具备高光吸收能力和良好的生物相容性的等离子纳米探针在光声分子成像中得到了广泛应用.理论分析发现,由于纳米探针的小尺寸效应,其比表面积急剧增大,致使其光、热性质及光声能量转换机制对尺寸具有强烈依赖性.本文利用有限元分析的方法,以金纳米球和金纳米棒为例,定量讨论了浸没在水中具有不同尺寸的纳米探针在受到脉冲激光照射时的光学吸收、温度场分布及热膨胀随时间演绎的过程,并获得了尺寸在20-150nm范围内探针光声转换效率对尺寸的依赖关系.结果表明:纳米探针的光-声转换效率对尺寸有较强的依赖性,金纳米球和金纳米棒在20-150nm范围内均存在最佳尺寸使得光声转换效率最大.定量评价金纳米粒子光声转换效率的尺寸效应为指导通过优化纳米探针尺寸实现构建高效率光声探针提供了理论依据.%Efficient contrast agents such as gold nanoparticles ( GNPs) are highly desirable for good-performance photo-acoustic ( PA) imaging. Theoretical analysis found that, owing to the small size effect, GNPs have a unique microscopic mechanism of PA conversion from photons to ultrasound. Here, by quantitatively modeling the optical absorption, the time-resolved temperature field and thermal expansion based on analytical and finite element analysis method, we ob-tained the quantitative size-dependent PA conversion efficiency of gold nanospheres/nanorods spanning a comprehensive range of particle size (20-150 nm). Results show that, both the plasmon-mediated absorption and energy conversion from absorbed laser energy to ultrasound are strongly dependent on the GNPs size, which comes from their sharply in-creased surface-to-volume ratios. The gold nanospheres and nanorods possess peak size values for maximizing the PA conversion efficiency in the size ranging from 20 nm to 150 nm. Our work gives theoretical guidelines for constructing high-sensitive PA nanoprobes through rational optimization of the GNPs size.
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