Fig. 6: Fermentation of glucose and sucrose, but not xylose, xylitol, or saline by S. mutans visualised with pH-sensitive nanosensors.

Positively charged pH-sensitive nanosensors at a concentration of 1 mg mL⁻¹ were added to planktonic S. mutans NCTC 10449 grown overnight and normalised to an OD₆₀₀ of 1. Time-lapse images were taken with a Nikon widefield microscope. a Representative fluorescence images of cells with nanosensors in saline before the addition of either saline, glucose, sucrose, xylose or xylitol (top panel) to a final concentration of 1% or after 30 min (bottom panel). An overlay image of the fluorescence channels for green (OG-FAM) and red (TAMRA) is shown. b pH calibration of the nanosensors using the ratio between OG-FAM and TAMRA calculated from the fluorescence intensities. Linear regression was calculated and used for pH determination of samples. c The pH of each condition at the indicated timepoints was calculated and plotted against the time of addition. Error bars represent standard error measured for different images, where n = 9.