Djorović Aleksa, Oldenburg Steven J, Grand Johan, Le Ru Eric C
The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand.
nanoComposix, 4878 Ronson Court Suite K, San Diego, California 92111, United States.
ACS Nano. 2020 Dec 22;14(12):17597-17605. doi: 10.1021/acsnano.0c08431. Epub 2020 Dec 11.
Gold nanoparticles (AuNPs) have become an essential tool for a variety of fields across the biological, physical, and chemical sciences. The characterization of AuNPs by UV-vis spectroscopy is simple and commonly used but remains prone to error because of size and shape polydispersity and uncertainties in the dielectric function. We here propose and demonstrate a method to significantly improve this routine characterization technique by measuring not only the extinction but also the absorption spectrum. Specifically, we show that by considering the ratio of the extinction to absorption spectra, denoted η, we are able to determine the volume of AuNPs with a significant increase in accuracy compared to the UV-vis extinction method. We also prove an important property of η: it is independent of particle shape within the quasi-static/dipolar approximation, typically for particle sizes up to 100 nm. This shape independence results in very strong constraints for the theoretical predictions to agree with the experiments. We show that the spectral shape of η can therefore be used to discriminate between different proposed data sets for the dielectric function of gold, a long-standing challenge in plasmonics research.
金纳米颗粒（AuNPs）已成为生物、物理和化学科学等多个领域的重要工具。通过紫外可见光谱对AuNPs进行表征简单且常用，但由于尺寸和形状的多分散性以及介电函数的不确定性，仍容易出现误差。我们在此提出并展示了一种方法，通过不仅测量消光光谱还测量吸收光谱来显著改进这种常规表征技术。具体而言，我们表明，通过考虑消光光谱与吸收光谱的比值η，与紫外可见消光法相比，我们能够以显著提高的精度确定AuNPs的体积。我们还证明了η的一个重要特性：在准静态/偶极近似范围内，通常对于尺寸达100 nm的颗粒，它与颗粒形状无关。这种形状无关性对理论预测与实验结果相符提出了非常严格的限制。我们表明，η的光谱形状因此可用于区分关于金介电函数的不同提议数据集，这是等离激元研究中长期存在的一个挑战。
