GHz ultrasonic sensor for ionic content with high sensitivity and localization

Sensing the ionic content of a solution at high spatial and temporal resolution and sensitivity is a challenge in nanosensing. This paper describes a comprehensive investigation of the possibility of GHz ultrasound acoustic impedance sensors to sense the content of an ionic aqueous medium. At the 1.55 GHz ultrasonic frequency used in this study, the micron-scale wavelength and the decay lengths in liquid result in a highly localized sense volume with the added potential for high temporal resolution and sensitivity. The amplitude of the back reflected pulse is related to the acoustic impedance of the medium and a function of ionic species concentration of the KCl, NaCl, and CaCl2 solutions used in this study. A concentration sensitivity as high as 1 mM and concentration detection range of 0 to 3 M was achieved. These bulk acoustic wave pulse-echo acoustic impedance sensors can also be used to record dynamic ionic flux. [Display omitted] •A pulse-echo bulk acoustic wave GHz ultrasonic sensor for ionic content is developed•GHz ultrasonic wavefronts allow for high spatial and temporal resolution•The sensor is a label-free and sensitive method to detect acoustic impedance•Both ionic content and dynamic ionic flux can be measured as a function of time Ultrasound technology; Physics; Applied physics; Radiation physics; Sensor system; Devices