Taotao Zhu

Magnetic-Field-Assisted Fabrication and Manipulation of Nonspherical Polymer Particles in Ferrofluid-Based Droplet Microfluidics.

We report a novel magnetic-field-assisted method for the fabrication and manipulation of nonspherical polymer particles within a ferrofluid-based droplet microfluidic device. Shape control and chain assembly of droplets with tunable lengths have been achieved.

Continuous separation of non-magnetic particles through negative magnetophoresis inside ferrofluids

We present a simple, low-cost, effective, and label-free continuous flow non-magnetic microparticle separation scheme in a microfluidic device under static magnetic fields. The separation process is based on negative magnetophoresis and uses water-based ferrofluids. We exploit the difference in particle sizes to achieve continuous binary separation of fluorescent microparticles with high throughput and efficiency. We demonstrate size-based separation (2.1 μm and 9.9 μm; 2.1 μm and 4.8 μm) of microparticles with close to 100% separation efficiency and a minimum of 10 particles/hour throughput. This new approach opens the door for the development of label-free continuous cellular separation in microfluidic devices with high throughput, efficiency, and reliability.

Synchronizing stochastic circadian oscillators in single cells of Neurospora crassa

The synchronization of stochastic coupled oscillators is a central problem in physics and an emerging problem in biology, particularly in the context of circadian rhythms. Most measurements on the biological clock are made at the macroscopic level of millions of cells. Here measurements are made on the oscillators in single cells of the model fungal system, Neurospora crassa, with droplet microfluidics and the use of a fluorescent recorder hooked up to a promoter on a clock controlled gene-2 (ccg-2). The oscillators of individual cells are stochastic with a period near 21 hours (h), and using a stochastic clock network ensemble fitted by Markov Chain Monte Carlo implemented on general-purpose graphical processing units (or GPGPUs) we estimated that >94% of the variation in ccg-2 expression was stochastic (as opposed to experimental error). To overcome this stochasticity at the macroscopic level, cells must synchronize their oscillators. Using a classic measure of similarity in cell trajectories within droplets, the intraclass correlation (ICC), the synchronization surface ICC is measured on >25,000 cells as a function of the number of neighboring cells within a droplet and of time. The synchronization surface provides evidence that cells communicate, and synchronization varies with genotype.

Focusing microparticles in a microfluidic channel with ferrofluids

We report a novel on-chip microparticles focusing scheme using stable magnetic nanoparticles suspension (i.e., ferrofluids). The principle of focusing is based on magnetic buoyancy forces exerted on non-magnetic particles within ferrofluids under non-uniform magnetic fields. The design, modeling, fabrication and characterization of the prototype focusing device are presented. Our scheme is simple, low-cost, fast, and applicable to virtually all particles.

Ferrofluidic platform for cell and droplet manipulation

We report a novel on-chip cell and droplet manipulation scheme using magnetic nanoparticles suspension (i.e., ferrofluids). The design and characterization of a size-based cell-sorting device are presented. Magnetic field-assisted fabrication and manipulation of non-spherical polymer particles within a ferrofluidic droplet device is also presented.