Miller Molly M, Lazarides Anne A
Department of Mechanical Engineering and Materials Science, Duke University, Box 90300, Durham, North Carolina 27708-0300, USA.
J Phys Chem B. 2005 Nov 24;109(46):21556-65. doi: 10.1021/jp054227y.
Electrodynamic simulations of gold nanoparticle spectra were used to investigate the sensitivity of localized surface plasmon band position to the refractive index, n, of the medium for nanoparticles of various shapes and nanoshells of various structures. Among single-component nanoparticles less than 130 nm in size, sensitivities of dipole resonance positions to bulk refractive index are found to depend only upon the wavelength of the resonance and the dielectric properties of the metal and the medium. Among particle plasmons that peak in the frequency range where the real part of the metal dielectric function varies linearly with wavelength and the imaginary part is small and slowly varying, the sensitivity of the peak wavelength, lambda, to refractive index, n, is found to be a linearly increasing function of lambda, regardless of the structural features of the particle that determine lambda. Quasistatic theory is used to derive an analytical expression for the refractive index sensitivity of small particle plasmon peaks. Through this analysis, the dependence of sensitivity on band position is found to be determined by the wavelength dependence of the real part, epsilon', of the particle dielectric function, and the sensitivity results are found to extend to all particles with resonance conditions of the form, epsilon' = -2chin(2), where chi is a function of geometric parameters and other constants. The sensitivity results observed using accurate computational methods for dipolar plasmon bands of gold nanodisks, nanorods, and hollow nanoshells extend, therefore, to particles of other shapes (such as hexagonal and chopped tetrahedral), composed of other metals, and to higher-order modes. The bulk refractive index sensitivity yielded by the theory serves as an upper bound to sensitivities of nanoparticles on dielectric substrates and sensitivities of nanoparticles to local refractive index changes, such as those associated with biomolecule sensing.
利用金纳米颗粒光谱的电动力学模拟，研究了各种形状的纳米颗粒以及各种结构的纳米壳的局域表面等离子体带位置对介质折射率(n)的敏感性。在尺寸小于130nm的单组分纳米颗粒中，发现偶极子共振位置对体折射率的敏感性仅取决于共振波长以及金属和介质的介电特性。在金属介电函数实部随波长线性变化且虚部较小且变化缓慢的频率范围内达到峰值的粒子等离子体中，发现峰值波长(\lambda)对折射率(n)的敏感性是(\lambda)的线性递增函数，与决定(\lambda)的颗粒结构特征无关。使用准静态理论推导了小颗粒等离子体峰的折射率敏感性的解析表达式。通过该分析，发现敏感性对带位置的依赖性由颗粒介电函数实部(\epsilon')的波长依赖性决定，并且发现敏感性结果适用于所有具有(\epsilon' = -2\chi n^2)形式共振条件的颗粒，其中(\chi)是几何参数和其他常数的函数。因此，使用精确计算方法观察到的金纳米盘、纳米棒和空心纳米壳的偶极等离子体带的敏感性结果，扩展到由其他金属组成的其他形状（如六边形和截断四面体）的颗粒以及高阶模式。该理论得出的体折射率敏感性作为纳米颗粒在介电基板上的敏感性以及纳米颗粒对局部折射率变化（如与生物分子传感相关的变化）的敏感性的上限。
