Vibrating a sessile droplet to enhance mass transfer for high-performance electrochemical sensors

Based on surface reaction technology, electrochemical sensing methods are well suitable for small-volume samples, such as droplets. However, rapid mass transfer of analytes within droplets is usually hard to achieve due to small fluid volumes and minimal convection. Here, we present a mass transfer enhancement method achieved by actuating a sessile droplet into certain vibration modes. Electrodes for electrochemical detection, each with a droplet retainer, are placed on a vertically vibrating platform. The vibrational and mass transfer properties of the sessile droplets are experimentally tested with optical and electrochemical methods. Internal flows generated by the droplet vibration are visualized to explain the enhancement in mass transport. Compared with a static case, measurements with droplet vibration in the (0, 2) mode demonstrate an increase in mass transfer rate of over five times. Finally, improvement in sensing performance of electrochemical sensors caused by vibration is experimentally verified by detecting heavy metal ions and large molecules (proteins) using a gold working electrode.