Calculated absorption and scattering properties of gold nanoparticles of different size, shape, and composition: Applications in biological imaging and biomedicine
Calculated absorption and scattering properties of gold nanoparticles of different size, shape, and composition: Applications in biological imaging and biomedicine
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DOI：
10.1021/jp057170o
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发表时间：
2006-04-13
影响因子：
3.3
通讯作者：
El-Sayed, MA
中科院分区：
文献类型：
--
作者：
Jain, PK;Lee, KS;El-Sayed, MA
用于实现生物和细胞成像应用以及光热治疗应用的有效对比度的纳米颗粒的选择基于纳米颗粒的光学性质。我们使用米氏理论和离散偶极近似方法来计算三种常用的纳米粒子：金纳米球，硅-金纳米壳和金纳米棒的吸收和散射效率和光学共振波长。计算的光谱清楚地反映了众所周知的纳米粒子的光学性质，即依赖。共振波长，消光截面，和散射吸收的比率，对纳米粒子的尺寸。一个系统的定量研究的各种趋势。通过将金纳米球的尺寸从20 nm增加到80 nm，消光的幅度以及散射对消光的相对贡献迅速增加。通常采用的尺寸范围（类似于40 nm）的金纳米球显示出比常规吸收染料高5个数量级的吸收截面，而80 nm金纳米球的光散射幅度比强荧光染料的光发射高5个数量级。纳米球的等离子体激元波长最大值的变化，即，然而，从类似于520到550 nm的波长太有限，以致于不能用于体内应用。发现金纳米壳具有与纳米球相当甚至更高的光学横截面。此外，它们的光学共振有利地位于近红外区域。共振波长可以通过增加总的纳米壳尺寸或增加核壳半径的比率来快速增加。纳米壳的总消光率与其总尺寸呈线性关系，但与核/壳半径比无关。通过增加纳米壳的尺寸或减小核/壳半径的比率，可以快速增加相对散射对消光的贡献。然而，金纳米棒显示出与纳米球和纳米壳相当的光学横截面，有效尺寸小得多。通过改变纳米棒的有效尺寸或纵横比，可以在近红外区域线性调谐它们的光学共振。总消光和相对散射贡献随有效尺寸的增大而迅速增大，但与纵横比无关。为了比较不同尺寸的纳米颗粒对于真实的生物医学应用的有效性，计算尺寸归一化的光学截面或每微米系数。金纳米棒显示出每微米的吸收和散射系数比纳米壳和纳米球高一个数量级。虽然具有较高纵横比的纳米棒沿着具有较小的有效半径是最好的光吸收纳米颗粒，但是用于成像应用的最高散射对比度是从具有较大有效半径的高纵横比的纳米棒获得的。
The selection of nanoparticles for achieving efficient contrast for biological and cell imaging applications, as well as for photothermal therapeutic applications, is based on the optical properties of the nanoparticles. We use Mie theory and discrete dipole approximation method to calculate absorption and scattering efficiencies and optical resonance wavelengths for three commonly used classes of nanoparticles: gold nanospheres, silica-gold nanoshells, and gold nanorods. The calculated spectra clearly reflect the well-known dependence of nanoparticle optical properties viz. the resonance wavelength, the extinction cross-section, and the ratio of scattering to absorption, on the nanoparticle dimensions. A systematic quantitative study of the various trends is presented. By increasing the size of gold nanospheres from 20 to 80 nm, the magnitude of extinction as well as the relative contribution of scattering to the extinction rapidly increases. Gold nanospheres in the size range commonly employed (similar to 40 nm) show an absorption cross-section 5 orders higher than conventional absorbing dyes, while the magnitude of light scattering by 80-nm gold nanospheres is 5 orders higher than the light emission from strongly fluorescing dyes. The variation in the plasmon wavelength maximum of nanospheres, i.e., from similar to 520 to 550 nm, is however too limited to be useful for in vivo applications. Gold nanoshells are found to have optical cross-sections comparable to and even higher than the nanospheres. Additionally, their optical resonances lie favorably in the near-infrared region. The resonance wavelength can be rapidly increased by either increasing the total nanoshell size or increasing the ratio of the core-to-shell radius. The total extinction of nanoshells shows a linear dependence on their total size, however, it is independent of the core/shell radius ratio. The relative scattering contribution to the extinction can be rapidly increased by increasing the nanoshell size or decreasing the ratio of the core/shell radius. Gold nanorods show optical cross-sections comparable to nanospheres and nanoshells, however, at much smaller effective size. Their optical resonance can be linearly tuned across the near-infrared region by changing either the effective size or the aspect ratio of the nanorods. The total extinction as well as the relative scattering contribution increases rapidly with the effective size, however, they are independent of the aspect ratio. To compare the effectiveness of nanoparticles of different sizes for real biomedical applications, size-normalized optical cross-sections or per micron coefficients are calculated. Gold nanorods show per micron absorption and scattering coefficients that are an order of magnitude higher than those for nanoshells and nanospheres. While nanorods with a higher aspect ratio along, with a smaller effective radius are the best photoabsorbing nanoparticles, the highest scattering contrast for imaging applications is obtained from nanorods of high aspect ratio with a larger effective radius.