Three-Dimensional Branched Crystal Carbon Nitride with Enhanced Intrinsic Peroxidase-Like Activity: A Hypersensitive Platform for Colorimetric Detection

Graphitic carbon nitride (g-C₃N₄) as a metal-free nanozyme has attracted huge attention for catalytic applications. However, the catalytic activity of pure g-C₃N₄ causes very moderate H₂O₂ activation. Herein, a novel three-dimensional (3D) branched carbon nitride nanoneedle (3DBC-C₃N₄) nanozyme has been proposed to overcome such shortcoming. This unique 3D branched structure of 3DBC-C₃N₄ facilitated effective mass transfer during catalytic reaction and induced a lightning rodlike effect to accelerate electron collection at the tip area for H₂O₂ activation. With improved H₂O₂ activation for hydroxyl radical (^•OH) generation, 3DBC-C₃N₄ showed excellent peroxidase-like activity toward 3,3′,5,5′-tetramethylbenzidine oxidation in the presence of H₂O₂. As for H₂O₂, the V_max value of 3DBC-C₃N₄ was found to be 20 times higher than that of natural horseradish peroxidase. Moreover, the 3D branched structure of 3DBC-C₃N₄ offered large interface for the reversible conjugation of single-stranded DNA, which enhanced the colorimetric sensitivity. Moreover, 3DBC-C₃N₄ exhibited high sensitivity toward oxytetracycline detection, with the detection limit and quantitative limit of 1 and 50 μg/L, respectively.