Widefield Super-Resolution Infrared Spectroscopy and Imaging of Autofluorescent Biological Materials and Photosynthetic Microorganisms Using Fluorescence Detected Photothermal Infrared (FL-PTIR).
Craig B Prater, Kevin J Kjoller, Andrew P D Stuart, David A Grigg, Rinuk 'Limurn, Kathleen M Gough
Author Information
Craig B Prater: Photothermal Spectroscopy Corporation, Santa Barbara, California, USA. ORCID
Kevin J Kjoller: Photothermal Spectroscopy Corporation, Santa Barbara, California, USA.
Andrew P D Stuart: Photothermal Spectroscopy Corporation, Santa Barbara, California, USA.
David A Grigg: Photothermal Spectroscopy Corporation, Santa Barbara, California, USA.
Rinuk 'Limurn: Department of Chemistry, University of Manitoba, Winnipeg, Canada.
Kathleen M Gough: Department of Chemistry, University of Manitoba, Winnipeg, Canada. ORCID
We have demonstrated high-speed, super-resolution infrared (IR) spectroscopy and chemical imaging of autofluorescent biomaterials and organisms using camera-based widefield photothermal detection that takes advantage of temperature-dependent modulations of autofluorescent emission. A variety of biological materials and photosynthetic organisms exhibit strong autofluorescence emission under ultraviolet excitation and the autofluorescent emission has a very strong temperature dependence, of order 1%/K. Illuminating a sample with pulses of IR light from a wavelength-tunable laser source causes periodic localized sample temperature increases that result in a corresponding transient decrease in autofluorescent emission. A low-cost light-emitting diode-based fluorescence excitation source was used in combination with a conventional fluorescence microscopy camera to detect localized variations in autofluorescent emission over a wide area as an indicator of localized IR absorption. IR absorption image stacks were acquired over a range of IR wavelengths, including the fingerprint spectral range, enabling extraction of localized IR absorption spectra. We have applied widefield fluorescence detected photothermal IR (FL-PTIR) to an analysis of autofluorescent biological materials including collagen, leaf tissue, and photosynthetic organisms including diatoms and green microalgae cells. We have also demonstrated the FL-PTIR on live microalgae in water, demonstrating the potential for label-free dynamic chemical imaging of autofluorescent cells.
