2.4 Fluorescence intensity measurement
The growth condition of cells was monitored by absorbance at 600 nm (OD600) by microplate reader. 1 mL of cells were centrifuged at 12 000 rpm for 10 min and then was resuspended with 1 mL of phosphate-buffered saline (PBS), followed by transferring 200 μL of the resuspensions to 96-well Black Opti plate 96F plates. The fluorescence was detected with excitation wavelength at 485 nm and emission wavelength at 520 nm, with each group in triplicates.