A multiplexed magnetic tweezer with precision particle tracking and bi-directional force control

Abstract

BackgroundIn the past two decades, methods have been developed to measure the mechanical properties of single biomolecules. One of these methods, Magnetic tweezers, is amenable to aquisition of data on many single molecules simultaneously, but to take full advantage of this "multiplexing" ability, it is necessary to simultaneously incorprorate many capabilities that ahve been only demonstrated separately.MethodsOur custom built magnetic tweezer combines high multiplexing, precision bead tracking, and bi-directional force control into a flexible and stable platform for examining single molecule behavior. This was accomplished using electromagnets, which provide high temporal control of force while achieving force levels similar to permanent magnets via large paramagnetic beads.ResultsHere we describe the instrument and its ability to apply 2–260 pN of force on up to 120 beads simultaneously, with a maximum spatial precision of 12 nm using a variety of bead sizes and experimental techniques. We also demonstrate a novel method for increasing the precision of force estimations on heterogeneous paramagnetic beads using a combination of density separation and bi-directional force correlation which reduces the coefficient of variation of force from 27% to 6%. We then use the instrument to examine the force dependence of uncoiling and recoiling velocity of type 1 fimbriae from Eschericia coli (E. coli) bacteria, and see similar results to previous studies.ConclusionThis platform provides a simple, effective, and flexible method for efficiently gathering single molecule force spectroscopy measurements.

Environmentally controlled magnetic nano-tweezer for living cells and extracellular matrices

“…Although there are many setups dealing with several permanent magnetic poles 23 , 24 , the highest forces are generally obtained with a one-pole microneedle geometry that can be either achieved using permanent magnets 25 or electromagnets with soft iron cores 16 , 26 – 30 . Our setup for the magnetic tweezer consists of a single solenoid that contains a high-permeability soft iron core, which is connected to a conventional remote-controlled micromanipulator.…”

Design and operation of magnetophoretic systems at microscale: Device and particle approaches

“…In other instance, pulling force can also be applied either upward and/or downward through the combined use of two pairs of electromagnets located at the top and bottom of the bead, respectively (Fig. 9B) [92]. By using a 7.8 μm magnetic bead, upper magnetic force up to approximately 130 pN and lower magnetic force up to 3.5 pN can be applied by using this design.…”

“…(A) torque rotating device; the figure is redrawn from the original image of reference [91]. (B) gradient pulling device; the figure is redrawn from the original image of reference [92] and (C aggregation control device; the figure is redrawn from the original image of reference [93].…”

“…9A, by using a cylindrical magnet it is possible to apply a magnetic torque by adjusting the vertical alignment (white dotted line) of the magnet with the magnetization axis of the particle (Fig. 9A) [91,92]. As long as large enough horizontal component (perpendicular to the white dotted line) of magnetic fields is available (through size mismatch between the large cylindrical magnet and the particles), the beads will faithfully follow rotation of the permanent magnet.…”

Sample preparation method to improve the efficiency of high-throughput single-molecule force spectroscopy

“…High-throughput single-molecule force spectroscopy (H-SMFS) systems are developed to shorten the SMFS experiment period and enhance resolution within limited time via statistical algorithms (Neuman and Nagy 2008). All H-SMFS systems, such as magnetic tweezers and acoustic tweezers, have the potential to manipulate hundreds of molecules simultaneously (Johnson et al 2017;Lu et al 2017;Madariaga-Marcos et al 2018). Normal SMFS systems, such as optic tweezers (OT) and atomic force microscopy (AFM), have the ability to control specific individual molecules with higher strength often more than 100 pN and even 300 pN (Bennink et al 1999).…”