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Magnetic particles serve as an important tool for a variety of biomedical applications but often lack uniformity in their magnetic responsiveness. For quantitative analysis studies, magnetic particles should ideally be monodisperse and possess uniform magnetic properties. Here we fabricate magnetically uniform Janus particles with tunable magnetic properties using a spin-coating and thermal evaporation method. The resulting 2 μm ferromagnetic particles exhibited a 4% magnetic response variability, and the 10 μm ferromagnetic particles exhibited a 1% size variability and an 8% magnetic response variability. Furthermore, by reducing the film thickness, the particle behavior was tuned from ferromagnetic to superparamagnetic.

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We report on a distributed circuit model for multicolor light-actuated opto-electrowetting devices. The model takes into consideration the large variation of absorption coefficient (15x) of photoconductors in the visible spectrum and the nonuniform distribution of photo-generated carriers. With the help of this model, we designed opto-electrowetting devices with optimum thickness of photoconductors. This leads to significant improvement in performance compared with prior reports, including 200x lower optical power, 5x lower voltage, and 20x faster droplet moving speed. This enables the use of commercial projectors to create on-demand 'virtual' electrodes for large-scale, parallel manipulation of droplets. We have achieved simultaneous manipulation of 96-droplet array. Finally, we have demonstrated parallel on chip detection of Herpes Simplex Virus Type 1 within 45 minutes using a real-time isothermal polymerase chain reaction assay.

We present here an experimental, strictly one-dimensional rotational system, made by using single magnetic Janus particles in a static magnetic field. These particles were half-coated with a thin metallic film, and by turning on a properly oriented external static magnetic field, we monitor the rotational brownian motion of single particles, in solution, around the desired axis. Bright-field microscopy imaging provides information on the particle orientation as a function of time. Rotational diffusion coefficients are derived for one-dimensional rotational diffusion, both for a single rotating particle and for a cluster of four such particles. Over the studied time domain, up to 10 s, the variation of the angle of rotation is strictly brownian; its probability distribution function is gaussian, and the mean squared angular displacement is linear in time, as expected for free diffusion. Values for the rotational diffusion coefficients were also determined. Monte Carlo and hydrodynamic simulations agree well with the experimental results.