

Magnetic immunoassay[25] (MIA) is a novel type of diagnostic immunoassay utilizing magnetic beads as labels in lieu of conventional, enzymes , radioisotopes or fluorescent moieties. This assay involves the specific binding of an antibody to its antigen, where a magnetic label is conjugated to one element of the pair. The presence of magnetic beads is then detected by a magnetic reader (magnetometer) which measures the magnetic field change induced by the beads. The signal measured by the magnetometer is proportional to the analyte (virus, toxin, bacteria, cardiac marker,etc.) quantity in the initial sample.

Waste water treatment

Thanks to the easy separation by applying a magnetic field and the very large surface to volume ratio, magnetic nanoparticles have a good potential for treatment of contaminated water.[26] In this method, attachment of EDTA-like chelators to carbon coated metal nanomagnets results in a magnetic reagent for the rapid removal of heavy metals from solutions or contaminated water by three orders of magnitude to concentrations as low as micrograms per Litre.


Magnetic nanoparticles are being used or have the potential use as a catalyst or catalyst supports.[27] In chemistry, a catalyst support is the material, usually a solid with a high surface area, to which a catalyst is affixed. The reactivity of heterogeneous catalysts occurs at the surface atoms. Consequently great effort is made to maximize the surface area of a catalyst by distributing it over the support. The support may be inert or participate in the catalytic reactions. Typical supports include various kinds of carbon, alumina, and silica.

Biomedical imaging

Magnetic CoPt nanoparticles are being used as an MRI contrast agent for transplanted neural stem cell detection.[28]

Information storage

Research is going into the use of using MNPs for magnetic recording media. The most promising candidates for high-density storage is the face-centered tetragonal phase FePt alloy. Grain sizes can be as small as 3 nanometers. If its possible to modify the MNPs at this small scale, the information density that can be achieved with this media could easily surpass 1 Terabyte per square inch.[29]

Genetic engineering

Magnetic nanoparticles can be used for a variety of genetics applications. One application is the isolation of mRNA. This can be done quickly – usually within 15 minutes. In this particular application, the magnetic bead is attached to a poly T tail. When mixed with mRNA, the poly A tail of the mRNA will attach to the bead's poly T tail and the isolation takes place simply by placing a magnet on the side of the tube and pouring out the liquid. Magnetic beads have also been used in plasmid assembly. Rapid genetic circuit construction has been achieved by the sequential addition of genes onto a growing genetic chain, using nanobeads as an anchor. This method has been shown to be much faster than previous methods, taking less than an hour to create functional multi-gene constructs in vitro.[30]

See also

Magnetic chemistry


  1. ^ A.-H. Lu, W. Schmidt, N. Matoussevitch, H. Bönnemann, B. Spliethoff, B. Tesche, E. Bill, W. Kiefer, F. Schüth (August 2004). "Nanoengineering of a Magnetically Separable Hydrogenation Catalyst". Angewandte Chemie International Edition 43 (33): 4303–4306. doi:10.1002/anie.200454222. PMID 15368378. 
  2. ^ A. K. Gupta, M. Gupta (June 2005). "Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications". Biomaterials 26 (18): 3995–4021. doi:10.1016/j.biomaterials.2004.10.012. PMID 15626447. 
  3. ^ S. Mornet, S. Vasseur, F. Grasset, P. Verveka, G. Goglio, A. Demourgues, J. Portier, E. Pollert, E. Duguet (2006). Prog. Solid State Chem. 34: 237. 
  4. ^ B. Gleich, J. Weizenecker (2005). "Tomographic imaging using the nonlinear response of magnetic particles". Nature 435 (7046): 1214–1217. Bibcode 2005Natur.435.1214G. doi:10.1038/nature03808. PMID 15988521. 
  5. ^ T. Hyeon (2003). Chem. Commun.: 927. 
  6. ^ D. W. Elliott, W.-X. Zhang (2001). Environ. Sci. Technol. 35: 4922. 
  7. ^ J. Philip, Shima.P.D. B. Raj (2006). "Nanofluid with tunable thermal properties". Applied Physics Letters 92: 043108. 
  8. ^ J.Philip, T.J.Kumar, P.Kalyanasundaram, B.Raj (2003). "Tunable Optical Filter". Measurement Science & Technology 14: 1289–1294. 
  9. ^ a b c d e A.-H. Lu, E. L. Salabas and F. Schüth (2007). "Magnetic Nanoparticles: Synthesis, Protection, Functionalization, and Application". Angew. Chem. Int. Ed. 46 (8): 1222–1244. doi:10.1002/anie.200602866. 
  10. ^ An-Hui Lu, An-Hui; E. L. Salabas, and Ferdi Schüth (2007). "Magnetic Nanoparticles: Synthesis, Protection, Functionalization, and Application". Angew. Chem. Int. Ed. 46 (8): 1222–1244. doi:10.1002/anie.200602866. 
  11. ^ Kim, DK, G.; Mikhaylova, M et al. (2003). "Anchoring of Phosphonate and Phosphinate Coupling Molecules on Titania Particles". Chemistry of Materials 15 (8): 1617–1627. doi:10.1021/cm001253u. 
  12. ^ Johnson, Stephanie H.; C.L. Johnson, S.J. May, S. Hirsch, M.W. Cole, J.E. Spanier (2010). "Co@CoO@Au core-multi-shell nanocrystals". Journal of Materials Chemistry 20 (3): 439. doi:10.1039/b919610b. 
  13. ^ a b R. N. Grass, Robert N.; W. J. Stark (2006). "Gas phase synthesis of fcc-cobalt nanoparticles". J. Mater. Chem. 16 (16): 1825. doi:10.1039/B601013J. 
  14. ^ R.N. Grass, Robert N.; E.K. Athanassiou, W.J. Stark (2007). "Covalently Functionalized Cobalt Nanoparticles as a Platform for Magnetic Separations in Organic Synthesis". Angew. Chem. Int. Ed. 46 (26): 4909–12. doi:10.1002/anie.200700613. 
  15. ^ G.Gnanaprakash, S.Ayyappan, T.Jayakumar, John Philip & Baldev Raj (2006). "A simple method to produce magnetic nanoparticles with enhanced alpha to gamma-Fe2O3 phase transition temperature". Nanotechnology 17: 5851–5857. Bibcode 2006Nanot..17.5851G. doi:10.1088/0957-4484/17/23/023. 
  16. ^ G. Gnanaprakash, John Philip, T. Jayakumar, Baldev Raj (2007). "Effect of Digestion Time and Alkali Addition Rate on the Physical Properties of Magnetite Nanoparticles". J. Phys. Chem. B 111: 7978–7986. 
  17. ^ S.Ayyappan, John Philip & Baldev Raj (2009). "Solvent polarity effect on physical properties of CoFe2O3 nanoparticles". J. Phys. Chem. C 113: 590–596. 
  18. ^ S. Ayyappan, S. Mahadevan, P. Chandramohan, M. P.Srinivasan, John Philip & Baldev Raj (2010). "Influence of Co2 Ion Concentration on the Size, Magnetic Properties, and Purity of CoFe2O4 Spinel Ferrite Nanoparticles". J. Phys. Chem. C 114: 6334–6341. 
  19. ^ S S.Rana, J. Philip, B.Raj (2010). "Micelle based synthesis of Cobalt Ferrite nanoparticles and its characterization using Fourier Transform Infrared Transmission Spectrometry and Thermogravimetry". Materials Chemistry and Physics 124: 264–269. 
  20. ^ E. K. Athanassiou, Evagelos K.; R. N. Grass, W. J. Stark (2010). "Chemical Aerosol Engineering as a Novel Tool for Material Science: From Oxides to Salt and Metal Nanoparticles". Aerosol. Sci. Tech. 44 (2): 161–72. doi:10.1080/02786820903449665. 
  21. ^ Scarberry KE, Dickerson EB, McDonald JF, Zhang ZJ (2008). "Magnetic Nanoparticle-Peptide Conjugates for in Vitro and in Vivo Targeting and Extraction of Cancer Cells". Journal of the American Chemical Society 130 (31): 10258–62. doi:10.1021/ja801969b. PMID 18611005. 
  22. ^ Using Magnetic Nanoparticles to Combat Cancer Newswise, Retrieved on July 17, 2008.
  23. ^ Parera Pera N, Kouki A., Finne J., Pieters R. J., (2010). "Detection of pathogenic Streptococcus suis bacteria using magnetic glycoparticles". Organic & Biomolecular Chemi 8 (10): 2425–2429. doi:10.1039/C000819B. 
  24. ^ Highlights in Chemical Biology. (2007-06-13). Retrieved on 2011-10-07.
  25. ^ Magnetic immunoassays: A new paradigm in POCT IVDt, July/August 2008.
  26. ^ F.M. Koehler, Fabian M.; M. Rossier, M. Waelle, E.K. Athanassiou, L.K. Limbach, R.N. Grass, D. Günther, W.J. Stark, (2009). "Magnetic EDTA: Coupling heavy metal chelators to metal nanomagnets for rapid removal of cadmium, lead and copper from contaminated water". Chem. Commun. 32 (32): 4862–4. doi:10.1039/B909447D. 
  27. ^ A. Schätz, Alexander; O. Reiser, W.J. Stark (2010). "Nanoparticles as Semi-Heterogeneous Catalyst Supports". Chem. Eur. J. 16 (30): 8950–67. doi:10.1002/chem.200903462. 
  28. ^ Xiaoting Meng, Xiaoting; Hugh C. Seton, Le T. Lu, Ian A. Prior, Nguyen T. K. Thanh and Bing Song (2011). "Magnetic CoPt nanoparticles as MRI contrast agent for transplanted neural stem cells detection". Nanoscale 3 (3): 977–984. Bibcode 2011Nanos...3..977M. doi:10.1039/C0NR00846J. PMID 21293831. 
  29. ^ Natalie A. Frey and Shouheng Sun Magnetic Nanoparticle for Information Storage Applications
  30. ^ A Elaissari, J Chatterjee, M Hamoudeh and H Fessi (2010). "Chapter 14. Advances in the Preparation and Biomedical Applications of Magnetic Colloids". In Roque Hidalgo-√Ålvarez. Structure and Functional Properties of Colloidal Systems. CRC Press. pp. 315–337. doi:10.1201/9781420084474-c14. ISBN 978-1-4200-8447-4. 

External links

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Magnetic hyperthermia — is the name given to an experimental cancer treatment. It is based on the fact that magnetic nanoparticles, when subjected to an alternating magnetic field, produce heat. As a consequence, if magnetic nanoparticles are put inside a tumor and the… …   Wikipedia

  • Magnetic-activated cell sorting — (MACS) is a trademark name for a method for separation of various cell populations depending on their surface antigens (CD molecules). The term MACS is a registered trademark of Miltenyi Biotec. Magnetic cell separation using antibodies is also… …   Wikipedia

  • Magnetic immunoassay — (MIA) is a novel type of diagnostic immunoassay using magnetic beads as labels in lieu of conventional enzymes (ELISA), radioisotopes (RIA) or fluorescent moieties (fluorescent immunoassays). This assay involves the specific binding of an… …   Wikipedia

  • Magnetic chemistry — Cobalt nanoparticle with a graphene shell are among one of the kind of magnetic nanoparticles which are currently used for magnetic chemistry Magnetic chemistry are chemical reactions in which either reactant, reagent or product have magnetic… …   Wikipedia

  • Magnetic field — This article is about a scientific description of the magnetic influence of an electric current or magnetic material. For the physics of magnetic materials, see magnetism. For information about objects that create magnetic fields, see magnet. For …   Wikipedia

  • Magnetic semiconductor — Magnetic semiconductors are semiconductor materials that exhibit both ferromagnetism (or a similar response) and useful semiconductor properties. If implemented in devices, these materials could provide a new type of control of conduction.… …   Wikipedia

  • Magnetic force microscope — MFM images of 3.2 GB and 30 GB computer hard drive surfaces. Magnetic force microscope (MFM) is a variety of atomic force microscope, where a sharp magnetized tip scans a magnetic sample; the tip sample magnetic interactions are detected and used …   Wikipedia

  • Silver nanoparticles — Part of a series of articles on Nanomaterials Fullerenes …   Wikipedia

  • nanotechnology — /nan euh tek nol euh jee, nay neuh /, n. any technology on the scale of nanometers. [1987] * * * Manipulation of atoms, molecules, and materials to form structures on the scale of nanometres (billionths of a metre). These nanostructures typically …   Universalium

  • Nanoparticle — In nanotechnology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. Particles are further classified according to size[1] : in terms of diameter, coarse particles cover a range… …   Wikipedia