Modified biochar-based oxidase-like catalyst for dual-signal detection of soil alkaline phosphatase

Enzyme-like biochar has attracted considerable attention due to its simplicity and low cost. In this study, an innovative modified composite biochar, MnBBC, was synthesized by co-pyrolysis of hawthorn seeds (SZZ), bentonite, and manganese. The resulting MnBBC exhibits significantly enhanced oxidase (OXD)-like catalytic activity along with excellent stability. Benefiting from its catalytic performance toward 3, 3', 5, 5' -tetramethylbenzidine (TMB), a smartphone-integrated detection system combining colorimetric and photothermal strategies for the detection of alkaline phosphatase (ALP) was developed. This system achieved impressive detection limits of 0.24 U L^-1 for colorimetric analysis and 0.29 U L^-1 for photothermal analysis. The two homologous readouts, derived from oxidized TMB (oxTMB), provide complementary information that can be used for parallel comparison to enhance detection confidence. Furthermore, the practical utility of the system was successfully demonstrated by quantifying ALP activity in complex soil samples. This work not only provides an effective strategy for designing high-performance OXD-like biochar but also establishes a versatile and economical sensing methodology with significant potential for environmental monitoring.