The Observation Protein Position and Orientation Dynamics using an Unbleachable Probe

We develop a novel sensor (MagPI) for biophysical applications that can simultaneously measure the three-dimensional position and orientation of a nanoparticle probe. This probe is unbleachable and unblinking and therefore is ideally suited to many in vitro biophysical applications, where precision tracking of probe 3D-position and orientation could provide significant new insights, but long-timescale and high-temporal resolution imaging is required which precludes the use of single-molecule fluorescent probes. Orientation and position sensing are performed by imaging the magnetic dipole-field generated by the nano-particle probe. The physical mechanism for magnetic-field imaging is the B-field-induced shift of the photo luminescence intensity of nitrogen-vacancy centers in a diamond sensor. We demonstrate MagPI imaging in a tethered-particle-motion analysis of Lac-repressor induced DNA looping