In situ detection of metabolic activity and microenvironmental conditions in a dental biofilm outside the mouth. Microsensors were used to measure concentration profiles of NO3-, O2, NO, N2O and pH in dental plaque. The medium contained a non-buffered mineral mix and 2% sucrose. The upper panels (a-d) show measurements with 50 μM NaNO3 (open red symbols) in the overlying medium. The lower panels (e-h) show measurements in the absence of NaNO3 (black symbols) and in the presence of 760 μM NaNO3 (red and green symbols). Measurements depicted by the green symbols were performed in the presence of phosphate-buffered saline (pH 7.2) and 760 μM NaNO3. The horizontal line represents the biofilm surface. Measurements were done in the same sample spot and thus are directly comparable.