Trimethylamine N ‐Oxide Electrochemical Biosensor with a Chimeric Enzyme

Abstract : For the first time, an enzyme‐based electrochemical biosensor system for determination of trimethylamine N‐oxide (TMAO) is described. It employs an active chimeric variant of TorA in combination with an enzymatically deoxygenating system and a low‐potential mediator for effective regeneration of the enzyme and cathodic current generation. TMAO reductase (TorA) is a molybdoenzyme found in marine and most enterobacteria that specifically catalyzes the reduction of TMAO to trimethylamine (TMA). The chimeric TorA, named TorA‐FDH, corresponds to the apoform of TorA from Escherichia coli reconstituted with the molybdenum cofactor from formate dehydrogenase (FDH). Each enzyme, TorA and TorA‐FDH, was immobilized on the surface of a carbon electrode and protected with a dialysis membrane. The biosensor operates at an applied potential of −0.8 V [vs. Ag/AgCl (1 M KCl)] under ambient air conditions thanks to an additional enzymatic O2‐scavenger system. A comparison between the two enzymatic sensors revealed a much higher sensitivity for the biosensor with immobilized TorA‐FDH. This biosensor exhibits a sensitivity of 14.16 nA/μM TMAO in a useful measuring range of 2–110 μM with a detection limit of LOD=2.96 nM (S/N=3), and was similar for TMAO in buffer and in spiked serum samples. With a response time of 16±2 s, the biosensor is stable over prolonged daily measurements (n=20). This electrochemical biosensor provides suitable applications in detecting TMAO levels in human serum.