The electrochemical detection of droplets in microfluidic devices

This paper presents a new electrochemical method for the detection and characterisation of aqueous droplets in an organic carrier fluid ( 1,2-dichloroethane) formed in flow-focusing microfluidic devices. The devices consist of a conventional flow-focusing channel 250 mu m wide and 250 mu m deep cast out of poly( dimethylsiloxane) ( PDMS) which is sealed onto a glass substrate containing a set of microelectrodes 100 mu m long. Chronoamperometric analysis of a suitable electrolyte contained in the organic phase is presented for characterising the droplet frequency and size. This chronoamperometric method is then extended to a dual working electrode approach in order to determine the velocity of the droplet. Good agreement between experimental measurements and theory was observed.