Margaret F. Bennewitz1, Michael K. Nkansah1, Tricia L. Lobo2, Erik M. Shapiro1,2
1Department of Biomedical Engineering, Yale University, New Haven, CT, USA; 2Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT, USA
Inorganic manganese particles are attractive for molecular and cellular imaging due to their potential to provide bright contrast on MRI. We have fabricated pH-sensitive, poly(lactic-co-glycolic-acid) (PLGA) encapsulated manganese oxide (MnO) nanocrystals. Particles were fabricated at 140-nm and 1.7-μm, and incorporated 15 to 20-nm MnO nanocrystals. Intact particles at physiological pH cause little MRI contrast, but following endocytosis into low pH compartments within cells, particles erode, and MnO dissolves to release Mn2+, causing cells to appear bright on MR images. The change in MRI properties is as high as 35-fold, making it the most dynamic smart MRI contrast agent yet reported.