Label-Free High-Resolution Photothermal Optical Infrared Spectroscopy for Spatiotemporal Chemical Analysis in Fresh, Hydrated Living Tissues and Embryos

Abstract

Label-free chemical imaging of living and functioning systems is the holy grail of biochemical research. However, existing techniques often require extensive sample preparation to remove interfering molecules such as water, rendering many molecular imaging techniques unsuitable for in situ structural studies. Here, we examined freshly extracted tissue biopsies and living small vertebrates at submicrometer resolution using optical photothermal infrared (O-PTIR) microspectroscopy and demonstrated the following major advances: (1) O-PTIR can be used for submicrometer structural analysis of unprocessed, fully hydrated tissue biopsies extracted from diverse organs, including living brain and lung tissues. ( 2) O-PTIR imaging can be performed on living organisms, such as salamander embryos, without compromising their further development. (3) Using O-PTIR, we tracked the structural changes of amyloids in functioning brain tissues over time, observing the appearance of newly formed amyloids for the first time. (4) Amyloid structures appeared altered following standard fixation and dehydration procedures. Thus, we demonstrate that O-PTIR enables time-resolved submicrometer in situ investigation of chemical and structural changes in diverse biomolecules in their native conditions, representing a technological breakthrough for in situ molecular imaging of biological samples.

Mid-infrared Photothermal Imaging: Instrument and Life Science Applications

“…MIP was also used to detect amyloid plaques rich in β-sheet structures in the freshly extracted tissue . Additionally, in this study, time-resolved MIP images were demonstrated.…”

“…These applications encompass the analysis of proteins, carbohydrates, lipids, enzymes, nucleic acids, ranging from individual nanometer scale viruses to centimeter-scale tissue samples. Several notable examples of this include the demonstration of stable isotope probing in microbiological studies by the Goodacre group at Liverpool University, − isotope-labeled cell metabolism by the Davis group at Yale University, , and label-free analysis of degenerative disease metabolism by Oxana Klementieva and colleagues at Lund University. − In parallel, the Ideguchi group at the University of Tokyo imaged water exchanges in living cells . The Kosik group at the University of California Santa Barbara mapped azide-tagged fatty acids in human-derived model systems .…”

Triboelectric Spectroscopy for In Situ Chemical Analysis of Liquids

“…Chemical analysis is central to all fields of science, technology, engineering, and health. − Strategies for the analysis of ions and organics include optical, electrochemical, and chromatographic methods . Optical methods often lack selectivity and generally require large and expensive instrumentation, and mainstream chromatographic instruments remain far from portable and inexpensive .…”