Mesenchymal stem cell in vitro labeling by hybrid fluorescent magnetic polymeric particles for application in cell tracking. 
Mesenchymal stem cells (MSCs) are a type of adult stem cell that contains multi-differentiation and proliferative properties and that shows high treatment implications for many clinical problems.  The outcome of stem cell transplantation is still limited due to many factors, especially their survival and their interaction with the microenvironment after transplantation.  Molecular imaging is a challenging technique that has been used to overcome this limitation and is based on the concept of labeling cells with tractable, visible, and non-toxic materials to track the cells after transplantation.  In this study, magnetic polymeric nanoparticles (MPNPs) were used to directly label Wharton's jelly-derived MSCs (WJ-MSCs).  After labeling, the growth rate and the viability of the MSCs as well as the time of exposure were determined.  The 3D images of WJ-MSCs labeled with MPNPs for 24 h were created using confocal microscopy.  The results showed that, after incubation with fluorescent MPNPs for over 8 h, the growth rate and cell viability of the WJ-MSCs was similar to those of the control.  Three-dimensional imaging revealed that the fluorescent MPNPs could infiltrate into the cells and spread into the cytoplasm, which suggests that the synthesized fluorescent MPNPs could possibly label MSCs for cell tracking study and be further developed for in vivo applications.