To further assess the use of two-photon microscopy in the study of potential bioremediation techniques our earlier work on the enzymatic reduction of U VI O2 2+ was expanded to incorporate 2PE. Geobacter sulfurreducens, a Gram-negative anaerobic subsurface bacterium that has long been known to reduce U VI O2 2+ , was cultured according to literature procedure, washed, and resuspended in a carbonate buffer. Our previous report showed that in the absence of uranium very little autofluorescence was detected, however on addition of 5 mmol of UO2(CH3CO2)2 two changes were observed -the appearance extracellular features showing strong, characteristic uranyl emission and a significant increase in fluorescence associated with the bacterial cells.