Synthesis and characterization of pH-responsive ferrogels comprising sulfamethazine-based polymer and magnetic nanoparticles for sensing ammonia gas

Abstract

Ferrogels have been widely used in soft actuators and as carriers in drug delivery systems owing to their responsiveness to magnetic stimulus. Herein, a novel ferrogel that exhibits chemically modulated magnetism is synthesized, by dispersing magnetic nanoparticles (MNPs) in a hydrogel produced from a pH-responsive sulfamethazine-based polymer during polymerization and cross-linking. The MNPs exhibit dynamic rotations or oscillations in the rheological matrix under alternating current (AC) magnetic fields. The AC magnetization behavior of the incorporated MNPs is modulated by the swelling of the hydrogel in response to changes in pH over the range of 7–12. The ferrogels with larger swelling ratios exhibit enhanced Brownian relaxation during AC magnetization. Based on the pH response of the AC magnetization, the detection of ammonia gas is investigated using the ferrogel as a sensing label, and the sensitivity of 5.3 × 10−6 mol/L or lower has been achieved. Therefore, the as-prepared ferrogel is suitable for use as a sensing label in applications such as the sensing of ammonia emitted from human skin for health monitoring.