Department of Biomedical Engineering, University of Texas at Austin, Austin, Texas 78712, USA.
Nano Lett. 2011 Feb 9;11(2):348-54. doi: 10.1021/nl1042006. Epub 2011 Jan 18.
Photoacoustic signal generation by metal nanoparticles relies on the efficient conversion of light to heat, its transfer to the environment, and the production of pressure transients. In this study we demonstrate that a dielectric shell has a strong influence on the amplitude of the generated photoacoustic signal and that silica-coated gold nanorods of the same optical density are capable of producing about 3-fold higher photoacoustic signals than nanorods without silica coating. Spectrophotometry measurements and finite difference time domain (FDTD) analysis of gold nanorods before and after silica coating showed only an insignificant change of the extinction and absorption cross sections, hence indicating that the enhancement is not attributable to changes in absorption cross section resulting from the silica coating. Several factors including the silica thickness, the gold/silica interface, and the surrounding solvent were varied to investigate their effect on the photoacoustic signal produced from silica-coated gold nanorods. The results suggest that the enhancement is caused by the reduction of the gold interfacial thermal resistance with the solvent due to the silica coating. The strong contrast enhancement in photoacoustic imaging, demonstrated using phantoms with silica-coated nanorods, shows that these hybrid particles acting as "photoacoustic nanoamplifiers" are high efficiency contrast agents for photoacoustic imaging or photoacoustic image-guided therapy.
金属纳米粒子的光声信号产生依赖于光向热的有效转换、热向环境的传递以及压力瞬变的产生。在本研究中，我们证明了介电壳层对产生的光声信号幅度有很强的影响，并且具有相同光密度的二氧化硅包覆的金纳米棒能够产生比没有二氧化硅包覆的纳米棒高约 3 倍的光声信号。金纳米棒在二氧化硅包覆前后的分光光度测量和有限差分时域（FDTD）分析表明，消光和吸收截面仅发生了微不足道的变化，因此表明增强不是归因于二氧化硅包覆导致的吸收截面变化。改变了几种因素，包括二氧化硅厚度、金/二氧化硅界面和周围溶剂，以研究它们对二氧化硅包覆金纳米棒产生的光声信号的影响。结果表明，增强是由于二氧化硅包覆降低了金与溶剂之间的界面热阻所致。使用具有二氧化硅包覆纳米棒的体模进行的强对比增强光声成像表明，这些作为“光声纳米放大器”的混合粒子是用于光声成像或光声图像引导治疗的高效对比剂。
