Fig. 1. PICS method for label-free measurements of compartment-specific cellular dry mass.

a We upgrade a conventional transmitted light microscope with a quantitative phase imaging add-on module. b To avoid the intrinsic toxicity of fluorescent stains, we develop a two-step protocol imaging protocol where label-free images are recorded followed by fixation and staining. From the toxic stain recorded at the end of the experiment, we train a neural network capable of digitally staining the time-lapse sequence, thus enabling time-lapse imaging of otherwise toxic stains. c The digital stain is used to introduce specificity to label-free imaging by providing a semantic segmentation map labeling the components of the cell. From the time-lapse sequence, we calculate organelle-specific dry mass doubling times, in this case, the rates of growth for the nucleus and cytoplasm. d The PICS method is integrated into a fully automated plate reading instrument capable of displaying the machine learning results in real-time.