Towards the impedimetric tracking of single magnetically trailed microparticles

We present the design and the preliminary experimental characterization of a novel lab-on-a-chip platform for high-sensitivity impedimetric detection of single magnetic beads employed as magnetic cargos with molecular payload for accurate drug delivery. The real-time impedimetric detection of these superparamagnetic microbeads in saline solution is here experimentally demonstrated (20 nS conductance variation for a single 1μm bead), validating the insulating-sphere model and the finite-element simulations employed for optimal electrode design. A custom electronic front-end for impedance tracking in the 1-10 MHz range, required to compensate the impact of the large parasitic impedance due to the silicon substrate, is also presented. Thanks to introduction of an ad-hoc noise cancelling network based on a dummy circuit and a phase shifter for low-frequency phase noise counteraction by active subtraction, slow fluctuations are significantly reduced (by a factor 10), allowing a SNR > 10.