Nanoprobe achieves sharper MRIs of the inner ear

Doctors often struggle to get clear images of the inner ear, a tightly protected organ encased in bone. The body’s natural obstacles make it difficult to get magnetic resonance imaging (MRI) contrasts into the ear to diagnose tumors, infections, or malformations. Now a team of researchers has developed a nanoparticle-based MRI contrast that can grab on to inner ear cells and sneak its way inside (Chem. Biomed. Imaging 2025, DOI: 10.1021/cbmi.5c00049).

“Standard . . . imaging agents rarely reach this tissue and clear out very fast, forcing clinicians to use higher doses, which raises the risk of hearing damage and toxicity,” says Huan Wang, a biomedical chemist at Changchun Institute of Applied Chemistry and the study’s senior author. The challenge comes from a protective set of cells lining the blood vessels between the middle and inner labyrinth of the ear—the blood-labyrinth barrier, or BLB.

This cellular defense allows nutrients and oxygen to pass through but blocks other molecules, including many drugs and contrast agents. To address this, Wang’s team has created the first guided MRI nanoprobe shown to cross this BLB and accumulate in the inner ear.

The probe combines three features: an iron oxide core just 3.3 nm across that serves as the MRI contrast, a polyethylene glycol (PEG) coating that keeps the contrast circulating in the bloodstream, and a short peptide intermingled with the PEG called IETP2.

Wang explains that the IETP2 sticks to LRP1—a receptor found throughout the body but especially abundant in the BLB—which is able to ferry useful molecules across the barrier, essentially letting the nanoprobe hitch a ride into the inner ear. “By attaching the nanoparticles to a peptide which targets the receptor on the BLB, the team found a way to push the probes past the barrier,” says Carmen Burtea, a biomedical imaging researcher at Université de Mons who was not involved in the study.

In mice, the nanoprobes crossed the BLB efficiently and stayed in circulation long enough to reach the cochlea. They produced up to 84% stronger MRI signals than untargeted controls, with no damage to any major organs.

“The untargeted version of the nanoprobe is already known to enhance contrast at lower doses than [standard] gadolinium agents,” Burtea says. She adds that if the probe passes risk assessments, it could give doctors a new tool to diagnose both fluid buildup and structural changes within the inner ear.

Wang agrees that clinical translation will require toxicology tests and larger-animal studies. Johannes Gerb, a biomedical imaging researcher at Ludwig Maximilian University Munich who also was not involved in the study, notes that if the probe can match gadolinium’s performance at lower cost and with comparable safety in humans, “it could become a viable alternative.”

Looking ahead, Wang says that “the platform can also be used as a general platform to ferry drugs or gene therapies to the inner ear,” though he cautions that avoiding unintended delivery to other LRP1-expressing tissues would require troubleshooting. The potential also resonates with clinicians. “Modalities such as this are an exciting avenue as they can definitely reduce the toxic loads of current medications,” says Rajesh Bhardwaj, an otolaryngologist at MedFirst ENT Centre in India who was not involved in the study.