Presto Blue test
The wells were washed with PBS and then 90 μl PBS and 10 μl Presto Blue reagent were added to each. The plate was again placed in an incubator for 40 min. Then 100 μl of suspension was withdrawn from each well and transferred to a new plate. Fluorescence was examined with a FLUOstar Omega apparatus at excitation and emission wavelengths of 530 and 620 nm, respectively.