Single cells vary widely in their growth rate, a fundamental behavior that reflects biochemical and biophysical differences between cells and ultimately may govern their relative abundance within a population. Even genetically identical cells may grow at extremely different rates, owing to a combination of intrinsic molecular noise and various behavioral programs. We can not easily observe this variation using population-based growth assays, yet it has important consequences for human health. For example, cancer cells within an individual may vary drastically in growth potential, with subsets capable constant growth and proliferation and others being primarily stationary. Similarly, growth rate variation in bacterial populations can dictate the efficacy of antibiotic treatments, as slow- or non-growing cells tend to be more resistant to antibiotics. We present an approach to precisely and rapidly measure growth rates of many individual cells simultaneously. We introduce a micro-chip that incorporates an array of extremely sensitive mass sensors to weigh individual cells multiple times as they grow while flowing through a long microfluidic channel. Our chip reveals subpopulations of cells with different growth kinetics and enables assessment of cellular responses to antibiotics and antimicrobial peptides within minutes.
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