Synthesis, Characterization And Application Of Bi₂S₃Nanoparticles With High X-ray Absorption

X-ray computed tomography （CT） is regarded as one of the most powerful diagnosticimaging technique with the help of contrast agents. Currently, the CT contrast agentsapproved for clinical use are small iodinated molecules. For many years’ use as CTcontrast agents in vivo, these iodinated molecules exposed some shortages gradually.The appearance of nanobiotechnology provides a potential solving method for thedeficiency of iodine contrast agents. Bi₂S₃nanomaterials maybe is the most promisingcontrast agents, because Bi has the large atomic number （Bi,83） and X-ray attenuationcoefficient （Bi,5.74cm2g-1at100keV）, while the atomic number and X-ray attenuationcoefficient of iodine are53and1.94cm2g-1respectively. In this paper, we had prepareddifferent hydrophilic Bi₂S₃nanorods via a hot injection method, and modified one of themthe biological utility. We characterized the nanomaterials with X-ray diffraction （XRD）,fourier transform infrared spectrometer （FT-IR）, transmission electron microscopy（TEM）, and detected their CT contrast with a high-resolution CT system. Next, thecytotoxicity of hydrophilic Bi₂S₃nanomaterials was examined through an MTT assay andan extensive TEM analysis of hydrophilic Bi₂S₃nanomaterials taken up in RAW264.7cells was carried out to confirm the validity of the above cytotoxicity experiments. Themain work includes:（1） Bi₂S₃nanorods were synthesized through a hot injection method using BiCl3as abismuth precursor and elemental sulfur as a sulfur source. When the ratio of the precursors（ρ=[S]/[Bi]） was2:1, the nanorods were allowed to grow at170°C. If the ratio of theprecursors was1:5, the reaction was happened at130°C. In addition, hydrophilic Bi₂S₃nanorods were prepared by another strategy, using BiCl3as a bismuth precursor andthioacetamide as a sulfur source. The characterization of the nanocrystals suggests that thenanorods synthesized with the first strategy have an orthorhombic structure, the length anddiameter was14nm and7nm respectively. Next, we use these Bi₂S₃nanoparticles for thesurface modification.（2） Hydrophobic Bi₂S₃nanorods were surface modified for the hydrophilicity. Thereare two different strategies: Bi₂S₃nanorods were surface modified with tetraethylorthosilicate （TEOS） and2-[methoxy（polyethyleneoxy）propyl]yrimethoxysilane （PEG-silane）to yield Bi₂S₃@SiO₂-PEG nanoparticles; Pluronic F127, triblock copolymer of PEO-PPO-PEO,coated the Bi₂S₃nanorods to obtain the hydrophilic Bi₂S₃-PF127nanoparticles. The resultsof transmission electron microscopy （TEM） and fourier transform infraredspectrometer （FT-IR） results show that the resulting Bi₂S₃@SiO₂-PEG and Bi₂S₃-PF127have great hydrophilicity. X-ray phantom images were acquired using variousconcentration of Bi₂S₃@SiO₂-PEG and Bi₂S₃-PF127dispersed in water. It was found thatthe CT number, called Hounsfield units （HU）, increased linearly as the concentration ofthe nanoparticles increased. In other words, at the same X-ray absorption, the dosage ofBi₂S₃@SiO₂-PEG and Bi₂S₃-PF127is much less than iobitridol. The dose reduction meansit can significantly reduce the potential for adverse reactions in patients in clinicalapplications.（3） Next, the cytotoxicity of Bi₂S₃@SiO₂-PEG and Bi₂S₃-PF127were examinedthrough an MTT assay using murine macrophage （RAW264.7） cells. We carried out anextensive TEM analysis of Bi₂S₃@SiO₂-PEG taken up in RAW264.7cells to confirm theviability of the above cytotoxicity experiments. The cell viability was not hindered byBi₂S₃@SiO₂-PEG up to a concentration of2.1mg/mL and Bi₂S₃-PF127up to aconcentration of3.2mg/mL of Bi, which was an extremely high concentration. Probeswere directly in contact with tissue fluid and without visible harm to cell.