A Wireless Chemical Sensing Scheme using Ultrasonic Imaging of Silica-Particle-Embedded Hydrogels (Silicagel)

Abstract

In this paper, we introduce a wireless chemical sensing technique featuring ultrasonic imaging of a silica bead -embedded hydrogel, named "silicagel". By incorporating silica beads within a hydrogel network, its volume change in response to environmental stimuli can be remotely interrogated by ultrasonic imaging, either by directly measuring its dimensions (cross-section of the silicagel) or indirectly evaluating the back-scattered wave intensity. Various sizes (4 and 2 mm cube) and concentrations (0.05 and 0.1 w/v%) of silicagel fabricated with pH-sensitive poly (methacrylic acid-co-acrylamide) hydrogel is studied in vitro, using a 40 MHz ultrasonic imaging system. For the silicagel with 4 mm cube and 0.05 w/v% (as a representative), its cross-section sensing method results in a sensitivity of 0.83 (mm(2)/mm(2))/pH with a theoretical resolution of 0.001 pH while back-scattered intensity technique exhibit a sensitivity of 17.5 gray-scale intensity/pH with a resolution of 0.06 pH unit in the maximal response region (between pH 4 and 6). It is anticipated that the same technique can be applied to hydrogels sensitive to other stimuli (e.g., glucose, specific ions, biomarkers, etc.). (C) 2017 Elsevier B.V. All rights reserved.