Three-dimensional assembly and disassembly of Fe3O4-decorated porous carbon nanocomposite with enhanced transversal relaxation for magnetic resonance sensing of bisphenol A.

The design and construction of a novel magnetic resonance sensor (MRS) is presented for bisphenol A (BPA) detection. The MRS has been built based on the core component of magnetic Fe3O4 nanoparticles (~ 40 nm), which were uniformly distributed in nanoporous carbon (abbreviated as Fe3O4@NPC). The synthesis was derived from the calcination of the metal organic framework (MOF) precursor of Fe-MIL-101 at high temperature. Fe3O4@NPC was confirmed with enhanced transversal relaxation with r2 value of 118.2 mM-1 s-1, which was around 1.7 times higher than that of the naked Fe3O4 nanoparticle. This enhancement is attributed to the excellent proton transverse relaxation rate of Fe3O4@NPC caused by the reduced self-diffusion coefficient of water molecules in the vicinity of Fe3O4 nanoparticles in the nanoporous carbon. BPA antibody (Ab) and antigen (Ag)-ovalbumin (OVA) were immobilized onto the Fe3O4@NPC to form Ab-Fe3O4@NPC and Ag-Fe3O4@NPC, respectively. These two composites can cause the three-dimensional assembly of Fe3O4@NPC via immunological recognition. The presence of BPA can compete with antigen-OVA to combine with Ab-Fe3O4@NPC, thereby breaking the assembly process (disassembly). The difference in the change of the T2 value before and after adding BPA can thus be used to monitor BPA. The proposed MRS not only revealed a wide linear range of BPA concentration from 0.05 to 50 ng mL-1 with an extremely low detection limit of 0.012 ng mL-1 (S/N = 3), but also displayed high selectivity towards matrix interferences. The recoveries of BPA ranged from 95.6 to 108.4% for spiked tea π, and 93.4 to 104.7% for spiked canned oranges samples, respectively, and the RSD (n = 3) was less than 4.4% for 3 successive assays. The versatility of Fe3O4@NPC with customized relaxation responses provides the possibility for the adaptation of magnetic resonance platforms for food safety development. The magnetic Fe3O4 nanoparticles are uniformly dispersed in the nanoporous carbon (Fe3O4@NPC), which derived from the calcinating of the metal organic framework (MOF) precursor of Fe-MIL-101. And the magnetic Fe3O4@NPCs are adopted for the construction of magnetic resonance sensor (MRS) for bisphenol A (BPA) detection.