High-speed mid-infrared photothermal imaging of fatty acids and lipid droplets in living cells

Fatty acids (FAs) are a group of lipids with multiple, pivotal functions in cells, including energy production and storage, and signalling to control cell proliferation, metabolism and apoptosis.

After cellular uptake, FAs are involved in the formation of lipid droplets (LDs), whose size, number and dynamics are related to the cell state. Uptake, distribution and metabolism of free FAs occur fast and are tightly regulated in healthy cells.

If deregulated, lipid signalling contributes to inflammation, cancer and metabolic and cardiovascular diseases, and can ultimately trigger cell death.

Exactly how free FAs enter cells and form LDs is still poorly understood, mainly due to the lack of non-invasive imaging techniques with sufficient speed, sensitivity and selectivity at high spatial resolution to monitor the location of free FAs during cellular uptake in vivo.

In this project, we will use widefield mid-infrared photothermal heterodyne (WIPH) microscopy to image FAs tagged with vibrational probes absorbing in the cell-silent spectral region.

Live cell WHIP imaging with 300 nm spatial resolution, 100x100 µm field-of-view and full-frame image acquisition rates up to kHz will be implemented.

The aim is to visualize the uptake process of alkyne-tagged palmitic acid in living 3T3-L1 model cells and the behaviour of LDs with sub-second time resolution.

The results will be analysed together with fluorescence and mass spectrometry data in order to validate models of FA uptake.