A wireless chemical sensor featuring iron oxide nanoparticle-embedded hydrogels

In this paper, we introduce a wireless chemical sensor based on a magnetically functionalized hydrogels (ferrogels). By embedding superparamagnetic nanoparticles into the hydrogel network and laminating the hydrogel on a planar coil, the swelling state of the hydrogel, which depends on the chemical environment, can be interrogated by measuring its magnetic permeability. To validate the chemical sensing principle, a pH sensor is fabricated using a poly(methacrylic acid-co-acrylamide) pH sensitive hydrogel, and repeatable, reversible responses are obtained to pH changes, which are easily discriminated down to 0.1 pH unit. It is anticipated that the same scheme can be applied to hydrogels sensitive to different stimuli (e.g., glucose, specific ions, antigens, temperature, etc.), and that this sensor can be configured for implantation and wireless monitoring.