A wireless chemical sensor featuring iron oxidenanoparticle-embedded hydrogels

tIn this paper, we introduce a wireless chemical sensor based on a magnetically functionalized hydrogels(ferrogels). By embedding superparamagnetic nanoparticles into the hydrogel network and laminatingthe hydrogel on a planar coil, the swelling state of the hydrogel, which depends on the chemical envi-ronment, can be interrogated by measuring its magnetic permeability. To validate the chemical sensingprinciple, 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 downto 0.1 pH unit. It is anticipated that the same scheme can be applied to hydrogels sensitive to differentstimuli (e.g., glucose, specific ions, antigens, temperature, etc.), and that this sensor can be configured forimplantation and wireless monitoring.