Mid-infrared chemical imaging of intracellular tau fibrils using fluorescence-guided computational photothermal microscopy

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 midinfrared 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 fbrils,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 theβ-sheet for tau fibril structure is achieved.