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Research on medical diagnostics for point of care treatment (POCT) is driven by demand for rapid, high sensitivity, and inexpensive point of care diagnosis of heart disease, infection, allergies and cancer. Demands to improve quantification and affinity necessitate magnetic labels with sizes comparable to target molecules. However, it is extremely challenging to detect small concentrations of sub-200 nm functionalized magnetic labels using magnetoresistive-based sensors. In order to overcome these limitations we have developed a simple procedure for detecting ~ 130 nm sized magnetic labels via magnetically induced capture of micrometer sized superparamagnetic beads by several 130 nm-diameter target beads immobilized on substrates. Here we demonstrate a new method to improve the quantification of our protocol that exploits magnetically induced frictional forces between micro-sized beads and target magnetic labels. By reducing the external magnetic field, the magnetically captured micro-sized beads restart to flow due to electrostatic forces and the strength of the critical external magnetic field for release depends on the number of nano-sized beads immobilized on substrate. Our protocol has the possibility for quantitative biomaterial detection.
Date of Publication: Nov. 2012