Bio-Inspired, Melanin-Like Nanoparticles as a Highly Efficient Contrast Agent for T 1‑Weighted Magnetic Resonance Imaging

The development of nontoxic and biocompatible imaging agents will create new opportunities for potential applications in clinical MRI diagnosis. Synthetic melanin-like nanoparticles (MelNPs), analogous to natural sepia melanin (a major component of the cuttlefish ink), can be used as contrast agent for MRI. MelNPs complexed with paramagnetic Fe3+ ions show much higher relaxivity values than existing MRI T 1 contrast agents based on gadolinium (Gd) or manganese (Mn); MelNP values at 3T were r 1 = 17 and r 2 = 18 mM–1 s–1 (r 2/r 1 value of 1.1). With significant enhancement to MRI contrast, this biomimetic approach using MelNPs functionalized with paramagnetic Fe3+ ions and surface-modified with biocompatible poly(ethylene glycol) units, could provide new insight into how melanin-based bioresponsive and therapeutic imaging probes integrate with their various biological functions.