Label-free, nucleotide-mediated dispersion of magnetic nanoparticles for “non-sandwich type” MRI-based quantification of enzyme

► Nucleotide can efficiently adsorb on carboxylic acid-functionalized nanoparticles, such as magnetic nanoparticles (Fe3O4), manganese oxide nanoparticles (MnO), and upconverting nanophosphors, and stabilize the nanoparticles against aggregation. ► Adenosine bearing different numbers of phosphate groups has distinct stabilizing effect. ► A non-sandwich type magnetic relaxation-based detection system for quantitatively probing enzyme was developed.