Direct protein detection in the sample solution by monitoring rotational dynamics of nickel nanorods

The feasibility of a recently introduced homogeneous immunodiagnostic approach to directly detect analyte binding by optical observation of the hydrodynamic properties of magnetically rotated nanorods ("PlasMag") is demonstrated experimentally. Specifically, it is shown that the phase lag of the long axis of nickel nanorods (magnetic core parameters: length 182 nm, diameter 26 nm) with respect to externally applied rotating magnetic fields significantly increases on the adhesion of bovine serum albumin (BSA) protein to their surfaces. To validate these results, the amount of bound protein molecules is independently determined by analysis of the electrophoretic mobility of the nanorods. Furthermore, the data also demonstrate the applicability of recently developed empirical models based on numerical solutions of the Fokker-Planck equation for describing the dynamics of magnetic nanoparticles in rotating magnetic fields.