Holographic molecular binding assays use holographic video microscopy to directly detect molecules binding to the surfaces of micrometer-scale colloidal beads by monitoring associated changes in the beads’ light-scattering properties. Holograms of individual spheres are analyzed by fitting to a generative model based on the Lorenz-Mie theory of light scattering. Each fit yields an estimate of a probe bead’s diameter and refractive index with sufficient precision to watch a population of beads grow as molecules bind. Rather than modeling the molecular-scale coating, however, these fits use effective medium theory, treating the coated sphere as if it were homogeneous. This effective-sphere analysis is rapid and numerically robust and so is useful for practical implementations of label-free immunoassays. Here, we assess how measured effective-sphere properties reflect the actual properties of molecular-scale coatings by modeling coated spheres with the discrete-dipole approximation and analyzing their holograms with the effective-sphere model.

中文翻译：

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用有效介质理论解释全息分子结合测定

全息分子结合测定法使用全息视频显微镜通过监测微珠的光散射特性的相关变化，直接检测与微米级胶体微珠表面结合的分子。通过拟合基于劳伦兹-米氏光散射理论的生成模型来分析各个球体的全息图。每次拟合都会以足够的精度估算探针珠的直径和折射率，以观察随着分子结合而形成的珠的数量。但是，这些拟合不是使用分子尺度的涂层建模，而是使用有效的介质理论，将涂层球体视为均匀球体。这种有效范围分析是快速的，并且在数值上很稳健，因此对于无标记免疫分析的实际实施非常有用。这里，