Authors: T. Mitrelias, Z. Jiang, J. Llandro and J.A.C. Bland
Affilation: University of Cambridge, United Kingdom
Pages: 256 - 259
Keywords: magnetic biosensors, microfluidic channel, integrated cell
In this report we present an integrated microfluidic cell for detecting and sorting magnetic beads in solution. The cell has been developed for magnetic biosensing, which comprises both magnetoresistive sensors optimized for the detection of single 9 m ferromagnetic beads in suspension and electrodes to manipulate and sort the beads, integrated into a microfluidic channel. The suspended beads are moved along a 75x75 μm wide microfluidic channel patterned in SU8 over 10 μm diameter ring shaped sensors arranged in Wheatstone bridge, with two active elements in phase in the channel and two reference elements outside it. The device is designed to read out the real-time voltage signal as a bead perturbs an in-plane applied field in the vicinity of the active elements, changing their resistances and unbalancing the bridge by an amount proportional to the bead’s magnetic moment. Beads of different magnetic moments can thus be detected and sorted through a magnetostatic sorting gate into different branches of the microfluidic channel, using magnetic field gradients applied by the photolithography defined 120 nm thick Cu striplines carrying 0.2A DC. The cell is unique because it’s design facilitates the integration of magnetic sensors with the microfluidic channels and also because it has individually addressable sorting striplines that divert magnetic beads in flow by applying currents locally.