An Integrated Redox Cycling for Electrochemical Enzymatic Signal Enhancement

Highly sensitive analytical methods for the detection of proteins are still an urgent demand in early medical diagnosis and the discovery of biomarkers with ultralow abundance. Here an integrated electrochemical-chemical-enzymatic redox cycling is designed for significant enhancement of electrochemical enzymatic signal in biorecognition. This strategy efficiently utilizes the high specificity of the outersphere to innersphere redox reaction to mediate the enzymatic redox cycling with the nonenzymatic redox cycling. The oxygenation activity of tyrosinase as a label of the biorecognition event ensures low background and generates outersphere-reaction-philic/innersphere-reaction-philic redox couples, which leads to 13 300× amplification of electrochemical signal. The mediation of nonenzymatic redox cycling in the integrated system produces a 14-fold improved ratio of signal to background. The practicality of the proposed approach with clinical samples demonstrates its potential in clinical diagnostic and therapeutic monitoring. This work opens a new avenue to design novel signal amplification strategies for ultrasensitive bioanalysis.