Multifold enhanced T2 relaxation of ZnFe2O4 nanoparticles by jamming them inside chitosan nanospheres

ZnFe2O4 nanoparticles were tightly packed and encapsulated in chitosan nanospheres by a nonsolvent-aided counterion complexation method. The obtained hybrid nanospheres exhibited not only the superparamagnetic properties provided by pure ZnFe2O4 nanoparticles but also a much higher r(2) relaxivity value than separate ZnFe2O4 nanoparticles, representing an approximately 3 to 16 fold increase. This was attributed to the high ZnFe2O4 payload and ZnFe2O4 nanoparticle clustering effect in the core of the nanospheres. The MR images generated in vivo demonstrated that the hybrid nanospheres showed an excellent contrast in T-2 weighted MRI and a high MRI sensitivity in the tumor sites for both passive and active targeting samples. In addition, the biodistribution analysis revealed that the obtained hybrid nanospheres could accumulate at tumor sites via passive and active targeting strategies.