BACKGROUND:Studies have testified that nano-ultrasound contrast agents have a strong permeability, making it possible to image the targeted tissues outside blood vessels and overcome the limitation that micron contrast agents are only available for the blood pool imaging. OBJECTIVE:To construct the folate-modified nanoparticles targeting breast cancer as ultrasound contrast agents, as wel as to observe their ability to specifical y bind to cel s and imaging effect in vitro. METHODS:Both contrast agents, pegylated lactic acid-glycolic acid copolymer wrapping liquid fluorocarbon formed nanoparticles (mPP/PFOB) and folate modified pegylated lactic acid-glycolic acid wrapping liquid fluorocarbon formed nanoparticles (mPPF/PFOB), were constructed by phacoemulsification-evaporation method. (1)Biocompatibility detection:HFF-1 and MCF-7 cel s in the logarithmic phase were cultivated with various concentrations (0, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2 and 1 g/L) of mPP/PFOB or mPPF/PFOB for 24 hours respectively, and then the cel viability was measured. (2)Targeting ability detection in vitro:HFF-1 and MCF-7 cel s in the logarithmic phase were divided into three groups. Cy5-labled mPP/PFOB and mPPF/PFOB were added into groups A and B, respectively;the cel s in group C were pretreated with folate for 2 hours, and sequential y Cy5-labled mPPF/PFOB was added into group C. Fluorescence intensity was detected by flow cytometry after 0.5 hours of culture. The distribution of contrast agents in cel s was observed using confocal microscopy after 20 minutes of culture. (3)Ultrasound imaging in vitro:there were three groups:saline was as group A;the suspension of saline and mPPF/PFOB nanoparticles was prepared as group B;MCF-7 cel s were resuspended with the mixture of saline and mPPF/PFOB nanoparticles to prepare the suspension of nanoparticles and cel s as group C. In each group, the suspension was added into latex gloves, that were then tightened and immersed in water. Final y, the ultrasound was use to detect the ultrasound imaging effect in vitro. RESULTS AND CONCLUSION:Neither nanoparticles were with significant cytotoxicity. The flow cytometry showed that the mean fluorescence intensity in MCF-7 cel s of group B was significantly higher than that of groups A and C. But there were no significant differences in the mean fluorescence intensity in HFF-1 cel s among the three groups. It was observed that mPPF/PFOB mainly gathered around the MCF-7 cel membrane, while mPP/PFOB randomly distributed in the cytoplasm. After mPPF/PFOB binding to MCF-7 cel s, they could enhance ultrasound echo in vitro. These findings indicate that the targeted nanoparticles mPPF/PFOB have good biocompatibility and can specifical y bind to breast cancer MCF-7 cel s in vitro and enhance the imaging capability.