Watch Webinar
Optical Photothermal Infrared (O-PTIR) spectroscopy represents a significant advancement in the field of biomedical imaging and analysis. In a recent webinar, Professor Christoph Krafft shared his extensive experience with infrared spectroscopy techniques, highlighting the capabilities of O-PTIR for studying live cells, tissues, and single-cell bacteria with submicron resolution.
Key Findings
O-PTIR spectroscopy has demonstrated unique capabilities in several biomedical applications:
Bacterial Identification at Single-Cell Level: Unlike traditional FTIR methods that require bulk samples, O-PTIR enables the collection of spectra from individual bacterial cells. This revealed previously undetectable variations between cells of the same species, opening new avenues for rapid bacterial identification without cultivation.
Subcellular Resolution in Mammalian Cells: O-PTIR achieved unprecedented resolution of subcellular features in mesenchymal stem cells, clearly distinguishing between the cell body (~24μm), nucleus (~6μm), nucleoli (~1.4μm), and even membrane structures (~200nm). The technique also successfully differentiated between various cell lines, including leukemia and non-leukemia cells, with high accuracy.
Tissue Analysis Without Scattering Artifacts: O-PTIR effectively eliminated the problematic scattering effects that plague traditional FTIR when analyzing tissues. In lung tissue samples, which are particularly challenging due to their porous nature, O-PTIR produced virtually background-free spectra without the band shifts typically caused by anomalous scattering.
Single Cell Nuclei Resolution in Tissues: The technique successfully resolved individual cell nuclei within spleen tissue follicles—a feat previously unattainable with FTIR imaging. This capability is particularly valuable for pathological examination of tissues, where nuclear features are diagnostically significant.
Technical Advantages
O-PTIR offers several distinct advantages over traditional infrared spectroscopy methods:
- Submicron Resolution: The technique achieves spatial resolution down to 100nm, far exceeding the capabilities of conventional FTIR.
- Freedom from Scattering Artifacts: Unlike FTIR, O-PTIR spectra are free from Mie scattering effects and dispersive line shifts, producing cleaner spectra even from challenging samples.
- Substrate Flexibility: O-PTIR works with a wide range of substrates, including inexpensive glass slides—a significant advancement as traditional infrared techniques require specialized, costly substrates.
- Liquid Sample Compatibility: The technique allows measurement of cells in aqueous environments, preserving their natural state and preventing the denaturation of biomolecules that occurs during drying.
- Rapid Image Acquisition: Selected wavenumber images can be collected in minutes, with full spectra obtainable from specific positions of interest.
- Complementarity with Raman Spectroscopy: When combined with Raman spectroscopy, which detects aromatic amino acids nearly invisible to infrared techniques, O-PTIR enables more comprehensive molecular characterization and potentially more accurate classification models.
The innovative detection scheme utilizing quantum cascade lasers (QCLs) as radiation sources and optical photothermal detection eliminates many limitations of traditional infrared spectroscopy. By detecting the signal through modulation of a visible probe beam rather than direct infrared detection, O-PTIR effectively removes fluorescence interference that still impacts Raman measurements.
This technology represents a significant step forward for biomedical applications, particularly in pathology, microbiology, and cell biology, where submicron resolution and artifact-free spectra are critical for accurate analysis and diagnosis.
