Bioorthogonal Reactions Amplify Magnetic Nanoparticles Binding and Assembly for Ultrasensitive Magnetic Resonance...

Conventional transverse relaxation time (T₂)-mediated magnetic resonance sensors (MRS) that utilizing the target-induces state change of magnetic nanoparticles (MNPs) mainly suffer from low sensitivity. Recent T₂-MRS that based on target-induced amount change of MNPs can achieve a higher sensitivity, but these sensors can hardly accommodate small molecules. We herein develop an ultrasensitive T₂-MRS that enable the detection of small molecules based on cascade bioorthogonal reactions (BRs)-realized MNPs binding and assembly. Benefiting from rapid and highly selective cascade BRs, a single small molecule target can not only increase MNPs binding but also assembly MNPs, which greatly amplifies T₂ signal for sensing based on both the state and amount change of MNPs for the first time. Our strategy is capable of sensing chlorpyrifos with a liner range of 0.1 ng/mL to 1000 ng/mL. We justify the practicability of our assay by detecting chlorpyrifos in apple and cabbage samples, whose accuracy is higher than that of enzyme linked immunosorbent assay. Our assay provides a cascade BRs-mediated MRS that can greatly broaden the use of T₂-based MRS for ultrasensitive sensing trace small molecules in complex samples.