Vibrating an air bubble to enhance mass transfer for an ultra-sensitive electrochemical sensor

Rapid mass transfer of analytes is essential for effective electrochemical sensing. Here, we present a vibrating air bubble as a stirrer and evaluate the optimal working frequency. A vibration system that contains a flexible piezoelectric plate coupled with a trapped bubble integrated with a gold working electrode is employed. The vibrational properties and mass transfer of the coupled system are experimentally tested with optical and electrochemical methods, respectively. Streaming flows generated by the vibrating bubble are characterized by visualization to explain the enhancement of mass transport to the working electrode. Compared with a static case, measurements with a vibrating bubble demonstrate a twelve-times enhancement in mass transfer coefficient. Enhanced sensing performance is experimentally quantified with the bubble stirrer and its integrated electrochemical metal ion sensor. This integrated system can be used for various types of electrochemical sensing applications that are limited by slow molecular diffusion.