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

Graphitic carbon nitride (g-C 3 N 4 ) as a metal-free nanozyme has attracted huge attention for catalytic applications. However, the catalytic activity of pure g-C 3 N 4 causes very moderate H 2 O 2 activation. Herein, a novel three-dimensional (3D) branched carbon nitride nanoneedle (3DBC-C 3 N 4 ) nanozyme has been proposed to overcome such shortcoming. This unique 3D branched structure of 3DBC-C 3 N 4 facilitated effective mass transfer during catalytic reaction and induced a lightning rodlike effect to accelerate electron collection at the tip area for H 2 O 2 activation. With improved H 2 O 2 activation for hydroxyl radical ( • OH) generation, 3DBC-C 3 N 4 showed excellent peroxidase-like activity toward 3,3′,5,5′-tetramethylbenzidine oxidation in the presence of H 2 O 2 . As for H 2 O 2, the V max value of 3DBC-C 3 N 4 was found to be 20 times higher than that of natural horseradish peroxidase. Moreover, the 3D branched structure of 3DBC-C 3 N 4 offered large interface for the reversible conjugation of single-stranded DNA, which enhanced the colorimetric sensitivity. Moreover, 3DBC-C 3 N 4 exhibited high sensitivity toward oxytetracycline detection, with the detection limit and quantitative limit of 1 and 50 μg/L, respectively.