Yin_2024_Food.Chem_465_142164

Overcoming the intrinsic low activity of most photoinduced oxidase mimics has been extremely challenging. In this work, we developed a methyl viologen (MV(2+)) mediated strategy to enhance the oxidase-like activity of fluorescein. The presence of MV(2+) gives it a high affinity for TMB with a low Michaelis-Menten constant (K(m)) of 0.053 mM, which is about 2.8 times lower than that of fluorescein and with a remarkable catalytic constant (K(cat)) as 0.2490 s(-1), which is 3 times as high as that of fluorescein. Fluorescein diacetate (FDA) without oxidase-like activity can be hydrolyzed in situ to produce fluorescein in the presence of carboxylesterases (CaE). Based on the inhibition of CaE activity by organophosphorus pesticides (OP), a novel colorimetric signal biosensor was established with a wide linear range from 1.0 to 200 ng/mL. This work not only provides a convenient and feasible strategy for enhancing the activity of photoinduced oxidase mimics but also blazes a new pathway for the sensitive detection of OP.