Electrochemical detection of endotoxin using recombinant factor C zymogen

We have developed a zymogen-based electrochemical sensor. Zymogen is an inactive enzyme precursor (proenzyme) and it is necessary to transform it biochemically (e.g., by hydrolysis and conformational change) to make it an active enzyme. In this study, we demonstrated the detection of endotoxin by using recombinant Factor C (rFC), which is a protease zymogen activated by endotoxin binding. The activated rFC hydrolyzes a synthetic substrate of Boc-Val-Pro-Arg-p-nitroanilnide to generate an electrochemical active compound, p-nitroaniline (pNA). The liberated pNA was detected by differential pulse voltammetry at -0.75 V. By using this electrochemical process, 5000 endotoxin units (EU) L^-1 and 1000 EU L^-1 were detected in a Tris-Ac buffer with a pH of 7.5 at 37 °C for reaction times of 1 h and 3 h, respectively. The concept of zymogen-based electrochemical sensors is expected to lead to the development of new biosensors.