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The importance of biological reactors used in growing artificial tissue is rising. To monitor the metabolic state of living cells in the bioreactor, a non-disruptive measurement is required. Fluorescence-lifetime measurements provide the perfect tool for this analysis. Many applications already exist in order to determine the fluorescence-lifetime, but the majority of these require the addition of fluorescence-active substances to enable measurements. Every usage of such foreign material has an associated experimental risk to the cell. This paper investigates the use of auto-fluorescing substances and their changes in Saccharomyces cerevisiae (Baker's yeast) as a risk free alternative to fluorescence-active substance enabled measurements. The quantity of NAD(H), NADP(H) and certain amino acids are good markers for measuring the metabolic state of cells and can be identified by their fluorescence-lifetime and spectral properties. Fluorescence lifetimes can be determined from the decay of the measurement signals, which in turn characterizes the individual materials and their surrounding environment. Information about the quantity of the fluorescence-active substances can also be measured based on the received signal intensity. Here, we have shown there is a correlation between the fluorescence lifetime and the metabolic state of Saccharomyces cerevisiae.

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