An efficient strategy for unmodified nucleotide-mediated dispersion of magnetic nanoparticles, leading to a highly sensitive MRI-based mercury ion assay

► Single-stranded oligonucleotide (ssDNA) can adsorb efficiently on carboxylic acid-functionalized magnetic nanoparticles (CAMNPs). ► We use ssDNA to stabilize the CAMNPs against aggregation in weakly acidic solution. ► We develop a non-sandwich type magnetic relaxation-based detection system for quantitatively probing mercury ion (Hg2+). ► We use the MRI-based high-throughput screening method to detect Hg2+ in 40 samples at the same time.