Substrate Specificity of Adenine-Cu-PO₄ Nanozyme: Ascorbic Acid Oxidation and Selective Cytotoxicity

Though nanozymes are becoming promising alternatives to natural enzymes due to their superior properties, constructing nanozyme with high specificity is still a great challenge. Herein, with Cu²⁺ as an active site and adenine as a ligand, Adenine-Cu-PO₄ is synthesized in phosphate-buffered saline. As an oxidase mimic, Adenine-Cu-PO₄ could selectively catalyze oxidation of ascorbic acid (AA) to dehydroascorbic acid, but not universal substrates (3,3',5,5'-tetramethylbenzidine (TMB), 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and 2,4-dichlorophenol (2,4-DP)), small biomolecules (dopamine, glutathione, glucose, galactose), other vitamins (vitamin A acid, vitamin B₁, vitamin K₁) and even dithiothreitol (a common interference of AA). Such the specific AA catalytic oxidation is revealed that Adenine-Cu-PO₄ selectively binds with AA through hydrogen bonds, accompanied with catalyzing AA oxidation, and concurrently O₂ transferring to H₂O₂ via O₂⋅^-, further to H₂O via ⋅OH. Based on the produced reactive oxygen species, with AA as a pro-oxidant, Adenine-Cu-PO₄ nanozyme efficiently triggers severe intratumor oxidative stress to induce tumor cell death. This work opens a new avenue to design intrinsic nanozymes with high specificity, and also presents a promising application in the field of AA oxidation induced cancer therapy.