Magnetic micro and nano nonlinear oscillators with applications to the dynamic detection of a single bacterium and to physical and chemical sensing.

Abstract

The nonlinear rotation of a magnetic particle, suspended in a viscous fluid, occurs when a driving magnetic field, used to rotate the magnetic particle, exceeds some critical frequency. This type of rotational dynamics depends on physical parameters, such as the particle's magnetic moment, the external magnetic field, and the rotational drag that the particle experiences. Therefore, by studying the rotational dynamics of a magnetic particle, a variety of physical properties can be measured on the microscale and nanoscale. Accordingly, this thesis gives a detailed theoretical analysis for measurements of (1) local magnetic fields, (2) magnetic particle characteristics, (3) viscosity and (4) chemical binding, along with their corresponding experimental demonstrations. The idea of combining physical measurements with chemical sensors is also discussed. One of the most promising applications for nonlinear magnetic oscillators---that result from changes in drag---is for the fluid-based detection of single biological agents. This application was demonstrated using a particle to mimic a bacteria and also with Escherichia coli, where an easily measurable change in the nonlinear rotation frequency was made in both cases. This concept can be extended to study of single bacterial growth dynamics with potential applications for antibiotic susceptibility measurements.