A benzothiazole-based water soluble and pH-independent probe for nitroreductase with a dramatic change of chromogenic and fluorogenic properties

A pH-independent and water soluble fluorescent probe based on a benzothiazole moiety was prepared for the detection of nitroreductase under biological conditions. Upon the addition of nitroreductase in the presence of NADH, the probe displayed both a colorless-to-yellow optical change and a fluorescence turn-on response in the visible region, with a very low limit of detection of the enzyme (LOD = 9.8 ng/mL) in PBS buffer. Due to its hydroxyethyl tethering group, the probe was highly soluble in water and exhibited the characteristic optical response in a wide range of pH values. Further cellular application was successfully performed and clear mitochondrial images were obtained with A549 cells.