Towards on-chip chemical reaction monitoring by EWOD impedance measurement

This paper demonstrates the use of impedance sensing in an electrowetting-on-dielectric (EWOD) chip to monitor the progress of a chemical reaction. Sensing is achieved by measuring the current through a sample droplet with the aid of a lock-in amplifier. Monitoring of the reaction of HCl with NaOH (i.e., during a titration) was demonstrated. A sharp minimum in the impedance signal was observed at the titration equivalence point, enabling the endpoint to be determined electronically. Future work is aimed at extending reaction monitoring to additional acid-base systems and other classes of reactions.