Picture of the magnetic separation chip showing the position of the microfluidic channel and the passive soft magnetic elements. The external homogenous magnetic field is applied vertically in the plane of the paper.
Fabrication scheme (cross-section view). (a) shows the starting double polished Si wafer. In (b) a photoresist mask is applied using UV lithography. In (c) trenches for both the microfluidic channel and magnetic elements are etched. RCA-clean, oxide growth (, wet), and seed layer deposition ( , E-beam evaporation) with intentionally low step coverage is performed in (d). The areas designated for magnetic elements are connected through conducting paths and isolated from the rest of the wafer. In (e) a thin layer of Cu is electroplated in these places, and the seed layer is removed on the rest of the wafer using the Cu layer as etch mask. After Cu-removal permalloy are electroplated into the conducting paths and magnetic elements. After seed layer and oxide removal a pyrex lid is bonded anodically to the wafer in (f).
Normalized magnetic hysteresis curve of the magnetic separation chip. The inset shows the low-field region.
Magnetic hysteresis curve for the fluorescent magnetic beads (Spherotec FCM-1052-2). The inset shows the low-field region.
The applied magnetic field and the measured fluorescent signal for the three sections of the microfluidic channel as a function of time.
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