A wireless chemical sensing scheme using ultrasonic imaging of microbubble embeded hydrogel

In this paper, we demonstrate a wireless chemical sensing scheme using ultrasonic imaging of a microbubble-functionalized hydrogel, which we call “bubblegel.” By incorporating oxygen microbubbles into a hydrogel, its volume transition, which is responsive to its chemical microenvironment, can be wirelessly monitored by ultrasonic imaging; measuring volume directly or measuring the reflected acoustic intensity from the surface of the bubblegel. Here a bubblegel fabricated with pH-sensitive poly (methacrylic acid-co-acrylamide) hydrogel is investigated in vitro. The sensor shows a sensitivity of 19.49 gray-scale intensity/pH and a resolution of 0.25 pH unit in the linear response region (between pH 4 and 6). It is expected that the concept can be adapted to hydrogels sensitive to other stimuli (e.g., glucose, biomarkers, etc.).