Colorimetric logic gate for protamine and trypsin based on the Bpy-Cu nanozyme with laccase-like activity

A novel logic gate for protamine and trypsin was developed based on a nanozyme with laccase-like activity. It is found for the first time that the nanomaterial (Bpy-Cu) made from 4,4′-bipyridine (Bpy) and Cu2+ has significant laccase-like activity, which could oxidize the typical laccase substrate (2,4-dichlorophenol) and the oxidation product was coupled with 4-aminoantipyrine to form a red dye product. It is also observed that heparin (Hep) can bond to the surface of Bpy-Cu, and obviously enhanced the laccase-like activity of Bpy-Cu by showing a stronger colorimetric reaction. In addition, because of the strong interaction between heparin and protamine, the addition of protamine to the complex of Bpy-Cu/Hep caused the decrease of surface charges as well as the laccase-like activity. Furthermore, protamine could be hydrolyzed by trypsin, and the inhibited laccase-like activity of Bpy-Cu/Hep complex by protamine could be recovered by trypsin. According to the above results, a novel sensing strategy for protamine and trypsin, and an IMPLICATION logic gate was developed. This work provided a new sensing pathway for biological molecules on the basis of the controlled regulation the laccase-like activity of nanozymes.