Superconducting quantum interference device detection of magnetically tagged microorganisms

H. L. Grossman, S. Lee, W. Myers, Y. R. Chemla, Y. Poon, H. M. Cho, R. McDermott, R. Stevens, M. D. Alper, John Clarke

Research output: Contribution to journalConference articlepeer-review


A fast and versatile technique has been developed for detecting small quantities of specific microorganisms or molecules with high specificity. The target analytes are bound to a substrate and placed in the measurement cell of a "microscope" based on a high-transition temperature Superconducting QUantum Interference Device (SQUID). A solution containing nanometer-size magnetite particles, coated with antibodies specific to the target, is added. The particles, which bind to the target via the antibody-antigen interaction, are superparamagnetic with a Néel relaxation time of ∼1s. A pulsed magnetic field aligns the dipole moments, and the SQUID measures the magnetic relaxation signal when the field is turned off. Unbound magnetic particles relax rapidly (∼15μs) by Brownian rotation and are not detected. On the other hand, particles bound to targets cannot rotate and instead relax slowly by the Néel mechanism. As a result, only bound particles contribute to the signal, allowing for quantification of the number of targets present without the need for a wash step. The current system can detect as few as 2000 magnetic particles. This technique could be used to detect a wide range of bacteria, viruses, and molecules, with potential applications in the food industry, clinical settings, or research laboratories.

Original languageEnglish (US)
Pages (from-to)122-125
Number of pages4
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - 2001
Externally publishedYes
EventAdvanced Environmental Sensing Technology II - Newton, MA, United States
Duration: Oct 31 2001Nov 1 2001

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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