High-speed transport and magneto-mechanical resonant sensing of superparamagnetic microbeads using magnetic domain walls*

Surface-functionalized superparamagnetic (SPM) microbeads are of great interest in biomedical research and diagnostic device engineering for tagging, manipulating, and detecting chemical and biological species in a fluid environment [1-5]. Recent work has shown that magnetic domain walls (DWs) can be used to shuttle individual SPM microbeads and magnetically tagged entities across the surface of a chip [1-5]. This talk will describe the dynamics of SPM microbead transport by nanotrack-guided DWs, and show how these coupled dynamics can be exploited for on-chip digital biosensing applications. Using curvilinear magnetic nanotracks, we demonstrate rapid transport of SPM microbeads at speeds approaching 1000 $\mu $m/s [3], and present a mechanism for selective transport at a junction that allows for the design of complex bead routing networks. We further demonstrate that a SPM bead trapped by a DW exhibits a distinct magneto-mechanical resonance that depends on its hydrodynamic characteristics in the host fluid [4, 5], and that this resonance can be used for robust size-based discrimination of commercial microbead populations. By embedding a spin-valve sensor within a DW transport conduit, we show that the resonance can be detected electrically and on-the-fly [5]. Thus, we demonstrate a complete set of essential bead handling functions, including capture, transport, identification, and release, required for an integrated lab-on-a-chip platform.\\[4pt] [1] G. Vieira et al., Phys. Rev. Lett. 103, 128101 (2009).\\[0pt] [2] M. Donolato et al., Lab Chip. 11, 2976--2983 (2011).\\[0pt] [3] E. Rapoport and G.S.D. Beach, Appl. Phys. Lett. 100, 082401 (2012).\\[0pt] [4] E. Rapoport and G.S.D. Beach, J. Appl. Phys. 111, 07B310 (2012).\\[0pt] [5] E. Rapoport, D. Montana, and G.S.D. Beach, Lab Chip. 12, 4433-4440 (2012)