Direct heating of aqueous droplets using high frequency voltage signals on an EWOD platform

We demonstrate a new technique of heating aqueous droplets on conventional EWOD electrodes by using high-frequency high-voltage AC signals. At high actuation frequencies (10–1000 kHz), the droplet temperature rises due to Joule heating from the ohmic currents inside the drop. Using this direct heating technique, we were able to achieve temperatures of 93–94 °C, which is significant for several biochemical applications. The technique is studied extensively using experiments and modelling. Several performance parameters of this heating technique were compared with a standard microheater through experiments and simulation. For the presented technique, the substrate near the droplet was cooler in comparison to the microheater. This will reduce parasitic heating of nearby droplets. A comprehensive study regarding the optimization of the geometrical parameters and the capability to heat solutions to higher temperatures using lower voltage and higher frequency were also performed using simulations. As conventional EWOD electrodes are used for heating the liquid, separate microheaters are not required. This significantly simplifies design and allows us to heat any droplet at any location on the chip. This on demand reconfigurability of droplet heating is the primary benefit of this technique. To establish the abilities of our suggested method, two biochemical experiments were demonstrated.