User:SELVAKUMAR PALANISAMI

 LACCASE BIOSENSOR 

Recently, the fabrication of enzyme based biosensors has received much attention for selective and sensitive detection of CC, since the enzyme based biosensors are highly sensitive and selective towards CC than non-enzymatic CC sensors17. For instance, tyrosinase, polyphenol oxidase and laccase based biosensors have been widely used for selective detection of polyphenolic compounds including CC18. Among them, laccase is a blue multi-copper-oxidase and the largest subgroup of multicopper oxidases, has more specific advantages such as the ability to catalyze electron-transfer reactions and high stability over tyrosinase and polyphenol oxidase based biosensors18. Different nano and micromaterials modified electrodes have been used for immobilization of laccase, since direct immobilization of laccase on unmodified electrode is difficult18. For instance, carbon nanomaterials19, metal nanoparticles20,21, metal oxides21, conducting polymers22, and ionic liquids23 have been used as an immobilization matrix for laccase. Graphene (GR) is a 2D carbon nanomaterial, has showed an extraordinary thermal and electrical properties than other carbon nanoforms such as fullerene and carbon nanotubes24,25. Recently, GR has been widely used as a support for fabrication of biosensors due to its high conductivity and biocompatibility26,27. However, the direct immobilization of redox active enzymes on GR surface is difficult due to its strong hydrophobic nature and the presence of only sp2 hybridized carbon atoms28. Hence, the GR based composites have been largely used for the immobilization of laccase29–31. It is reported earlier that the carbohydrate polymers and surfactants dispersed GR has been used as a potential material for immobilization of range of redox active proteins including laccase31. In addition, carbohydrate polymers have highly enriched with hydrophilic chemical groups on GR and result into the formation of water soluble GR hybrids32. Among different carbohydrate polymers, cellulose microfibers (CMF) are hydrophilic and water-insoluble carbohydrate polymer, has been served as a promising biomaterial for immobilization of redox active proteins owing to its unique chemical properties and high biocompatibility33. In addition, CMF has showed a high surface area and high porosity and has a tendency to bind with the range of conductive materials including carbon nanomaterials33–36. Despite the unique chemical properties of CMF, in the present work we have used CMF as a dispersing agent for GR and the resulting GR-CMF composite is used as an immobilization matrix for laccase. Moreover, the induced hydrophilic nature of CMFs could effectively prevent aggregation of GR and forms the stable GR-CMF composite for immobilization of laccase. According to our literature review, all the reported GR/cellulose composites have been prepared by the chemical reduction of graphene oxide with cellulose34–37, yet no attempt has been made so far for the direct preparation of GR-CMF composite. In addition, the direct preparation of GR-CMF does not involve any toxic chemical regents when compared to chemically prepared GR-CMF composites. To the best of our knowledge, the GR-CMF based composites have never been demonstrated yet for any electrochemical biosensor applications including immobilization matrix for any redox active enzymes or proteins