配体修饰的金纳米颗粒的二次谐波散射多极子分析

Second harmonic scattering multipole analysis of ligand-decorated gold nanoparticles

贵金属纳米颗粒的配体修饰在生化传感、催化、纳米科学等领域有着广泛的应用需求,深入了解其配体作用过程机制有着深刻的意义.二次谐波散射技术(SHS)由于具有较高的表面敏感性和无标记检测的优势特征,成为研究金属纳米颗粒配体修饰过程的重要手段.本文通过实验方法,测量了在两种配体修饰分子(十六烷基三甲基氯化铵和L-半胱氨酸)吸附同样尺寸金纳米球前后的二次谐波(SH)散射图样,观察了散射图样的强度和形状的变化并进行了分析.基于Dadap的多极子理论,本文推导了较大尺寸纳米球的SH散射场的多极子展开式,以及多极子(到八极子)贡献和纳米球半径的关系,并由此提出等效尺寸效应来描述不同配体吸附情况对散射图样的影响,较好地解释了图样的变化趋势.本文提供了一种分析不同配体修饰的二次谐波散射过程的方法,同时也为纳米粒子表面配体的界面物理化学分析提供了一种可能的定量方法.

Ligand decoration of noble metallic nanoparticles is often needed for some applications,such as biochemical sensing,catalysis and nanotechnology,and the understanding of its process is of great importance.The second harmonic scattering(SHS)technique with advantages of surface-sensitivity and label-free detection,provides intrinsic information for such a research.In this work,the second harmonic(SH)scattering patterns of two types of ligands(cetyltrimethylammonium chloride and L-cysteine)capped gold nanoparticles(GNPs)with the same radii are measured.Both the intensities and shapes of the SH scattering patterns are changed after the ligand exchange process.In order to explain the pattern changes,the analytic expressions of SH scattering are derived theoretically for a relatively large nanoparticle based on Dadap’s multipolar theory.Considering the derived relationship between the multipole(up to octopole)contributions and the power of the nanosphere radius,the effective size effect is introduced to express the SH scattering signal change for different ligand decorations and well explain the experimental results.This theory provides a new perspective of the SH scattering response to different capping ligands and offers a possible quantitative method to analyze interface physical chemistry for ligands on the surface of nanoparticles.