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Magnetic Properties

The magnetic properties of magnetite (Fe3O4) nanoparticles vary with size, and are typically superparamagnetic at small particle sizes and ferromagnetic at larger particle sizes. Our particles are superparamagnetic at room temperature, meaning that an external magnetic field can magnetize the nanoparticles similarly to a paramagnet but with a much larger magnetic susceptibility.

Zero field cooling (ZFC) and field cooling measurements of 20 nm magnetite shows the blocking temperature at around 250 K, characteristic of superparamagnetic behavior. The temperature at the peak point of the ZFC curve is the blocking temperature. Below blocking temperature, superparamagnetic material loses its preferred direction of magnetization in zero magnetic fields.

Superconducting quantum interference device (SQUID) measurements show no hysteresis for the 20 nm particles until they are cooled using liquid helium (1.8 K); at ambient temperatures we observe characteristic superparamagnetic behavior.

Frequently Asked Questions

  1. Are magnetite nanoparticles toxic?
    Several studies have examined the toxicity potential of a variety of magnetite nanoparticles with a range of surface coatings and have consistently found low or no toxicity associated with magnetite nanoparticles until high exposure levels are reached.
  2. Can magnetite nanoparticles be coated with a different capping agent?
    We routinely functionalize our materials with alternative capping agents or biomolecules. Please see our custom synthesis section for more information.
  3. Can I buy magnetite nanoparticles with a different size?
    We routinely offer an assortment of different sizes of nanomaterials for our customers. Please see our custom synthesis section for more information.
  4. Why are the materials provided in a citrate buffer
    We observe greater long-term stability of the magnetite particles when suspended in a citrate buffer, compared with suspension in pure water. The particles may be processed into another solvent through centrifugation or magnetic separation if required.
  5. What is the expected magnetic responsiveness of your particles?
    Our ability to define the magnetic responsiveness of our particles is dependent upon multiple factors. Contact us today to discuss so we can suggest the particles best suited for your application.

Custom Magnetic Nanomaterials from nanoComposix

NanoComposix has extensive experience with the synthesis and development of complex nanomaterials and coatings, and has produced a broad assortment of well-characterized, precisely-tuned magnetic nanoparticles on a custom basis. We are able to synthesize magnetic nanomaterials of varying compositions, sizes, morphologies, and surface functionalities, examples of which are shown below. Contact us today to inquire about your custom magnetic nanoparticle needs.

Magnetic-Plasmonic Gold Nanoshells

Gold nanoshells typically consist of a dielectric core, a thin layer of silica and a uniformly thin outer layer of gold with unique and tunable optical properties. This material can be used for medical diagnostic assays and photothermal therapies. NanoComposix has fabricated magnetic-responsive versions of these materials using superparamagnetic nanoparticle cores coated with a silica spacer followed by a gold shell. The optical properties can be tuned by adjusting the overall particle size or the diameter of the gold shell. The gold surface provides a useful substrate for functionalization with biological molecules or other custom surface functionality.

The reaction conditions have been tuned to modify sizes between 100–300 nm.

Magnetic-Fluorescent Nanoparticles

We have also fabricated magnetic-fluorescent composite particles, consisting of a magnetic core, silica spacer, and fluorescent quantum dots covalently bound to the silica surface. The quantum dots are functionalized to allow further coupling of biomolecules or other molecules.

Iron oxide nanoparticles with a diameter of ~60 nm were fabricated, coated with uniform silica shells and quantum dots covalently bound for a final particle of ~100 nm. The reaction conditions can be tuned to modify the size of the core and shell thickness, and quantum dots with different emission properties can be easily be substituted to produce samples with tailored fluorescence.

Iron Oxide Nanoparticles

A wide variety of magnetic nanomaterials can be produced via the thermal decomposition of organometallic precursors at high temperature in organic solvents, producing highly monodisperse, organic-solvent compatible nanoparticles. Iron oxide nanoparticles coated with oleic acid can range from 4 to 20 nm in diameter by modifying reaction conditions, and easily dispersed into a wide variety of organic solvents. The particles can be transferred into aqueous-compatible solvents by modifyingthe surface or by growing a uniform silica coating around the particles. These nanomaterials can be further customized with surface functionality tailored for your applications.

Iron Platinum Nanoparticles

NanoComposix has experience with fabricating a wide variety of magnetic metal ferrite and alloy nanoparticles, which can be produced with customizable sizes, shapes and compositions. The size and iron-to-platinum ratio can be adjusted to alter the magnetic and catalytic properties. Monodisperse iron platinum (FePt) nanoparticles, shown below, were fabricated with diameters of approximately 3 nm.