REMOTE 2-PHOTON EXCITED FLUORESCENCE SENSING IN A SIMULATED FERMENTATION BROTH

The feasibility of direct quantitation of a fluorescent fermentation product by means of two-photon excited molecular fluorescence and a fiber-optic probe was investigated. The fermentation broth environment was simulated using buffered baker's yeast solutions. To demonstrate that a two-photon induced signal is unperturbed by the presence of microorganisms, the fluorescence intensity from a fixed amount of fluorophore was monitored versus increasing baker's yeast cell density (0-60 g l-1). The resultant two-photon induced signal remained relatively constant, in comparison to a one-photon induced signal. Quantitation via one-photon excitation without a fiber optic showed the characteristic inner-filter roll-off of optically dense systems and quantitation became impossible at cell densities higher than approximately 20 g l-1. The effect of mie-scattering on the observed two-photon induced signal is discussed, and is hypothesized to be the cause of a slight decline in signal with increasing cell density.