An enzyme-free ultrasensitive electrochemical immunosensor for calprotectin detection based on PtNi nanoparticles functionalized 2D Cu-metal organic framework nanosheets

•PtNi@Cu-TCPP(Fe) hybrid nanosheets with high electro-catalytic activity have been synthesized.•An enzyme-free electrochemical immunosensor for the ultrasensitive determination of calprotectin (CALP) was constructed.•The electrochemical CALP immunosensor exhibited high sensitivity with the detection limit of 137.7 fg mL-1. In this work, a novel high electro-catalytic material was synthesized using PtNi nanospheres to functionalize two-dimensional (2D) ultrathin Cu-TCPP(Fe) nanosheets (PtNi@Cu-TCPP(Fe)), and was further applied to develop an enzyme-free electrochemical immunosensor for the ultrasensitive determination of calprotectin (CALP). The bimetallic Cu-TCPP(Fe) nanosheets with large surface area and massive accessible active sites permitted multiple PtNi to attach their surface, which not only enhanced the catalytic ability and conductivity for non-enzymatic amplification but also provided the modified active sites for antibody immobilization as signal labels. Upon the dual electro-catalytic activity of Cu-TCPP(Fe) and PtNi towards H2O2 reduction for signal amplification, this proposed sandwich CALP immunosensor exhibited a wide linear range of 200 fg mL−1 ∼ 50 ng mL−1 and a low detection limit of 137.7 fg mL−1. The functionalized MOF nanosheets-based biosensing method offered an enzyme-free signal amplification strategy, which provided great promise for further bioanalysis and clinical study.