A novel magnetic resonance tuning-magnetic relaxation switching sensor based on Gd-MOF/USPIO assembly for sensitive and convenient aflatoxin B1 detection

Aflatoxin B1 (AFB1) can accumulate in different organs or tissues and seriously harm humans. Traditional magnetic relaxation switching (MRS) sensors have relatively low sensitivity, but are complex to use. Rapid small-trace molecule analysis in complex samples is challenging. In this study, we used a gadolinium-based metal–organic framework (Gd-MOF) and ultra-small superparamagnetic iron oxide (USPIO) assembly to develop a magnetic resonance tuning-magnetic relaxation switching (MRET-MRS) sensor to improve conventional MRS sensor sensitivity and simplify operational steps in complex samples. Importantly, the local magnetic field generated by USPIO interfered with Gd-MOF electron spin fluctuation and directly affected dipole–dipole interactions between Gd electrons and water molecules, thus rendering relaxation signal changes more sensitive. The sensitivity (0.54 pg mL−1) was 833 times more sensitive than that of a conventional MRS sensor (0.45 ng mL−1). Finally, a convenient one-step detection approach can be achieved by mixing antigen/antibody functionalized Gd-MOF/USPIO and target samples.