Aggregation‐Augmented Magnetism of Lanthanide‐Doped Nanoparticles and Enabling Magnetic Levitation‐Based Exosome Sensing

Abstract Due to the presence of unpaired electron orbitals in most lanthanide ions, lanthanide‐doped nanoparticles (LnNPs) exhibit paramagnetism. However, as to biosensing applications, the magnetism of LnNPs is so weak that can hardly be employed in target separation. Herein, it is discovered that the magnetism of the LnNPs is highly associated with their concentration in a confined space, enabling aggregation‐augmented magnetism to make them susceptive to a conventional magnet. Accordingly, a magnetic levitation (Maglev) sensing system is designed, in which the target exosomes can specifically introduce paramagnetic LnNPs to the microbeads’ surface, allowing aggregation‐augmented magnetism and further leverage the microbeads’ levitation height in the Maglev device to indicate the target exosomes' content. It is demonstrated that this Maglev system can precisely distinguish healthy people's blood samples from those of breast cancer patients. This is the first work to report that LnNPs hold great promise in magnetic separation‐based biological sample sorting, and the LnNP‐permitted Maglev sensing system is proven to be promising for establishing a new generation of biosensing devices.