Quantifying the algal metabolome through photothermal microscopy

Microalgae exhibit high photosynthetic efficiencies and have demonstrated capability to accumulate high value bioproducts of commercial and societal interest such as food and livestock feed supplements, biofuels, and bioplastics. As a renewable crop, algae biomass bio-products have an opportunity to provide an eco-friendly solution to the increasing global demand for sustainable sourcing of goods. A barrier to the commercial viability of algae cultivation is the small size of alga microbes which limits the amount of metabolite produced. To optimize yield and monitor cell growth, we propose a non-destructive label-free imaging tool that can track metabolic pathways within the cell through chemical specific molecular absorptions in the infrared (IR) fingerprint. This allows differentiation of key metabolites in order to quantify total yield and has the added benefit that cells with high metabolite concentrations can be selectively propagated to increase future production efficiency. To visualize these subcellular features at high spatial resolution (400 nm) requires a nonlinear imaging technique that encodes molecular specific IR absorptions into visible photons. We implement this in a wide-field imaging geometry for video-rate imaging of hundreds of cells per frame through photothermal- quantitative phase imaging microscopy. The proposed phase-shifting add-on module will be easily integrated with standard microscope frames commonly used in imaging laboratories and is compatible with other imaging techniques for multimodal synergy. To demonstrate proof-of-concept we will image wild and mutant strains of commercially used algae and show the differences in metabolite concentrations. We will target amide-I, carbonyl, and methyl vibrational modes to test strains with increased lipid and protein content which are highly desirable for the biofuel and livestock feed industries, respectively. Our imaging tool will service algae producers and processors both as a quality control tool used to monitor crop production for predictive yields and as a means for product validation to ensure targeted concentration levels of the desired metabolite are met.