Electromagnetic needles with submicron pole tip radii for nanomanipulation of biomolecules and living cells

We describe the design and fabrication of a temperature-controlled electromagnetic microneedle (EMN) to generate custom magnetic field gradients for biomedical and biophysical applications. An electropolishing technique was developed to sharpen the EMN pole tip to any desired radius between 100 nm and 20 mum. The EMN can be used to apply strong static or dynamic forces (>50 nN) to micrometer- or nanometer-sized magnetic beads without producing significant heating or needle movement. Large tip radii (20 mum) allow magnetic force application to multiple magnetic beads over a large area, while small radii (0.1-6 mum) can be used to selectively pull or capture single magnetic beads from within a large population of similar particles. The customizable EMN is thus well suited for micro- and nanomanipulation of magnetic particles linked to biomolecules or living cells. (C) 2004 American Institute of Physics.