Phase sensitive enhancement for biochemical detection using rotating paramagnetic particle chains

Abstract

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.

Rotating magnetic particles for lab-on-chip applications – a comprehensive review

“…Mixing of fluid can be effectuated by applying a rotating field to a chain of MPs 2,[6][7][8][9][10][11][12][13][14][15] (Fig. 1A).…”

“…One year later the same group published a paper showing that these rotating magnetic particle chains can be used to capture biological molecules. 9 This principle has been extensively studied in the years thereafter 11 and was used in many bio-sensing applications 35,37,38,42,43 (Fig. 1B and C) to significantly shorten assay times, typically from 60-120 min to 15-30 min.…”

Integrated lab-on-chip biosensing systems based on magnetic particle actuation – a comprehensive review

“…Vuppu et al 36,37 were one of the first to discover that superparamagnetic particles form rotating chains in a rotating magnetic field. The rotors could be assembled dynamically and the length and speed were found to be varying in time (see Fig.…”

Improved signal extraction from fluorescence immunoassay image sequences

“…In a recently proposed technique, the distributed fluorescent signal spontaneously forms localized fluorescent signal objects [3]. The application of a magnetic field to a colloidal paramagnetic particle suspension causes them to build supraparticle chains.…”