Objective:To explore the efficiency of super-paramagnetic iron oxide(SPIO)of different concentrations in vitro labeling human fibroblast cells as well as the influence on cellular viability

and to investigate the characteristics of magnetic resonance imaging.Methods:Respectively mix pure SPIO(concentration of iron:200 μg/ml) and SPIO-PLL compound of different concentrations with substrate(final concentrations of iron:150

100

50

25 μg/ml;final concentration of PLL:7.5 μg/ml).Then incubate it with Hfbs for 12

24

48 h and 72 h.Collect the cells.Assess cellular viability with Trypan Blue Dye Exclusion Method;test iron particles distribution in cells with Prussian blue Stain;observe the positions of iron particles with optical microscope and TEM and calculate the labeling rate of SPIO;perform MR scanning to measure the signal intensity change of the cells.Results:Labeling efficiency of SPIO-PLL compound is much higher than that of pure SPIO(P<0.05).Trypan Blue Dye Exclusion test shows the viability difference between the cells labeled with 100 μg Fe/ml or lower iron content solutions and the comparison is not statistically significant(P>0.05).Prussian blue Stain test shows there are more or less blue dyed iron particles inside cytoplasm of each labeled cells.And those iron particles concentrate in endosome and lysosome(with electron microscope).Culture solution of concentration in the range of 25～50 μg Fe/ml is safe for labeling stem cells with SPIO

and 95%～100% of the cells will be effectively labeled in 18～24 h.And the MR scanning shows obvious reduction of signal intensity of the labeled cells.Conclusion:Human fibroblast cells can be easily and safely labeled with self-made SPIO-PLL compound.Labeling with appropriate solution(iron content of 25 μg/ml) is highly efficient and has little influence on cellular viability

furthermore

with SPIO labeling

the signal intensity of cells scanned with MR is dramatically reduced.