Batch-fabricated hydrogel/polymeric-magnet bilayer for wireless chemical sensing

This paper introduces a fabrication and wireless chemical sensing scheme using a hydrogel/polymeric-magnet bilayer. The swelling/deswelling of the hydrogel in response to chemical stimuli (e.g. pH, glucose etc.) results in vertical movement of the polymeric permanent magnet located on top of the hydrogel film. The hydrogel volume change is wirelessly detected by a giant magnetoresistance (GMR) sensor. A pH-sensitive hydrogel magnet bilayer is fabricated and tested as proof of the concept. The sensor shows a sensitivity of 0.01 Oe/pH, a resolution of 0.05 pH unit between pH 4 and pH 6, and a response time of 30 minutes. The described device is the first integrated wireless hydrogel/polymeric-magnet transducer with potential applications in biomedical and environmental sensing areas.