  Biopolymer topology is critical for determining interactions inside cell
environments, exemplified by DNA where its response to mechanical perturbation
is as important as biochemical properties to its cellular roles. The dynamic
structures of chiral biopolymers exhibit complex dependence with extension and
torsion, however the physical mechanisms underpinning the emergence of
structural motifs upon physiological twisting and stretching are poorly
understood due to technological limitations in correlating force, torque and
spatial localization information. We present COMBI-Tweez (Combined Optical and
Magnetic BIomolecule TWEEZers), a transformative tool that overcomes these
challenges by integrating optical trapping, time-resolved electromagnetic
tweezers, and fluorescence microscopy, demonstrated on single DNA molecules,
that can controllably form and visualise higher order structural motifs
including plectonemes. This technology combined with cutting-edge MD
simulations provides quantitative insight into complex dynamic structures
relevant to DNA cellular processes and can be adapted to study a range of
filamentous biopolymers.
