Abstract
Amorphous calcium carbonate (ACC) plays a key role as transient precursor in the early stages of biogenic calcium carbonate formation in nature. However, due to its instability in aqueous solution, there is still rare success to utilize ACC in biomedicine. Here, we report the mutual effect between paramagnetic gadolinium ions and ACC, resulting in ultrafine paramagnetic amorphous carbonate nanoclusters (ACNC) in the presence of both gadolinium occluded highly hydrated ACC-like environment and poly(acrylic acid). Gadolinium is confirmed to enhance the water content in ACC, and the high water content of ACNC (23 molecules H2O per 1 Gd) contributes to the much enhanced magnetic resonance imaging (MRI) contrast efficiency compared with commercially available gadolinium-based contrast agents. Furthermore, the enhanced T1 weighted MRI performance and biocompatibility of ACNC are further evaluated in various animals including rat, rabbit and beagle dog, in combination with promising safety in vivo. Overall, exceptionally facile mass-productive ACNC exhibits superb imaging performance and impressive stability, which provides a promising strategy to design MR contrast agents.
TEM Investigations of Amorphous Calcium Carbonate Formation in Seawater