Phase sensitive enhancement for biochemical detection using rotating paramagnetic particle chains

Anil K. Vuppu, Antonio Garcia, Mark Hayes, Karl Booksh, Patrick Phelan, Ronald Calhoun, Sanjoy K. Saha

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Paramagnetic particle suspensions placed in a rotating unidirectional magnetic field form magnetic chains that rotate with the same frequency as the field. The motion of the fluid and particles surrounding the chain differs in phase and frequency from the chain rotation, a phenomenon that forms the basis of a sensitive detection scheme. Fluorescent particles that bind to the paramagnetic particles through their surface chemistry are used to demonstrate the concept. Epifluorescence video microscopy is used to capture images of the rotating chains. View windows placed over sequential images of rotating chains allows for measurement of the fluorescence brightness in the window, which is composed of periodic signal from the steady rotation of the chain plus the background. A lock-in reference synchronized to the chain rotation is used to enhance the fluorescence signal from chain and improve signal to noise. Two different modes of chain rotation and signal collection are demonstrated. This technique can be used to develop a fast and sensitive, homogenous microdevice based solid-phase immunoassay.

Original languageEnglish (US)
Pages (from-to)6831-6838
Number of pages8
JournalJournal of Applied Physics
Issue number11
StatePublished - Dec 1 2004

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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