Immobilization of flavin adenine dinucleotide (FAD) onto carbon cloth and its application as working electrode in an electroenzymatic bioreactor

A high porosity carbon cloth with immobilized FAD was employed as working electrode in electrochemical NADH-regeneration procedure. Carbon cloth was oxidized with hot acids to create surface carboxyl group and then coupled by adenine amino group of FAD with carbodiimide in the presence of N-hydroxysulfosuccinimide. The bioelectrocatalytic NADH-regeneration was coupled to the conversion of achiral substrate pyruvate into chiral product l-lactate by l-lactate dehydrogenase (l-LDH) within the same reactor. The conversion was completed at 96 h in bioreactor with FAD-modified carbon cloth, resulting in about 6 mM of l-lactate from 10 mM of pyruvate. While with bare carbon cloth, the yield at 120 h was around 5 mM. Immobilized FAD on the surface of carbon cloth electrode facilitated it to carry electrons from electrode to electron transfer enzymes; thereby NADH-regeneration was accelerated to drive the enzymatic reaction efficiently.