magnetictweezer

Magnetictweezer is a term used to describe a class of experimental methods that use magnetic fields to apply controlled forces and torques to microscopic beads tethered to biomolecules or cells. In practice, magnetictweezer systems employ magnetic beads functionalized to bind molecules of interest. By placing beads in a spatially varying magnetic field generated by permanent magnets, electromagnets, or microfabricated coils, a force is exerted along the field gradient. Rotating or oscillating fields can also apply torque. Beads of diameters typically 0.5–5 micrometers are used; forces commonly range from a fraction of a piconewton to tens of piconewtons, enabling single-molecule manipulation over timescales from seconds to hours.

Because of the low mechanical noise and slow drift, magnetictweezer enables long-duration measurements of molecular extension, folding, and interactions. The technique is widely used to study DNA and RNA mechanics, protein unfolding and folding pathways, motor protein forces, and ligand-receptor binding under load. It is also used in cell mechanics experiments by attaching beads to cell-surface receptors.

Calibration and data interpretation in magnetictweezer experiments rely on known force models, bead tracking, and thermal fluctuations; commonly used approaches include the fluctuation-dissipation relation and drag-based calibration. Advantages include simplicity, minimal photodamage, and the ability to apply relatively constant forces and torque over long periods. Limitations include lower spatial resolution compared with optical tweezers, heterogeneity in bead properties, and the need for careful calibration of field gradients and tether properties.