The design of a ferrofluid magnetic pipette

An electromagnetic pipette using a ferrofluid was designed to sample liquid volumes smaller than 0.2 microliter. Submicroliter sample sizes are desirable for reducing the amount of costly reagents and reducing sample requirement for large-scale analysis. The pipette consists of four electromagnets arranged such that air-gaps are aligned to accommodate a tube. A light-hydrocarbon-based ferrofluid is contained in the tube and acts as a plunger. The position of the ferrofluid in the tube was controlled to within 0.2 mm by combining adjacent air-gap magnetic fields. The position of the ferrofluid as a function of time and magnetic pressure as a function of position was measured in one electromagnet air-gap from the device. Maximum pressure measured was 770 Pa which corresponds to a maximum velocity of 0.9 cm/s. The assembled pipette weighs approximately 25 g, and it measures 4 cm long, 1 cm wide, and 3 cm high.