8 May 2014 Optoelectrowetting for continuous microdroplet actuation
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Abstract
Microfluidics technologies have received great attention and appear in many bioanalyses applications. A recent microfluidics subset has appeared as droplet-based digital microfluidics (DMF). Here, microdroplets are manipulated in a two-dimensional on-chip plane using electric fields, contrasting the one-dimensional pressure-based channel flow of continuous flow microfluidics. These DMF systems fundamentally offer reconfigurability, whereby one device performs many bioanalysis tasks. A subset of DMF systems called optoelectrowetting is also of recent interest due to its ability for intricate microdroplet routing processes in the on-chip plane. For an optoelectrowetting chip, the DMF structure is modified with optically triggered electrodes with arrayed photoconductive switches. The arrayed photoconductive switches are optically-activated so microdroplets in the vicinity are routed to the illuminated switch. Unfortunately, such systems still require intricate electrode arrays, limiting microdroplet actuation resolution by the electrode size. This work proposes an on-chip optofluidic device with a continuous and planar semiconductor layer as the photoconductive mechanism. An illuminated section of the semiconductor layer acts as a localized electrode, with the photogenerated charge-carriers attracting nearby microdroplets. Given this planar topology, the illuminating beam is used to move the microdroplets continuously over the on-chip plane with precise optical control. The resolution for such a process is ultimately limited by charge-carrier diffusion, so an alternative material, a nanocomposite, is introduced to the on-chip device design. The nanocomposite consists of 20 nm semiconductor nanoparticles embedded in an insulative polymer host. This gives restricted diffusion length, being on the nanometer-scale of the nanoparticle diameter. Experimental device operation is demonstrated.
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Christopher M. Collier, Kyle A. Hill, Mark A. DeWachter, Alex M. Huizing, Jonathan F. Holzman, "Optoelectrowetting for continuous microdroplet actuation", Proc. SPIE 9129, Biophotonics: Photonic Solutions for Better Health Care IV, 91293Q (8 May 2014); doi: 10.1117/12.2052040; https://doi.org/10.1117/12.2052040
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