Application of Fenton chemistry in electrochemical determination of pyrophosphatase activity and fluoride

Fenton chemistry has aroused widespread concern due to its application in the green oxidation and mineralization of organic wastes. Inorganic pyrophosphatase (PPase) catalyzes the hydrolysis of pyrophosphate ions (PPi) and provides a thermodynamic driving force for many biosynthetic reactions. Fluoride (F−) is widely applied to fight against tooth decay and reduce cavities. The electrochemical determination of PPase activity and F− was realized based on Fenton chemistry in this work. Glassy carbon electrode modified with poly (azure A) and acetylene black (GCE/PAA-AB) was fabricated. Hydroxyl radicals (∙OH) that were generated from a Cu2+-catalyzed Fenton-type reaction could oxidize PAA in the near-neutral medium, leading to a great increase of the cathodic peak current (Ipc). A coordination reaction between PPi and Cu2+ exerted a negative effect on Fenton reaction and hindered the Ipc enhancement. Cu2+-PPi complex was decomposed due to the hydrolysis of PPi induced by PPase, which caused the reappearance of the notably increased current response. F− could effectively inhibit PPase activity. As a result, the stable Cu2+-PPi complex remained and the high Ipc suffered from the decline again. The Ipc difference was used for the highly sensitive determination of PPase activity in the content range of 0.001–20 mU mL−1 with a detection of limit (LOD) at 0.6 μU mL−1 and that of F− in the concentration range of 0.01–100 μM with a LOD at 7 nM. The proposed PPase and F− sensor displayed a good selectivity, stability and reproducibility, and a high accuracy.