The lack of effective siRNA delivery vector with low toxicity limited the development of siRNA therapy.The cationic molecule diethylenetriamine (DETA) with low molecular weight was grafted on the block copolymer (PEG-PAsp) of poly(aspartic)(PAsp) and poly(ethylene glycol)(PEG) to make a ternary copolymer PEG-PAsp(DETA)30.The MTT analytical results demonstrated that the PEG-PAsp(DETA)30-SPIONs have lower cytotoxicity.The biodegradable of PEG-PAsp and the low molecular weight of DETA endow the nanocarrier with good biocompatibility.Furthermore

the MR contrast imaging agent SPIO was introduced into copolymer via a ligand exchange method

yielding a MR-visible nanocarrier for imaging siRNA delivery and therapy simultaneously.The SPIONs didn't affect the loading of siRNA.Based on the data of zeta potential and diameter

the N/P=12 was used to prepare the PEG-PAsp(DETA)30-SPIONs@siRNA nanoparticle.The MRI-visible polyplexs of N/P=12 exhibited higher T2 relaxivity (r2=147 Fe (mmol/L)-1 s-1) than WSPIO (r2=46.4 Fe (mmol/L)-1 s-1)

indicating high MRI T2-weighted imaging sensitivity.Using the laser confocal microscope and prussian blue staining

the efficient co-delivery of siRNA and SPIO was confirmed in the present study.Moreover

the luciferase gene-specific siRNA delivered with vector could effectively inhibit the firefly luciferase gene expression in cancer cells.SPIO co-delivered with siRNA provides a real-time and noninvasive approach to guide the optimization of the properties of siRNA delivery vector.