Amyloid proteins are associated with a broad spectrum of neurodegenerative diseases. However, it remains a grand challenge to extract molecular structure information from intracellular amyloid proteins in their native cellular environment. To address this challenge, we developed a computational chemical microscope integrating 3D mid-infrared photothermal imaging with fluorescence imaging, termed Fluorescence-guided Bond-Selective Intensity Diffraction Tomography (FBS-IDT). Based on a low-cost and simple optical design, FBS-IDT enables chemical-specific volumetric imaging and 3D site-specific mid-IR fingerprint spectroscopic analysis of tau fibrils, an important type of amyloid protein aggregates, in their intracellular environment. Label-free volumetric chemical imaging of human cells with/without seeded tau fibrils is demonstrated to show the potential correlation between lipid accumulation and tau aggregate formation. Depth-resolved mid-infrared fingerprint spectroscopy is performed to reveal the protein secondary structure of the intracellular tau fibrils. 3D visualization of the β-sheet for tau fibril structure is achieved.

淀粉样蛋白与多种神经退行性疾病有关。然而，从天然细胞环境中的细胞内淀粉样蛋白中提取分子结构信息仍然是一个巨大的挑战。为了应对这一挑战，我们开发了一种将 3D 中红外光热成像与荧光成像相结合的计算化学显微镜，称为荧光引导键选择性强度衍射断层扫描 (FBS-IDT)。基于低成本和简单的光学设计，FBS-IDT 能够对细胞内环境中的 tau 纤维（淀粉样蛋白聚集体的一种重要类型）进行化学特异性体积成像和 3D 位点特异性中红外指纹光谱分析。对含有/不含种子 tau 原纤维的人体细胞进行无标记体积化学成像，结果显示脂质积累与 tau 聚集体形成之间的潜在相关性。深度分辨中红外指纹光谱揭示了细胞内 tau 原纤维的蛋白质二级结构。实现了 tau 原纤维结构 β-折叠的 3D 可视化。