title: Depth-resolved mid-infrared photothermal imaging of living cells and organisms with submicrometer spatial resolution.
abstract: Chemical contrast has long been sought for label-free visualization of biomolecules and materials in complex living systems. Although infrared spectroscopic imaging has come a long way in this direction, it is thus far only applicable to dried tissues because of the strong infrared absorption by water. It also suffers from low spatial resolution due to long wavelengths and lacks optical sectioning capabilities. We overcome these limitations through sensing vibrational absorption-induced photothermal effect by a visible laser beam. Our mid-infrared photothermal (MIP) approach reached 10 μM detection sensitivity and submicrometer lateral spatial resolution. This performance has exceeded the diffraction limit of infrared microscopy and allowed label-free three-dimensional chemical imaging of live cells and organisms. Distributions of endogenous lipid and exogenous drug inside single cells were visualized. We further demonstrated in vivo MIP imaging of lipids and proteins inCaenorhabditis elegans. The reported MIP imaging technology promises broad applications from monitoring metabolic activities to high-resolution mapping of drug molecules in living systems, which are beyond the reach of current infrared microscopy.
authors.affiliation: Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Delong
authors.identifier: 0000-0002-9734-3573
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Chen
authors.initials: C
authors.lastname: Li
authors.affiliation: Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Chi
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, USA.; Department of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Mikhail N
authors.identifier: 0000-0003-3311-9385
authors.initials: MN
authors.lastname: Slipchenko
authors.affiliation: Jonathan Amy Facility for Chemical Instrumentation, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Gregory
authors.identifier: 0000-0002-2486-3471
authors.initials: G
authors.lastname: Eakins
authors.affiliation: Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, USA.; Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA.; Purdue Institute of Inflammation, Immunology and Infectious Disease, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Ji-Xin
authors.identifier: 0000-0002-5607-6683
authors.initials: JX
authors.lastname: Cheng
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000648:ultrastructure; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007834:Lasers; D008055:Lipids / Q000737:chemistry / Q000302:isolation & purification; D008853:Microscopy / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods*; D011506:Proteins / Q000302:isolation & purification / Q000648:ultrastructure; D013055:Spectrophotometry, Infrared / Q000379:methods*
chemical_list: D008055:Lipids; D011506:Proteins
keywords: Label-free imaging; in vivo imaging; infrared microscopy; infrared spectroscopy; live cell imaging