Max Planck Institute for the Science of Light, Erlangen, Germany; Max-Planck-Zentrum für Physik und Medizin, Erlangen, Germany; Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.
Max Planck Institute for the Science of Light, Erlangen, Germany; Max-Planck-Zentrum für Physik und Medizin, Erlangen, Germany.
Biophys Rep (N Y). 2024 Jun 12;4(2):100156. doi: 10.1016/j.bpr.2024.100156. Epub 2024 Apr 24.
The quantification of physical properties of biological matter gives rise to novel ways of understanding functional mechanisms. One of the basic biophysical properties is the mass density (MD). It affects the dynamics in sub-cellular compartments and plays a major role in defining the opto-acoustical properties of cells and tissues. As such, the MD can be connected to the refractive index (RI) via the well known Lorentz-Lorenz relation, which takes into account the polarizability of matter. However, computing the MD based on RI measurements poses a challenge, as it requires detailed knowledge of the biochemical composition of the sample. Here we propose a methodology on how to account for assumptions about the biochemical composition of the sample and respective RI measurements. To this aim, we employ the Biot mixing rule of RIs alongside the assumption of volume additivity to find an approximate relation of MD and RI. We use Monte-Carlo simulations and Gaussian propagation of uncertainty to obtain approximate analytical solutions for the respective uncertainties of MD and RI. We validate this approach by applying it to a set of well-characterized complex mixtures given by bovine milk and intralipid emulsion and employ it to estimate the MD of living zebrafish (Danio rerio) larvae trunk tissue. Our results illustrate the importance of implementing this methodology not only for MD estimations but for many other related biophysical problems, such as mechanical measurements using Brillouin microscopy and transient optical coherence elastography.
生物物质物理特性的定量分析为理解功能机制提供了新的方法。基本的生物物理特性之一是质量密度（MD）。它影响亚细胞区室中的动力学，在定义细胞和组织的光声特性方面起着主要作用。因此，质量密度可以通过众所周知的考虑物质极化率的洛伦兹-洛伦兹关系与折射率（RI）联系起来。然而，基于 RI 测量来计算 MD 存在挑战，因为它需要对样品的生化组成有详细的了解。在这里，我们提出了一种如何考虑样品生化组成假设和相应 RI 测量的方法。为此，我们使用 RI 的 Biot 混合规则以及体积加和的假设来找到 MD 和 RI 的近似关系。我们使用蒙特卡罗模拟和不确定度的高斯传播来获得 MD 和 RI 各自不确定度的近似解析解。我们通过将其应用于一组由牛奶和脂肪乳组成的特征明确的复杂混合物来验证这种方法，并将其用于估计活体斑马鱼（Danio rerio）幼虫躯干组织的 MD。我们的结果说明了不仅对于 MD 估计，而且对于许多其他相关生物物理问题（例如使用布里渊显微镜进行力学测量和瞬态光学相干弹性成像），实施这种方法的重要性。
