Enhanced infrared LSPR sensitivity of cap-shaped gold nanoparticles coupled to a metallic film.
Enhanced infrared LSPR sensitivity of cap-shaped gold nanoparticles coupled to a metallic film.
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DOI：
10.1021/la403407g
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发表时间：
2014-02
期刊：
影响因子：
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通讯作者：
H. Takei;N. Bessho;A. Ishii;T. Okamoto;A. Beyer;H. Vieker;A. Gölzhäuser
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文献类型：
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作者：
H. Takei;N. Bessho;A. Ishii;T. Okamoto;A. Beyer;H. Vieker;A. Gölzhäuser
我们报告的光学性质的金沉积在二氧化硅纳米球随机吸附在薄的金层。在可见光区和近红外区都观察到光密度大于2的消光峰。后者的峰值波长受到顶层厚度的精细影响。使用氦离子显微镜（HIM）仔细观察伴随沉积厚度变化的形态转变。晶粒结构生长成封端的二聚体结构伴随着可见峰的轻微蓝移和近红外峰的显著更大的红移。我们的时域有限差分（FDTD）计算表明，这些峰值在可见光和近红外可以分别归因于偶极模式与自由电子在金帽二聚体的横向和纵向振荡。为了研究这些峰的折射率敏感性，我们使用了两种方法：浸入不同折射率的溶液中和涂覆有机层。对于表征体灵敏度的第一种方法，可见峰显示出122 nm/RIU的灵敏度，而近红外峰以506 nm/RIU的速率移位。第二种方法反映了局部灵敏度，表面被碱性磷酸酶（ALP）饱和，其随后的反应导致形成薄的不溶性有机层，导致可见峰的相对较小的蓝移，在7 nm以下，以及在缓冲液中测量时近红外峰的大得多的红移，超过50 nm。当在空气中在终点处测量相同的反应时，对于近红外峰，位移大至444 nm。
We report on optical properties of gold deposited on SiO2 nanospheres randomly adsorbed on a thin gold layer. Extinction peaks with optical density of more than 2 are observed in the visible as well as near-IR regimes. The peak wavelength of the latter was affected exquisitely by the thickness of the top layer. A helium ion microscope (HIM) was used for careful observation of morphological transformation accompanying the change in the deposition thickness. Growth of grain structures into a capped-dimer structure was accompanied by slight blue-shift of the visible peak and significantly greater red-shift of the near-IR peak. Our finite-difference time-domain (FDTD) calculations show that these peaks in the visible and near-IR can be respectively attributed to dipole modes associated with transverse and longitudinal oscillations of free electrons in the gold-capped dimer. To investigate the refractive index sensitivity of these peaks, we used two approaches: immersion in solutions of varying refractive index and coating with an organic layer. With the first approach that characterizes the bulk sensitivity, the visible peak shows sensitivity of 122 nm/RIU, while the near-IR peak shifts at the rate of 506 nm/RIU. With the second approach that reflects the local sensitivity, the surface was saturated with alkaline phosphatase (ALP), whose subsequent reaction led to formation of a thin insoluble organic layer, causing a relatively small blue-shift, under 7 nm, of the visible peak and much larger red-shift, over 50 nm, of the near-IR peak when measured in buffer. When the same reaction was measured at end points in the air, the shift was as large as 444 nm for the near-IR peak.