A bead-based electrochemical biosensor with integrated magnetic manipulation for controllable sample preconcentration

We developed a novel lab-on-a-chip device for immunoassays that use paramagnetic bead as the solid carrier of biomolecules. The device combines interdigitated electrodes (IDEs), as the biomolecule detection element, with an array of patterned soft magnetic materials (e.g. NiFe stripes or pads), as the bead manipulation element. The purpose of magnetic bead manipulation is to provide sample preconcentration in close proximity of the IDE sensing region. In the presence of an external uniform magnetic field, the NiFe features create local magnetic field gradients that capture the paramagnetic beads to the IDE sensing region from a dilute bead suspension flowing in a microchannel. With NiFe pads in size comparable to the magnetic beads, the control of individual beads is realized, which allows us to conveniently adjust the distribution and number density of the beads in the sensing region. Using paramagnetic beads immobilized with enzyme molecules, we explored the effectiveness of IDE sensing of the enzyme product as a function of the distribution and number density of the beads, which represents the distribution and level of the preconcentration of enzyme molecules.