Magnetic nanoparticles colourization by a mixing-frequency method

Liang Tu, Kai Wu, Todd Klein, Jian Ping Wang

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


Brownian and Néel relaxation of magnetic nanoparticles (MNPs) can be characterized by a highly sensitive mixing-frequency method using a search-coil based detection system. The unique magnetic properties of MNPs have been used for biomarkers detection. In this paper, we present a theory and implement an experimental detection scheme using the mixing-frequency method to identify different MNPs simultaneously. A low-frequency sinusoidal magnetic field is applied to saturate the MNPs periodically. A high-frequency sinusoidal magnetic field is then applied to generate mixing-frequency signals that are highly specific to the magnetization of MNPs. The spectra of each MNP can be defined as the complex magnetization of the MNPs over the field frequency. The magnetic spectra of various MNPs and magnetic beads have been characterized and compared. The differences between the MNPs spectra enable us to identify the individual MNPs at the same time. A test has been done to verify the ratio of two different MNPs in mixed samples based on the proposed theory. The experimental results show that the mixing-frequency method is a promising method for MNPs colourization.

Original languageEnglish (US)
Article number155001
JournalJournal of Physics D: Applied Physics
Issue number15
StatePublished - Apr 16 2014


  • Brownian/Ńeel relaxation
  • biomarker detection
  • magnetic colourization
  • magnetic nanoparticle
  • mixing-frequency method

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