Graphene quantum dots-based magnetic relaxation switch involving magnetic separation for enhanced performances of endoglin detection using ultra-low-field nuclear magnetic resonance relaxometry

Magnetic relaxation switches (MRS) based on target-induced state changes of magnetic nanoparticles are vital approaches for biomolecule detection in in vitro diagnosis. Recently, magnetic graphene quantum dots have been employed as magnetic probes instead of iron oxide nanoparticles and showed high sensitivity. Introducing magnetic separation into an MRS assay before the relaxometry measurements can enhance the sensitivity, elevate accuracy, and expand the linear region. In this work, magnetic separation-assisted MRS was developed to detect endoglin utilizing iron oxide as the magnetic carrier and magnetic graphene quantum dots as the magnetic probe. The assay possesses a broad linear region from 5 ng/mL to 50 μg/mL and a sensitive limit of detection of 1.3 ng/mL, which is two orders of magnitude lower than that of MRS without magnetic separation. The high accuracy and consistency have been proved for endoglin (CD105) detection in real samples. This graphene quantum dot-based MRS involving magnetic separation provides a new route for enhancing the sensitivity and accuracy of biomolecule detection.