Magnetically uniform and tunable Janus particles

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98670/1/ApplPhysLett_98_024101.pd

Nanoparticle Induced Cell Magneto-Rotation: Monitoring Morphology, Stress and Drug Sensitivity of a Suspended Single Cancer Cell

Single cell analysis has allowed critical discoveries in drug testing, immunobiology and stem cell research. In addition, a change from two to three dimensional growth conditions radically affects cell behavior. This already resulted in new observations on gene expression and communication networks and in better predictions of cell responses to their environment. However, it is still difficult to study the size and shape of single cells that are freely suspended, where morphological changes are highly significant. Described here is a new method for quantitative real time monitoring of cell size and morphology, on single live suspended cancer cells, unconfined in three dimensions. The precision is comparable to that of the best optical microscopes, but, in contrast, there is no need for confining the cell to the imaging plane. The here first introduced cell magnetorotation (CM) method is made possible by nanoparticle induced cell magnetization. By using a rotating magnetic field, the magnetically labeled cell is actively rotated, and the rotational period is measured in real-time. A change in morphology induces a change in the rotational period of the suspended cell (e.g. when the cell gets bigger it rotates slower). The ability to monitor, in real time, cell swelling or death, at the single cell level, is demonstrated. This method could thus be used for multiplexed real time single cell morphology analysis, with implications for drug testing, drug discovery, genomics and three-dimensional culturing

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

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.Ph.D.Biological SciencesBiophysicsPhysicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126507/2/3253353.pd

High frequency asynchronous magnetic bead rotation for improved biosensors

Biosensors with increasingly high sensitivity are crucial for probing small scale properties. The asynchronous magnetic bead rotation (AMBR) sensor is an emerging sensor platform, based on magnetically actuated rotation. Here the frequency dependence of the AMBR sensor’s sensitivity is investigated. An asynchronous rotation frequency of 145 Hz is achieved. This increased frequency will allow for a calculated detection limit of as little as a 59 nm change in bead diameter, which is a dramatic improvement over previous AMBR sensors and further enables physical and biomedical applications