Figure 18.

Sketch of the biosensing principle making use of magnetic particle labels with intrinsic optical shape anisotropy: (a) Rod-shaped nanoprobe comprising a magnetic core and a noble metal shell with antibodies on the particle surface for specific binding of target proteins; (b) The ferromagnetic nanorod follows the applied rotating magnetic field (RMF) with a phase lag α due to the drag torque experienced in the sample solution, which depends on the hydrodynamic nanoprobe volume; (c) Binding of target proteins increases the hydrodynamic drag and, consequently, the phase lag α; (d) The transmission of linearly polarized light is detected. Its intensity directly relates to the actual orientation of the nanoprobe with respect to the polarization direction (angle α). Comparison of the optical signal with the momentary orientation of the RMF allows deduction of the angle α. Reprinted with permission from [291]. Copyright 2016, American Chemical Society.