Ultrafast Widefield Mid-Infrared Photothermal Heterodyne Imaging.
Eduardo Maia PaivaFlorian M SchmidtPublished in: Analytical chemistry (2022)
Mid-infrared photothermal (MIP) microscopy is a valuable tool for sensitive and fast chemical imaging with high spatial resolution beyond the mid-infrared diffraction limit. The highest sensitivity is usually achieved with heterodyne MIP employing photodetector point-scans and lock-in detection, while the fastest systems use camera-based widefield MIP with pulsed probe light. One challenge is to simultaneously achieve high sensitivity, spatial resolution, and speed in a large field of view. Here, we present widefield mid-infrared photothermal heterodyne (WIPH) imaging, where a digital frequency-domain lock-in (DFdLi) filter is used for simultaneous multiharmonic demodulation of MIP signals recorded by individual camera pixels at frame rates up to 200 kHz. The DFdLi filter enables the use of continuous-wave probe light, which, in turn, eliminates the need for synchronization schemes and allows measuring MIP decay curves. The WIPH approach is characterized by imaging potassium ferricyanide microparticles and applied to detect lipid droplets (alkyne-palmitic acid) in 3T3-L1 fibroblast cells, both in the cell-silent spectral region around 2100 cm<sup>-1</sup> using an external-cavity quantum cascade laser. The system achieved up to 4000 WIPH images per second at a signal-to-noise ratio of 5.52 and 1 μm spatial resolution in a 128 × 128 μm field of view. The technique opens up for real-time chemical imaging of fast processes in biology, medicine, and material science.
Keyphrases
- high resolution
- single molecule
- photodynamic therapy
- high speed
- stem cells
- optical coherence tomography
- drug delivery
- induced apoptosis
- public health
- cancer therapy
- computed tomography
- living cells
- magnetic resonance
- molecular dynamics
- fluorescence imaging
- high frequency
- cell proliferation
- drug release
- mesenchymal stem cells
- cell therapy
- cell death
- quantum dots
- endoplasmic reticulum stress
- cell cycle arrest
- pi k akt
- high throughput
- fatty acid
- real time pcr