Covalent Functionalization of FeCo/Graphitic Shell Nanocrystals via 1,3-Dipolar Cycloaddition

Covalently functionalized water-soluble FeCo/graphitic shell nanocrystals (f-FeCo/GC NCs) were synthesized via 1,3-dipolar cycloaddition of azomethine ylides generated in situ from sarcosine and glucose. The FeCo core has superparamagnetic properties at room temperature, and the graphitic shell exhibits near-infrared optical absorbance. Acetylation of the hydroxyl groups on the f-FeCo/GC NCs gives doubly functionalized FeCo/GC (ff-FeCo/GC) NCs that are soluble only in organic solvents such as ethyl acetate. The f-FeCo/GC NCs were shown to be excellent T-1 or T-2 MRI contrast agents. Especially, due to the hydrophilic and compact surface functionalization, f-FeCo/GC NCs exhibit a doubled r(1) relaxivity and half r(2)/r(1) ratio compared to those of the non-covalently PL-PEG-functionalized FeCo/GC NCs. This work shows not only the first synthesis of covalently functionalized highly water-soluble metal NCs coated with a single-layered graphitic shell, but also for the first time the MR enhancing properties of the covalently functionalized magnetic NCs.