Magnetic tweezers use flux instead of current to enhance precision
Magnetic tweezers use flux instead of current to enhance precision lead image
Magnetic tweezers can apply controlled forces at a range of size scales – from the molecular dynamics of a DNA strand to the mechanical properties of cells. Most tweezers have a solenoid coil wrapped around a ferromagnetic core, where the force exerted by the tweezers is modulated by adjusting the current flowing through the coil. Selby et al designed a magnetic tweezer that uses flux density-based control instead of current-based control, allowing for more precise force application in delicate biophysical experiments.
In magnetic tweezers, current is only a proxy for the magnitude of the magnetic force, giving no information about the shape or strength of the magnetic field at the tweezers’ tip. The strength and shape can change based on the temperature of the system and the history of magnetization in the ferromagnetic core, even if the current is the same.
The tweezers designed by the researchers adjust the current based on the strength of the magnetic field at the back end of the tweezers. This allows them to, in real time, compensate for heat generated in the core by the solenoid current, as well as other effects.
“To ask and answer more biophysically targeted questions, I believe that you need to have more precise biophysical measurements, where you can apply forces or displacements to cells and take real-time changes into account,” coauthor John Selby said.
The tweezers are constructed from commercially available hardware and software, making it an accessible piece of technology for laboratories. The scientists plan to integrate the tweezers with traction force microscopy to study how force is transmitted between human epidermal cells, especially in the case of rare blistering skin diseases, such as pemphigus vulgaris.
Source: “Magnetic tweezers with magnetic flux density feedback control,” by Waddah I. Moghram, Anton Kruger, Edward A. Sander, and John C. Selby, Review of Scientific Instruments (2021). The article can be accessed at https://doi.org/10.1063/5.0039696 .
