Fig. 4
Online measurement of cIPTG ester intermediates and NP-uncaging product. Fluorescence intensity (λEx = 326 nm, λEm = 407 nm, black cross in Fig. 2) of 12 E. coli cultures before and after UV-A irradiation for 0–60 s (a) and fluorescence intensity measured directly after irradiation as a function of duration of UV-A exposure (b). At the beginning of the cultivation, 400 µM cIPTG were added to the medium. After 10 h, optical induction was performed with the LED array (λmax = 368 nm, I = 52mW/cm2). The amount of ester intermediates increases with increasing duration of UV-A exposure and can be fitted with first-order kinetics (solid lines and equations in B, R2 > 0.995). Reduced irradiance leads to lower rate constants (black triangles, I = 13 mW/cm2) and reduced cIPTG concentration to lower amplitude (green diamonds, 50 µM cIPTG). Cultivation conditions: 800 µL Wilms-MOPS mineral medium (20 g/L glucose, 0.2 M MOPS) per well in a 48-FlowerPlate, 30 °C, shaking frequency: 1000 rpm, shaking diameter: 3 mm. Not all data shown in a (complete set provided in Additional file 8)