Automated detection of particle concentration and chemical reactions in EWOD devices

Abstract Real-time measurement of electrical properties are used to perform the first real-time detection of particle concentration and chemical reactions in electrowetting on dielectric devices without the need for optical access. For particle laden droplets, the change in both resistance and capacitance was found to be linear from zero to five-hundred particles with a resolution of approximately six particles for both measurements. Electrical properties were also measured for mixtures of alkaline phosphatase and p-Nitrophenyl Phosphate; reagents commonly used in immunoassays as the resultant chemical reaction produces a yellow precipitate. Experiments were performed with mixtures created off-chip and in droplet that were statically mixed on chip. The difference between the measured and expected capacitance was found to increase with the concentration of alkaline phosphatase and chemical reactions could be positively identified in mixtures made both on and off the chip. Real-time measurements of reagents mixed in a four electrode electrowetting on dielectric mixer were also taken. In these experiments, chemical equilibrium was reached after approximately 20 cycles and the difference between the measured and expected capacitance was over 8.5 times greater than the experimental uncertainty.

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