Rapid assessment of intracellular lipid using a dissolvable fluorescent sensing layer for single-cell,...

Standard extraction-based lipid and protein assays cannot resolve the dynamic population distributions that occur in cellular cultures. To support bioreactor control and productivity monitoring, a user-friendly sensor was developed in which an optical platform incorporates a shelf-stable, dissolvable layer that releases all necessary dyes and additives upon addition of the culture sample. When the sample is imaged with fluorescence microscopy, an AI-based computer-vision model identifies each cell, then quantifies the fluorescent signal and biovolume of each cell. By measuring the intracellular components of hundreds to thousands of individual cells in near real time, the system captures the rapid changes in intracellular composition that occur during culture growth and environmental change. Because this method captures population-level distributions rather than bulk averages, it reveals biological heterogeneity and temporal responses that are not detectable using standard extraction-based assays. The effectiveness of the shelf-stable dye-delivery layer was demonstrated for lipids and protein-associated biomass using commercial fluorescence dyes and microalgae and mammalian cells. The use of this technique for rapid intracellular measurements for bioprocess monitoring and control was demonstrated through intraceullar measurements of model microalga C. reinhardtii under industrially relevant conditions.