A microfluidic sensor based on ferromagnetic resonance induced in magnetic bead labels

Abstract

This report details preliminary studies towards the development of a microfluidic sensor that exploits ferromagnetic resonance, excited in magnetic bead labels, for signal transduction. The device consists of a microwave circuit in which a slotline and a coplanar waveguide are integrated with a biochemically activated sensor area. The magnetic beads are immobilized in the sensor area by bio-specific reactions. A microwave signal applied to the slotline is coupled to the coplanar waveguide only in the presence of magnetic beads at the functionalized sensor area. Ferromagnetic resonance in the beads further enhances the coupling. This inductive detection technique lends itself to miniaturization, is inexpensive to fabricate and can be adapted for the detection of a wide range of molecules for which bio-specific ligands are available. Experimentally, the variation of the output signal as a function of the location of magnetic beads was studied for the proposed technique. Subsequently, a prototype device was constructed by biotinylation of the sensor area and integration with a microfluidic chip fabricated in polydimethyl siloxane (PDMS). Preliminary experiments were conducted on this prototype using streptavidin-functionalized magnetic beads as labels. It was shown that the magnetic beads, immobilized at the sensor area by streptavidin–biotin linkage, produced a distinct ferromagnetic resonance response easily discernable from the background signal.